1. Chapter 20
Reproduction

2. Reproduction Reproductive System Sexual reproduction
Not needed for the survival of the individual
Species survival
Sexual reproduction
Genes from two individual
Combine at random
Creates new combinations
Increases chances of species survival

3. Sexual Reproduction Each individual produces gametes
Formed in gonads by meiosis
Male: testes produce:
Sperm
Testosterone
Female: ovaries produce:
Ova
Estrogens, Progesterone
Gametes unite in process of fertilization
Restores diploid number
Forms zygote

4. Sexual Determination Each zygote inherits Kinds of chromosomes
23 chromosomes from mother
23 chromosomes from father.
23 pairs of homologous chromosomes.
alleles
Kinds of chromosomes
1-22 pairs of chromosomes: autosomal
23rd pair are sex chromosomes.
Male: XY
Female: XX
Chromosomal gender of zygote determined by fertilizing sperm.

5. Formation of Testes
First 40 days after conception the gonads of males and females are similar in appearance.
During this time:
Spermatogonia and oogonia migrate from yolk sac to developing embryonic gonads
Gonads could become either.
TDF (testis-determining factor):
hypothetical
promotes the conversion to testes:
gene located on short arm of Y, called SRY (sex determining region of Y chromosome)
Found in all mammals

6. Formation of Testes Structures in the testes:
Seminiferous tubules: 43 to 50 days post conception
Germinal cells: sperm.
Nongerminal cells: Sertoli cells (sustentacular cells).
Leydig cells (interstitial cells):
Appear about day 65.
Endocrine function: secrete androgens
Main: Testosterone

7. Formation of Testes Leydig cells secrete testosterone.
Begins 8th week and peaks at 12-14th week.
Masculinizes embryonic structures.
Testosterone then declines to very low levels until puberty.
Decline occurs by end of second trimester
Testes descend into scrotum shortly before birth.
Temp about 3 degrees below internal temp
35 degrees C

8. Formation of Ovaries
Absence of Y chromosome and TDF, female develop ovaries.
Ovarian follicles do not appear until 2nd trimester.

10. Development of Accessory Sex Organs and Genitalia
Presence or absence of testes determines the accessory sex organs and external genitalia.
Male accessory organs derived from wolffian ducts.(mesonephric)
Sertoli cells secrete MIF(mullerian inhibition factor).
Female accessory organs derived from mullerian ducts. (paramesonephritic)

12. Development of Accessory Sex Organs and Genitalia
Both duct systems in both sexes between days 25 and 50
Regression of mullarian ducts begins about day 60
Testosterone
responsible for development of male accessory sex organs
External genitalia identical first 6 weeks, then testosterone stimulates development of penis
Not the active agent in all cells
converted to dihydrotestosterone (DHT) in some target cells
Needed for penis, spongy urethra, scrotum, prostrate
Testosterone directly needed for wolfian derivatives:
Epididymis, ductus deferens, ejaculatory duct, SV

13. Development of Accessory Sex Organs and Genitalia

15. Endocrine Regulation of Reproduction
First trimester
Embryonic testes are active endocrine glands
Secrete large amounts of testosterone
Embryonic ovaries not mature until third trimester
Time of birth:
Gonads in both sexes relatively inactive
Before puberty:
Low levels of sex steroids in both
Due to lack of stimulation
Puberty:
Increased stimulation from gonadotropic hormones
Induce increase in sex steroids

16. Endocrine Regulation of Reproduction
Hypothalamus releases LHRH (GnRH) into hypothalamo-hypophyseal portal vessels.
Anterior pituitary secretes:
LH: luteinizing hormone.
In male: interstitial-cell stimulating hormone (ICSH)
FSH: follicle-stimulating hormone.
Secreted in pulsatile fashion to prevent desensitization and down regulation of receptors.

17. Endocrine Interactions
Primary effects of LH and FSH on gonads:
Stimulation of spermatogenesis and oogenesis.
Stimulation of gonadal hormone secretion.
Maintenance of gonadal structure.

18. Endocrine Regulation Negative Feedback:
Inhibit GnRH from hypothalamus.
Inhibit anterior pituitary response to GnRH.
Inhibin secretion inhibit anterior pituitary release of FSH.
By sertoli cells
Female: estrogen and progesterone.
Male: testosterone.

20. Onset of Puberty
FSH and LH high in newborn, falls to low levels in few weeks.
Puberty: driven by increased secretion of FSH and LH

21. Onset of Puberty FSH and LH LH:
Brain maturation increases GnRH secretion.
Decreased sensitivity of GnRH to negative feedback.
LH:
Increased secretion triggers puberty
Late puberty, pulsatile secretion of LH and FSH increase during sleep.
Stimulate a rise in sex steroid secretion.

22. Onset of Puberty Stimulate rise in testosterone and estradiol-17b.
Produce secondary sexual characteristics.
Age of onset related to the amount of body fat and physical activity in the female
Leptin secretion from adipocytes may be required for puberty.

23. Pineal Gland Secretes melatonin.
Secretion influenced by light-dark cycles.
Inhibit gonadotropin secretion.
Role in humans not established.

24. 4 Phases of Human Sexual Response
Excitation phase (arousal):
Myotonia and vasocongestion.
Engorgement of a sexual organ with blood.
Erection of the nipples.
Plateau phase:
Clitoris becomes partially hidden.
Erected nipples become partially hidden by swelling of areolae.
Orgasm:
Uterus and orgasmic platform of vagina contract.
Contractions accompanying ejaculation.
Resolution phase:
Body return to preexcitation conditions.
Refractory period
In males
Erection possible, but not ejaculation

25. Male Reproduction System
Testes:
Seminiferous tubules:
Where spermatogenesis occurs.
Contain receptor proteins for FSH in Sertoli cells.
Leydig cells:
Secrete testosterone.
Contain receptor proteins for LH.

26. Control of LH and FSH Secretion
Negative feedback:
Testosterone inhibits LH and GnRH production.
Inhibin inhibits FSH secretion.
Aromatization reaction producing estadiol in the brain is required for the negative feedback effects of testosterone on LH.
Brain is a target organ for testosterone
Converted to derivatives

28. Testosterone Secretion
Responsible for initiation and maintenance of body changes in puberty.
Stimulate growth of muscles, larynx, and bone growth until sealing of the epiphyseal discs.
Promote hemoglobin synthesis.
Acts in paracrine fashion and is responsible for spermatogenesis.

29. Testosterone Secretion
Negative feedback of testosterone and inhibin
Keep relatively constant levels of gonadotropins
Results in relatively constant levels
Different in female
At menopause: no more sex steroids
In males, gradual decrease

30. Endocrine function: testes
Testosterone: main androgen
Sertoli and Leydig cells secrete small amounts of estradiol.
Have receptors for estradiol (as do other male structures)
May be needed for spermatogenesis
Estradiol may be responsible for:
Negative feedback in brain.
Sealing of epiphyseal plates.
Regulatory function in fertility.

31. Spermatogenesis Spermatogonia:
Replicate initially by mitosis.
Produce two cells
One becomes a primary spermatocytes undergoes meiosis:
2 nuclear divisions.
2nd meiotic division produce 4 spermatids.

32. Spermiogenesis Maturation of spermatozoa.
Cytoplasm is pinched off and ingested by the Sertoli cell cytoplasm.

33. Sertoli Cells Blood-testes barrier:
Prevents autoimmune destruction of sperm.
Produce FAS ligand which binds to the FAS receptor on surface to T lymphocytes, triggering apoptosis.
Secretes inhibin.
Phagocytize residual bodies:
Transmit information molecules from germ cells to Sertoli cells.
Secrete ABP (androgen-binding protein):
Binds to testosterone and concentrates testosterone in the tubules.

34. Hormonal Control of Spermatogenesis
Testosterone required for completion of meiosis and spermatid maturation.
Testes secrete paracrine regulators:
IGF-1.
Inhibin.
FSH necessary in the later stages of spermatid maturation.

35. Male Accessory Organs Epididymis: Prostate secretes:
Maturational changes.
Resistance to pH changes and temperature.
Storage.
Prostate secretes:
Alkaline fluid.
Citric acid.
Ca++.
Coagulation proteins.
Seminal vesicles secrete:
Fructose.

36. Erection, Emission, and Ejaculation
Increased vasodilation of arterioles.
NO is the NT.
Blood flow into the erectile tissues of the penis.
Parasympathetic
Emission:
Movement of semen into the urethra.
Sympathetic
Ejaculation:
Forcible expulsion of semen from the urethra out of the penis.

37. Female Reproductive System
Ovaries:
Contain large number of follicles which enclose ova.
Extensions called fimbriae partially cover each ovary.
At ovulation, secondary oocyte is extruded.

38. Female Reproductive System
Fallopian (uterine) tubes:
Ova drawn into the tube by cilia.
Uterus:
Womb.
Endometrium shed during menstruation.
Vagina:
Cervical mucus plug.

39. Ovarian Cycle 5 mo. gestation ovaries contain 6-7 million oogonia.
Oogenesis arrested in prophase of 1st meiotic division (primary oocyte).
Apoptosis occurs:
2 million primary oocytes at birth.
400,000 primary oocytes at puberty.
400 oocytes ovulated during the reproductive years.

40. Ovarian Cycle Primary oocytes contained in primary follicles.
FSH stimulates cell growth.
Develop into secondary follicles.
Fusion of its vesicles into the antrum.
Mature graafian follicle:
1st meiotic division completed (secondary oocyte).

42. Ovarian Cycle Secondary oocyte: Under FSH stimulation:
Theca cells secrete testosterone. Granulosa cells: contain the enzyme aromatase to convert testosterone into estrogen.

43. Ovulation Graafian follicle forms bulge on surface of ovary.
Extrudes secondary oocyte into the uterine tube.
Empty follicle becomes corpus luteum and secretes:
Progesterone.
Estrogen.
If not fertilized becomes corpus albicans.

44. Menstrual Cycle 3 phases: Ovarian Follicular Phase Ovulation
Luteal Phase
Duration approximately 28 days.
Day 1 is the first day of menstruation.

45. Follicular Phase
FSH:
Stimulates production of FSH receptors on granulosa cells.
Follicles grow and become secondary follicle.
Granulosa cells secrete estradiol.
Increases sensitivity of FSH receptors.
FSH and estradiol stimulate production of LH receptors in graafian follicle.

46. Follicular Phase Rapid rise in estradiol:
Negative feedback on LH and FSH.
Hypothalamus increase frequency of GnRH pulses.
Augments the ability of anterior pituitary to respond to GnRH to increase LH secretion.

47. Follicular Phase Positive feedback:
LH surge begins 24 hours before ovulation.
Triggers ovulation.
FSH increase stimulates development of new follicles.

48. Ovulation Under FSH, graafian follicle grows large and thin-walled.
Triggers LH surge.
Wall of graafian follicle ruptures.
Day 14.
Ist meiotic division is completed.

49. Luteal Phase
LH stimulates formation of the empty follicle into corpus luteum.
Corpus luteum secretes:
Progesterone:
Plasma concentration rapidly rises.
Estradiol.
Negative feedback on LH and FSH.
Inhibin: suppress FSH.

50. Luteal Phase Corpus luteum regresses unless fertilization occurs:
Estradiol decreases.
Progesterone decreases.
Withdrawal of estradiol and progesterone cause menstruation to occur.

53. Endometrial Changes 3 phases of endometrium changes:
Proliferative phase.
Secretory phase.
Menstrual phase.

54. Proliferative Phase Ovary is in follicular phase.
Estradiol stimulate growth of endometrium.
Spiral arteries develop.
Stimulate production of receptor proteins for progesterone.
Cornification of vaginal epithelium occurs.

55. Secretory Phase Ovary is in luteal phase.
Progesterone stimulates development of uterine glands, which become engorged with glycogen.
Endometrium becomes thick, vascular and spongy.
Cervical mucus thickens and becomes sticky.

56. Menstrual Phase Progesterone cause constriction of spiral arteries.
Necrosis and sloughing of endometrium occurs.
Lasts 1-5 days.

58. Menopause Cessation of ovarian activity. Age ~ 50 years.
Ovaries depleted of follicles.
Estradiol and inhibin withdrawl causes hot flashes, and atrophy of the vaginal wall.
LH and FSH increase.

59. Fertilization
Ejaculation 300 million sperm, 100 reach (uterine) fallopian tube.
Fertilization occurs in the uterine tubes
Acrosomal reaction:
Acrosome of sperm contains hyaluronidase, an enzyme that digests a channel through zona pellucida.
Sperm fuses with ovum cell membrane.

60. Fertilization
As fertilization occurs, secondary oocyte completes 2nd meiotic division.
Sperm enters ovum cytoplasm.
Ovum nuclear membrane disappears, zygote formed.

61. Blastocyct Formation Cleavage: Blastocyst develops:
30-36 hrs. after fertilization the zygote divides by mitosis.
Blastocyst develops:
Inner cell mass: fetus.
Surrounding chorion: trophoblasts form placenta.

62. Implantation
6th day after fertilization, blastocyst attaches to uterine wall.
Blastocyst secretes enzymes that allow blastocyst to burrow into endometrium.
Trophoblast cells secrete hCG.

63. hCG Human chorionic gonadotropin. Trophoblast cells secrete hCG.
Signals corpus luteum not to degenerate until placenta secretes adequate [hormone].
Effects similar to LH.
Basis of pregnancy test.

64. Placenta
Syncytiotrophoblast secretes enzymes that create blood filled cavities in the maternal tissue.
Cytotrophoblast then from projections (villi) that grow into the venous blood.
Producing chorion frondosum on the side that faces the uterine wall.
Other side of chorion bulges into the uterine cavity.

65. Placental Changes Decidual reaction:
Endometrial growth.
Accumulation of glycogen.
Decidua basalis: maternal tissue in contact with the chorion frondosum.
Maternal and fetal blood do not mix.

66. Amnion Envelop the embryo.
Amnionic fluid contains sloughed cells of the fetus.

67. Placenta Function Gas exchange: Nutrient exchange. Waste exchange.
02 and C02.
Nutrient exchange.
Waste exchange.
Synthesis of proteins and enzymes.

68. Placental Hormones hCS: Chorionic somatomammotropin. GH effects.
Diabetic-like effect:
Glucose sparing effect.
Polyuria.
Lipolysis.

69. Placental Hormones Fetal-placental unit: Estrogen stimulates:
Placenta must cooperate with the adrenal cortex in the fetus to produce estrogen.
Estrogen stimulates:
Endometrial growth.
Inhibit prolactin secretion.
Growth of mammary ducts.
Enlargement of mother’s uterus.

70. Placental Hormones Progesterone: Suppresses uterine contractions.
Stimulates uterine growth .
Suppresses LH and FSH.
Stimulate development of alveolar tissue of the mammary gland.

71. Parturition Estrogen in late pregnancy: Uterine contractions:
Increases amount of oxytocin stored.
Stimulate production of oxytocin receptors in myometrium.
Stimulate prostaglandin production.
Uterine contractions:
Oxytocin.
Prostaglandins.

72. Lactation Hypothalamus releases PRH.
Anterior pituitary releases prolactin:
Stimulate milk production.
Oxytocin needed for “milk letdown”.