Ch 46: Animal Reproduction

1. Ch 46: Animal Reproduction

2. ►ASEXUAL REPRODUCTION: • 1 parent • mitotic cell division • examples: binary fission, budding, fragmentation/regeneration

3. ► SEXUAL REPRODUCTION: • Fusion of 2 haploid gametes to form a zygote • Reproduction cycles are controlled by a combination of hormonal & environmental cues (temp., rainfall, day length, lunar cycles) Sperm cell Egg cell fertilization Zygote

4. ► PHEROMONES: • chemical signals released by 1 organism that influence the behavior of other individuals of the same species; • many function as mate attractants

5. HUMAN MALE REPRODUCTIVE SYSTEM Functions: • Produce sperm; • Produce androgens (male sex hormones); • Deliver sperm to female repro. tract.

6. MALE REPRODUCTIVE SYSTEM - Anatomy ● TESTES -develop in abdomen; descend into scrotum before birth; -made up of tightly coiled tubes (SEMINIFEROUS TUBULES) where sperm are formed; *tubules are lined by germinal epithelial cells -scattered between tubules are the LEYDIG CELLS (produce testosterone and other androgens).

7. (Leydig cells) TESTIS

8. SPERMATOGENESIS: • The first stage of sperm production requires the division of germline epithelium by mitosis • These cells (spermatogonia) then undergo a period of growth. • This is followed by two meiotic divisions that result in four haploid daughter cells. • These haploid cells then differentiate to form sperm cells. • The developing sperm cells are nourished throughout by the Sertoli cells

9. LH:  Stimulates the interstitial cells (Leydig cells) to produce testosterone FSH:  Stimulates the (first) meiotic division of spermatogonia Testosterone:  Stimulates the (second) meiotic division of spermatogonia and the maturation of spermatozoa through differentiation

11. MALE REPRODUCTIVE SYSTEM - Anatomy ● EPIDIDYMIS -6 meters of tubes; sperm cells are here for approx. 20 days; -location where sperm become motile & gain ability to fertilize.

12. MALE REPRODUCTIVE SYSTEM - Anatomy *If ejaculation occurs… ● VAS DEFERENS (muscular tube) ● EJACULATORY DUCT (where Vas Def. meets seminal vesicle) ● URETHRA -tube that drains both repro. & excretory products

13. MALE REPRODUCTIVE SYSTEM - Anatomy ● PENIS -3 cylinders of erectile tissue (when filled with blood, penis becomes erect); -head of penis = glans penis; has thinner covering; is covered by foreskin.

15. MALE REPRODUCTIVE SYSTEM There are 3 sets of accessory glands (add secretions to semen): 1) SEMINAL VESICLES (2): -produce 60% of semen volume/fluid; -alkaline fluid contains mucus, fructose sugar (energy!), coagulating enzyme, prostaglandins.

16. MALE REPRODUCTIVE SYSTEM Accessory glands (continued): 2)PROSTATE GLAND: -secretes thin, milky fluid directly into the urethra; -contains: anticoagulant enzymes, citrate (sperm nutrient) -fluid helps to balance the pH environment of the vagina.

17. MALE REPRODUCTIVE SYSTEM Accessory glands (continued): 3) BULBOURETHRAL GLANDS (2): -secrete clear mucus to neutralize any acidic urine in the urethra; -carries some sperm; -a.k.a. Cowper’s glands.

18. MALE REPRODUCTIVE SYSTEM *typical semen production = 2-5 mL; each mL may contain 50 – 130 million sperm! *once in female reproductive tract, prostaglandins thin cervical mucus & stimulate uterine contractions

19. *alkalinity of semen helps neutralize acidic environment of the vagina *when first ejaculated, semen coagulates (easier to move sperm into uterus); then anticoagulants thin the semen & sperm begin to swim through the female reproductive tract…

20. FEMALE REPRODUCTIVE SYSTEM Functions: • Produce egg cells; • Produce female hormones; • Nurture & protect developing fetus.

21. FEMALE REPRODUCTIVE SYSTEM - Anatomy ● OVARIES: -about size & shape of almonds -contains many FOLLICLES…

22. The follicles… *surround, nourish, protect egg cells; *produce estrogen; *mature and release egg during monthly cycle (aka:OVULATION; ≈1 follicle per month, starting at puberty and ending at menopause; *each follicle becomes a CORPUS LUTEUM following ovulation; *disintegrates if egg is not fertilized.

24. OOGENESIS: • Begins during fetal development, when a large number of cells (oogonia) are formed by mitosis before undergoing a period of growth • These cells begin meiosis but are arrested in prophase I until puberty • At puberty, some of these follicles continue to develop each month in response to FSH secretion • These follicles complete the first meiotic division to form two cells of unequal size • cell with less cytoplasm is a polar body (which will degenerate); it may or may not divide again (possibly giving 3rd polar body) • larger cell forms a secondary oocyte • The secondary oocyte begins the second meiotic division but is arrested in prophase II (until fertilization) • It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilization occurs, will complete meiosis • The second meiotic division will produce an ovum and a second polar body

25. OOGENESIS: Explained different way • Germinal epithelium lines the outer surface of the ovary • In utero, divides by MITOSIS to form numerous oogonia which grow & enlarge into primary oocytes • Primary oocytes begin MEIOSIS I but do not complete it (surrounded by follicle cells  primary follicles) • Each menstrual cycle, a few primary follicles continue to develop & usually only 1 completes Meiosis I & matures • have secondary oocyte & 1st polar body • secondary oocyte released during ovulation (rupture of follicle wall) • secondary oocyte suspended in Meiosis II until fertilization

27. FEMALE REPRODUCTIVE SYSTEM - Anatomy ● OVIDUCTS (“FALLOPIAN TUBES”): -cilia “pull” the egg cell in and convey the egg down the duct; -normal fertilization occurs HERE!!!

28. FEMALE REPRODUCTIVE SYSTEM - Anatomy ● UTERUS (“womb”): -thick, muscular organ; expands during pregnancy; -inner lining = ENDOMETRIUM, which is highly vascularized *Menstruation: death & sloughing off of endometrial tissue

29. FYI: Endometriosis • occurs when bits of the tissue that lines the uterus (endometrium) grow on other pelvic organs, such as the ovaries or fallopian tubes • outside the uterus, endometrial tissue thickens and bleeds, just as the normal endometrium does

30. FEMALE REPRODUCTIVE SYSTEM - Anatomy ● CERVIX (neck of uterus) ● VAGINA (birth canal) -thin-walled chamber where sperm are deposited; -hymen = vascularized membrane which covers vaginal opening from birth until it is ruptured

31. FEMALE REPRODUCTIVE SYSTEM - Anatomy ● BARTHOLIN’S GLANDS -small glands near vaginal opening; -secrete mucus during sexual arousal response to facilitate intercourse. ● LABIA MINORA / LABIA MAJORA -enclose and protect vaginal & urethral opening, and clitoris

33. How are these processes the same? • How are they different?

34. Differences between spermatogenesis & oogenesis: SPERMATOGENESIS: • All 4 meiotic products are functional (develop into mature sperm) • Sperm cells continue to develop throughout a male’s life (from puberty) • Stages of meiosis occur continuously, in an uninterrupted sequence

35. Differences between spermatogenesis & oogenesis: OOGENESIS: • Unequal cytoplasmic division in cytokinesis; most cytoplasm goes to secondaryoocyte (ovum); the other 2 or 3 products (polar bodies) disintegrate • Female is born with all of her egg cells/follicles • Female has long “resting” periods of meiosis