Biology Exam 3 Study Guide 10/31/2016

What is Gametes?

Meiosis, Spermatogenesis, and Oogenesis

∙ Meiosis

o Meiosis creates two identical daughter cells

o Would create clones-genetically identical offspring

o This is called asexual reproduction

o Creates 4 dissimilar haploid daughter cells (2nn, n, n, and n) o Creates gametes

∙ Gametes

o Sex cells, either sperm or egg

o Gametes are usually haploid

∙ Diploids vs. Haploids

o Diploids have 2 sets of chromosomes

o Haploids have 1 set of chromosomes

∙ Gametogenesis

o The production of the gametes

o Males and females have different forms of gametogenesis: Don't forget about the age old question of cell biology exam 2

 Spermatogenesis (male) Don't forget about the age old question of psy 235 purdue

 Makes haploid sperm

 Begins at puberty

 Occurs in the seminiferous tubules of testes

 Oogenesis (female)

 Makes haploid egg cells

 Begins prior to birth

 Stops after birth UNITL puberty

What is Gametogenesis?

Why don’t we look the same as our siblings?

o Meiosis produces genetically different gametes:

 Crossing-over

 Random assortment of chromosomes (independent  assortment) Don't forget about the age old question of music appreciation exam 1

∙

∙ Meiosis Summary

o Meiosis reduces the chromosome number in half (In humans,  this is diploidhaploid)

o Meiosis creates genetically dissimilar gametes by two  processes:

 Crossing-over

 Random alignment of homologous chromosomes

o Errors in meiosis leads to polyploidy

Plant Reproduction

∙ Plant Evolution

o Mosses (bryophytes) use gametes and spores to reproduce,  but flowering plants (angiosperms) use gametes and seeds. o Vascular tissue improves water and nutrient transport in  plants and they grow larger

∙ Ploidy of Plants

o Plants can be..

 Haploid n

 Diploid 2n

 Triploid 3n

What is Plant Evolution?

 Tetraploid 4n

 Pentaploid 5n

 Hexaploid 6n

 Etc…

∙ Moss

o Golden diploid sporophyte part grows out of green haploid  gametophyte base part (the moss we see)

Flowers—Gamete production, fertilization, and seed & fruit  development see link:  

https://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Mature_flower_ diagram.svg/2000px-Mature_flower_diagram.svg.png 

Chapter 22: Reproductive and Developmental Biology

Endocrine Disruptors: a class of chemicals altering the actions of the  hormone-producing endocrine system Don't forget about the age old question of uncc mun

Asexual Reproduction: A single organism reproduces by itself,  without mating with another

∙ Offspring are genetically identical to the parents and to each other o MitosisDon't forget about the age old question of ch4o lewis structure

o Binary fission: single cell splits into two identical daughter  cells

o Budding: daughter cell remains attached to the parent until  sufficiently grown to break away

Asexual reproduction in organisms:

∙ Binary fission—Bacteria

∙ Asexual—Sponge

∙ Budding—Yeast, hydra, etc.

∙

o Meiosis is not used in asexual reproduction

Sexual Reproduction: the fusion of gametes from two different  individuals (male and female)

∙ Produces genetically diverse offspring

∙ Gamete: sex cell; egg or sperm

o Haploid (n)

∙ Gonads: gamete-producing structures

o Ovaries: produce eggs in females

o Testes: produce sperm in males

∙ Zygote: a fertilized egg cell resulting from sexual reproduction o Diploid (2n)

How many chromosomes do human GAMETES contain? (A: 23) ∙ Human BODY cells contain 46 chromosomes

Hermaphrodites: animals that have both male and female reproductive systems

∙ Earthworms

o Donate or receive sperm during mating

Methods of Fertilization If you want to learn more check out tony hsieh served as ceo of _____, and eventually sold the firm to amazon for $900 million.

∙ Internal Fertilization: Sperm deposited in or near female  reproductive tract

o Sharks, reptiles, birds, and mammals

∙ External Fertilization: Female lays eggs in water and male releases  sperm over eggs

o Aquatic invertebrates, most fish, and amphibians

 Highly sensitive to environmental contaminants in water

Environmental contaminants in the water

∙ Organisms developing in water most affected

∙ Herbicide atrazine

o Male frogs develop female reproductive structures

Reproductive System: Consists of external and internal structures ∙ Allows the production and maturation on gametes

∙ Signals the synthesis and secretion of substances required for  reproductive function

∙ Provides a route to deliver the gametes through ducts

Male Reproductive Anatomy: External and internal components ∙ Testes produce sperm and androgens

Gametogenesis: The production of gametes (sex cells)

∙ Involves the process of meiosis

o Reduces chromosome number by half

 Human body cell with 46 chromosomes

 Diploid (2n)

 Gamete with 23 chromosomes

 Haploid (n)

o Other changes after meiosis enable mature, functional  gametes for fertilization

Spermatogenesis: Production of sperm

Female Reproductive Anatomy

Effects on human fertility:

∙ Diethylstilbestrol (DES): endocrine disrupting chemical that mimics  estrogen

o Used to prevent miscarriages from 1938 to 1971

o 24% of daughters of women who took DES are infertile  (misshapen uterus)

∙ Declining sperm counts in developed countries

o Endocrine disruptor not identified yet, possibly a pesticide. Oogenesis: production of egg cells

Fertility: Ability to produce gametes for fertilization

∙ Women are fertile each month from puberty to menopause (meiosis  completes and follicle maturation)

o Oogonia stop undergoing mitosis during fetal period. Only  those oogonia can undergo meiosis. NO MORE NEW EGGS! ∙ Men are fertile throughout their lifetime

o Mitosis of “stem cell”/spermatogonia continuously followed  by meiosis. NEW SPERM!

Ovulation: releasing the egg from the ovary

The Menstrual Cycle: Cyclic changes occurring in the uterus ∙ Hypothalamus secretes GnRH to stimulate pituitary gland to release FSH and LH

∙ FSH influences follicle to grow inside the ovary

o Estrogen produced

∙ Large follicle and high estrogen levels stimulate GnRH release  (positive feedback).

∙ Spike in FSH and LH levels lasts for 24 hours

o Ovulation occurs 10-12 hours after LH peak

∙ Corpus Luteum produces estrogen and progesterone

o Inhibits LH production (negative feedback)

o Maintains early pregnancy (uterine lining)

Menstruation: The excretion of the endometrium (uterine lining) if no pregnancy has occurred

∙ Corpus luteum degenerates 10 days after ovulation

∙ Progesterone and estrogen levels fall

∙ Uterus spasms and sheds the endometrium

Female Infertility

Endometriosis: Menstrual tissues grow in other areas besides the  uterus (e.g., oviducts and ovaries)

∙ Causes scarring and inflammation of oviducts

∙ Disrupts ovulation

Polycystic Ovarian Syndrome: Fluid-filled cysts develop in the  ovaries

∙ Disrupts ovulation

∙ Evidence correlates plasticizers (chemicals added to make plastics  softer) with these conditions

Sexually transmitted infections: Bacterial Pathogens

∙ Chlamydia

∙ Gonorrhea

∙ Syphilis

Sexually transmitted infections: Viral pathogens

∙ AIDS/HIV

∙ Genital Warts

∙ Hepatitis B

∙ Herpes

Sexually transmitted infections: Insect, protozoan, and fungal  pathogens

∙ Pubic lice

∙ Trichomoniasis

∙ Yeast infections

Chlamydia is the most common form of sexually transmitted disease in the US with THREE MILLION new cases each year

Contraception

Birth control methods:

∙ Hormonal Methods

o Pills supply low, continuous doses of estrogen and  

progesterone that do not stimulate LH secretion

∙ Barrier methods

∙ Other methods

o Intrauterine devices

o Male or female sterilization

Development

∙ The series of events that take place after fertilization

Fertilization and the Pre-embryonic Stage

∙ Embryo—term has varied meanings

o Some authorities assert that the fertilized egg or the two-cell  stage is an embryo

o Other authorities assert that an individual becomes an  embryo when it is 16 days old and consists of three primary  germ layers

 Ectoderm, Mesoderm, and Endoderm

 Embryogenesis—events leading up to this stage

 Pre-embryonic stage is the first 16 days after  fertilization 

Sperm Migration

∙ Egg must be fertilized within 12-24 hours of ovulation, if it is to  survive

∙ Sperm must encounter the egg somewhere in the distal one-third of  the uterine tube (closer to ovary than uterus)

Most sperm don’t make it to the egg

∙ Destroyed by vaginal acid or drain out of vagina

∙ Fail to penetrate the mucus of the cervical canal

∙ Destroyed by leukocytes in the uterous

∙ Half go up wrong uterine tube

∙ **Of the 300 million that were ejaculated, approx. only 200 sperm  reach the egg

Sperm Capacitation

∙ The process that migrating sperm must undergo to make it possible  to penetrate an egg

o Membrane of fresh sperm is tough

o Female fluids leach cholesterol from the sperm plasma  membrane and dilute inhibitory factors in semen

o Sperm membrane becomes fragile and permeable to calcium o Calcium diffuses into sperm causing more powerful lashing of  the tail

Fertilization

∙ Sperm are viable for up to 6 DAYS after ejaculation o Conception optimal if sperm are deposited a few days before  ovulation to 14 hours after

∙ When sperm encounter an egg, the sperm undergoes an  acrosomal reaction. The head of the sperm, acrosome, releases  the enzymes needed to penetrate the egg

o Enzymes of MANY sperm are released to clear a path for the  one that will penetrate the egg

o Penetrates granulosa cells, then zona pellucida

∙ Two acrosomal enzymes degrade the connections of the follicular  cells around the egg

∙ When a path has been cleared, a sperm binds to the zona  pellucida, releases its enzymes, and digests a path through the  zona until it contacts the egg itself

∙ Sperm head and mid-piece enter the egg

o Egg destroys the sperm mitochondria

o Passes only maternal mitochondria onto the offspring

Fertilization combines the haploid (n) set of sperm chromosomes with  the haploid set of egg chromosomes, producing a diploid (2n) set

Polyspermy—Fertilization by two or more sperm, which would produce  a doomed fertilized egg

∙ There are TWO mechanisms to prevent polyspermy

o Fast Block: Binding the sperm to the egg opens sodium  channels in the egg membrane. Inflow of sodium electrically  alters (depolarizes) the membrane and inhibits the  

attachment of any more sperm

o Slow Block: New chemically altered membrane between  the egg and the zona pellucida is formed. No more sperm can  penetrate

Meiosis II

∙ The secondary oocyte begins meiosis II before ovulation but  completes it only if fertilized. Second polar body is formed. ∙ Sperm and egg nuclei swell and become pronuclei

∙ Each pronucleus ruptures and the chromosomes of the two gametes mix into a single diploid set

∙ The fertilized egg, now called the zygote, is ready for its first  mitotic division

Dizygotic Twins

∙ About 2/3 of twins are dizygotic

∙ Two eggs are ovulated and both are fertilized by separate sperm  forming two zygotes

∙ No more or less genetically similar than any other siblings ∙ Implant separately in the uterine wall and each forms its own  placenta

Monozygotic Twins

∙ One egg is fertilized (one zygote) but embryoblast later divides into  two

∙ Genetically identical (or nearly so), of the same sex, and very  similar in appearance

Embryonic Development

∙ Zygote undergoes a series of changes to produce a multicellular  structure

∙ Cleavage: rapid cell divisions in the oviduct

∙ Pre-Embryo: stages of development after zygotic divisions until  three tissue layers develop (first 16 days)

∙ Embryo: until body structures appear in the 9th week

The Pre-Embryonic Stage

∙ Pre-Embryonic Stage—First 16 days of development culminating in  the existence of an embryo

o Involves three major processes

 Cleavage

 Implantation

 Ebryogenesis

∙ Cleavage—Mitotic divisions that occur in the first 3 days while  conceptus migrates down uterine tube

o First cleavage occurs within 30 hours after fertilization  Zygote splits into two daughter cells

o By the time the conceptus arrives in the uterus

 About 72 hours after ovulation

 Morula Stage—Solid ball of 16 cells

 Still no larger than zygote

 Cleavage produces smaller and smaller cells

∙ Morula lies free in uterine cavity for 4 to 5 days

o Divides into 100 cells or so

o Zona pellucida disintegrates and releases conceptus, called  blastocyst

∙ Blastocyst: A hollow sphere

o Trophoblast—Outer layer of cells, destined to form the  placenta for nourishment of the embryo

o Embryoblast—Inner cell mass, destined to become the  embryo

o Blastocoel—Internal cavity

∙ Implantation

o Blastocyst attaches to uterine wall 6 days after ovulation  Usually on the fundus or posterior wall of the uterus o Implantation: Process of attachment to uterine wall  Begins when blastocyst adheres to endometrium ∙ Trophoblasts on attachment side separate into two layers o Superficial layer is in contact with the endometrium  The plasma membranes break down

 Trophoblastic cells fuse into a multinucleate mass  (syncytiotrophoblast):

 Deep layer close to embryoblast

∙ Cytotrophoblast: retains individual cells  

divided by membranes

o Also secretes human chorionic gonadotropin (HCG)

 HCG stimulates the corpus luteum to secrete estrogen  and progesterone

 Progesterone suppresses menstruation (maintains

endometrium for implanted pre-embryo)

 HCG levels rise in mother’s blood until the end of  

second month

 Trophoblast develops into membrane called the  

chorion

∙ Chorion takes over production of  

estrogen and progesterone

∙ HCG not needed now and corpus luteum  

undergoes atresia

∙ Ovaries become INACTIVE for remainder of  

pregnancy

∙ Superficial cells grow into uterus like little roots

o Digested endometrial cells along the way

o Endometrium reacts to this by growing over the blastocyst  and covering it

o Conceptus becomes completely buried in endometrial tissue ∙ Implantation takes about 1 week

o Completed about the time the next menstrual period would  have started had the woman not become pregnant

∙ Embryoblast separates slightly from the trophoblast ∙ Creates a narrow space between them, called the amniotic cavity  o Embryogenesis—Arrangement of cells into three primary  germ layers:

 Ectoderm, mesoderm, and endoderm

 Next few slides

o Epiblast facing the amniotic cavity

o Hypoblast facing away

 Hypoblast cells multiply and form the yolk sac

∙ Primitive Streak—Thickened cell layer that forms along midline of  the epiblast

o Primitive Groove: Running down its middle

∙ Embryo is bilaterally symmetrical

o Define its future right and left sides, dorsal (back) and ventral  (tummy side) surfaces, and cephalic (head) and caudal (tail)  ends

∙ Gastrulation—Multiplying epiblast cells migrate medially into  primitive groove

o Replace the original hypoblast with a layer called endoderm ∙ Day later, migrating epiblast cells form a THIRD layer between the  first and second—mesoderm

∙ Remaining epiblast is called the ectoderm

∙ Mesoderm—A more loosely organized tissue which differentiates  into a loose fetal connective tissue, called mesenchyme o Gives rise to muscle, bone, and blood

o Composed of a loose network of wispy mesenchymal cells  embedded in a gelatinous ground substance

∙ Once the three primary germ layers are formed,  embryogenesis is complete

o Individual considered an embryo

o 2mm long and 16 days old

Ectopic Pregnancy

∙ Ectopic Pregnancy—Blastocyst implants somewhere other than  the uterus

o 1 out of 300 pregnancies

∙ Tubal Pregnancies—Implantation in the uterine tube

o Usually due to obstruction such as constriction resulting from  pelvic inflammatory disease, tubular surgery, previous ectopic pregnancies, or repeated miscarriages

o Tube ruptures within 12 weeks

∙ Abdominal Pregnancy—Implantation occurs in abdominal cavity o 1 out of 7,000

o Can threaten mother’s life

o 9% result in live birth by cesarean section

Effect of Environmental Chemicals on Sperm

∙ Trichloroethylene (TCE): Industrial solvent used to remove grease o Males exposed to TCE have larger numbers of misshapen  sperm

 Such sperm are less likely to fertilize eggs

o TCE can enter the water supply

 Via air emissions from metal-degreasing plants

 Via wastewater from manufacturing plants

Three Layers of Tissue: Gastrula layers differentiate into adult cells  and tissues with specific functions

∙ Ectoderm: The outer layer

o Gives rise to the skin, nervous system, and sense organs ∙ Mesoderm: The middle layer

o Gives rise to muscles, excretory organs, circulatory organs,  and skeleton

∙ Endoderm: The inner layer

o Lines the digestive and respiratory organs

Chemical Signals for Differentiation: Growth of a particular tissue  or organ relies on chemical stimulus

∙ Development is very sensitive to disruption

Development of human reproductive organs

∙ Until week 7 of pregnancy

o Reproductive organs of male and female embryos are  

indistinguishable

∙ Sex-specific genes determine the differentiation into male or female gonads

o Two ductal structures exist side by side

 Only one persists in each after differentiation

o External structures arise from the same starting tissue

Cryptorchidism: undescended testes

∙ Nonhuman evidence shows relationship to fungicide and herbicide  exposure

o Endocrine disruptors that block androgen receptors

∙ Decreased sperm development due to higher than optimum  temperatures in the abdomen

∙ Occurs in 2-4% of human male newborns

o Corrected by surgery

o No particular chemical exposure as known cause

Pregnancy: Gestation; involves carrying a developing baby within the  female reproductive tract; lasts 38 weeks in humans

∙ Embryo makes it way to uterus

o Inner cell mass becomes the fetus

o Trophoblast: outer ring of cells becomes part of the placenta ∙ Enzymes from the trophoblast enable embryo to implant ∙ Placenta sustains pregnancy

o Closely positioned maternal and fetal blood supplies exchange nutrients and wastes

Effects of Chemicals on Developing Fetus

∙ Exposure to secondhand cigarette smoke

o Decreases birth weight

o Increased respiratory and heart problems

∙ Exposure to alcohol

o Severe developmental problems

∙ Polychlorinated biphenyls (PCBs)

o Low birth weight

o Increased risk of premature birth

Childbirth: Labor and delivery

∙ Increased estrogen levels at the end of pregnancy

∙ Oxytocin receptors form on the uterus

o Use positive feedback loop to induce labor

Newborn exposure to toxic chemicals

∙ DEHP: plasticizer

o Safety concerns about use in pacifiers and teething rings o Not definite endocrine disruptor

∙ Bisphenol A: Concern about leaching from plastic bottles and  feeding cups

o Possible effects on brains and behavioral development

Evidence of endocrine disruptors in water>

∙ No conclusive evidence shows that endocrine disruptors in the  water harm human reproductive health

o No reason to disregard this hypothesis

o Further research is necessary

Biology Exam 3 Study Guide 10/31/2016

Meiosis, Spermatogenesis, and Oogenesis

∙ Meiosis

o Meiosis creates two identical daughter cells

o Would create clones-genetically identical offspring

o This is called asexual reproduction

o Creates 4 dissimilar haploid daughter cells (2nn, n, n, and n) o Creates gametes

∙ Gametes

o Sex cells, either sperm or egg

o Gametes are usually haploid

∙ Diploids vs. Haploids

o Diploids have 2 sets of chromosomes

o Haploids have 1 set of chromosomes

∙ Gametogenesis

o The production of the gametes

o Males and females have different forms of gametogenesis:

 Spermatogenesis (male)

 Makes haploid sperm

 Begins at puberty

 Occurs in the seminiferous tubules of testes

 Oogenesis (female)

 Makes haploid egg cells

 Begins prior to birth

 Stops after birth UNITL puberty

Why don’t we look the same as our siblings?

o Meiosis produces genetically different gametes:

 Crossing-over

 Random assortment of chromosomes (independent  assortment)

∙

∙ Meiosis Summary

o Meiosis reduces the chromosome number in half (In humans,  this is diploidhaploid)

o Meiosis creates genetically dissimilar gametes by two  processes:

 Crossing-over

 Random alignment of homologous chromosomes

o Errors in meiosis leads to polyploidy

Plant Reproduction

∙ Plant Evolution

o Mosses (bryophytes) use gametes and spores to reproduce,  but flowering plants (angiosperms) use gametes and seeds. o Vascular tissue improves water and nutrient transport in  plants and they grow larger

∙ Ploidy of Plants

o Plants can be..

 Haploid n

 Diploid 2n

 Triploid 3n

 Tetraploid 4n

 Pentaploid 5n

 Hexaploid 6n

 Etc…

∙ Moss

o Golden diploid sporophyte part grows out of green haploid  gametophyte base part (the moss we see)

Flowers—Gamete production, fertilization, and seed & fruit  development see link:  

https://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Mature_flower_ diagram.svg/2000px-Mature_flower_diagram.svg.png 

Chapter 22: Reproductive and Developmental Biology

Endocrine Disruptors: a class of chemicals altering the actions of the  hormone-producing endocrine system

Asexual Reproduction: A single organism reproduces by itself,  without mating with another

∙ Offspring are genetically identical to the parents and to each other o Mitosis

o Binary fission: single cell splits into two identical daughter  cells

o Budding: daughter cell remains attached to the parent until  sufficiently grown to break away

Asexual reproduction in organisms:

∙ Binary fission—Bacteria

∙ Asexual—Sponge

∙ Budding—Yeast, hydra, etc.

∙

o Meiosis is not used in asexual reproduction

Sexual Reproduction: the fusion of gametes from two different  individuals (male and female)

∙ Produces genetically diverse offspring

∙ Gamete: sex cell; egg or sperm

o Haploid (n)

∙ Gonads: gamete-producing structures

o Ovaries: produce eggs in females

o Testes: produce sperm in males

∙ Zygote: a fertilized egg cell resulting from sexual reproduction o Diploid (2n)

How many chromosomes do human GAMETES contain? (A: 23) ∙ Human BODY cells contain 46 chromosomes

Hermaphrodites: animals that have both male and female reproductive systems

∙ Earthworms

o Donate or receive sperm during mating

Methods of Fertilization

∙ Internal Fertilization: Sperm deposited in or near female  reproductive tract

o Sharks, reptiles, birds, and mammals

∙ External Fertilization: Female lays eggs in water and male releases  sperm over eggs

o Aquatic invertebrates, most fish, and amphibians

 Highly sensitive to environmental contaminants in water

Environmental contaminants in the water

∙ Organisms developing in water most affected

∙ Herbicide atrazine

o Male frogs develop female reproductive structures

Reproductive System: Consists of external and internal structures ∙ Allows the production and maturation on gametes

∙ Signals the synthesis and secretion of substances required for  reproductive function

∙ Provides a route to deliver the gametes through ducts

Male Reproductive Anatomy: External and internal components ∙ Testes produce sperm and androgens

Gametogenesis: The production of gametes (sex cells)

∙ Involves the process of meiosis

o Reduces chromosome number by half

 Human body cell with 46 chromosomes

 Diploid (2n)

 Gamete with 23 chromosomes

 Haploid (n)

o Other changes after meiosis enable mature, functional  gametes for fertilization

Spermatogenesis: Production of sperm

Female Reproductive Anatomy

Effects on human fertility:

∙ Diethylstilbestrol (DES): endocrine disrupting chemical that mimics  estrogen

o Used to prevent miscarriages from 1938 to 1971

o 24% of daughters of women who took DES are infertile  (misshapen uterus)

∙ Declining sperm counts in developed countries

o Endocrine disruptor not identified yet, possibly a pesticide. Oogenesis: production of egg cells

Fertility: Ability to produce gametes for fertilization

∙ Women are fertile each month from puberty to menopause (meiosis  completes and follicle maturation)

o Oogonia stop undergoing mitosis during fetal period. Only  those oogonia can undergo meiosis. NO MORE NEW EGGS! ∙ Men are fertile throughout their lifetime

o Mitosis of “stem cell”/spermatogonia continuously followed  by meiosis. NEW SPERM!

Ovulation: releasing the egg from the ovary

The Menstrual Cycle: Cyclic changes occurring in the uterus ∙ Hypothalamus secretes GnRH to stimulate pituitary gland to release FSH and LH

∙ FSH influences follicle to grow inside the ovary

o Estrogen produced

∙ Large follicle and high estrogen levels stimulate GnRH release  (positive feedback).

∙ Spike in FSH and LH levels lasts for 24 hours

o Ovulation occurs 10-12 hours after LH peak

∙ Corpus Luteum produces estrogen and progesterone

o Inhibits LH production (negative feedback)

o Maintains early pregnancy (uterine lining)

Menstruation: The excretion of the endometrium (uterine lining) if no pregnancy has occurred

∙ Corpus luteum degenerates 10 days after ovulation

∙ Progesterone and estrogen levels fall

∙ Uterus spasms and sheds the endometrium

Female Infertility

Endometriosis: Menstrual tissues grow in other areas besides the  uterus (e.g., oviducts and ovaries)

∙ Causes scarring and inflammation of oviducts

∙ Disrupts ovulation

Polycystic Ovarian Syndrome: Fluid-filled cysts develop in the  ovaries

∙ Disrupts ovulation

∙ Evidence correlates plasticizers (chemicals added to make plastics  softer) with these conditions

Sexually transmitted infections: Bacterial Pathogens

∙ Chlamydia

∙ Gonorrhea

∙ Syphilis

Sexually transmitted infections: Viral pathogens

∙ AIDS/HIV

∙ Genital Warts

∙ Hepatitis B

∙ Herpes

Sexually transmitted infections: Insect, protozoan, and fungal  pathogens

∙ Pubic lice

∙ Trichomoniasis

∙ Yeast infections

Chlamydia is the most common form of sexually transmitted disease in the US with THREE MILLION new cases each year

Contraception

Birth control methods:

∙ Hormonal Methods

o Pills supply low, continuous doses of estrogen and  

progesterone that do not stimulate LH secretion

∙ Barrier methods

∙ Other methods

o Intrauterine devices

o Male or female sterilization

Development

∙ The series of events that take place after fertilization

Fertilization and the Pre-embryonic Stage

∙ Embryo—term has varied meanings

o Some authorities assert that the fertilized egg or the two-cell  stage is an embryo

o Other authorities assert that an individual becomes an  embryo when it is 16 days old and consists of three primary  germ layers

 Ectoderm, Mesoderm, and Endoderm

 Embryogenesis—events leading up to this stage

 Pre-embryonic stage is the first 16 days after  fertilization 

Sperm Migration

∙ Egg must be fertilized within 12-24 hours of ovulation, if it is to  survive

∙ Sperm must encounter the egg somewhere in the distal one-third of  the uterine tube (closer to ovary than uterus)

Most sperm don’t make it to the egg

∙ Destroyed by vaginal acid or drain out of vagina

∙ Fail to penetrate the mucus of the cervical canal

∙ Destroyed by leukocytes in the uterous

∙ Half go up wrong uterine tube

∙ **Of the 300 million that were ejaculated, approx. only 200 sperm  reach the egg

Sperm Capacitation

∙ The process that migrating sperm must undergo to make it possible  to penetrate an egg

o Membrane of fresh sperm is tough

o Female fluids leach cholesterol from the sperm plasma  membrane and dilute inhibitory factors in semen

o Sperm membrane becomes fragile and permeable to calcium o Calcium diffuses into sperm causing more powerful lashing of  the tail

Fertilization

∙ Sperm are viable for up to 6 DAYS after ejaculation o Conception optimal if sperm are deposited a few days before  ovulation to 14 hours after

∙ When sperm encounter an egg, the sperm undergoes an  acrosomal reaction. The head of the sperm, acrosome, releases  the enzymes needed to penetrate the egg

o Enzymes of MANY sperm are released to clear a path for the  one that will penetrate the egg

o Penetrates granulosa cells, then zona pellucida

∙ Two acrosomal enzymes degrade the connections of the follicular  cells around the egg

∙ When a path has been cleared, a sperm binds to the zona  pellucida, releases its enzymes, and digests a path through the  zona until it contacts the egg itself

∙ Sperm head and mid-piece enter the egg

o Egg destroys the sperm mitochondria

o Passes only maternal mitochondria onto the offspring

Fertilization combines the haploid (n) set of sperm chromosomes with  the haploid set of egg chromosomes, producing a diploid (2n) set

Polyspermy—Fertilization by two or more sperm, which would produce  a doomed fertilized egg

∙ There are TWO mechanisms to prevent polyspermy

o Fast Block: Binding the sperm to the egg opens sodium  channels in the egg membrane. Inflow of sodium electrically  alters (depolarizes) the membrane and inhibits the  

attachment of any more sperm

o Slow Block: New chemically altered membrane between  the egg and the zona pellucida is formed. No more sperm can  penetrate

Meiosis II

∙ The secondary oocyte begins meiosis II before ovulation but  completes it only if fertilized. Second polar body is formed. ∙ Sperm and egg nuclei swell and become pronuclei

∙ Each pronucleus ruptures and the chromosomes of the two gametes mix into a single diploid set

∙ The fertilized egg, now called the zygote, is ready for its first  mitotic division

Dizygotic Twins

∙ About 2/3 of twins are dizygotic

∙ Two eggs are ovulated and both are fertilized by separate sperm  forming two zygotes

∙ No more or less genetically similar than any other siblings ∙ Implant separately in the uterine wall and each forms its own  placenta

Monozygotic Twins

∙ One egg is fertilized (one zygote) but embryoblast later divides into  two

∙ Genetically identical (or nearly so), of the same sex, and very  similar in appearance

Embryonic Development

∙ Zygote undergoes a series of changes to produce a multicellular  structure

∙ Cleavage: rapid cell divisions in the oviduct

∙ Pre-Embryo: stages of development after zygotic divisions until  three tissue layers develop (first 16 days)

∙ Embryo: until body structures appear in the 9th week

The Pre-Embryonic Stage

∙ Pre-Embryonic Stage—First 16 days of development culminating in  the existence of an embryo

o Involves three major processes

 Cleavage

 Implantation

 Ebryogenesis

∙ Cleavage—Mitotic divisions that occur in the first 3 days while  conceptus migrates down uterine tube

o First cleavage occurs within 30 hours after fertilization  Zygote splits into two daughter cells

o By the time the conceptus arrives in the uterus

 About 72 hours after ovulation

 Morula Stage—Solid ball of 16 cells

 Still no larger than zygote

 Cleavage produces smaller and smaller cells

∙ Morula lies free in uterine cavity for 4 to 5 days

o Divides into 100 cells or so

o Zona pellucida disintegrates and releases conceptus, called  blastocyst

∙ Blastocyst: A hollow sphere

o Trophoblast—Outer layer of cells, destined to form the  placenta for nourishment of the embryo

o Embryoblast—Inner cell mass, destined to become the  embryo

o Blastocoel—Internal cavity

∙ Implantation

o Blastocyst attaches to uterine wall 6 days after ovulation  Usually on the fundus or posterior wall of the uterus o Implantation: Process of attachment to uterine wall  Begins when blastocyst adheres to endometrium ∙ Trophoblasts on attachment side separate into two layers o Superficial layer is in contact with the endometrium  The plasma membranes break down

 Trophoblastic cells fuse into a multinucleate mass  (syncytiotrophoblast):

 Deep layer close to embryoblast

∙ Cytotrophoblast: retains individual cells  

divided by membranes

o Also secretes human chorionic gonadotropin (HCG)

 HCG stimulates the corpus luteum to secrete estrogen  and progesterone

 Progesterone suppresses menstruation (maintains

endometrium for implanted pre-embryo)

 HCG levels rise in mother’s blood until the end of  

second month

 Trophoblast develops into membrane called the  

chorion

∙ Chorion takes over production of  

estrogen and progesterone

∙ HCG not needed now and corpus luteum  

undergoes atresia

∙ Ovaries become INACTIVE for remainder of  

pregnancy

∙ Superficial cells grow into uterus like little roots

o Digested endometrial cells along the way

o Endometrium reacts to this by growing over the blastocyst  and covering it

o Conceptus becomes completely buried in endometrial tissue ∙ Implantation takes about 1 week

o Completed about the time the next menstrual period would  have started had the woman not become pregnant

∙ Embryoblast separates slightly from the trophoblast ∙ Creates a narrow space between them, called the amniotic cavity  o Embryogenesis—Arrangement of cells into three primary  germ layers:

 Ectoderm, mesoderm, and endoderm

 Next few slides

o Epiblast facing the amniotic cavity

o Hypoblast facing away

 Hypoblast cells multiply and form the yolk sac

∙ Primitive Streak—Thickened cell layer that forms along midline of  the epiblast

o Primitive Groove: Running down its middle

∙ Embryo is bilaterally symmetrical

o Define its future right and left sides, dorsal (back) and ventral  (tummy side) surfaces, and cephalic (head) and caudal (tail)  ends

∙ Gastrulation—Multiplying epiblast cells migrate medially into  primitive groove

o Replace the original hypoblast with a layer called endoderm ∙ Day later, migrating epiblast cells form a THIRD layer between the  first and second—mesoderm

∙ Remaining epiblast is called the ectoderm

∙ Mesoderm—A more loosely organized tissue which differentiates  into a loose fetal connective tissue, called mesenchyme o Gives rise to muscle, bone, and blood

o Composed of a loose network of wispy mesenchymal cells  embedded in a gelatinous ground substance

∙ Once the three primary germ layers are formed,  embryogenesis is complete

o Individual considered an embryo

o 2mm long and 16 days old

Ectopic Pregnancy

∙ Ectopic Pregnancy—Blastocyst implants somewhere other than  the uterus

o 1 out of 300 pregnancies

∙ Tubal Pregnancies—Implantation in the uterine tube

o Usually due to obstruction such as constriction resulting from  pelvic inflammatory disease, tubular surgery, previous ectopic pregnancies, or repeated miscarriages

o Tube ruptures within 12 weeks

∙ Abdominal Pregnancy—Implantation occurs in abdominal cavity o 1 out of 7,000

o Can threaten mother’s life

o 9% result in live birth by cesarean section

Effect of Environmental Chemicals on Sperm

∙ Trichloroethylene (TCE): Industrial solvent used to remove grease o Males exposed to TCE have larger numbers of misshapen  sperm

 Such sperm are less likely to fertilize eggs

o TCE can enter the water supply

 Via air emissions from metal-degreasing plants

 Via wastewater from manufacturing plants

Three Layers of Tissue: Gastrula layers differentiate into adult cells  and tissues with specific functions

∙ Ectoderm: The outer layer

o Gives rise to the skin, nervous system, and sense organs ∙ Mesoderm: The middle layer

o Gives rise to muscles, excretory organs, circulatory organs,  and skeleton

∙ Endoderm: The inner layer

o Lines the digestive and respiratory organs

Chemical Signals for Differentiation: Growth of a particular tissue  or organ relies on chemical stimulus

∙ Development is very sensitive to disruption

Development of human reproductive organs

∙ Until week 7 of pregnancy

o Reproductive organs of male and female embryos are  

indistinguishable

∙ Sex-specific genes determine the differentiation into male or female gonads

o Two ductal structures exist side by side

 Only one persists in each after differentiation

o External structures arise from the same starting tissue

Cryptorchidism: undescended testes

∙ Nonhuman evidence shows relationship to fungicide and herbicide  exposure

o Endocrine disruptors that block androgen receptors

∙ Decreased sperm development due to higher than optimum  temperatures in the abdomen

∙ Occurs in 2-4% of human male newborns

o Corrected by surgery

o No particular chemical exposure as known cause

Pregnancy: Gestation; involves carrying a developing baby within the  female reproductive tract; lasts 38 weeks in humans

∙ Embryo makes it way to uterus

o Inner cell mass becomes the fetus

o Trophoblast: outer ring of cells becomes part of the placenta ∙ Enzymes from the trophoblast enable embryo to implant ∙ Placenta sustains pregnancy

o Closely positioned maternal and fetal blood supplies exchange nutrients and wastes

Effects of Chemicals on Developing Fetus

∙ Exposure to secondhand cigarette smoke

o Decreases birth weight

o Increased respiratory and heart problems

∙ Exposure to alcohol

o Severe developmental problems

∙ Polychlorinated biphenyls (PCBs)

o Low birth weight

o Increased risk of premature birth

Childbirth: Labor and delivery

∙ Increased estrogen levels at the end of pregnancy

∙ Oxytocin receptors form on the uterus

o Use positive feedback loop to induce labor

Newborn exposure to toxic chemicals

∙ DEHP: plasticizer

o Safety concerns about use in pacifiers and teething rings o Not definite endocrine disruptor

∙ Bisphenol A: Concern about leaching from plastic bottles and  feeding cups

o Possible effects on brains and behavioral development

Evidence of endocrine disruptors in water>

∙ No conclusive evidence shows that endocrine disruptors in the  water harm human reproductive health

o No reason to disregard this hypothesis

o Further research is necessary