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Week 2 A&P Notes

by: Annie Estes

Week 2 A&P Notes HS 220

Annie Estes
Whitworth University

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These notes cover week two of lecture.
Anatomy and Physiology
Class Notes
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This 9 page Class Notes was uploaded by Annie Estes on Thursday September 29, 2016. The Class Notes belongs to HS 220 at Whitworth University taught by Ulbright in Fall 2016. Since its upload, it has received 4 views. For similar materials see Anatomy and Physiology in Health Sciences at Whitworth University.

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Date Created: 09/29/16
CELLULAR LEVEL OF ORGANIZATION A cell is the basic living structural and functional unit of the body. Remember that all living things exhibit these characteristics:  Metabolism  Responsiveness  Movement  Growth  Differentiation  Reproduction A Generalized View of the Cell  A generalized view of the cell is a composite of many different cells in the body. No single cell includes all of the features seen in the generalized cell.  The cell can be divided into three principal parts for ease of study. o Plasma (cell) membrane o Cytoplasm o Nucleus 1. The Plasma Membrane  A flexible, but sturdy, selectively permeable barrier that surrounds and contains the cytoplasm of the cell.  Lipid bilayer o The lipid bilayer is the basic framework of the plasma membrane and is made up of three types of lipid molecules: 75% phospholipids (selectively permeable barrier), 20% cholesterol (strength), and 5% glycolipids (identification sites) o The bilayer arrangement occurs because the lipid molecules are amphipathic. They have both polar (charged, hydrophilic) and nonpolar (uncharged, hydrophobic) ends with the polar “head” of the phospholipid pointing out and the nonpolar “tail” pointing toward the center of the membrane.  Membrane proteins o The membrane proteins are divided into:  Integral proteins: extend into or across the entire lipid bilayer.  Peripheral proteins: found at the inner or outer surface of the membrane and can be stripped away from the membrane without disturbing membrane integrity. o Membrane proteins can function as channels (pores), transporters, receptors, enzymes, cell-identity markers, and linkers depending on the type of cell. o Glycoproteins and glycolipids form the glycocalyx, which helps cells recognize one another, adhere to one another, and be protected from digestion by enzymes in the extracellular fluid.  Membrane fluidity o Membranes are fluid structures, like cooking oil, because most of the membrane lipids and many of the membrane proteins easily move in the bilayer. This is useful when repairs are needed, like after a needle is pushed in.  Membrane permeability o Plasma membranes are selectively permeable, meaning that some things can pass through and others cannot. o The lipid bilayer is permeable to water and small, nonpolar, uncharged molecules (e.g. O 2 CO ,2some small steroids), but impermeable to ions and charged or polar molecules (e.g. Na , Cl ). o Transmembrane proteins that act as channels or transporters increase the permeability of the membrane to molecules that cannot cross the lipid bilayer. o Macromolecules are unable to pass through the plasma membrane, except by vesicular transport.  Gradients across the plasma membrane o A concentration gradient is the difference in the concentration of a chemical between one side of the plasma membrane and the other. +  For example, Na ions are more concentrated outside a nerve cell membrane than on the inside. Consequently, the inner surface of the membrane is more negatively charged and the outer surface is more positively charged. This sets up an electrical gradient, called the membrane potential. o Most thing+ will diffuse across the plasma membrane, down the gradient (e.g. Na will move inside the cell to the area of lower concentration). Diffusion rate across plasma membranes is influenced by several factors:  Steepness of the concentration gradient  Temperature  Size or mass of the diffusing substance  Surface area  Diffusion distance o Maintaining concentration and electrical gradients are important to the life of the cell because it helps regulate the movement of substances across the membrane! Transport Across the Plasma Membrane  Transport processes to move substances across the cell membrane are essential to the life of the cell. o Classified as:  Mediated transport: involves moving materials through the membrane with the assistance of a transporter protein.  Non-mediated transport: does not require a transporter protein.  Passive transport: a substance uses its own kinetic energy to move DOWN/WITH a concentration gradient.  Active transport, a substance uses its kinetic energy AND energy from ATP to move UP/AGAINST a concentration gradient. o Examples:  Living cells typically use three passive transport processes, one of which is non-mediated (diffusion through the lipid bilayer) and) and two that are mediated (diffusion through a channel and facilitated diffusion).  Living cells use active mediated processes distinguished by the types of transporters (uniporters, symporters, and antiporters).  Vesicular transport involves the formation of membrane-surrounded vesicles to move materials into or out of the cell by endocytosis or exocytosis. Passive Transport of Materials Into and Out of Cells  Osmosis: the movement of water (down its concentration gradient) across the selectively permeable membrane from an area of higher concentration to an area of lower concentration. o Water molecules penetrate the membrane by diffusion through the lipid bilayer or through aquaporins (transmembrane proteins that function as water channels). o Osmosis occurs only when the membrane is permeable to water, but not to certain solutes. o Tonicity of a solution relates to the direction of water into and out of cells. Water will always try to move toward high concentrations of solutes, which have a lower concentration of water.  Isotonic solution: there is no gradient to promote water movement into or out of a cell.  Hypotonic solution: there is a gradient that promotes water movement into cells (rehydration) because there are more solutes in the cell than in the solution.  Hypertonic solution: there is a gradient that promotes water movement out of cells (dehydration) because there are more solutes in the solution than in the cell. o Energy Cost: free o Limit: equilibrium  Diffusion through the lipid bilayer: passive diffusion of a substance down its concentration gradient through channels that span a lipid bilayer o Non-polar and/or hydrophobic molecules such as respiratory gases (e.g. O 2 CO 2, some lipids, small alcohols, and ammonia can diffuse across the lipid bilayer. o It is important for gas exchange, absorption of some nutrients, and excretion of some wastes. o Energy Cost: free o Limit: equilibrium  Diffusion through membrane channels: passive diffusion of a substance down its electrical gradient through membrane channels that span a lipid bilayer o Most membrane channels are ion channels, allowing passage of small, + + - inorganic, hydrophilic ions (e.g. K , Na , Cl ). o Ion channels are selective, specific and may close or open at any time. o Slower process due to less surface area for diffusion. o Energy Cost: free o Limit: equilibrium  Facilitated Diffusion: passive diffusion of a substance down its concentration gradient via membrane proteins that act as transporters. o A substance binds to a specific transporter on one side of the membrane and is released on the other side after the transporter undergoes a conformational change. o Substances that move across membranes by facilitated diffusion include glucose, urea, fructose, galactose, and some vitamins. o Cost: free o Limit: equilibrium, when transporter becomes saturated, or total number of transporters on membrane. Active Transport of Materials Into and Out of Cells  Primary active transport: energy derived from ATP changes the shape of a transporter protein, which pumps a substance across a plasma membrane against its concentration gradient. + +- o The most prevalent primary active transport mechanism is the Na -K ATPase pump, which drives the Na -K electrochemical gradient for most human cells. o Cost: ATP o Limit: ATP availability, number of pumps  Secondary active transport: the energy stored in the form of a Na or H ion + concentration gradient is used to drive other substances against their own concentration gradients. o Na or H ion concentration gradients are maintained by ATP pumps. o Cost: ATP o Limit: ATP availability, number of transporters, Na /H gradients  Endocytosis: receptor-mediated uptake of materials into a cell via a vesicle formed from the plasma membrane. o Cost: ATP o Limit: ATP availability, until the job is done  Exocytosis: membrane-enclosed vesicles that form inside the cell and fuse with the plasma membrane, then release their contents outside the cell. o Cost: ATP o Limit: neural or hormonally controlled 2. Cytoplasm  Cytosol, the intracellular fluid (ICF), is the semifluid portion of cytoplasm. o Composed mostly of water (75-90%), plus proteins, CHOs, lipids, and inorganic substances. o Functionally, cytosol is the medium in which many metabolic reactions occur.  Organelles are specialized structures within the cell (and surrounded by cytosol) that have characteristic shapes and perform specific functions related to cellular growth, maintenance, and reproduction. These include: o Cytoskeleton  A network of protein filaments that extend throughout the cytoplasm and provides the structural framework for the cell. Consists of:  Microfilaments (smallest): most are composed of actin and function in movement and mechanical support.  Intermediate filaments (medium): composed of several different proteins and help anchor organelles.  Microtubules (largest): composed of a protein called tubulin, help determine cell shape, and function in the intracellular transport of organelles (e.g. a subway in the cell) and the migration of chromosomes during cell division. o Centrosomes  Dense area of cytoplasm that contain the centrioles, which are paired cylinders that play a role in building the cell’s infrastructure and preparing for cellular division. o Cilia and Flagella  Cilia: numerous, short, hair-like projections that extend from the surface of a cell and function to move materials across the surface of the cell.  Flagella: similar to cilia, but much longer. They function to move an entire cell. o Ribosomes (“the work bench”)  Tiny spheres that consist of ribosomal RNA and are the sites of protein synthesis.  “Free” ribosomes make proteins that are used within the cell.  Ribosomes bound to the ER make proteins that are destined for the plasma membrane or export from the cell. o Endoplasmic Reticulum (“the factory”)  A network of membranes that form flattened sacs or tubules called cisternae.  Rough ER is continuous with the nuclear membrane and has its outer surface studded with ribosomes.  Synthesizes glycoproteins and phospholipids that are later used for the plasma membrane or secreted from the cell.  Smooth ER extends from the rough ER to form a network of membrane tubules, but does not contain ribosomes on its membrane surface.  Synthesizes fatty acids and steroids (e.g. testosterone and estrogen).  Detoxifies some drugs, especially in the liver.  Stores and releases Ca 2+to help trigger muscle contractions o Golgi Complex (“the distribution hub”)  Consists of 3-20 stacked, flattened membranous sacs (cisterns)  Processes, sorts, and delivers proteins and lipids to the plasma membrane, lysosomes or other areas within the cell, and forms secretory vesicles for secretion. o Lysosomes (“the recycling plant”)  Membrane-enclosed vesicles that form within the Golgi complex and contain powerful digestive enzymes for intracellular digestion of  Foreign molecules from endocytosis  Worn-out organelles  Cellular contents o Peroxisomes (“the detox center”)  Similar in structure to lysosomes, but are smaller.  Contain several enzymes that oxidize (remove H ) various organic substances.  Fatty acids and AAs also metabolized here. o Mitochondria (“the power station”)  Bound by a double membrane - the outer membrane is smooth while the inner membrane is arranged in folds called cristae.  Mitochondria are the site of ATP production in the cell by the catabolism of nutrient molecules during cellular respiration.  Mitochondria self-replicate using their own DNA. If needed, they can improve the cell’s energy system by producing more.  Mitochondrial DNA (genes) are usually inherited from the mother. 3. Nucleus  Usually the most prominent feature of a cell.  Most body cells have a single nucleus, however, some have none (e.g. red blood cells), whereas others (e.g. skeletal muscle fibers) have several.  The parts of the nucleus include the nuclear envelope, which is perforated by channels called nuclear pores, nucleoli, and genetic material (DNA).  Within the nucleus are the cell’s hereditary units, called genes, which are arranged in single file along chromosomes. o Each chromosome is a long molecule of DNA that is coiled together with several proteins. o Human somatic cells have 46 chromosomes arranged in 23 pairs.  Primary functions of the nucleus include: o Provide codes or instruction to direct synthesis of specific structural proteins. o Provide codes or instruction to direct synthesis of specific enzymatic proteins and cellular activities. o Produce ribosomes in nucleoli. Protein Synthesis  Much of the cellular machinery is devoted to synthesizing large numbers of diverse proteins. The proteins determine the physical and chemical characteristics of cells. o Primary protein functions:  Support: structural proteins provide strength, organization, and support for cells, tissues, and organs  Movement: contractile proteins are responsible for muscular contraction and cell locomotion.  Transport: lipids, gases, some minerals (e.g. iron), and some hormones can only be transported in the blood when first bound to special transport proteins. Also, proteins transport materials from one part of a cell to another.  Buffering: help regulate pH balance by acting as a buffer.  Metabolic regulation: enzymes accelerate chemical reactions in cells and help control function of specific organs and organ systems.  Coordination and control: protein hormones can influence the metabolic activities of every cell in the body or affect the function of specific organs or organ systems.  Defense: tough, waterproof proteins of the skin, hair, and nails protect the body from our environment. Protein antibodies are also components of immune response and help protect us from disease. o DNA vs. RNA  DNA: housed within the nucleus, it provides the instructions for PRO synthesis.  Messenger RNA (mRNA): directs the synthesis of a protein within the cytoplasm or ribosomes.  Ribosomal RNA (rRNA): joins with ribosomal proteins to make ribosomes.  Transfer RNA (tRNA): binds to an AA and helps until the AA is built into a protein. o Protein synthesis involves two processes:  Transcription: the process by which genetic information encoded in DNA is copied onto a strand of mRNA, which directs PRO synthesis. This occurs in the nucleus.  Translation: the process of reading the mRNA blueprints to determine the AA sequence of the protein. This occurs in the cytoplasm or ribosome. Normal Cell Division  Cell division is the process by which cells reproduce themselves. It consists of nuclear division (mitosis and meiosis) and cytoplasmic division (cytokinesis). o Cell division that results in an increase in body cells is called somaticell division and involves a nuclear division called mitosis, plus cytokinesis o Cell division that results in the production of sperm and eggs is called reproductive cell division and consists of a nuclear division called meiosis plus cytokinesis.  The reproduction cycle in human somatic cells is a sequence of events by which a cell duplicates its contents and divides in two. It consists of two phases: o Interphase: the cell carries on every life process, while growing in preparation for cell division. It is divided into three phases:  Gap 1 (G1) phase: the cell is metabolically active, duplicating its organelles (making enough organelles for two complete cells) and cytosolic components except for DNA. May take 8 hrs to months. Cellular activity may slow if it is working hard to prepare for splitting.  Synthesis (S) phase: chromosomes or DNA are replicated. May take 6-8 hours.  Gap 2 (G2) phase: DNA replication has ended, so last minute protein synthesis occurs in preparation for cell division. May take 2-5 hours. o Mitotic phase: The process of cell division. It consists of two phases:  Mitosis: nuclear division and distribution of two sets of chromosomes, one set into each of two separate nuclei. Subdivided into four additional phases:  Prophase: the chromatin condenses and shortens into chromosomes, centrosomes move to poles.  Metaphase: the chromatid pairs line up at the exact center of the mitotic spindle, a region called the metaphase plate  Anaphase: the splitting and separation of centromeres or pairs and the movement of the two sister chromatids of each pair toward opposite poles of the cell.  Telophase: begins as soon as chromatid movement stops; the identical sets of chromosomes at opposite poles of the cell uncoil and revert to their threadlike chromatin form, microtubules disappear or change form, a new nuclear envelope forms, new nucleoli appear, and the new mitotic spindle eventually breaks up.  Cytokinesis: division of a parent’s cell’s cytoplasm and organelles. It begins in late anaphase and continues until two new cells are formed with their own nucleus and each surrounded by their own cell membrane.  Control of cell destiny o Three possible destinies of a cell:  Remain alive and functioning without dividing  Grow and divide  Die o Chemical factors that can affect cell division  Maturation promoting factor (MPF): induces cell division or triggers mitosis.  Growth hormone (GH): stimulates growth, cell division, and differentiation.  Prolactin: stimulates cell growth, division, development.  Nerve growth factor (NGF): stimulates nerve cell repair and development.  Epidermal growth factor (EGF): stimulates stem cell divisions and epithelial repairs.  Erythropoietin: primarily stimulates stem cell divisions within the kidneys and maturation of red blood cells in the circulation. o Additional related points…  Cell death, a process called apoptosis, is triggered either from outside the cell or from inside the cell due to a “cell-suicide” gene  Necrosis is a pathological cell death due to injury  Tumor-suppressor genes can produce proteins that normally inhibit cell division, damage to these genes can result in the uncontrollable cell growth known as cancer. Aging Effect on Cell Homeostasis  Aging is a normal process accompanied by a progressive alteration of the body’s homeostatic adaptive responses o The physiological signs of aging are gradual deterioration in body functions and capacity to respond to environmental stresses. o These signs are related to a net decrease in the number of cells in the body and to dysfunction of the cells that remain. o The extracellular components of tissues (e.g. collagen fibers and elastin) also change with age.


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