MCAT Biology Review Sheet
MCAT Biology Review Sheet
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GI Tract Think of food as consisting of three kinds of substances carbohydrate protein and fat Carbohydrate is sometimes referred to as starch Digestion is the process of taking food in and using enzymes to breakup the starch the protein and the fat into small molecules that can be absorbed You should know the five stations of the human digestive tract mouth esophagus stomach small intestine and large intestine The mouth secretes an enzyme called amylase Amylase is in the saliva and it begins the breakdown of starch From the mouth food moves to the esophagus The esophagus then wriggles and pushes the food into the stomach The rhythmic wriggling motion of the esophagus is called peristalsis Peristalsis therefore moves food through the esophagus into the stomach The rhythmic movement continues throughout the digestive tract The esophagus doesn t secrete any enzymes No digestion occurs in the esophagus When food reaches the stomach the process of digestion continues The stomach is acidic The parietal cells of the stomach secrete hydrochloric acid into the stomach and the stomach is therefore acidic Stomach acid secretion is stimulated by the vagus nerve One of the reasons that the stomach is acidic is this the chief cells of the stomach secrete an enzyme called pepsin Pepsin helps digest protein and it works best in an acidic environment The important enzymes that function in the small intestine are produced in the pancreas and they reach the small intestine by traveling through the pancreatic duct They are called pancreatic enzymes These enzymes function in the digestion of starch protein and fat There s another duct that makes the delivery to the small intestine called the common bile duct It delivers bile Bile is made in the liver and then sent to the gallbladder to be stored When food enters the small intestine the gallbladder sends bile through the common bile duct into the small intestine Bile is not a digestive enzyme It s an emulsifier It breaks fat particles into smaller fat particles It does not however break fat particles into smaller molecules Bile is important because if large particles of fat were not broken into smaller particles of fat lipase which is the enzyme that digests fat would not be able to do as good a job The liver is an important organ It not only makes bile but it converts glucose to glycogen converts amino acid to keto acids and urea detoxify some drugs and poisons in the body and phagocytosis worn out red blood cells All you really have to know about the large intestine is that it reabsorbs a lot of water Once food has passed through the stomach it enters the small intestine through the pyloric sphincter In the intestine food is exposed to enzymes that digest starch protein and fat In their inactive state these enzymes are called zymogens Zymogens must be cleaved to be activated The pancreatic enzyme that digests starch is called pancreatic amylase The pancreatic enzyme that digests fat is called pancreatic lipase There are two pancreatic enzymes that digest protein one is called trypsin and the other is called chymotrypsin Once food is broken down it is absorbed in the small intestine enters the blood and is processed by the liver Waste products are passed on to the large intestine When the pancreas secretes its pancreatic enzymes into the small intestine it secretes a lot of water along with them That water becomes a part of the mush that enters the large intestine The large intestine then reabsorbs a lot of that water and takes it into the bloodstream What is left to food after water is absorbed in the large intestine is feces It moves out of the large intestine into the rectum and from there it is excreted Hormones A hormone is a complex chemical substance produced in one part or organ of the body that initiates or regulates the activity of an organ or a group of cells in another part of the body Hormones are secreted by the endocrine glands and are carried through the bloodstream to the target organ Some hormones have an effect on only one organ and some have an effect on many organs and cells Pancreas The pancreas produces three digestive enzymes and sends them into the small intestine by way of the pancreatic duct Those enzymes are not hormones because they don t travel through the bloodstream The pancreas does produce two hormones for this reason the pancreas is an endocrine organ These two hormones are insulin and glucagon Insulin The pancreas produces insulin and secretes it into the bloodstream Insulin has an effect on most of the body cells and that effect is to make them more permeable to glucose So by secretion of insulin into the bloodstream the glucose that sitting around the blood suddenly starts moving into most of the body cells This hormone causes the glucose concentration in the blood to go down Glucagon The other hormone that pancreas produces is glucagon Glucagon has an effect opposite to that of insulin The target organ is the liver and glucagon causes the liver to release glucose into the blood So when the pancreas secretes glucagon the blood glucose level goes up Adrenal Gland The adrenal gland is actually two endocrine glands One is called the adrenal medulla and the other is called the adrenal cortex These two endocrine glands have absolutely nothing to do with each other with reference to what they do They just happened physically to be part of one structure Adrenal Medulla The adrenal medulla secretes two hormones They are epinephrine and norepinephrine These two hormones increase the heart rate and blood pressure and they also increase alertness Adrenal Cortex The adrenal cortex secretes a lot of hormones Remember that many of the hormones it secretes are steroids In fact a lot of the adrenal cortex hormones are called corticosteroids Remember this some of the corticosteroids are called glucocorticoids Glucocorticoids have a lot of effect on a lot of organs One of them is similar to glucagon s effect These hormones increase the blood s concentration of glucose and help the body to adapt to stress Remember that cortisone is a glucocorticoid Some corticosteroids are called mineral corticoids Mineral corticoids help the kidney regulate sodium and phosphate balance One mineral corticoid is called aldosterone Thyroid and Parathyroid The thyroid gland is located in your neck It secretes thyroid hormone Thyroid hormone acts on most body cells and increases the rate of metabolism The thyroid also secretes calcitonin which decreases the blood s concentration of calcium The parathyroid gland is also in the neck It secretes parathyroid hormones Parathyroid hormone increases the blood s concentration of calcium Important that thyroid gland itself is under the influence of another hormone secreted by another gland When this other gland secretes its hormone and that hormone reaches the thyroid gland the thyroid is stimulated to secrete thyroid hormone So the thyroid is an endocrine gland and is also the target organ of another endocrine gland Anterior Pituitary Gland The anterior pituitary gland is in the brain It secretes a hormone called thyroid stimulating hormone That hormone is secreted into the bloodstream and when it reaches the thyroid gland it causes the thyroid to secrete thyroid hormone The anterior pituitary gland also secretes adrenocorticotropic hormone This hormone is called ACTH for short Its effect is to stimulate the adrenal cortex to secrete glucocorticoids Other than the two hormones mentioned before the anterior pituitary gland secretes two other hormones They are the growth hormone and prolactin Growth hormone targets the organs bone and muscle and it stimulates them to grow Children who are deficient in growth hormone don t grow normally Prolactin s target organ is the breast It stimulates milk production In addition to secreting the four hormones we have just discussed the anterior pituitary gland is a key player in the female menstrual cycle and releases FSH and LH We will discuss these hormones in just a little while Posterior Pituitary Gland The posterior pituitary secretes two hormones One hormone secreted by the posterior pituitary gland is called vasopressin Vasopressin causes the kidney to retain water Vasopressin is also known as ADH Antidiuretic hormone So Vasopressin is similar in its effect to the mineralocorticoids The other hormone secreted by the posterior pituitary is called oxytocin When it is time for a pregnant woman to give birth oxytocin causes the uterus to contract and pushes the baby through the birth canal Both vasopressin and oxytocin are first made in the hypothalamus and then transported to the pituitary for storage Therefore the posterior pituitary gland does not produce any hormones it stores them Hypothalamus The hypothalamus is also in the brain and releases hormones that have the anterior pituitary gland as their target organ These hormones inhibit or stimulate the release of anterior pituitary hormones Female Menstrual Cycle 2 The female menstrual cycle is a cycle of hormone secretion The key players in the female menstrual cycle are the ovaries and the anterior pituitary gland The female menstrual cycle has three phases In phase one the anterior pituitary secretes two hormones They are called follicle stimulating hormone FSH and luteinizing hormone LH These two hormones FSH and LH stimulate one of the follicles in the ovary to grow So during phase one a follicle in the ovary is growing Phase one is actually called the follicular phase The growing follicle secretes a hormone called estrogen Therefore during the follicular phase a total of three hormones are being secreted FSH LH and estrogen The follicular phase lasts about 10 days and just before it is over the anterior pituitary suddenly secretes a very large amount of LH this is called the surge The sudden increase in LH secretion by the anterior pituitary is called the luteal surge Do not forget at the end of the follicular phase the anterior pituitary suddenly secretes a lot of luteinizing hormone LH that is called the luteal surge The luteal surge causes the follicle to release the ovum into the fallopian tube So the luteal surge produces ovulation When the follicular phase ends an ovum is sitting in the fallopian tube and a broken follicle is left behind in the ovary The broken follicle is called the corpus luteum The corpus luteum which is still sitting in the ovary starts to secrete two hormones These two hormones are estrogen and progesterone The progesterone gets the uterus ready for pregnancy The uterus develops some new glands and blood vessels Usually of course there is no pregnancy but the progesterone gets the uterus ready just the same After about 13 days the corpus luteum stops secreting estrogen and progesterone Once the corpus luteum stops secreting estrogen and progesterone the uterus sheds its new glands and blood vessels that what causes menstrual bleeding The bleeding last about five days and that completes the cycle If the ovum is fertilized there is no flow and the developing placenta secretes human chorionic gonadotropin HCG HCG is a hormone that stimulates the continuous release of progesterone by the corpus luteum Testes Testes are endocrine organs Each testis has seminiferous tubules in it and within the seminiferous tubules spermatozoa are formed Lying around in the testes there are some cells that are not part of the seminiferous tubules These cells are called interstitial cells These cells secrete a hormone called testosterone Testosterone is the male sex hormone In children the testes secretes only a little bit of testosterone At puberty the testes secret a lot of testosterone into the bloodstream and it reaches every part of the body Testosterone causes the cells inside the seminiferous tubules to start undergoing meiosis and spermatogenesis It also promotes the secondary sexual characteristics such as deepening of the voice muscle development and facial hair development Biochemistry The main things that goes on inside the cell are chemical reactions Catalyst helps reactions happen faster Enzymes are organic catalyst that catalyzed biological reactions They help get reactants together and therefore make the reactions happen more quickly The word substrate is used to refer to reactants in an enzyme catalyzed reaction The place at which the substrate attached to the enzyme molecule is called the active site Enzymes specificity refers to the fact that one enzyme is usually designed to fit the reactants for only one particular reaction When the substrate is attached to the enzyme they caused a slight change in the shape of the enzyme which is called an induced fit When the reaction is over the enzyme resumes its usual shape Remember that an enzyme is not a reactant and that all enzymes are made of protein A living cell is similar to a bag full of chemicals Many of the chemicals have the potential to react with many other of the chemicals Enzymes determine which chemicals will react with which chemicals Therefore it is the availability of enzymes that determines what reactions will take place in a cell and what reactions will not An enzyme would not work just anywhere and it would not work under any and every condition either One of the very important things to remember about enzymes is that everyone has an optimum pH which is the pH at which it works best When pH differs even a little bit from an enzymes optimum pH the enzyme works very poorly Enzymes also work better at high temperatures As temperature increases enzymes work better For every enzyme there some temperature that is too high When temperature is raised high enough any enzyme denatures When an enzyme denatures it does not work anymore Once the amount of substrate added matches the amount of enzyme at work the reaction rate levels off and adding substrate will not increased the reaction rate Many enzymes would not work alone but need to perform in the presence of inorganic substance called cofactor or an organic molecule called coenzyme The activity of enzymes is also affected by feedback inhibition Feedback inhibition means that a function of an enzyme is inhibited by the product of the reaction it catalyzes This way you do not end up with too much of any one product in the cell because an excess of the product will turn off the enzyme Every cell uses energy and they get their energy from ATP ATP is the energy currency ATP is made of an adenosine molecule which is the nitrogenous base adenine with the rival sugar tacked on and three phosphate molecules attached to it In almost all living cells ATP is the lowest recognizable chemical form in which energy is found before it is taken to perform work You will have to know a little bit how cellular energy is stored and the initial and final compounds of each step Cells store energy in the form of glucose Glucose is a six carbon molecule and it has energy in it The energy is in the chemical bonds between carbon atoms and in the chemical bonds between carbon and hydrogen atoms ATP is made by putting together an ADP molecule and a phosphate molecule using the energy from glucose When cells need to get some glucose out of storage to form some ATP they start with the process called glycolysis In the process of glycolysis the cell starts with the molecule of glucose Glucose uses two ATPs to start the process The cell ends up with two molecules of pyruvic acid and four ATPs Therefore when a glucose molecule goes through the process of glycolysis it ends up with the net production of two ATP molecules Remember that the glycolysis is anaerobic process It occurs without oxygen After glycolysis is complete the cell has form some ATP and is left with tow molecules of pyruvic acid Each molecule of pyruvic acid is then converted to a molecule of acetyl CoA which is a two carbon molecule by oxidative decarboxylation The cell now has two molecules of acetyl CoA With its two molecules of acetyl CoA the cell next undergoes the Kreb cycle which is also called the citric acid cycle When the cell undergoes the Kreb cycle acetyl CoA combines with the four carbon molecule to form a six carbon molecule Within the Kreb cycle each molecule of acetyl CoA produces one molecule of GTP The GTP molecule is then readily converted to an ATP molecule The cell starts out with two molecules of acetyl CoA which means that it undergoes the Kreb cycle twice So for each molecule of glucose that cell starts out with the Kreb cycle yields two molecules of ATP four molecules of CO2 six molecules NADH and two molecules of FADH2 The Kreb cycle is the final common pathway in the oxidation of fatty acids into amino acids The Kreb cycle requires oxygen that means the process is available to aerobic organisms but it is not available to anaerobic organisms Anaerobic bacteria can conduct glycolysis because that does not require oxygen but they cannot conduct the Kreb cycle because that requires oxygen The Kreb cycle occurs inside a cells mitochondrion A mitochondrion has an outer membrane and inner membrane a space between the two membranes and a matrix After the Kreb cycle there are two more processes that occur the electron transport via the electron transport chain and oxidative phosphorylation After the Krebs cycle is complete the cell is left with lots of NADH and FADH2 Each FADH2 gives up H2 then the H2 molecule divides to form 2 hydrogen atoms and each hydrogen atom gives up an electron NADH gives up an H atom and then H atom gives up one electron Each electron is transferred to the electron transport chain The electron transport chain involves a lot of carrier molecules that contain iron Once the electrons are transferred over to the electron transport system The system hands each electron down from one carrier to the next With each hand down of an electron energy is released The cell takes the energy and uses it to pump hydrogen ions from the inside of the mitochondrial matrix to the space between the two mitochondrial membranes That means the cell ends up with more hydrogen ions outside the matrix than inside That produces an electro chemical gradient Once an electron has been handed down through all of the carriers in a series of redox reactions it gets together with another electron that has come down the carrier system and the two electrons are passed finally to an atom of oxygen That forms a negatively charged oxygen Each negatively charged oxygen ion then gets together with two charged hydrogen ions and forms a molecule of water Since the electron transport system ultimately passes each electron to an oxygen molecule it requires oxygen and its anaerobic process Because of the electrochemical gradient that is produced during electron transport hydrogen ions start right away via passive diffusion to diffuse inward back into the mitochondrial matrix Now as the hydrogen ions diffuse back across the inner mitochondrial membrane ADP and phosphate that are sitting right on the membrane get together and form ATP So when the hydrogen ion crosses the inner membrane it causes the production of ATP from ADP and phosphate The hydrogen ion crosses the inner mitochondrial membrane by passing through channels made of a substance called ATP synthase which is also sitting on the inner membrane Even though there are separate processes electron transport an oxidative phosphorylation happen at the same time As the electron transport chain starts to pump hydrogen ions out across the inner mitochondrial membrane the hydrogen ion start right away to cross back into the matrix So the hydrogen ion gradient is not allowed to progress very far In anaerobic organism the cell conducts fermentation This means that the two molecules are pyruvic acid left from glycolysis are transformed to either ethanol or lactic acid Fermentation produces only two ATPs When a rapidly exercising human muscle can t get all of the oxygen it needs to conduct aerobic respiration it conducts fermentation and produces lactic acid Chromosomes We will now talk a little a bout chromosomes Chromosomes are made of deoxyribonucleic acid which is called DNA Chromosomes are found in the nucleus of every cell through out the entire body Human beings have a total of 46 chromosomes but these chromosomes exist in pairs So sometimes we say that human beings have 23 pairs of chromosomes Think for a second about one pair of chromosomes the two members of any recognized pair of chromosomes are similar but not exactly alike The two members of a recognized pair of chromosomes are called homologous chromosomes If we took the 23 pairs of chromosomes from a human cell and then from each cell we removed one number of the pair will be left altogether with 23 different chromosomes and this cell would be called haploid When we say haploid we mean a cell for which the chromosomes are not paired A normal human cell that has 23 pairs of chromosomes is said to have a diploid number of chromosomes and the cell is therefore called a diploid cell Now let us talk a little about DNA DNA is made of little subunits called nucleotides A nucleotides is made up of pentose sugar attach to a phosphate and to a nitrogenous base A nucleotide can have as its base anyone of the following four possible bases adenine guanine cytosine and thymine One strand of DNA is formed when many nucleotides bond together in one base order or another and form a chain A chromosome can be thought of as two strands of DNA put together side by side Each stand is said to be the compliment of the other A chromosome looks like a ladder the sides of the ladder are made up of the phosphate sugar components of all of the nucleotides Each wrung of the ladder is made from a pair of bases One base comes from a nucleotide on one strand of DNA and the other base comes from nucleotide on the other strand of DNA By convention when we list the sequence of nucleotides in a nucleotide strand we read from the five prime to the three prime end When two strands of DNA get together to form a chromosome the wrungs are formed by the bonding of two bases But it turns out that each base is only willing to get together with one of the other bases You must remember that adenine bonds with thymine and guanine bonds with cytosine There are two hydrogen bonds between adenine and thymine and three hydrogen bonds between guanine and cytosine If you know the base sequence of one strand you can figure out the base sequence of its compliment Suppose we tell you that in one area of a DNA molecule one of the strands has the base sequence adenine cytosine thymine and guanine by knowing the base pairing rules you can figure out the base sequence of the complimentary strands which is thymine guanine adenine and cytosine One other thing you should know is that two of these bases are called Purines and two are called Pyrimadines It is easy to remember which are which Remember out alphabetized list of nucleotides bases adenine is a purine cytosine is pyrimadine guanine is a purine and thymine is a pyrimadine Notice that the first one is a purine and that the terms pyrimadine and purine alternate along the rest of the list You will also notice that each purine bonds with one of the pyrimadines and likewise each pyrimadine bonds with one of the purines Purines do not bond with purines and pyrimadine do not bond with pyrimadines When the double stranded DNA molecule is fully formed it is twisted The twisted ladder shape is called a double helix Watson and Crick are the scientist who figured out the shape of DNA And that is why the double helix shape is sometimes called the Watson Crick model of DNA or the Watson Crick double helix It is easy to see how DNA reproduces its self The first thing that happens is that using DNA helices enzymes the double helix unwinds and unzipped so that the two strands of DNA can separate Remember DNA synthesis always proceeds in a five prime to three prime direction DNA synthesis begins at a particular site called the origin of replication An RNA primer is used to add subunits to the three prime end of the DNA strand The next thing that happens is that with help of the enzymes DNA polymerase the nucleotides line up according to the rules of base pairing Cytosine s line up next to guanines and guanines line up next to cytosines adenines line up next to thymines and thymines line up to next to adenines Along side of each separated strand nucleotides lines up and form a new second strand both strand are replicated at the same time One strand continuously called the leading strand and the other strand discontinuously called the lagging strand Bonds formed between the base pairs and among the sugar phosphate components of the nucleotides An organism s chromosomes contain all of its genetic information In terms of what you are born with chromosomes make you who you are They do that basically by determining what proteins your cell will manufacture Since proteins often serves as enzymes chromosomes determine what enzymes your cells manufacture Enzymes determine what chemical reactions will and will not occur in your cells and that s what makes you more or less who you are DNA directs protein synthesis through RNA RNA looks like very much like DNA but there are three important differences between them RNA is single stranded The nucleotides that form RNA have ribose instead of deoxyribose as their sugar In fact RNA stands for ribonucleic acid and DNA stands for deoxyribonucleic acid RNA nucleotides never contain thymine as a base instead they contained a base called uracil So the four bases found in RNA nucleotides are adenine cytosine guanine and uracil RNA is formed under the direction of DNA Sometimes a DNA molecule will unzipped when it is not planning to replicate and one of the strands will serve as template for the formation of an RNA molecule The RNA molecule is formed using the enzyme RNA polymerase usually one strand is transcribed The process can be induced or suppressed depending on the needs of the cell In RNA molecule is formed just like a DNA molecule except that you think of uracil instead of thymine If a DNA strand has the sequence guanine thymine adenine and cytosine the RNA molecule that it forms will have the sequence cytosine adenine uracil and guanine The order of nucleotides and the RNA molecule is determined by the order of nucleotides on the DNA strand that produces it If a different DNA strand had served as template a different RNA molecule would have resulted The process of making RNA molecules from DNA is called transcription Since RNA is formed from chromosomes it is formed in the nucleus However after it is formed it moves out into the cytoplasm RNAs are important because they are involved in protein synthesis There are three types of RNAs First there is mRNA which id formed in the nucleus from a DNA template This is the RNA that goes out into the cytoplasm to locate itself on ribosome s it called messenger RNA because it carries a message from the nucleus to the cytoplasm second is tRNA TRNA stands for transfer RNA The tRNA reads the mRNA codon and brings the appropriate amino acid into line The third RNA is called rRNA RRNA stands for ribosomal RNA Ribosomal RNA is made in the nucleolus and it makes a part of the ribosome Every three RNA nucleotides bases are called a codon Each codons specifies an amino acid each codons are like a message from the chromosomes directing the ribosomes to produce a certain proteins The three base sequence on the tRNA molecule is called an anti codon The anti codon can recognize a codon on the mRNA by complimentary base pairing Translation is the process in which the amino acids line up in accordance with the codons that appears on a molecule of RNA The ribosome has subunits a large one and a small one The ribosome also has two special tRNA binding sites called the A site and P site A special tRNA called methanol tRNA is the initiator of protein synthesis It attaches at one end to methionine and to a sequence of three nucleotide bases at the other end This initiator binds to the ribosome at the P site The P stands for peptidyl tRNA binding site Once initiation is complete the amino acids are ready to added one by one to the initial amino acid which is methionine The next amino acid is carried by a TRNA a peptide bond is formed between the two amino acids after the peptide bond is formed methionine is now attach to the tRNA at the A site The tRNA is released from the P site The tRNA at the A site carries the growing polypeptide Next the tRNA in the A site jumps to the P site This is called translocation This process allows for the next tRNA to come in and attach to the next amino acid This translocation process requires energy which is provided by the hydrolysis of GTP The mRNA moves through the ribosome in the five prime to three prime direction Chromosomes are the template from which mRNA is formed That means that the base sequence in an mRNA molecule is a reflection of the base sequence of the DNA molecule that served as its template The mRNA goes out into the cytoplasm and there each of its three base sequences or codons attracts the molecule of tRNA with a complimentary three base sequence or anti codon The tRNA molecule is attached to a particular amino acid for which it is specific The amino acids thus line up in an order dictated by the order of the codons on the mRNA molecule Now remember this chromosomes are DNA molecules These DNA molecules give rise to complimentary mRNA molecules A molecule dictates the order in which amino acids get together to form proteins Proteins serves as enzymes and enzymes determine what chemical reaction occur in our bodies Genetics Chromosomes make us who we are because they carry all of the genetic information that governs your biochemical activity The genetic information is found in the DNA The DNA has nucleotide basis of either A T C or G We know that the particular sequence of a segment of DNA is very important A specifically ordered string of nucleotide basis determines that a particular enzyme is made When a particular enzyme is made its biochemical effect will produce some trait that we will exhibit A particular sequence of nucleotides and DNA that codes for a specific enzyme is called a gene A gene produces an enzyme and an enzyme produces a trait A gene is inherited by an organism s offspring and because the gene is inherited the trait that the gene produces is inherited Genes are located along the length of a chromosome and the exact location of a gene on a chromosome is called its locus The locus of a gene actually pinpoints the genes physical place on its assigned chromosome In homologous chromosomes the locus for one gene is lined up right next to the locus for the same gene on its chromosome partner In homologous chromosomes those two genes sitting next to each other code for one particular trait Allele is the name given to each gene of the set that code for the same trait Alleles for a particular trait are genes that can exist in slightly different forms The two alleles that make up the genes for a trait are called the genotype for that trait When a person s alleles are different and that they code for different expressions of a trait the person is said to be heterozygous for that trait For an organism that is heterozygous for a trait both alleles can be thought of as competing for expression of that trait The allele which wins is called the dominant allele The dominant allele will appear as the characteristic trait of the organism We symbolize a dominant allele for a trait with a capital letter The alternative allele of the pair remains as part of the genotype for that trait but you can t detect it in the appearance of the organism This allele is called the recessive allele We symbolize a recessive allele for a trait with a small letter You should know a little about Mendel s laws Mendel s law of segregation says that for any given trait in the diploid parent cell one allele for the trait goes to one gamete and the other allele for the trait goes to another gamete Mendel s law of independent assortment says that for any group of traits in an organism each trait will segregate independently of the other traits during meiosis It s important to know that crossing over leads to genetic recombination The chromatids of each homologous pair do not have the same arrangement of genes after crossing over as they did before crossing over The chromatids have a new combination of genes as a result of crossing over Remember the Hardy Weinberg law which states that even with all of the shuffling of genes that go on individual alleles for traits still prevail overtime They don t get lost in the shuffle The more prevalent gene doesn t become even more prevalent and the less prevalent gene doesn t disappear However the Hardy Weinberg law applies only to ideal populations Meaning it is subject to these five conditions very high numbers of individuals in a population no mutations no immigration or emigration random mating and any one gene has the same chance of reproducing as any other If these five conditions are met you can be pretty sure that there is equilibrium in the gene pool of a given population Remember this Hardy Weinberg equation P2 ZPQ Q2 l or P Q 1 There s a thing called genetic drift which says that when a population is small some genes get lost overtime and some genes become more frequent overtime The 23rd chromosome pair is the sex chromosome When the sex chromosomes are XX they determine that a person will be female When the sex chromosomes are XY they determine that a person will be male Because it is only the male who carries the Y chromosome the Y chromosome of the male offspring can only be inherited from a father Since each parent contributes one half of the sex chromosome pair then the X chromosome of the male offspring must come from the mother On the other hand since the female has sex chromosomes that are XX and each parent contributes one half of the chromosomes then one X chromosome of the female offspring must come from the mother and one X chromosome come from the father When traits get carried on the pair of sex chromosomes these traits are called sex linked traits and are usually carried only on the X chromosome and not on the Y chromosome If a female carries a recessive abnormal trait on only one X chromosome she will still appear normal for that trait because the accompanying X chromosome overrides the recessive trait The male has no spare X once the Y chromosome directs that the offspring is to be male It has little else to do with inherited traits That X chromosome that a male receives from his mother determines his faith with regard to a sex linked trait If the X chromosome carries the trait then the male will show that trait even though that trait can be recessive Implantation The fertilized egg travels to the uterus where it grows into the side of the uterine wall This is called implantation At this site it will eventually form a structure called the placenta Placenta is made of both fetal and maternal cells It allows the transfer of the maternal nutrients to the fetus and prevents the mixing of maternal and fetal blood It is basically a barrier that lets food get in and waste get out Another structure the umbilical cord connects the fetus to the placenta and conducts all the stuff between mother and fetus At fertilization a haploid ovum and a haploid sperm get together and together they produce a diploid zygote The sperm has 23 chromosomes the ovum has 23 chromosomes and the zygote then has 46 chromosomes The zygote undergoes mitosis over and over and over again and all of the cells of the developing embryo are diploid You should know a few things and a few words that pertain to the development of a new organism The sperm and ovum are gametes they are haploid the two get together to form the beginnings of the new organism When they get together they form the first cell of the new organism and that first cell is called a zygote The zygote is diploid and it starts dividing It goes through lots of stages and its name changes many times and ultimately it becomes a new organism A newly forming organism naturally changes shape many times in many ways before it completes the developmental process that is called morphogenesis The first thing a zygote does is it undergoes mitosis Then each daughter cell also undergoes mitosis The resultant daughter cells continue to undergo mitosis several more times This series of mitotic divisions is called cleavage Cleavage is the first thing to happen after fertilization After the zygote has undergone several mitotic divisions it is not called the zygote anymore It is a morula As the cells divide and pressed against to each other it forms a hollow sphere of cells and it is called a blastula The space in the sphere is called a blastocoele After the blastula is formed it quickly invaginates and it is called a gastrula The gastrula gives rise to three different cell layers called germ layers These three layers are named ectoderm mesoderm and endoderm Every cell tissue and organ in the body derives from one of these three cell layers The digestive tract and all the structures attached to it like the esophagus stomach small intestine large intestine pancreas gall bladder and the liver arise from endoderm The inner lining of respiratory tract bronchi bronchioles alveoli arise from endoderm Ectoderm gives rise to the epidermis the nervous system and the eye Everything else arises from mesoderm After gastrulation some mesodermal cells move under the ectoderm and shape themselves into something that looks like a long rod called the notochord The ectoderm above the notochord starts to thicken and it is called the neural plate The neural plate rolls up into a tube by itself and it is called the neuronal tube This tube sits just above the notochord and it becomes the brain and spinal chord This process is called neurulation After the embryo undergoes neurulation it is called a neurula Differentiation is when one cell of a developing organism develops a long one line of specialization and another cell develops along another line of specialization Differentiation is controlled by induction Induction causes a nearby tissue to develop along some line of specialization The name induction pertains to the fact that one tissue is inducing another tissue to develop in a certain way Kidney A kidney is made up of nephrons It filters the blood gets rid of the waste material and keeps nutrients in the blood Nephrons keep our body uid at the right balance of solutes and water Bowman s capsule looks like a baseball glove It captures all of the blood that passes within its enclosure Glomerulus is a bunch of blood vessels that sit within Bowman s capsule pocket of space Therefore the blood passing through these vessels ends up getting through the Bowman s capsule Note Blood filtration through the Bowman s capsule means that all sorts of things that were in the blood before reaching the Bowman s capsule are now out of the blood and inside the nephron of the kidney Things that do get filtered are ions water other molecules and small proteins Things that do not get filtered are cells and large proteins The uids and solutes that have been filtered through the Bowman s capsule travel along the entire nephron From the Bowman s capsule it passes through some convolutions in the tubule then it goes down one side of a long loop and back up the other side Next it passes through some more convolutions The section of convolutions closest or most proximal to the Bowman s capsule is the proximal convoluted tubule The long loop that goes down and then up is the loop of Henle The section of convolutions furthest from the Bowman s capsule is the distal convoluted tubule Once the filtrate makes it from the Bowman s capsule all the way to the distal convoluted tubule and passes the distal convoluted tubule it enters a collecting duct The collecting duct collects all of the filtrate that completed the tour of the nephron and the filtrate coming from other nephrons The filtrate is now called urine Urine enters the ureter and gets stored in the urinary bladder and it leaves the body through the urethra Just outside the loop of Henle we find that salt concentration is relatively low near the top of the loop and relatively high near the bottom Therefore the tissue outside the loop of Henle shows a salt concentration gradient Concentration is lowest toward the top of the loop and highest toward the bottom As the filtrate moves down the loop on Henle the concentration of salt and the fluid outside the loop is increasing Therefore the filtrate wants to equalize the concentrations on each side of the loop In order for this process to occur it must take salt into the loop andor move water out Note The walls of the descending portion of the loop are permeable both to water and sodium so as the filtrate descends the loop water diffuses passively from the loop outward into the surrounding medium and passively from the surrounding medium inward into the loop As the filtrate moves up the loop of Henle the concentration of salt and the fluid outside the loop progressively decreases so the filtrate tries to equalize the concentrations on each side of the loop again But now the walls of the ascending portion of the loop are impermeable to water and permeable to salt Therefore as the filtrate moves up the ascending loop salt diffuses passively from the loop outward to the surrounding medium but water cannot move in either direction At corresponding portions of the ascending and descending limbs of the loop the concentration of the filtrate is pretty much equal The filtrate concentration is 300 moles per liter at the top of the descending loop and it is 300 moles per liter also at the top of the ascending loop Something important does happen in the loop of Henle On the descending side of the loop the filtrate takes in sodium and ejects water On the ascending side of the loop the filtrate ejects salt but does not take in any water Therefore the trip up and down the loop of Henle has increased the water volume outside the loop and decreased the water volume inside the loop Concentrations are equal at corresponding points of the ascending and descending limbs of the loop but volumes are not The trip down and up the loop of Henle has decreased filtrate volume Water is taken out of the filtrate and put back into the tissues outside the tubules The filtrate is ultimately tossed out of the body as urine As you see the loop of Henle maintains water concentration in the body Otherwise most of the water that enter the nephron would still be in the urine when it is kicked out of the body The body would be losing a lot of water all the time The loop of Henle causes the body to take a lot of water out of the filtrate to keep it in the tissues outside the nephron and hence to prevent it from leaving the body as urine That is why it has been said that the loop of Henle promotes bodily conservation of water Remember that in addition to the passive diffusion of salt outward into the surrounding tissue the ascending limb does some active pumping of salt also outward The active pumping of salt is done to reduce the concentration of the filtrate at the top of the ascending limb so that it is a little less than that of the fluid at the top of the descending limb It is this active transport of salt that ultimately produces the concentration gradient outside the loop of Henle Salt concentration in the surrounding tissue increases as the filtrate moves from top to bottom of the collecting duct Keep in mind that in the collecting duct filtrate is now called urine As any other uid the urine wants to equalize the concentration across the tubular wall Unfortunately for urine the tubular wall is impermeable to salt so it cannot achieve this goal by moving salt One of the body s glands secretes a hormone called antidiuretic hormone ADH ADH makes the collecting duct very permeable to water If there is not so much ADH around the collecting duct is not very permeable to water ADH regulates the collecting duct s permeability to water In the presence of relatively large amounts of ADH water diffuses passively out of the collecting duct in large quantities and the urine becomes quite concentrated In the presence of relatively small amounts of ADH water diffuses passively out of the collecting duct only in small quantities and the urine is relatively dilute Therefore ADH decides whether the urine is going to be concentrated or dilute because ADH regulates the collecting duct s permeability to water Lots of ADH means concentrated urine Small amounts of ADH mean dilute urine After passing through the collecting duct the urine has become more concentrated a lot more concentrated if there is lots of ADH around and only a little more concentrated if there is not so much ADH around From the collecting duct the urine is passed into the ureter into the bladder into the urethra and out of the body Populations and Evolution Gene pool is all the genes in a population of one particular species Genetic variability is the fact that gene pools have lots of different alleles in them Genetic variability arises through the process of random mutation Evolution can be summarized in the following three statements 1 Due to ongoing random mutation there is always within a species population genetic variability So there are lots of different genes running around in the gene pooL 2 At some time or other for some reason or other some portion of the population finds itself in a new environment In the new environment one of the genes that is running around in the gene pool confers an advantage on the individuals who happen to have it Those individuals survive and reproduce in greater numbers than do the individuals without that particular gene The population in the new environment has a gene pool that is different from the population in the old environment 3 Speciation just means the creation of a new species Speciation results from prolonged evolution If two populations evolve separately for a long time they will ultimately be so different from one another that they would not be able to interbreed anymore When a mutation allows one individual to take advantage of its environment in some new way and thus to minimize competition with other individuals it is called adaptive radiation Adaptive radiation produces new species Make sure you know which of these terms describes what process Speciation means that over a long period of time and under certain conditions a new species can develop Adaptive radiation means that a new species can arise from the parent species by adapting to a different ecological niche The Hardy Weinberg Law says that in a large population the gene pool tends to remain stable generation after generation Genetic drift means that in a small population the gene frequency drifts randomly Species are identified according to this scheme kingdom phylum class order family genus and species Here is an easy way to remember all that King Philip Came Over From Germany So The following is all you need to know about comparative anatomy Chordates are a phylum that includes invertebrates and vertebrates You should know that chordates are noted for having three things a dorsal nerve cord gill slits and a notochord Vertebrates are noted for having four things vertebral column closed circulatory system developed nervous system and developed sensory apparatus Symbiosis is about two organisms that live together in very close association The word symbiosis does not tell you what is going on between the two organisms They may be hurting each other or they may be helping each other Symbiosis just means that two organisms live together in close association Mutualism is when two organisms of different species live in close association and somehow help each other out Commensalism is when one organism benefits from another and the other organism gets no benefit and suffers no harm Parasitism is when one organism feeds off another and does cause harm to the other Microorganisms Bacteria A bacterium is a single celled organism and it usually has a cell wall A bacterium is a prokaryotic cell A typical bacterium has one ring shaped chromosome made of DNA At some point in its life the bacterium replicates the whole chromosome The bacterium then develops a cell wall across its transverse length and divides into two daughter bacteria each of which has one chromosome The whole process is asexual and it is called binary fission Bacteria however have ways of mixing their chromosomes with chromosomes from other bacteria In that way they achieve genetic recombination There are three words that signify the ways in which bacteria achieve genetic recombination conjugation transformation and transduction Conjugation is when two bacteria can get together and one can transfer some DNA to another through structures called pili One bacterium is called the donor and it has a plasmid called the F factor that participates in the transfer of DNA The other bacterium is called the recipient Transformation is when one bacterium receives pieces of DNA from a second bacterium The two bacteria do not actually get together as they do in conjugation Instead pieces of chromosome from the second bacterium have gotten loose and are floating around on their own the first bacterium incorporates those pieces into its own chromosome Transduction is when a virus takes some DNA from bacterium and carries it to another Some bacteria are round they are called cocci singular is coccus Some bacteria are spiral they are called spirilla singular is spirillum Some bacteria look like straight rods they are bacilli singular is bacillus Remember the following types of organisms and their method of obtaining nutrition Autotrophs are organisms that can produce their own nutrition via photosynthesis Heterotrophs are organisms that cannot perform photosynthesis and must derive their nutrition from an outside source Parasites are organisms that have no digestive system and absorb nutrients from the living body of a host organism at the expense of the host Saprophytes are organisms that have no digestive system and absorb nutrients from the dead bodies of other organisms Carnivores are organisms that have digestive systems and eat animals Herbivores are organisms that have digestive systems and eat plants Now remember the following types of bacteria and their need for oxygen Obli gate anaerobes derive energy via fermentation only They cannot survive in the presence of oxygen Facultative anaerobes derive energy via aerobic respiration or fermentation and can survive with or without oxygen Aerobes derive energy via aerobic respiration only and cannot survive without oxygen Some bacteria are called nitrogen fiXing bacteria which mean that they have the ability to take nitrogen from the air and often provided to the plants Virus A virus does not have a plasma membrane It does not have a nucleus and it does not have any of the organelles we have talked about A virus has a coat which is called a capsid This coat is made of protein Inside the virus protein coat there is nucleic acid There are two kinds of nucleic acids DNA and RNA Some viruses have DNA and are called DNA viruses Some have RNA and are called RNA viruses A virus cannot reproduce without the help of some other cell So when a virus wants to reproduce here is what it does First it latches on to some other cell It might latch on to a bacterial cell fungal cell plant cell or animal cell The other cell is called the host Second once the virus has latched on to his host it injects its nucleic acid into the host Third the virus nucleic acid somehow uses the host cell s equipment to reproduce itself many times While inside the host cell the virus nucleic acid replicates itself repeated and each copy of the viral nucleic acid somehow causes a new protein coat to form around the nucleic acid Fourth the new viral particles now burst out of the host cell and emerge Bursting is called host cell lysis The sequence of events in a lysogenic infection is a little different The virus latches on the cells as usual and injects its nucleic acid Then the viral nucleic acid integrates into the host s nucleic acid When the host cell replicates itself the viral nucleic acid which is now called prophage also replicates Certain conditions can cause the prophage to become lytic and follow the lytic phase There is something about a virus protein coat that decides what kind of host cell it will attack A virus cannot settle on a host cell unless the host cell has some kind of receptor for the virus protein coat on its surface There is a type of virus called bateriophage A bateriophage is a virus that uses bacteria as its host The bateriophage like all other viruses has a protein coat and nucleic acid inside it The nucleic acid inside a bateriophage is DNA A bateriophage also has a tail A bateriophage reproduces just like other viruses except that when it latches on to its host it uses its tail Fungi It is hard to decide whether fungi are plants or animals It is also hard to decide whether a fungus is a single celled organism or a multi celled organism A fungus is like many cells all joined together in one and that is why it sometimes called a multi nucleated cell A fungus is like a plant and that it has one big cell wall around it It is also a eukaryotic cell and that it has many many copies of the usual organelles and many nuclei Fungi are usually haploid Some of them reproduce asexually and some reproduce sexually Some however can reproduce asexually or sexually Budding is when a piece of a fungus breaks off and becomes a brand new fungus Spores are tiny cells that a fungus expels usually from long structures called hyphae These spores germinate is some suitable environment and a new fungus grows The new fungus is an identical twin to the original because its chromosomes are exactly the same as the original Fungi reproduce by each contributing a piece of itself by conjugation Each piece has a haploid number of chromosomes and when they get together to form a zygote the zygote has the deployed number of chromosomes The zygote hangs around in a dormant state for a few months and does not do much This dormant state is the only part of the fungus life cycle that is diploid After the zygote is through dormancy it undergoes mitosis and forms spores each one having the haploid number of chromosomes The spores germinate somewhere and we get new fungi each having the haploid number of chromosomes so spores can be produce sexually and asexually Nerves Nerve cells are called neurons A neuron is like any other cell It has a nucleus cytoplasm and the usual array of organelles The middle of the neuron is called the cell body and that is where the nucleus and all of the usual cellular organelles are located The neuron has two things that other cells do not have It has dendrites and it has an axon The neuron also has a cell membrane The cell membrane surrounds the entire neuron including the axon and dendrites The neuron is something that receives signals and sends signals Signals are received at the dendrites Signals are sent out via the axon Simple Re ex Arc Let us consider a knee strike with a hammer When we strike the knee the dendrites sense the blow They have received the signal so the neuron fires When the neuron fires it sends an impulse through it cell body and out into its axon The impulse is transmitted from the end of the axon to the dendrites of a second neuron Now the second neuron has received the signal from the first neuron The second neuron now fires and sends an impulse through its cell body out into its axon When the impulse reaches the end of the second axon it is transmitted to the muscle on which the second neuron is sitting and the muscle contracts In short when one neuron picks up a signal from the environment and it then sends an impulse to a second neuron and the second neuron then causes a bodily response the whole setup is called a simple re ex arc The neuron that picks up the signal is called the sensory neuron The neuron that produces the response is called the effector neuron Therefore in our knee jerk example the first neuron is the sensory neuron and the second neuron is the effector neuron Remember some sensory neurons are sensitive to being hit others might be sensitive to light and others might be sensitive to sound Different sensory neurons are sensitive to different things There are other simple reflex arcs For example if you tap the Achilles tendon with a hammer the ankle will jerk That is called the Achilles reflex Simple reflex arc involves only one sensory neuron and one effector neuron More complicated pathways involve a third kind of neuron called an interneuron The interneuron acts between a sensory and effector neuron as a link When a neuron is at rest when it is not picking up and sending signals there are two concentration gradients across its cell membrane To begin with the inside of the neuron has a much higher potassium ion concentration than does the outside and it has a much lower concentration of sodium ions than does the outside So when it comes to the resting neuron there are two concentration gradients across the cell membrane a potassium ion gradient and a sodium ion gradient Remember that the inside of the neuron is high in potassium ions and low in sodium ions The concentration gradient across the neuron cell membrane is created by the process of active transport At rest or equilibrium there are pumps that are busy pushing sodium out of the cell and pumping potassium into the cell This sodium potassium pump mechanism is what creates and maintains the concentration gradients Remember that neurons use an energy dependent pump that maintains a high concentration of sodium outside of the cell and a high concentration of potassium inside the cell Keep in mind that the resting neurons are by the process of active transport constantly pushing sodium ions out of the cell and pulling potassium ions into the cell The membrane of the resting neuron has a very low permeability to sodium and potassium so the concentration gradients are maintained The sodium gradient is of greater magnitude than the potassium gradient The imbalance of sodium across the neuron s membrane is greater than the imbalance of potassium This means the inside of the membrane is negatively charged The negative charge is 70 millivolts Because the resting neuron is negatively charged relative to the outside the resting neuron is said to be polarized Every neuron is sensitive to some kind of stimulus rather In order to cause a neuron to respond the stimulus has to be of sufficient intensity to excite the neuron That level of intensity is called the threshold Therefore a neuron s threshold is the intensity of stimulus that is necessary to cause its response When you reach a neuron s threshold by stimulating its dendrites with sufficient intensity a small area of the cell membrane suddenly becomes very permeable to sodium ions Sodium then rushes into the cell along the concentration gradient Now the inside of the cell has a lot of potassium ion and a lot of sodium ion As soon as sodium rushes into the cell the inside of the cell becomes positively charged relative to the outside of the cell The charge increases from 70 millivolts to 50 millivolts The increase to 50 millivolts is called the action potential When a neuron is stimulated to its threshold it becomes permeable to sodium which rushes into the cell and creates a positive charge of 50 millivolts relative to the outside of the cell We can also say that the cell has become depolarized Now at one small area the neuron is depolarized There is a charge of 50 millivolts inside the neuron Next the same area of membrane becomes impermeable to sodium and highly permeable to potassium Potassium rushes out of the cell along its concentration gradient This causes the inside of the cell to become negatively charged again and it is called repolarized Therefore the sequence of events in exciting a neuron is in the beginning the cell is polarized it has a relative charge inside of 70 millivolts When the neuron is excited to its threshold it becomes highly permeable to sodium Sodium rushes inward and the cell is depolarized its relative charge inside is 50 millivolts That charge is called the action potential The cell becomes permeable to potassium Potassium rushes outward and the cell is repolarized It has a negative charge inside of 70 millivolts The cell cannot respond to another stimulus for a while after an action potential This period is called the refractory period There are special voltage gated channels along the axon These channels open or close based on voltage changes in their area The whole action potential takes place thanks to voltage gated sodium channels and voltage gated potassium channels When the membrane becomes a little bit depolarized from some stimulation that triggers a few voltage gated sodium channels to open and sodium enters the cell The sodium ion coming into the cell depolarizes the cell a little more causing more sodium ion channels to open more sodium ions to come in and more depolarization This will go on until the membrane potential of the cell goes all the way from 70 millivolts to 50 millivolts and initiate an action potential At 50 millivolts the electrochemical force driving sodium ions into the cell is zero and the sodium channel becomes inactivated They gradually start to close and they stay closed until the membrane recovers its resting potential Meanwhile voltage gated potassium ion channels had also opened when the membrane was depolarized but these potassium ion channels open slowly Potassium permeability increases right about the time that sodium ion channels are inactivated The potassium ions entering the cell help bring the cell back to its resting state which also happens to be the equilibrium potential for potassium ions Now the potassium ion channel is closed and the sodium ion channels are ready for the next stimulus to come along and start the whole thing over again Remember that stimulus must reach threshold for an action potential to happen That means that the stimulus must be strong enough to open enough sodium ion channels to trigger an action potential The sequence of depolarization followed by repolarization describes an action potential As soon as one little area of a neuron undergoes an action potential the action potential spreads like a chain reaction along the neuron s entire length Within milliseconds every area of the neuron in sequence becomes depolarized and then repolarized meaning every area of the neuron in sequence becomes permeable to sodium and then permeable to potassium When one small area of a neuron undergoes an action potential every other area in sequence undergoes it too The spreading of action potential is called a nerve impulse In order for an impulse to travel it synapses with other neurons When the nerve impulse from a neuron reaches the end of the axon it causes the axon to release a chemical into the synapse When the chemical comes in contact with the dendrites of the next neuron it brings on an action potential in that neuron This chemical is called a neurotransmitter A neurotransmitter is the means by which a nerve impulse crosses the synapse When the neurotransmitter reaches the neuron it binds to a receptor on the surface of the neuron This binding opens li gand gated channels for a particular ion when the ligand gated channels open the permeability of the neuron to a particular ion changes These ions rush in and bring on an action potential in the neuron That is how a neurotransmitter transmits a nerve impulse Remember that one important neurotransmitter is a chemical called acetylcholine Acetylcholine triggers muscle contractions Remember also that excess acetylcholine is broken down by cholinesterase Another neurotransmitter is norepinephrine It is released by sympathetic neurons and some neurons in the brain and spinal cord There is a kind of cell that tends to be around neurons This cell is called a Schwann cell Sometimes Schwann cells wrap themselves around axons These cells are now called myelin sheath The space between myelin sheaths is called the node of Ranvier Axons that have myelin sheaths conduct nerve impulses more quickly than those that do not Myelin sheaths wrapped around an axon do not let any current along the axon leak out The only way a current can get anywhere is by jumping from point to point at the nodes of Ranvier This kind of conduction is called saltatory The Nervous System The whole nervous system is divided into two parts the central nervous system and the peripheral nervous system The central nervous system consists of the brain and spinal cord Remember that the brain consists of the cerebral cortex the largest part of the brain which integrates all sensory input and voluntary motor activity the cerebellum which is concerned with muscle coordination the hypothalamus which regulates homeostasis via hormones and the medulla which regulates involuntary actions such as coughing and breathing As for the spinal cord remember that its inner region is called the gray matter and its outer region is called the white matter The gray matter is dark because it contains cell bodies The white matter is white because it contains mostly myelinated axons Spinal nerves which contain both sensory and motor neurons are associated with the spinal cord Sensory neurons enter through the dorsal root and motor neurons exit through the ventral root The peripheral nervous system is divided into two parts One part is the somatic nervous system The other part is the autonomic nervous system The autonomic nervous system is divided itself into two components the sympathetic and the parasympathetic components Those parts of the body that are controlled by the autonomic nervous system have neurons from both the sympathetic and parasympathetic parts of the autonomic nervous system The parasympathetic and sympathetic neurons have opposite effects on the body parts they control The parasympathetic neurons have an effect that is opposite to that of the sympathetic neurons The heart for example is under the control of the autonomic nervous system so it is supplied with sympathetic and parasympathetic neurons When the sympathetic neurons fire the heart beats faster When the parasympathetic neurons fire the opposite happens The heart beats slower Receptors are nerve cells The way to remember where these receptors are is to know that we have five senses sight touch smell taste and hearing The skin receptors sense touch as well as pressure heat cold and pain Other receptors in the body are sensitive to the changing tensions in the muscles and tendons Olfaction is another word for smell Sensory receptors lining the nasal cavity detect many odors Taste receptors have hair like projections that are found in the taste buds and detect chemicals in the mouth There are four different types of taste registered sour bitter salty and sweet You should know a little about the ear The best way to remember the important structures in the ear is to follow the path of sound through the ear As sound enters the ear it comes in contact with these structures pinna the auditory canal tympanic membrane the malleus incus and stapes cochlea and finally the auditory nerve also called the cochlear nerve The cochlea is important because it contains hair cells which send impulses to the auditory nerve when they are activated by a sound wave Another name for the hair cells and related structures in the cochlea is the organ of Corti Remember that the ear has three parts external which consists of the auditory canal middle which consists of malleus incus and stapes and the inner which consists of cochlea and vestibular system The vestibular system helps us maintain our balance It has three semicircular canals in the inner ear that contain hair cells which detect certain types of movement When you move your head the fluid in the canals puts pressure on the hair cells which then send impulses to the vestibular nerve and the brain Now just as we did for the ear we are going to follow the structures in the path of light as it goes through the eye cornea aqueous humor pupil lens vitreous humor light receptors and finally the optic nerve The iris regulates the size of the pupil while the ciliary muscle regulates the shape of the lens The light receptors which contain pigments are called rods and cones and are located in the retina Cones detect color while rods are designed to work under poor lighting conditions Now remember this if you are nearsighted light focuses in front of the retina when the object is far away If you are farsighted light focuses behind the retina when the object is near Human Physiology Let us start with breathing Breathing is involuntary The body gets ordered to breath The signal to breath originates in the medulla oblongata which is a primitive part of the brain The signal originates in a part of the medulla that is called the respiratory center It travels to the diaphragm via a nerve called the phrenic nerve The diaphragm is a muscle and when stimulated by the phrenic nerve it contracts Contraction of the diaphragm begins the process of breathing in which is called inspiration Before the diaphragm contracts it is shaped like a dome then when it contracts it attens out and creates empty space within the thoracic cavity The empty space creates negative pressure The rib cage expands as the diaphragm contracts which increases the negative pressure In order to fill the space and eliminate the negative pressure the lungs expand The lungs have a natural elasticity tending to keep them from expanding When the lungs expand they create a negative pressure inside themselves In order to eliminate that negative pressure air rushes into the lungs to fill the empty space that completes the process of inspiration First air enters the nose and flows into the trachea Next it reaches the bronchi The bronchi break up into smaller branches and these smaller branches splits several times more The tiny twig like branches are called bronchioles The trachea and bronchi have rings that help keep them open The respiratory tract begins with the nose The nose cleans warms and moistens incoming air Large particles are trapped in hairs lining the nostrils Particles that make it pass the nose get stuck in mucus which lines the lower parts of the respiratory tract Ciliated cells sweep the dirty mucus back out of the system Very small particles can make it all the way to the alveoli which are at the end of the bronchioles and these particles are eaten by phagocytic cells lining the alveoli Each alveolus is a hollow sphere situated at the end of a tiny bronchiole Alveoli are the terminal points of the respiratory tract When air is inspired and drawn through the respiratory tract it ends up in the alveoli The alveoli take oxygen from the air and supply it to the blood They also take carbon dioxide from the blood and send it out into the atmosphere Atmospheric air is richer in oxygen than it is carbon dioxide On inspiration the inner surface of the alveolus naturally comes in contact with the atmospheric air the lungs have inspired The outer surface of every alveolus is in contact with the capillary carrying blood whose relative composition of oxygen and carbon dioxide is opposite to that of atmospheric air The alveolar wall and capillary wall are both permeable to oxygen and carbon dioxide Oxygen therefore moves by passive diffusion along its concentration gradient It passes from the alveolus into the blood Carbon dioxide moves by passive diffusion along its concentration gradient It passes from the blood into the alveolus Gas exchange can continue only if the respiratory system somehow reestablishes oxygen and carbon dioxide gradients between the alveoli and the capillaries that surround them The system must rid each alveolus of the air it contains and then afford it a new supply that is rich in oxygen and poor in carbon dioxide In order to empty the alveoli the medulla oblongata stops sending its signal to the diaphragm and the diaphragm stops contracting The lungs under the force of their own elasticity then recoil That forces air out of the alveoli upward through the respiratory tract and out into the atmosphere that is called expiration The alveolus has a film of fluid covering its inner surface The uid produces a force called surface tension and because of surface tension the alveolus has a tendency to collapse In order to avoid collapsing the alveolus needs something to reduce its surface tension There is a substance that does that called surfactant Carbon dioxide is byproduct of cellular metabolism Cells are perpetually dumping carbon dioxide into the blood The carbon dioxide travels through the bloodstream and ultimately reaches the capillaries that surround alveoli When carbon dioxide leaves the cells and enters the bloodstream it usually combines with water and forms carbonic acid Most of this carbonic acid then dissociates into hydrogen ions and bicarbonate Carbon dioxide does not always combine with water to form carbonic acid sometimes it combines with hemoglobin In the bloodstream carbon dioxide travels as carbonic acid or bicarbonate ion or it travels within a hemoglobin molecule When any of these molecules reach a capillary that surrounds an alveolus the molecular carbon dioxide reemerges The respiratory center is sensitive to the blood s oxygen content and to its carbon dioxide content When the oxygen content decreases the respiratory center signals the diaphragm to increase the rate of respiration Similarly when the blood s carbon dioxide content increases the respiratory center signals the diaphragm to increase the rate of respiration Remember that when carbon dioxide enters the blood from the cells it combines with Water to form carbonic acid and the carbonic acid in return dissociates into hydrogen and hydrogen carbonate That means that if the cell starts to produce some greater amounts of carbon dioxide the blood pH tends to fall Remember that these things make the respiratory center raise the respiratory rate lower the blood oxygen concentration increase blood carbon dioxide concentration increase blood hydrogen ion concentration which means lower the pH Reproduction Cells normally reproduce by dividing The division is called mitosis You should know that mitosis has four stages and you have to know what goes on in each stage You should also know what goes on before mitosis Before a cell undergoes mitosis every single chromosome in its nucleus has to reproduce itself That is called interphase It is called interphase because it takes place in between two mitotic divisions It happens after a previous mitotic division has occurred and before the next one occurs Most of the cell s life is spent in interphase After interphase each chromosome and its duplicate are joined in the middle by a centromere so they make one discrete physical structure called a chromosome made of two chromatids So for example in a human cell even though all chromosomes have been duplicated we say that after interphase the cell still has a total of 46 chromosomes After interphase the cell is ready to begin mitosis When the cell s chromosomes have fully replicated the cell is ready to begin mitosis The following are the four steps of mitosis observed under the microscope In step one or prophase the chromosomes thicken and become visible Meanwhile the centrioles move to opposite poles of the cells and next a bunch of lines called tubules form a spindle Aster fibers appear Aster fibers form around each centriole Finally the nuclear membrane begins to fall apart In step two or metaphase the double stranded chromosome line up in a column at the center of the cell In step three or anaphase each double stranded chromosome divides at the centromere The chromatids separate The separated chromatids then move toward opposite poles along the spindle Each chromatid has now become a single stranded chromosome In step four or telophase the cytoplasm divides This is called cytokinesis The nuclear membranes re form and two daughter cells result each with single stranded chromosomes Now we will talk a little about meiosis Meiosis is the process from which sperm and ova arise Ova and sperm are haploid not diploid When we think about humans we remember that ova and sperm are the only haploid cells in the body and they only arise through meiosis That means meiosis must somehow start with a diploid cell and produce a haploid cell The easiest way to understand meiosis is to compare it to mitosis and see how it is similar and how it is different Let us talk about the formation of sperm cells or spermatozoa Before meiosis begins the diploid cell goes through interphase just as it does before it begins mitosis It is then called a primary spermatocyte In humans the spermatogonium has 46 single stranded chromosomes and the primary spermatocyte has 46 double stranded chromosomes Meiosis features the same four stages that are associated with mitosis prophase metaphase anaphase and telophase However in meiosis during prophase synapsis occurs The two pairs of homologous chromosomes come together and form a tetrad When synapsis occurs pieces of DNA can be exchanged This exchange of genetic material is called crossing over This results in genetic recombination In mitosis every double stranded chromosome lines up on the spindle and then in anaphase the centromere separates the two single stranded chromosomes In meiosis however the two pairs of homologous chromosomes a tetrad line up together on the spindle Then in anaphase the centromere does not break up The two identical pairs of double stranded chromosomes separate each with its centromere intact At telophase two daughter cells are formed Both cells are now called second spermatocytes each containing 23 double stranded chromosomes and is called a haploid cell Each daughter now contains duplicate chromosomes still joined by a centromere Each of the two daughter cells goes through a second division that is just like mitosis There is a prophase metaphase anaphase and telophase In each cell a spindle forms and the 23 double stranded chromosomes joined by a centromere line up and then separate at the centromeres The result is four daughter cells each one with 23 single stranded chromosomes At this stage they are called spermatids So actually there are two cell divisions The first division is called the first meiotic division It is also called the reduction division since the two daughter chromosomes end up with 23 double stranded chromosomes instead of 46 single stranded chromosomes The second division is very much like mitosis In each daughter cell a spindle forms and the 23 centromeres separate Then the centromeres divide and each daughter cell in turn gives rise to two new daughter cells each one having 23 single stranded chromosomes The testis is where meiosis takes place in male The testis has a lot of little tubes called seminiferous tubules in it These seminiferous tubules get together to form one big tube called the vas deferens The wall inside of the seminiferous tubule is made of cells and the cells are called spermatogonia Spermatogonia like most cells are diploid but they undergo meiosis and produce haploid cells which are sperm cells or spermatozoa Once spermatozoa are produced they move through the seminiferous tubules to a structure called the epididymis When spermatozoa leave the epididymis they are mature Then they pass into the vas deferens The vas deferens leads to the urethra Fluid is added by two accessory glands the seminal vesicles and the prostate The urethra is the way out and it runs the length of the penis Ovaries are the site of meiosis in females Females have two ovaries When they undergo meiosis they produce egg cells One egg cell is called an ovum and the plural for ovum is ova The formation of ova is called oogenesis So the cells inside the female ovary undergo meiosis and produce ova In the male the cell that undergoes meiosis is called a spermatogonium In the female it is called an oogonium The oogonium like most other cells is diploid but it undergoes meiosis and produces a haploid ovum The one major difference is that oogenesis produces only one ovum not four In spermatogenesis one spermatogonium undergoes meiosis and produces four spermatozoa In oogenesis one primary oocyte produces only one ovum The reason for this is that the primary oocyte undergoes the first meiotic division just like the spermatogonia It produces two daughter cells called secondary oocytes and each one has 23 double stranded chromosomes Each daughter cell goes on into the second meiotic division and produces two new haploid daughter cells but three of those cells get only a tiny amount of cytoplasm and degenerate So we are left with only one haploid daughter cell and that is called an ovum The three tiny cells that degenerate during oogenesis are called polar bodies Oogenesis produces only one ovum because it wants to conserve as much cytoplasm as possible There is one more difference between oogenesis and spermatogenesis At birth all the oogonia are present and arrested in prophase of the first meiotic division At the time of ovulation the ovum is sent out of the ovary into the fallopian tube which connects the ovary to the uterus If at the time the ovum is released there happens to be a spermatozoan in the fallopian tube fertilization occurs Fertilization means that the sperm cell penetrates the ovum The sperm has enzymes in a portion of its head called the acrosome which enable the sperm to penetrate the layers of cells that cover the ovum The outer layer is called the corona radiata and the inner layer is called the zones pellucida The result is a zygote which develops into an embryo The Heart The heart has four chambers two on the right and two on the left On each side of the heart right and left the top half is called the atrium and the bottom half is called the ventricle So the human heart has a right atrium a left atrium a right ventricle and a left ventricle Blood has to move throughout the body all of the time The heart is a pump whose job is to keep the blood moving throughout the body all of the time Blood goes around the body and through the heart in a continuous cycle and that cycle is called the circulation We will start at the point in the circulation at which the blood leaves the heart to begin its tour around the body The blood leaves the heart from the left side specifically from the left ventricle After leaving the left ventricle the blood tours the entire body It enters a huge blood vessel which is called the aorta The aorta is the largest artery in the human body Remember that arteries take blood away from the heart Shortly after it takes off from the left ventricle the aorta divides into smaller arteries and then into even smaller arteries and these small arteries go off in all different directions throughout the body When the arteries get very small they are called arterials and when they get very very small they are called capillaries Some of these capillaries go to the skin They have the ability to constrict in cold weather thus retaining body heat and to dilate in warm weather so these capillaries are involved in thermal regulation which is an important function of the skin Capillaries coalesce to form bigger and bigger blood vessels eventually forming veins Veins always take blood towards the heart Finally all of the blood ends up in two large veins and these two veins return the blood to the heart One vein is called the anterior vena cava and the other is called the posterior vena cava The anterior and the posterior vena cava take the blood into the right side of the heart specifically into the right atrium On each side of the heart there are two trap doors between the atria and the ventricles There is a trap door between the right atrium and the right ventricle There is also a trap door between the left atrium and the left ventricle The trap door between the right atrium and the right ventricle is called the tricuspid valve The trap door between the left atrium and the left ventricle is called the bicuspid valve or mitral valve Because of these trap doors blood that s on the right side of the heart can move from the right atrium to the right ventricle Blood that s on the left side of the heart can move from the left atrium to the left ventricle Blood cannot move however directly from the right side of the heart to the left side of the heart The blood doesn t stay in the right ventricle Blood is always on the move The next thing it does is to leave the right ventricle and pass into the pulmonary circulation The pulmonary circulation is another system of arteries arterials capillaries venules and veins separate from the one we talked about before The pulmonary circulation involves only the lungs When blood leaves the right ventricle it immediately enters a large artery called the pulmonary artery This pulmonary artery then divides into a right pulmonary artery which goes to the right lung and a left pulmonary artery which goes to the left lung The pulmonary arteries carry deoxygenated blood Within the lung each pulmonary artery branches repeatedly to form capillaries then the capillaries coalesce to form venules small veins larger veins and finally all of the blood from the right lung is collected in two large veins called the right pulmonary veins and all of the blood from the left lung is collected in two large veins called the left pulmonary veins The pulmonary veins carry oxygenated blood All four of the pulmonary veins two from the right lung and two from the left lung then conduct blood into the heart s left atrium From the left atrium it passes through a valve into the left ventricle From the left ventricle it passes out into the aorta and the circulatory cycle begins again Contraction of the atrium is called diastole Contraction of the ventricles is called systole Because during systole blood is pushed from the left ventricle out into the entire body all of the arteries in the body feel a push of blood called the arterial pulse The heart contracts and relaxes automatically about 72 times per minute throughout life The signal for every contraction originates in the heart itself The place of origin is located in the right atrium and it is called the sinoatrial node It is also called the SA node When you think of the signal to contract spreading throughout the heart just think of the letters SABP The signal begins at S the sinoatrial node It next reaches A the atrioventricular node From the atrioventricular node the signal passes to B the bundle of His and from there it travels through both ventricles via P the Purkinje fibers Blood contains three types of cells red blood cells white blood cells and platelets It also contains proteins Red blood cells carry the blood gases oxygen and carbon dioxide The white blood cells are called leukocytes which form pus and eat foreign particles like bacteria and lymphocytes which we will discuss later Platelets are necessary for blood clotting All the blood cells originate from precursor cells in the bone marrow A hematocrit is the percentage of whole blood volume that is occupied by red blood cells Plasma is whole blood without the cells Serum is the uid that is left over after the plasma has clotted As blood flows through the capillary two types of pressure are at work hydrostatic and osmotic Hydrostatic pressure causes fluids to be pushed out of the capillary and osmotic pressure causes fluids to be pulled into the capillary At the arterial end the hydrostatic pressure is greater than osmotic pressure so fluids are pushed out of the capillary At the Venous end the osmotic pressure is greater than the hydrostatic pressure so uids are pulled into the capillary This is the fate of 99 of the uid The rest of the fluid gets picked up by the lymph system The Lymphatic System The lymph system is another system of vessels with liquid in them The vessels are called the lymphatics and the uid is called the lymph Every so often along the course of every lymph vessel there is a little thing called a lymph node A lymph node is made up mostly of some cells called lymph cells Another word for lymph cells is lymphocytes Lymphocytes are found not only in the lymph nodes but they circulate in the blood as well Lymph nodes collect and return interstitial uid to the blood They are composed of lymphocytes and are therefore important in protecting the body against infection The spleen is like one giant lymph node full of lymphocytes The spleen also destroys old red blood cells The thymus is important in the development of lymphocytes There are two main types of lymphocytes T lymphocytes arise in the bone marrow and mature in the thymus They are responsible for cellular immunity B lymphocytes are made in the bone marrow also They are responsible for humoral immunity In order to have a fully functioning immune system you need to have both B and T lymphocytes in your lymphatics and your blood Since lymphocytes do circulate in the blood they are regarded as blood cells When foreign substances known as antigens enter the blood they cause B lymphocytes to make protein antibodies These antibodies bind to the foreign materials and make them easier to destroy There are many different types of T lymphocytes T lymphocytes destroy antigens and often work with B lymphocytes The Cell We will start the biology section with the cell Cells are the fundamental units of life and you are required to know about them There are two types of cells eukaryotic cells and prokaryotic cells Eukaryotic cells are the ones with the well defined nucleus a nuclear membrane and organelles like the mitochondria Golgi bodies endoplasmic reticulum etc Think of the eukaryotic cell in three regions Region one the outer cell wall and membrane Region two the cytoplasm which contains the organelles and cytosol Region three the nucleus which is encased in a nuclear membrane Remember that all cells except animal cells usually have a cell wall and a cell membrane Animal cells have a cell membrane only They do not have a cell wall Remember also that cell walls are made of carbohydrates Cell membranes are made of proteins and phospholipids Since the cell membrane has two layers of phospholipids it is sometimes called a phospholipid bilayer The cell membrane is made of proteins and phospholipids You need to remember one theory about the arrangement of protein and phospholipid This theory depicts the cell membrane as a bilayer of phospholipids with proteins kind of stuck into it on the inner and outer surfaces The proteins stuck at the outer surface or the inner surface are called peripheral proteins The proteins that are entirely inside the phospholipid bilayer are called integral proteins Some of these proteins are large enough to penetrate the bilayer and protrude through both ends A phospholipid molecule has a head and a tail The head is water soluble or hydrophilic and the tail is water insoluble or hydrophobic The hydrophilic heads point outward to the surface and inward to the cytoplasm The hydrophobic tails meet in the interior of the bilayer The cell membrane is important therefore because it regulates and maintains the cell s internal environment and it determines what gets into the cell and what stays out To understand how the cell membrane does this imagine a balloon filled with freshwater and imagine that the balloon is a cell Imagine also that the balloon is freely permeable to salt Now suppose we put the balloon in a tank of salt water The water inside the balloon does not have salt in it but the water outside the balloon does Now remember this rule every solution tends to equalize the concentration of solutes throughout its Volume and unless something stands in its way it will do exactly that Since we said the balloon is freely permeable to salt salt will pass in the balloon until the salt concentration inside the balloon is the same as that outside the balloon Now suppose by some process we change the balloon s properties in two ways First we make it impermeable to salt Second we make it possible for water to pass into the balloon but impossible for water to pass out of the balloon Now imagine that we take the balloon out of the salt water tank and put it into a fresh water tank Since the water inside the balloon has salt in it but the water outside the balloon does not some salt would like to move out of the balloon in order to equalize the concentration But that cannot happen and because the system keeps trying to equalize the salt concentration inside and outside the balloon it keeps moving water into the balloon and the balloon eventually pops When in a solution or system of connected solutions like the balloon in the tank two different regions have different concentrations of the same solute We call that difference a concentration gradient Any movement of solvent or solute that tends to equalize concentrations will of course tend to eliminate the concentration gradient and that movement is called movement with or along the concentration gradient When you think about a membrane that is permeable to all of the solvents and solutes in its surroundings then you call movement through that membrane simple diffusion Think about a membrane that is not permeable to a solute but is permeable to a solvent When the solvent which is usually water moves across the membrane in order to equalize concentrations we call that movement osmosis Think about the expanding balloon in the example Its solute concentration is higher than that of its surrounding medium We say then that the uid in the balloon is hypertonic If the balloon in our example had a solute concentration that was lower than its surrounding medium we say that the uid in the balloon is hypotonic Think again about the expanding balloon in our example Because the fluid inside is hypertonic and because the balloon is impermeable to the outward flow of water there is a tendency for water to move into the balloon The balloon s tendency to suck water in by osmosis is called osmotic pressure Osmotic pressure is the tendency of water to move into a solution by osmosis When a membrane is permeable to some substances but not others it is called semi selectively permeable or semipermeable The cell membrane is semipermeable because of its structure Remember that the cell membrane is composed of a lipid bilayer and protein Substances that are lipid soluble tend to pass through the lipid bilayer pretty easily by simple diffusion But for substances that are lipid insoluble such as proteins and charged ions the lipid bilayer is a barrier to movement Lipid insoluble substances cannot get through the lipid bilayer unless they have some special help This special help comes from the membrane s protein components For these lipid insoluble substances the cell membrane s protein components somehow facilitate movement through the bilayer In fact when a lipid insoluble substance is able to move through the cell membrane along a concentration gradient or electrical gradient we say that the substance is undergoing facilitated diffusion or facilitated transport The way facilitated diffusion works is not clearly known There is however a popular theory which states that some of the membrane s protein molecules act as carrier molecules and because of their particular structure they have the ability to combine with a particular solute usually hydrophilic to form a complex This complex is soluble in the lipid bilayer of the membrane and it passes through without coming in contact with the hydrophobic interior of the lipid bilayer At the other end of the channel the carrier molecule and the solute separate and the solute is released It is important to know that the membrane s properties of permeability are not constant and can change from moment to moment The membrane s permeability is adjusted according its protein components At one moment the membrane might be permeable to outward movement of sodium but not to its inward movement At another moment the situation might be reversed and sodium might move freely into the cell but be unable to move outward The cell membrane is also thought to have tiny channels or pores with each channel somehow selective in its permeability to lipid insoluble substances There are thought to be special potassium channels special calcium channels and special glucose channels Just as selective permeability is related to specific carrier molecules selective permeability is related to the presence of membrane channels It is hypothesized that the channels have gates on them that can be opened or closed Remember this any movement of solute or solvent that tends to produce or increase a concentration gradient requires the expenditure of energy and that is called active transport If a system wants to move charged particles against an electrical gradient it must expend energy and that is also called active transport The process of active transport is also called a pump An example of active transport mechanism is the sodium potassium pump Simple diffusion and osmosis do not require the cell to expend energy These two processes therefore represent passive transport Facilitated transport does not require energy because movement occurs along a concentration gradient or electrical gradient For that reason facilitated transport is not considered active transport But even though the process does not require energy the cell membrane has some active involvement in it and therefore the process is not considered to be a form of passive transport either So remember that substances may cross the cell membrane by l passive transport which includes osmosis and simple diffusion 2 facilitated transport and 3 active transport and fourth kind called endocytosis Passive transport facilitated transport and active transport apply to the movement of molecules and ions in and out of the cell In order to take in larger particles cell membranes use endocytosis in which a portion of membrane engulfs the object and pinches off to contain it within a vesicle inside the cytoplasm Phagocytosis or cell eating is the endocytosis of relatively large particles Pinocytosis or cell drinking is the endocytosis of dissolved materials Receptor mediated endocytosis is the endocytosis of specific particles using protein receptors found in clathrin coated pit regions of the membrane The cell membrane is actually one section of a larger membrane system This system begins at the outer border of the cell branches into the cytoplasm winds its way through the cytoplasm and then surrounds the cell s nucleus Where this membrane is located at the periphery of the cell it is called the cell membrane Where it is located in the cytoplasm it is called the endoplasmic reticulum Where it surrounds the nucleus it is called the nuclear membrane The endoplasmic reticulum looks like a network of channels Endoplasmic reticulum can be smooth or rough Some portions of the endoplasmic reticulum have bumps on them so these portions are called rough endoplasmic reticulum The portions without the bumps are called smooth endoplasmic reticulum These bumps sitting on the rough endoplasmic reticulum are ribosomes Ribosomes are the sites at which the cell synthesizes protein Smooth endoplasmic reticulum is not attached to ribosomes and it is not involved in protein synthesis The smooth endoplasmic reticulum is involved in lipid synthesis At one or more points along its course the smooth endoplasmic reticulum changes shape and looks like a network of attened sacs instead of a network of channels This region of endoplasmic reticulum is called the Golgi apparatus The Golgi apparatus pinches off little pieces of itself and these are called vesicles Make sure you do not confuse these vesicles with the vesicles that result from pinocytosis and phagocytosis Golgi apparatus is involved in the packaging of proteins to be sent out of the cell It packages these proteins in vesicles These packaged proteins are modified along the way and usually carbohydrates are added to them Remember that sending materials out of the cell is called exocytosis The cells must stick together to form body tissues They do this by forming three types of cellular adhesions with each other They are tight junctions desmosomes and gap junctions Tight junctions prohibit the passage of most substances between cells while gap junctions allow the passage of small ions and molecules from cell to cell Desmosomes hold adjacent cells together but allow substances to pass through The endoplasmic reticulum the ribosomes and the Golgi apparatus are three cellular organelles and they happen to be closely associated with one another There are eleven other structures associated with the cell and you are required to know a little about them Let us review these organelles and their functions Chromosomes are composed of DNA and contain genetic information Lysosomes contain hydrolytic enzymes and digest foreign substances and worn organelles Centrioles are hollow rods composed of microtubules and form the spindle fibers during mitosis Peroxisomes contain enzyme catalase and metabolize oxygen or hydrogen peroxide Cilia and flagella function in cell movement by acting in a whip like motion Microfilaments are thin fibers made of actin associated with movement of cytoplasm Microtubules form part of the cell s skeleton and are involved in movement of chromosomes and also the structure from which cilia and flagella are formed Nucleolus is the site at which ribosomal RNA is formed and is located in the nucleus Vacuoles are fluid filled spaces that function in expelling wastes Plastids contain pigment and are found only in plants Mitochondrion is a double membrane organelle with an inner matrix and it produces ATP Musculoskeletal System Bone is made of two substances mixed together The substances are collagen and something called hydroxyapatite Hydroxyapatite is a combination of calcium salt crystals These are deposited on the collagen which is a protein There are two types of bone spongy bone and compact bone Bones are held together by joints Joints come in three main varieties Those made out of collagen fibers called fibrous and those made out of cartilage called cartilaginous and the variety called synovial Synovial joints are found all over the body in the shoulder in the knee and in the jaw These kinds of joints are covered by a capsule and inside there is a synovial membrane that makes synovial uid This uid keeps the bones from rubbing against each other The ends of the bones are also covered by something called articular cartilage which protects against rubbing When you look closely at compact bone under the microscope you see a bunch of circles and each circle is called a Haversian system At the center of the Haversian system is a canal it is called a Haversian canal Blood vessels and nerves run through the Haversian canal On the periphery of the Haversian canal are little wells called lacunae in which bone cells live Bone cells are called osteocytes Bone also contains osteoblast and osteoclast which are involved in bone remodeling Osteoblasts are bone building cells and osteoclast breakdown bone Bones can move because of the muscles that are attached to them Muscles are attached to bones by tendons Li gaments however are for bone to bone attachments Note that the muscles that allow us to move our skeletons are the ones over which we conscious voluntary control They are called skeletal muscle or voluntary muscle When we look at skeletal muscle under the microscope we see striations stripes Know that skeletal muscle is striated How skeletal muscles make us move Let us say that muscle A is attached to two bones across the front side of the elbow joint When this muscle gets shorter the bones move closer to each other and the arm bends at the elbow joint Let us look at another scenario that involves muscle B Muscle B is attached to the same set of bones that muscle A is attached to but muscle B crosses the back side of the elbow joint If muscle B contracts its contraction causes the arm to open because muscle B is attached across the back side of the elbow joint Muscle B and muscle A have opposite actions because they are attached across opposite sides of the same joint Muscle B and muscle A have antagonistic actions They do opposite things One muscle opens the arm at the elbow joint and another closes it Muscle is composed of cells These muscle cells are called muscle fibers A muscle fiber is composed of sarcomeres Sarcomeres are responsible for contraction Sarcomere has filaments in it and the filaments are made of protein The thin filaments are made of a protein called actin and the thick filaments are made of a protein called myosin The thin filaments are attached to rods called Z lines Actin and myosin give a muscle the ability to contract The entire length of the thick filament is called the A band The space between thick filaments is the I band and the space between thin filaments is the H band The actin filaments and the myosin filaments can be connected by cross bridges which move like hinge levers When these hinge movement occurs the actin and myosin slide past each other and the sarcomere gets shorter Remember that during contraction only the H and I bands shorten and the A band remains the same When a sarcomere gets shorter so does the muscle fiber and consequently the whole muscle In a muscle fiber an endoplasmic reticulum is called the sarcoplasmic reticulum When you want to move a part of your body you send a nerve signal down a motor neuron to the appropriate skeletal muscle When the muscle receives the nerve signal a number of things happened First the nerve releases acetylcholine The muscle undergoes an action potential that causes the sarcoplasmic reticulum to release calcium ions The calcium ions caused the actin and myosin to slide past each other which will cause the sarcomere to shorten The excess acetylcholine is broken down by the enzyme cholinesterase Muscle fibers have a lot of mitochondria to produce enough energy for muscle contraction When muscle is contracting actively it needs a big supply of oxygen and it produces a lot of carbon dioxide Therefore when a muscle is actively contracting the blood vessels that supply it will dilate to allow the muscle to get more blood and of course more oxygen In cases where the muscle contracts so actively that it cannot get enough oxygen to met it needs it cannot take pyruvic acid and put it into the Krebs cycle Therefore the muscle reduces pyruvic acid without oxygen by anaerobic oxidation In this reaction the pyruvic is converted to lactate Lactate will then build up in the muscle and will eventually cause some pain This is called oxygen death When a muscle is unable to get all of the oxygen it needs and so it starts to produce lactic acid There are three types muscle skeletal muscle smooth muscle and cardiac muscle Skeletal muscle is the muscle through which we undertake voluntary movements of our skeleton Cardiac muscle is the muscle that the heart is made of It is striated and has special junctions between muscle cells called intercalated disks It is under involuntary control Smooth muscle is all other muscle They function in every other part of the body The smooth muscles are found inside the blood vessels and glands our internal organs and ducts Smooth muscle is responsible for involuntary movements within our body it is under involuntary control Smooth muscle and cardiac muscle get their nerve supply from the autonomic nervous system Skeletal muscle gets its nerves supply from the somatic system Remember under the microscope smooth muscle does not have any stripes it is not striated but cardiac muscle and skeletal muscle are striated Ski n Skin is the largest organ in the body Our skin maintains our body temperature senses our environment and guards us against microorganisms The skin has three layers epidermis dermis and subcutaneous tissue The outer surface is epidermis covered by dead cells called the stratum corneum These cells are full of protein called keratin and form a barrier against invasion of microorganisms The dermis is just below the epidermis Here you find blood vessels nerve endings sebaceous glands which secrete oils and sweat glands It is the sweat glands that release water and ions in warm weather This keeps down temperature and also serves to maintain optimal levels of sodium and chloride in the body Finally there is the subcutaneous tissue which is mostly fat
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