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Chapter 27

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Chapter 27

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  1. Chapter 27 Reproduction and Embryonic Development

  2. Baby Bonanza • The increased use of fertility drugs has caused an increase in the number of multiple births in the United States • Infertility affects about one in seven couples in the United States • Fertility drugs are an example of technology affecting the normal reproductive cycle

  3. ASEXUAL AND SEXUAL REPRODUCTION • 27.1 Sexual and asexual reproduction are both common among animals • In asexual reproduction, one parent produces genetically identical offspring • Budding, fission, fragmentation/ regeneration • Allows isolated animals to reproduce without having to find mates • Produces offspring quickly • Diminishes genetic diversity of offspring

  4. Sexual reproduction involves the fusion of gametes from two parents • Two haploid gametes unite to produce a diploid zygote • Male sperm is small, flagellated • Female ovum is larger and not self-propelled • Increases genetic variability among offspring • May enhance reproductive success in changing environments

  5. Many animals can reproduce both sexually and asexually • Rotifer • Asexual in good environmental conditions • Sexual in more stressful conditions • Hermaphrodites • Each individual has both female and male reproductive systems • Most mate with another member of their species

  6. LE 27-01c “Head” Intestine Ovary Eggs LM 210

  7. Video: Rotifer

  8. External fertilization is common in aquatic animals • Parents release their gametes into the environment, where fertilization occurs • Internal fertilization occurs in nearly all terrestrial animals • Sperm are deposited in or close to the female reproductive tract • Gametes unite within the tract • Usually requires copulation

  9. LE 27-01e Eggs

  10. HUMAN REPRODUCTION • 27.2 Reproductive anatomy of the human female • Both sexes in humans • Have a set of gonads where gametes are produced • Have ducts for delivery of the gametes and structures for copulation

  11. Ovaries • Produce egg cells (ova) • Follicles protect and nourish the eggs and produce estrogen • Ovulation • One egg released every 28 days, starting at puberty • Remaining follicular tissue temporarily develops into corpus luteum • Secretes progesterone

  12. Oviducts (fallopian tubes) • Convey eggs to the uterus • Location of fertilization • Uterus (womb) • Thick wall and endometrium richly supplied with blood vessels • Actual site of pregnancy • Embryo: from first division of zygote until body structures begin to appear • Fetus: from about ninth week until birth

  13. In ectopic pregnancy, embryo implants somewhere other than uterus • Cervix: narrow neck of uterus • Vagina: Muscular opening from uterus • Receives penis during intercourse • Forms the birth canal • Other structures of the female reproductive system • Labia minora and majora, clitoris, Bartholin's gland

  14. LE 27-02a Ovaries Oviduct Follicles Corpus luteum Uterus Wall of uterus Endometrium (lining of uterus) Cervix (“neck” of uterus) Vagina

  15. LE 27-02c Oviduct Ovary Uterus Rectum (digestive system) Urinary bladder (excretory system) Pubic bone Cervix Urethra (excretory system) Shaft Vagina Clitoris Glans Bartholin’s gland Prepuce Anus (digestive system) Labia minora Labia majora Vaginal opening

  16. LE 27-02b Egg cell Ovary LM 200

  17. Animation: Female Reproductive Anatomy

  18. 27.3 Reproductive anatomy of the human male • Testes, housed outside the body in the scrotum, produce sperm • Pathway of sperm from testis to outside • Epididymis • Vas deferens • Ejaculatory duct • Ejaculation through urethra in penis • Connection between reproductive and excretory systems

  19. Several glands contribute to the formation of fluid that nourishes and protects sperm • Seminal vesicles • Prostate gland • Bulbourethral glands • Semen combines sperm and glandular secretions Animation: Male Reproductive Anatomy Animation: Male Hormones

  20. LE 27-03a Rectum (digestive system) Seminal vesicle Urinary bladder (excretory system) Vas deferens Pubic bone Ejaculatory duct Erectile tissue of penis Prostate gland Urethra (excretory system) Bulbourethral gland Penis Vas deferens Epididymis Glans of penis Testis Prepuce Scrotum

  21. LE 27-03b Urinary bladder (excretory system) Seminal vesicle (behind bladder) Prostate gland Bulbourethral gland Urethra Erectile tissue of penis Scrotum Vas deferens Epididymis Glans of penis Testis

  22. The process of ejaculation involves coordinated contractions and expulsion of fluids • Hormones control sperm production by the testes through a negative-feedback system

  23. LE 27-03c Urethra region here expands and fills with semen Sphincter contracts Urinary bladder Contractions of vas deferens Contractions of seminal vesicle Contractions of prostate gland Contractions of epididymis Sphincter contracts First stage Sphincter remains contracted Semen expelled Contractions of muscles around base of penis Contractions of urethra Sphincter relaxes Second stage

  24. LE 27-03d Stimuli from other areas in the brain Hypothalamus Releasing hormone Anterior pituitary Negative feedback FSH LH Androgen production Testis Sperm production

  25. 27.4 The formation of sperm and ova requires meiosis • Gametogenesis: the formation of diploid gametes from haploid sperm and ova during meiosis • Spermatogenesis: the formation of sperm cells • Diploid cells made continuously in seminiferous tubules of testes • Differentiated primary spermatocytes • Haploid secondary spermatocytes • Haploid sperm

  26. LE 27-04a Epididymis Penis Testis Scrotum Testis Diploid cell 2n Seminiferous tubule Differentiation and onset of Meiosis I Cross section of seminiferous tubule 2n Primary spermatocyte (in prophase of Meiosis I completed Meiosis I Secondary spermatocyte n n (haploid; double chromatids) Meiosis I Developing sperm cells n n n n (haploid; single chromatids) Differentiation Sperm cells n n n n Center of seminiferous tubule (haploid)

  27. Oogenesis occurs mostly in the ovaries • Before birth, a diploid cell in each developing follicle begins meiosis • At birth, each follicle contains a dormant diploid primary oocyte • After puberty, one primary oocyte is released each month • Continues meiosis • Unequal division of cytoplasm forms a single secondary oocyte • If fertilized, oocyte completes meiosis and becomes a haploid ovum

  28. LE 27-04b Diploid cell In embryo 2n Differentiation and onset of Meiosis I Primary oocyte Present at birth 2n (arrested in prophase of Meiosis I) Completion of Meiosis I and onset of Meiosis I Secondary oocyte First polar body (arrested at meta- phase of Meiosis II; released from ovary) n n Entry of sperm triggers completion of Meiosis II Ovum Second polar body n (haploid) n

  29. The development of an ovarian follicle involves many different processes • Comparison of oogenesis and spermatogenesis • Both produce haploid gametes • Only one ovum results from each diploid cell that undergoes meiosis • Cells from which gametes develop are thought not to divide throughout life in the female • Oogenesis has long resting periods; spermatogenesis is uninterrupted

  30. LE 27-04c Degenerating corpus luteum Start: Primary oocyte within follicle Corpus luteum Growing follicles Mature follicle Secondary oocyte Ovary Ovulation Ruptured follicle

  31. 27.5 Hormones synchronize cyclic changes in the ovary and uterus • The reproductive cycle in females involves an integrated process between the ovaries and the uterus • Ovarian cycle: produces the oocyte • Menstrual cycle: involves the monthly changes in the uterus • Hormonal messages synchronize the two cycles through intricate feedback systems

  32. Events in the menstrual cycle are coordinated with the ovarian cycle • Events synchronized by five hormones • Menstrual cycle prepares uterus for implantation of embryo • Menstruation lasts 3-5 days, corresponding to pre-ovulatory phase of ovarian cycle • Continues through time of ovulation (20-25 days) • If no embryo is implanted, menstruation begins again

  33. Hormonal events leading to ovulation • Hypothalamus signals the anterior pituitary to secrete FSH and LH • FSH stimulates growth of a follicle, with little estrogen secreted and negative feedback control of pituitary • Increased secretion of estrogen exerts positive feedback on hypothalamus • Pituitary secretes burst of FSH and LH levels • LH, FSH, and estrogen peak

  34. Hormonal events at ovulation and after • LH stimulates completion of meiosis and rupture of follicle • Ovulation occurs • Follicle becomes the corpus luteum • Corpus luteum secretes estrogen and progesterone • High levels of estrogen and progesterone exert negative feedback on hypothalamus and pituitary

  35. FSH and LH levels drop • Hypothalamus stimulates pituitary to secrete more FSH and LH, and a new cycle begins • Control of the menstrual cycle • When levels of estrogen and progesterone drop, endometrium begins to slough off • Menstrual bleeding begins on day 1 of a new cycle

  36. LE 27-05 Control by hypothalamus Inhibited by combination of estrogen and progesterone Hypothalamus Stimulated by high levels of estrogen Releasing hormone Anterior pituitary FSH LH Pituitary hormones in blood LH peak triggers ovulation and corpus luteum formation LH FSH LH FSH Ovarian cycle Corpus luteum Degenerating corpus luteum Growing follicle Mature follicle Ovulation Pre-ovulatory phase Post-ovulatory phase Progesterone and estrogen Estrogen Ovarian hormones in blood Estrogen Progesterone Progesterone and estrogen Estrogen

  37. Animation: Ovulation Animation: Post Ovulation

  38. 27.6 The human sexual response occurs in four phases • Excitement phase: prepares the sexual organs for coitus • Plateau phase: breathing and heart rate increase • Orgasm: rhythmic contractions, pleasure for both partners, ejaculation • Resolution phase: completes the cycle and reverses the previous responses

  39. CONNECTION • 27.7 Sexual activity can transmit disease • Sexually transmitted diseases (STDs) are contagious diseases spread by sexual contact • Viral diseases are not curable but can be controlled by medication • Many STDs can cause long-term problems or even death if untreated • STDs are most prevalent among teenagers and young adults

  40. CONNECTION • 27.8 Contraception can prevent unwanted pregnancy • Contraception is the deliberate prevention of pregnancy • Contraception must be used correctly to prevent failure • "Safe sex" provided by condoms can prevent both unwanted pregnancy and sexually transmitted disease

  41. Common contraceptive methods • Abstinence • Tubal ligation or vasectomy • Rhythm method (natural family planning) • Withdrawal • Barrier methods: condom, diaphragm • Most effective if used with spermicide • Oral contraceptives • Morning after pills

  42. LE 27-08 Skin patch Condom Diaphragm Spermicide Birth control pills