Understanding Animal Reproduction: Asexual vs. Sexual Processes

1. Chapter 46 Animal Reproduction

2. Sexual & asexual reproduction • Asexual • offspring all have same genes (clones) • ______________ • Sexual • gametes (sperm & egg)  fertilization • mixing of genes  ___________

3. ___________________ • Development of an unfertilized egg • honey bees • drones = males produced through parthenogenesis  haploid • workers & queens = females produced from fertilized eggs  diploid queen worker drone

4. Different strokes… parthenogenesis in aphids sex-change in fish

5. ________________ • Having functional reproductive system of both sexes earthworms mating flat worm

6. Fertilization • Joining of egg & sperm • _____________ • usually aquatic animals • _____________ • usually land animals

7. Development • External • development in eggs • fish & amphibians in water • soft eggs= exchange across membrane • birds & reptiles on land • hard-shell amniotic eggs • structures for exchange of food, O2 & waste • sharks & some snakes • live births from eggs • Internal • placenta • exchange food & waste • live birth

8. Adaptive advantages? • What is the adaptive value of each type of sexual reproduction • number of eggs? • level of parental of care • habitat?

9. Human Reproduction: Reproductive hormones • ___________________ • from testes • Functions • Prenatal development of male genitalia • sperm production • 2° sexual characteristics • Maintenance of sex drive • _______________ • from ovaries • functions • egg production • prepare uterus for fertilized egg • 2° sexual characteristics LH &FSH testesorovaries

10. Sex hormone control in males Hypothalamus GnRH Pituitary FSH & LH Testes testosterone Body cells

11. Male reproductive system • Sperm production • over ____________ produced per day! • ~2.5 million released per drop!

12. Male reproductive system • Testes • produces sperm & hormones • _____________ • sac that holds testicles outside of body • Epididymis • where sperm mature • ______________ • tubes for sperm to travel from testes to penis • Prostate, seminal vesicles, Cowper’s (bulbourethal) glands • nutrient rich fluid to feed & protect sperm • buffer to counteract acids in vagina

13. seminiferous tubule Male reproductive system • Testes & epididymis • sperm production & maturation • Glands • seminal vesicles, prostate, bulbourethal • produce seminal fluid = nutrient-rich sperm spermatocytes

14. Spermatogenesis Spermatogenesis occurs within each testis in small tubules called _________________ _________________ This light micrograph shows a cross section of seminiferous tubules, blood vessels and the interstitial _______________. Leydig cells are responsible for the production of testosterone.

15. Spermatogenesis Mitosis and meiosis may be taking place at any time in the spermatogonia. Mitosis replenishes numbers of cells, meiosis produces actual sperm (spermatozoa) ____________ help nourish sperm cells during meiosis

16. Spermatogenesis Testis Epididymis Germ cell (diploid) Coiled seminiferous tubules 1° spermatocyte (diploid) MEIOSIS I 2° spermatocytes (haploid) MEIOSIS II Vas deferens Spermatids (haploid) Spermatozoa Cross-section of seminiferous tubule

17. Hormonal control of sperm production LH (_______________ hormone) stimulates Leydig cells to produce testosterone FSH (___________ - stimulating hormone) and testosterone stimulate meiosis in spermatogonia to produce spermatozoa

18. Role of epididymis, seminal vesicles, and prostate in semen production Sperm cells were produced in seminiferous tubules, carried thru the lumen, and sent to the epididymis. They are _______ briefly in the epididymis. On sexual arousal, millions of sperm cells are moved from the epididymis into the ________________. _________________ add large volume of fluid which has a high conc. of fructose for energy for the sperm cells to swim (approx. 70% of the fluid in semen is added by the seminal vesicles.) The _________ adds more fluid: alkaline which helps the sperm survive the acidic environment in a female’s vagina.

19. Female reproductive system

20. Female reproductive system • Ovaries • produces eggs & hormones • Uterus • nurtures fetus; lining builds up each month • ______________________ • tubes for eggs to travel from ovaries to uterus • _____________ • opening to uterus, dilates 10cm (4 inches) for birthing baby • Vagina • birth canal for birthing baby

21. Female reproductive system

22. Menstrual cycle Starting at puberty, human females begin a hormonal cycle called the menstrual cycle. Each cycle lasts (on average) 28 days. The purpose is to time the release of an egg (ovum) for possible fertilization and later implantation into the inner lining of the uterus (____________________) • The implantation must occur when the endometrium is rich with blood vessels. • The breakdown of the blood vessels leads to menstrual bleeding (________________); a sign that no pregnancy has occurred

23. Hormones regulatory center for the menstrual cycle. The hypothalamus produces a hormone called GnRH (gonadotrophin-releasing hormone). The target tissue of GnRH is the anterior pituitary gland, which results in the pituitary producing and secreting 2 hormones into the bloodstream: FSH and LH. The target tissues for these 2 hormones are the ovaries Hypothalamus Pituitary FSH & LH estrogen progesterone Endometrium of uterus

24. Effects of FSH and LH on the ovaries To increase the production and secretion of __________ by the follicle cells of the ovary Estrogen enters the bloodstream Its target tissue is the endometrium of the uterus Result is growth of lining (increase in blood vessels) Stimulates egg development in ovaries

25. Egg maturation in ovary • A spike in levels of FSH and LH leads to ovulation (release of oocyte from the follicle) • The outer ring of follicle cells begin to divide and fill in the ‘wound’ area left by ovulation which forms a ____________. The corpus luteum produces progesterone for 10-12 days after ovulation. • Progesterone (hormone) ___________ the thickened endometrium • If no pregnancy, the corpus luteum eventually breaks down = less estrogen and progesterone

26. Menstrual cycle … as estrogen and progesterone levels fall, the highly vascular endometrium can no longer be maintained. The capillaries begin to rupture and menstruation begins. The drop in progesterone and estrogen also signals the _____________ to begin secreting GnRH and another menstrual cycle begins. LH FSH ovulation = egg release egg development corpus luteum estrogen progesterone lining of uterus days 0 7 14 21 28

27. Oogenesis In ovaries, cells called ________ go thru mitosis repeatedly to build up numbers of cells. Then those oogonia grow into larger cells (primary oocytes) and start meiosis, but the process stops at Prophase I, until puberty. Then ____ periodically stimulates a follicle to grow and induces its primary oocyte to complete meiosis I and start meiosis II ovulation Meiosis 2 completed triggered by fertilization

28. Comparison of spermatogenesis and oogenesis Millions of sperm produced every day 4 gametes for every cell that begins meiosis Very small Occurs in testis Released during ejaculation Haploid nuclei Continues throughout all of life, starting at puberty One egg is ovulated per menstrual cycle One gamete is produced for each cell that begins meiosis (plus polar bodies) Eggs are ‘large’ Occurs in ovaries Released during ovulation Haploid nuclei Ovulation starts at puberty, occurs with each menstrual cycle, then stops at menopause Spermatogenesis Oogenesis

29. Fertilization

30. Fertilization Enzymes from acrosome are released at the _____________. Sperm head enters egg, plasma membranes fuse together. This initiates the ___________________.

31. Fertilization and the cortical reaction As soon as the sperm reaches the nucleus, the ________________ fuse with the cell membrane and release their enzymes to the outside, making it impermeable to any other sperm cells.

32. Early human embryonic development: Cleavage • Fertilization triggers the zygote to start repeated mitotic divisions as it moves down the Fallopian tube toward the uterus • By the time the embryo reaches the uterus, it is approx. 100 cells and is ready to implant into the endometrium of the uterus. At this point, it’s a hollow ball of cells called a ________________.

33. A few days later, the embryo imbeds itself in the uterine lining. At this point, a woman's body begins to secrete a pregnancy hormone known as _______. This hormone maintains production of progesterone from the ovary, a crucial factor in maintaining a pregnancy.

34. HCG specifics HCG = Human ____________ Gonadotrophin. It enters the bloodstream of the mother its target tissue is the ______________. HCG acts to maintain the secretory functions of this gland beyond the length of time typical of a normal menstrual cycle. The corpus luteum continues to make both estrogen and progesterone and the endometrium is maintained. Later on in pregnancy, the ________ will take over estrogen and progesterone production.

35. Organogenesis Umbilical blood vessels Mammalian embryo Chorion Bird embryo Amnion Yolk sac Allantois Fetal blood vessels Placenta Maternal blood vessels

36. Placenta • Materials exchange across membranes

37. Role of the Placenta When fully formed, 2 fetal blood vessels within the umbilical cord carry fetal blood to the placenta. The blood is ________________ and carries waste products (_____, urea, hormones). This fetal blood exchanges materials (not blood) with the maternal bloodstream. Another fetal blood vessel returns the ‘clean’ blood to the fetus (has oxygen and __________, hormones) At no time do the 2 bloods actually mix When the corpus luteum stops producing estrogen and progesterone, the placenta starts producing and secreting them.

38. Role of the amniotic fluid _____________ extends all the way around the fetus The fluid within it is called amniotic fluid Several functions: Provides cushioning effect if something happens to mom’s abdomen • Provides safe environment where fetus has free movement and can exercise its developing muscles and skeleton • Provides ______________ stability

39. Human fetal development 4 weeks 7 weeks

40. Human fetal development 10 weeks

41. Human fetal development 12 weeks 20 weeks

42. Human fetal development • 24 weeks (6 months; 2nd trimester) fetus is covered with fine, downy hair called lanugo. Its skin is protected by a waxy material called vernix

43. Human fetal development • 30 weeks (7.5 months) umbilical cord

44. Getting crowded in there!! • 32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

45. Hormone induction Birth positive feedback

46. Birth (36 weeks) Intestine Placenta Umbilical cord Wall of uterus Bladder Cervix Vagina

47. The end of the journey!