Animal Reproduction

1. Chapter 41 Animal Reproduction

2. Reproduction is the Biological Imperative • over time, individuals must replace themselves • promotes survival of species (no reproduction  extinction) • allows individuals to pass their genes onto next generation • Asexual Reproduction • one individual, no genetic diversity in offspring, less time/energy required • involves mitotic cell divisions • usually an alternative to sexual • binary fission, budding, fragmentation, parthenogenesis • development of offspring from an unfertilized egg • Sexual Reproduction • two individuals, genetic diversity in offspring, more time/energy required • gamete formation requires meiosis • fertilization of gametes • external • aquatic or semi-aquatic environment • bed of egg cells laid down first, sperm shed over top of them • fertilization is left largely to chance • usually little parental involvement • less time and energy • internal • occurs in terrestrial and aquatic species • usually involves copulation • reduces # of eggs and sperm • increases probability of fertilization • provides embryo with protection (female’s body or egg shell) • requires more time and energy

3. Invertebrate Sexual Reproduction • external fertilization • internal fertilization • monoecious species • all individuals produce both egg and sperm; no separate sexes • do not self-fertilize • some may be hermaphrodites  possess both male and female genitalia • dioecious species • separate sexes  males produce sperm; females produce eggs • species-specific mating rituals and organs (esp., insects) • Vertebrate Sexual Reproduction • all vertebrates are dioecious • fish and amphibians • external fertilization • internal fertilization • cloaca (“common chamber”) • fish, amphibians, reptiles, birds • receives products of digestive, excretory, reproductive systems • mating rituals (courtship) and some parental care • reptiles and birds • internal fertilization only (within cloaca) • reptiles: well developed copulatory organs • birds: reduced copulatory organs; cloacal contact • amount of parental care is variable in reptiles, high in birds • precocial vs. altricial young

4. mammals • internal fertilization only • no cloaca • monotremes • egg-laying mammals • marsupials • young born very premature, finish development in a pouch • placental mammals • young have connection to mother through placenta • uterus • organ in which embryo/fetus grows and develops • placenta • soft, spongy, highly vascularized tissue • connects mother with embryo/fetus • meets metabolic needs of embryo  all gas/nutrient exchange take place here • umbilical cord • connects embryo/fetus to placenta • amnion (amniotic cavity) • membrane filled with amniotic fluid, directly surrounding embryo/fetus • mammary glands (may lie within breast tissue) • produce milk

5. Placental anatomy and circulation

6. Inside of uterus • ovipary vs. vivipary vs. ovovivipary • zygote vs. embryo vs. fetus Amnion, filled with amniotic fluid Placenta Umbilical cord Embryo Human embryonic development, week 8

7. Human Male Reproduction • external genitalia • penis • consists mainly of three cylindrical bodies of erectile tissue fill with blood  erection • testes: produce sperm and secrete testosterone • contained within scrotum • helps to regulate temp. of testes  slightly cooler allows sperm to develop properly • internal anatomy • vas deferens: transports sperm (plus fluids) from testes to urethra • three glands • testes • seminiferous tubules  sperm cells • interstitial cells  testosterone • epididymis: stores sperm after it is produced in testes; connects with vas deferens • testes epididymis vas deferens  ejaculatory duct urethra  ejaculated out of body • supporting fluids • seminal vesicles • alkaline sugars to nourish sperm • prostate gland • increase mobility, energy, and activation of sperm • bulbourethral glands (Cowper's glands) • increase alkalinity and lubrication • semen: combination of sperm cells + supporting fluids • high alkalinity  packages sperm in protective environment

8. Fig. 41.6 Anatomy of the penis. Note the position of the three cylinders of erectile tissue and how vascularized they are.

9. Anatomy of the penis, more detailed view. Left – longitudinal view; Right – cross-section.

10. Fig. 41.5 The male reproductive system

11. Fig. 41.7 Internal anatomy of the testes

12. spermatogenesis • one diploid cell  4 haploid sperm cells • spermatogonium (2n)  begin meiosis I  primary spermatocytes (in prophase I; 2n)  complete meiosis I  secondary spermatocytes (n)  meiosis II spermatids (n)  mature spermatozoa (sperm cells = n) • structure of sperm • head (with acrosome), midpiece, flagella (tail) • acrosome contains digestive enzymes important at fertilization Fig. 41.7 Spermatogenesis

13. Human Female Reproduction • external genitalia (vulva) • mons pubis: mound of adipose tissue overlying the pubic bone; labia connect to it • labia majora (outer folds of tissue), labia minora (inner folds), clitoris (sexual sensitivity) • vestibular bulbs: subcutaneous erectile tissue, just inside each side of labia majora • greater vestibular (Bartholin’s), lesser vestibular, and paraurethral (Skene’s) glands • lubricate vulva and entrance to vagina • homologous to the three male glands • internal anatomy • vagina • internal environment is highly acidic  combat yeast and bacterial infections • contains no inner glands  lubricated by seepage of fluid through its walls (transudation) • uterus • Fallopian tubes (uterine tubes; oviducts) • ovaries: produce egg cells and secrete hormones • internal organization of females • cervix • lower, narrow portion of uterus  joins with back of vagina • uterine wall consists of three layers • mucosa  produces endometrium once every month • soft, highly vascularized, temporary layer of tissue that will receive embryo if fert. occurs • breaks up and is discharged in menstrual flow if no fert. occurs • smooth muscle • connective tissue

14. Fallopian tubes • extend off top left and right side of uterus  end in fimbriae (with cilia) • fimbriae surround the end portions of each ovary • no direct connection between ovaries and Fallopian tubes • fertilization occurs in far end of one of the Fallopian tubes The female reproductive system. Left – vulva and superficial external structures; Right – glands and subcutaneous structures.

15. Fig. 41.9 The female reproductive system

16. Reproductive anatomy of human females, frontal view

17. Reproductive anatomy of human females, more detailed frontal view

18. ovaries and oogenesis • ovaries produce egg cells and secrete estrogen and progesterone • all oocytes (immature egg cells) are formed before birth • form and develop within follicles (chambers) in ovaries • oogenesis • one diploid cell  1 viable, haploid egg cell • oogonium (2n)  starts meiosis I  primary oocyte (remain in prophase I; 2n)  age of sexual maturity 1 cell/month complete meiosis I secondary oocyte (n)  released from ovary  swept into Fallopian tubes by ciliated fimbriae begins meiosis II  fert. occurs  completes meiosis II  mature ovum (egg; n) • if no fertilization, sec. oocyte is flushed out with menstrual flow • unequal cell division polar bodies (too small to develop)  reabsorbed Fig. 41.10 An overview of oogenesis

19. A more detailed view of oogenesis

20. Fig. 41.10 Oogenesis within an ovary (the ovarian cycle)

21. Hormonal Control of Human Reproduction • hypothalamus secretes GnRH (gonadotropin releasing hormone)  anterior pituitary gonadotropins (FSH and LH)  will affect the gonads • FSH = follicle stimulating hormone • LH = leutinizing hormone • FSH and LH • activity in testes • FSH stimulates sperm production • regulated by the hormone inhibin and negative feedback • LH stimulates release of testosterone • regulated by negative feedback • primary sexual characteristics • development of male genitalia • male secondary sexual characteristics • changes that occur in males at puberty

22. Fig. 41.8 Hormonal control of the testes

23. activity in ovaries • FSH stimulates release of estrogen and progesterone • female secondary sexual characteristics • changes that occur in females at puberty • estrogen  monthly growth of endometrium • LH is involved in menstrual cycle (esp., ovulation) Fig. 41.11 Hormonal control of the ovaries

24. menstrual cycle • great example of multiple systems working together • release of a secondary oocyte from an ovary (ovulation) • growth of uterine endometrium • menstrual flow phase (days 1-4) • begins with first day of menstrual bleeding (menstruation) • menstrual blood = blood and tissue of endometrium • proliferative phase (days 5-13) • FSH/LH levels rise  release of est./prog. from ovaries increases • prim. oocyte becomes active and completes meiosis I  sec. oocyte • increased levels of estrogen prompt growth of endometrium • ovulation (day 14) • brought about by “LH surge” • huge rise in amount of LH present • caused by rising levels of estrogen • positive feedback • one sec. oocyte released from ovary and swept into a Fallopian tube • was released from a Graafian follicle • other physiological changes • e.g., body temp. fluctuations, etc. Light micrograph of ovulation

25. secretory phase (days 15-28) • high levels of LH  increase in release of progesterone • keeps endometriumintact • FSH/LH cause empty Graafian follicle to become a corpus luteum • secretes more est./prog.  enhances growth of endometrium • if fertilization occurs • sec. oocyte completes meiosis II  mature ovum (egg) • zygote forms/divides  tiny embryo sinks into endometrium • embryo secretes HCG (human chorionic gonadotropin) • keeps corpus luteum intact  continues releasing progesterone • maintains endometriumthroughout pregnancy • prevents new primary oocyte from maturing • triggers part of endometrium placenta • helps embryo develop properly • if fertilization does not occur • rising levels of est. and progest.  negative feedback  slows secretion of FSH and LH from anterior pituitary • no HCG is produced  corpus luteum breaks up • estrogen and progesterone levels drop • other physiological changes • endometrium degenerates and breaks up  menstrual flow  new cycle

26. Fig. 41.12 Female hormone levels during the ovarian and uterine cycles (of the menstrual cycle)