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Animal Reproduction

Animal Reproduction. Chapter 46. Reproduction in the Animal Kingdom. Sexual Asexual Fission Budding Fragmentation & Regeneration Parthenogenesis  egg develops without being fertilized. Parthenogenesis. Development of an unfertilized egg honey bees

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Animal Reproduction

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  1. Animal Reproduction Chapter 46

  2. Reproduction in the Animal Kingdom • Sexual • Asexual • Fission • Budding • Fragmentation & Regeneration • Parthenogenesis egg develops without being fertilized

  3. Parthenogenesis • 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. Reproductive Cycles and Patterns Most animals exhibit cycles in reproductive activity Often related to changing seasons Reproductive cycles Are controlled by hormones and environmental cues

  5. Fertilization • Plays an important part in sexual reproduction • Joining of egg & sperm • external • usually aquatic animals • internal • usually land animals

  6. Patterns of Sexual Reproduction • External fertilization, external development • Internal Fertilization, External Development • Internal Fertilization, Internal Development

  7. Hermaphrodites • Certain Organisms seldom encounter a mate • Solution  hermaphroditism • In which each individual has both male and female reproductive

  8. Figure 46.4 Sequential Hermaphroditism • An individual reverses its sex during its lifetime

  9. Male Reproductive System

  10. Male Reproductive System • Testicles • produces sperm & hormones • Scrotum • sac that holds testicles outside of body • Epididymis • where sperm mature • Vas deferens • 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

  11. Male reproductive system • Sperm production • over 100 million produced per day! • ~2.5 million released per drop! • Testes & epididymis • sperm production & maturation • Glands • seminal vesicles, prostate, bulbourethal • produce seminal fluid = nutrient-rich

  12. 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

  13. Female Reproductive System

  14. Female Reproductive System • Ovaries • produces eggs & hormones • Uterus • nurtures fetus; lining builds up each month • Fallopian tubes • tubes for eggs to travel from ovaries to uterus • Cervix • opening to uterus, dilates 10cm (4 inches) for birthing baby • Vagina • birth canal for birthing baby

  15. Female Reproductive System

  16. Oogenesis • What is the advantage of this development system? Meiosis 1 completed during egg maturation ovulation Meiosis 2 completed triggered by fertilization

  17. The reproductive cycle of the human female • The Ovarian Cycle • The Uterine (Menstrual) Cycle • Menopause

  18. Female Hormones • FSH & LH • release from pituitary • stimulates egg development & hormone release • peak release = release of egg (ovulation) • Estrogen • released from ovary cells around developing egg • stimulates growth of lining of uterus • lowered levels = menstruation • Progesterone • released from “corpus luteum” in ovaries • cells that used to take care of developing egg • stimulates blood supply to lining of uterus • lowered levels = menstruation

  19. The Ovarian Cycle • In the ovarian cycle • Hormones stimulate follicle growth, which results in ovulation • Following ovulation • The follicular tissue left behind transforms into the corpus luteum

  20. Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus Stimulated by high levels of estrogen GnRH (a) Anterior pituitary Inhibited by low levels of estrogen LH FSH 1 Pituitary gonadotropins in blood 2 (b) 6 LH FSH FSH and LH stimulate follicle to grow LH surge triggers ovulation Ovarian cycle 3 (c) 7 8 Corpus luteum Degenerating corpus luteum Growing follicle Mature follicle Ovulation Luteal phase Follicular phase Progesterone and estrogen secreted by corpus luteum Estrogen secreted by growing follicle in increasing amounts 4 Peak causes LH surge Ovarian hormones in blood (d) 5 Progesterone Estrogen 10 Progesterone and estro- gen promote thickening of endometrium Estrogen level very low 9 Uterine (menstrual) cycle (e) • Endometrium Secretory phase Menstrual flow phase Proliferative phase 25 28 Figure 46.13a–e 5 14 15 0 20 10 Days

  21. The Uterine (Menstrual) Cycle • Occurs when the endometrium is shed • Three Phases • Mentrual Flow Phase endometrium is shed and mentrual bleeding occurs • Proliferative Phase endometrium regenerates & thickens • Secretory Phaseendometrium thickens, if an embryo has not implanted by the end of this phaseA new menstrual flow commences

  22. Menopause • After about 450 cycles, human females undergo menopause • The cessation of ovulation and menstruation

  23. Fertilization

  24. Placental Mammals • Human Chorionic Gonadotropin • Secreted by embryo; acts like LH to maintain the Corpus Luteum • Excreted in urine • Parturition • Birth; in late pregnancy; estrogen increases • This stimulates oxytocin receptors • Oxytocin from fetus and mother stimulate contractions

  25. Hormonal Control of the Male Reproductive System • Testosterone and other androgens • Are directly responsible for the primary and secondary sex characteristics of the male

  26. Stimuli from other areas in the brain Hypothalamus GnRH from the hypothalamus reg- ulates FSH and LH release from the anterior pituitary. Anterior pituitary Negative feedback FSH acts on the Sertoli cells of the seminiferous tubules, promoting spermatogenesis. LH stimulates the Leydig cells to make testosterone, which in turn stimulates sperm production. Leydig cells make testosterone Primary and secondary sex characteristics Sertoli cells Spermatogenesis Testis Figure 46.14 Androgen secretion and sperm production controlled by hypothalamic and pituitary hormones

  27. Conception, Pregnancy and Birth • Blastocyst • Implants by burrowing; endometrium grows over • Provides nutrients first 2-4 weeks

  28. Placenta Derived from both maternal and fetal cells produce progesterone • Materials exchange across membranes

  29. Human fetal development • The fetus just spends much of the 2nd & 3rd trimesters just growing …and doing various flip-turns & kicks inside amniotic fluid Week 20

  30. 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

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

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

  33. Hormone induction Birth positive feedback

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

  35. The end of the journey!

  36. Mechanisms of some contraceptive methods

  37. RU486 • Progesterone analog • Blocks progesterone receptors in uterus; lining is shed • Prostaglandins also taken

  38. Reproductive Technologies • Ultrasound • Amniocentesis • Chorionic Villi Sampling (CVS) • In Vitro Fertilization (IVF) or GIFT

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