Chapter 20

1. Chapter 20 Is There Something in the Water?Reproductive and Developmental Biology

2. 20.1 Principles of Animal Reproduction Two main types of reproduction • Asexual reproduction • Sexual reproduction Asexual Reproduction • one parent produces offspring that are genetically identical to the parent

3. 20.1 Principles of Animal Reproduction Two main types of asexual reproduction • Binary fission – cells break away from parent to form offspring (e.g., sponges) • Budding – daughter cell remains attached to parent and breaks away when mature (e.g., hydra)

4. 20.1 Principles of Animal Reproduction – Sexual Reproduction • Sexual reproduction combines genomes of two individuals to create variable offspring • Females = individuals that produce large gametes (sex cells) • Males = individuals that produce small gametes • Gonads = Organs that produce gametes • Male gonad = testes • Female gonad = ovaries

5. 20.1 Principles of Animal Reproduction Methods of fertilization • Internal fertilization – sperm deposited by copulation in or near female reproductive tract. • Mammals, birds, reptiles, and sharks use internal fertilization. • External fertilization – eggs laid, male deposits sperm over eggs (usually in water). Most fish and amphibians use external fertilization. • Very susceptible to contaminants

6. 20.1 Principles of Animal Reproduction Environmental Contaminants and Sexual Reproduction • Developing frogs are extremely sensitive to environmental chemicals • Eggs develop in water • Embryos absorb toxins easily • Frogs are declining globally Figure 20.2

7. 20.1 Principles of Animal Reproduction - Endocrine Disruptors • Man-made chemicals alter endocrine regulation • interferes with normal gonad development. • Male amphibians have been feminized. • These chemicals affect animals living in water. • Are humans affected by drinking contaminated water?

8. 20.2 Human Reproduction Male Reproductive Anatomy • Penis • Contains spongy erectile tissue • Fills with blood to cause erection • Testes • Inside scrotum • produce sperm and testosterone Figure 20.4

9. 20.2 Human Reproduction Male Reproductive Anatomy • Accessory Glands • Prostate & seminal vesicles • Secrete fructose, mucous • Testes • Inside scrotum • produce sperm and testosterone • Epididymis • Stores sperm • Vas deferens Figure 20.4

10. 20.2 Human Reproduction Female Reproductive Anatomy • External genitalia • Labia majora & labia minora • clitoris • Reproductive tract • Vagina • Uterus • Paired oviducts • Fertilization • Separate urethral opening Figure 20.5

11. 20.2 Human Reproduction Female Reproductive Anatomy • Ovaries • Endocrine • Estrogen • Progesterone • Produces gametes • Follicle contains: • Egg • Endocrine cells Figure 20.5

12. 20.2 Human Reproduction –Endocrine Disruptors & Humans • Women • DES is a chemical known to act as an endocrine disruptor. • Given to women to prevent premature delivery • Daughters of women who took DES have a higher rate of infertility. • Men • Most common cause of male infertility is the inability to produce healthy sperm. • Sperm counts are declining globally

13. 20.2 Human Reproduction Gametogenesis = production of gametes (germ cells) • Involves meiosis • Reduces number of chromosomes by ½ • Human body cells contain 46 chromosomes, gamete contain 23 • (see chapter 5 for review) • Male and female gametes undergo further development to become functional

14. 20.2 Human Reproduction Spermatogenesis • Seminiferous tubules = functional unit of testis • Developing sperm cells • Sertoli cells – nurse cells for sperm • Leydig cells outside seminiferous tubules • Make and release testosterone Figure 20.6

15. 20.2 Human Reproduction Cell types in Spermatogenesis • Spermatogonia • Stem cells • Divide by mitosis • Primary spermatocytes • Enter Meiosis I • Secondary spermatocytes • Enter meiosis II • Spermatids • Undergospermiation • Cytodifferentiation • Spermatozoa Figure 20.6

16. 20.2 Human Reproduction Spermatozoa Structure • Head • Condensed nucleus • Acrosome • Contains enzymes for fertiliztion • Midpiece • Lots of mitochondria • Tail • Flagellum for swimming Figure 20.6

17. 20.2 Human Reproduction - Male Infertility Human infertility and endocrine disruptors • 90% of male infertility related is to problems with sperm formation or production • Low sperm counts • Improperly shaped sperm • Low motility • Chemical exposure (e.g., pesticides) can decrease sperm viability • Male infertility also increases with alcohol and drug use, including cigarettes • Sperm counts declining globally since WWII

18. 20.2 Human Reproduction PLAY Animation—The Male Reproductive System

19. 20.2 Human Reproduction Oogenesis • Two parts • Oocyte development • Follicular development Figure 20.7

20. 20.2 Human Reproduction Oocyte Development • All oogonia (stem cells) become primaryoocytes during her embryonic development • Each month during menstrual cycle • Primary oocytesenter meiosis I -> secondary oocytes • Secondary oocytescomplete meiosis II at fertilization • Polar bodies will deteriorate Figure 20.7

21. 20.2 Human Reproduction Follicular Development • Follicles include oocytesand surrounding endocrine cells • Primary follicle stores primary oocytes until use • FSH causes development to secondary follicle and then Graffian follicle (both with secondary oocyte) • Secrete estrogen • LH causes ovulation • Follicle become corpus luteum • Secretes estrogen & progesterone Figure 20.7

22. 20.2 Human Reproduction The Menstrual Cycle • Changes in the uterine endometrium • Prepare endometrium for pregnancy • Regulated by: • Pituitary FSH & LH • Ovarian estrogen & progesterone Figure 20.8

23. 20.2 Human Reproduction The Menstrual Cycle • Days 1-4 • Menstruation • Only FSH elevated • causes new follicle to grow • Days 5-14 • FSH causes follicle to grow & release estrogen • Causes endometrium to grow Figure 20.8

24. 20.2 Human Reproduction The Menstrual Cycle • Day 14 • Surge of LH causes ovulation & corpus luteum formation Figure 20.8

25. 20.2 Human Reproduction The Menstrual Cycle • Day 14-28 • FSH & LH cause ovary to secrete estrogen & progesterone • Prepares for pregnancy • Corpus luteum dies at end of cycle • Results in collapse of endometrium and menstruation Figure 20.8

26. 20.2 Human Reproduction Regulating The Menstrual Cycle Regulation involves both positive & negative feedback loops • High estrogen causes positive feedback on LH • Leads to LH surge • High progesterone causes negative feedback on LH & FSH Figure 20.9

27. 20.2 Human Reproduction Pregnancy • If the egg is fertilized, embryo secretes human chorionic gonadotropin (hCG) • hCG mimics LH and keeps corpus luteum alive • Progesterone maintains endometrium during pregnancy Birth Control Pills • Mimic pregnancy by providing estrogen and progesterone • prevent ovulation by blocking LH surge Figure 20.9

28. 20.2 Human Reproduction Female Infertility • One cause of female infertility is endometriosis • a condition where the endometrial cells can attach to the ovaries & oviducts • also grow and shed during menstrual cycle • Can cause damage and scarring to ovarian tissue • Can disrupt ovulation • Painful • May be related to exposure to environmental chemicals like DEHP

29. 20.2 Human Reproduction PLAY Animation—The Female Reproductive System

30. 20.3 Human Development Fertilization • Sperm penetrate follicle cells • Sperm head binds to zona pellucida • Acrosome enzymes released • Egg & sperm membranes fuse • Sperm nucleus enters egg cell Figure 20.11

31. 20.3 Human Development Endocrine Disruptors and Fertilization • Industrial solvents can mimic hormones and interfere with sperm development and fertilization. • Misshapen sperm cannot swim effectively and are unable to fertilize egg. • Males exposed to solvents, working as mechanics or dry cleaners, have a larger number of abnormal sperm. • While effect on adults lowers fertility, effects on developing fetus is more severe

32. 20.3 Human Development Human Embryonic Development • Human zygote undergoes a series of cleavages to produce an embryo • Embryo is stage from zygote until body structures appear • Blastocyst = hollow ball of cells • Gastrula = tissue layers start to appear Figure 20.12

33. 20.3 Human Development - Human Embryonic Development Gastrula has 3 tissue layers • Endoderm – forms digestive & respiratory • Mesoderm – forms muscles, skeleton, excretory, circulatory, & gonads • Ectoderm – forms skin, nervous & sensory • Growth of a particular tissue or organ relies on chemical stimulus • Very sensitive to chemical disruption

34. 20.3 Human DevelopmentDevelopment of Human Reproductive Organs • Male & female organs develop from same embryonic precursors • Hormonal signals cause development of male and female reproductive organs Table 20.3

35. 20.3 Human DevelopmentEndocrine Disruptors & Reproductive Organs • Chemicals can pass from mother’s blood to fetus • Common herbicides & fungicides can cause cryptorchidism • Undescendedtestes • 2 to 4 % of human males are now born with undescended testes Table 20.3

36. 20.3 Human DevelopmentPregnancy or Gestation • A placenta must develop to sustain pregnancy • Embryo blastocyst implants in the wall of the uterus • Maternal and fetal blood supplies are closely intertwined, allowing exchange of nutrients and wastes • 9 week old fetus has all its limbs and organs in place • Environmental chemicals can seriously effect embryo & fetus

37. 20.3 Human Development Childbirth • Decreasing estrogen in late pregnancy induces oxytocin receptors to form in uterine muscle • Hormone oxytocin uses a positive feedback loop to induce labor. Figure 20.15

38. 20.4 Is the Water Safe to Drink? Human correlations with endocrine disruptors • abnormal sperm • lower sperm counts • decreased fertility • cryptorchidism • endometriosis • uterine abnormalities EPA requires monitoring of municipal water supplies. • But it’s unclear what chemicals to monitor and what is a safe level of chemicals