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Chapter 26

Chapter 26. Human Reproduction. Sex Determination: Overview. Chromosomes 22 pairsAutosomes 1 pair Sex Chromosomes X - chromosome Y - chromosome. Figure 26-1: Human chromosomes. Sex Determination: Overview. Figure 26-2: Inheritance of X and Y chromosomes.

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Chapter 26

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  1. Chapter 26 Human Reproduction

  2. Sex Determination: Overview • Chromosomes • 22 pairsAutosomes • 1 pair Sex Chromosomes • X - chromosome • Y - chromosome Figure 26-1: Human chromosomes

  3. Sex Determination: Overview Figure 26-2: Inheritance of X and Y chromosomes

  4. Sexual Differentiation: Internal Embryonic Development • Conception to 6 weeks: Bipotential tissues: genes & hormones direct differentiation • Will the embryo develop testis or ovary? • Presence or absence of the SRY protein from the Y chromosome • Wolffian duct  Vas deferens • Mullerian duct  oviduct

  5. Pathway for Sexual Development: Review for Genes to Organs Figure 26-4: Role of the SRY gene in male development

  6. Sexual Differentiation: Internal Embryonic Development Figure 26-3a: Sexual development in the human embryo

  7. Sexual Differentiation: External Genitalia • Bipotential tissues: genital tubercle, urethral folds, urethral groove and labioscrotal swellings

  8. Sexual Differentiation: External Genitalia Figure 26-3b: Sexual development in the human embryo

  9. The Testes • Testes begin to develop inside the abdominal cavity and descend into the scrotal sacs during last two months of fetal development. • Scrotum helps regulate temperature of testes outside the abdominal cavity.

  10. Undescended testes • It’s important to maintain the testicular temperature just below body temperature for optimal sperm production. Don’t want them too hot or too cold. • 3% of male children are born with undescended testes where they remain in the abdominal cavity instead of moving down into the scrotum. • 80% of undescended testes will descend on their own by 1 yr, or else they must be helped along medically. • Undescended testes are called cryptochodism and can be unilateral or bilateral. • There are 2 reasons for concern: • Fertility—if the testes are at the wrong temperature, sperm will not be produced and the man will be infertile. • There’s a high incidence of testicular cancer in men with undescended testes. • If only 1 is undescended fertility will not be a problem, but there is still an increased risk for cancer.

  11. Testes do 2 things! • 1. make sperm • 2. make testosterone

  12. Overview of Gametogenesis: Producing Eggs or Sperm 4n 2n n Figure 26-5: Gametogenesis

  13. Crossing over events (during 1st meiotic division) RECOMBINATION EVENT From your mom From your dad 30-40 crossover events per meiotic division 1-2 crossovers per chromosome • Patchwork of homologous parental chromosomes. • Increases genetic variability of gametes.

  14. 1- first degree relative; share 1/2 of your genes 2- second degree relative; share 1/4 of your genes 3- third degree relative; share 1/8 of your genes 2 2 1 1 2 2 1 3 2 1 1 4 2

  15. Spermatogenesis: Sperm Production in the Testis

  16. Seminiferous tubules: sperm factories • Sertoli cells (sustenacular cells) are radially distributed around the circumference of the seminiferous tubules. • Spermatogonia are located between the Sertoli cells. • As their progeny undergo meiosis and spermiogenesis (differentiation), they are moved toward the lumen.

  17. Meiosis 2n  1n • 2n  1n • Diploid  Haploid

  18. Sertoli cells form a blood-testes barrier between the seminiferous tubule outside and inside the lumen where the haploid sperm are. Tight junctions! Blood-testes barrier Haploid sperm are viewed as “non-self”. You want to protect developing sperm from your own immunity agents in your blood. LUMEN BARRIER PERIPHERY

  19. Testes make testosterone Interstitial cells; Leydig cells

  20. Hormonal Regulation of sperm and testosterone in men. • Hypothalamus secretes gonadotropin-releasing hormone (GnRH). • Stimulates anterior pituitary to secrete: • Follicle-stimulating hormone (FSH). • Binds to Sertoli (sustenance cells) • Promotes sperm production. • Luteinizing hormone (LH). • Leydig Cells • Controls testosterone production. • Testosterone is essential for reproductive organs and male secondary sex characteristics.

  21. Regulation of Reproduction: General Pathways Figure 26-7: General pattern of hormonal control of reproduction

  22. Infertility in men • Erectile Dysfunction

  23. Infertility in Men • Infertility is the failure of a couple to become pregnant after one year of regular, unprotected intercourse. • In both men and women the fertility process is complex. Even under ideal circumstances, the probability that a woman will get pregnant during a single menstrual cycle is only about 30%. • And, when conception does occur, only 50% to 60% of pregnancies advance beyond week twenty. http://www.mercydesmoines.org/ADAM/WellConnected/articles/000067.asp

  24. A sperm count over 48 million per milliliter of semen, more than 63% of the sperm were moving (sperm motility), and more than 12% of the sperm had a normal shape and structure (sperm morphology). sperm counts below 13.5 million, less than 32% sperm motility fewer than 9% of the sperm had a normal appearance. Fertile men: Infertile men:

  25. What are some lifestyle habits that may induce low sperm count?

  26. Temporary and lifestyle causes of low sperm count • Emotional Stress.Stress may interfere with the hormone GnRH • Testicular Overheating.high fevers, saunas, and hot tubs, may temporarily lower sperm count. One French study suggested that driving for only two hours a day can increase temperature in the scrotum and reduce sperm count. • Substance Abuse.Cocaine or heavy marijuana use lower sperm count temporarily by 50%. Sperm actually have receptors for certain compounds in marijuana that may impair the sperm’s ability to swim and also inhibit their ability to penetrate the egg. • Smoking.Smoking impairs sperm motility, reduces sperm lifespan, and may cause genetic changes that affect the offspring. • Malnutrition and Nutrient Deficiencies.Deficiencies in certain nutrients, such as vitamin C, selenium, zinc, and folate, may be particular risk factors for infertility.

  27. Temporary and lifestyle causes of low sperm count • Obesity. Some studies, but not all, have found an association between obesity in men and infertility. • Bicycling. Pressure from the bike seat may damage blood vessels and nerves that are responsible for erections. Mountain biking, which involves riding on off-road terrain, exposes the perineum (the region between the scrotum and the anus) to more extreme shocks and vibrations. Men who cycle can reduce such risks by the following: • Taking frequent rests while biking. • Wearing padded bike shorts. • Using a padded or specially contoured bike seat that is raised high enough and sits at the proper angle.

  28. Erectile Dysfunction • Erectile dysfunction, commonly referred to as ED, is the inability to achieve and sustain an erection suitable for sexual intercourse. • This condition is not considered normal at any age and is different from other problems that interfere with sexual intercourse, such as lack of sexual desire and problems with ejaculation and orgasm.

  29. Cialis, Levitra, and Viagra. • All work by increasing the flow of blood into the penis, so that when a man is sexually stimulated, he can get an erection. • What's the Difference Between Cialis, Levitra and Viagra? • Cialis, Levitra and Viagra work by a similar mechanism to cause erection. • Levitra works a little longer than Viagra. They both take effect in about 30 minutes. • With Levitra, the effects last for about 5 hours. With Viagra, the effects last 4 hours. • Cialis takes a bit longer to work, but the effects last for much longer - two-to-three days.

  30. Viagra, Levitra and Cialis, are phosphodiesterase-5 (PDE-5) inhibitors. • In smooth muscle cells, cGMP (cyclic guanosine monophosphate) mediates smooth muscle relaxation. • The more cGMP, the more the muscles can relax, the more blood can flow in, and the better the erection. • PDE-5 breaks down cGMP, so PDE-5 inhibitorslike Levitra keep this from happening, helping to maintain high levels of cGMP.

  31. Female reproductive physiology

  32. Ovary: produces eggs and estrogen/progesterone Figure 26-12d: ANATOMY SUMMARY: Female Reproduction

  33. Ovary: up close

  34. LH surge

  35. Menstrual Cycle: 1 monthOvarian cycle; Uterine cycle • Follicular phase • Egg matures • Ovulation • Egg released • Luteal phase • Corpus luteum • Endometrium • Prep for blastocyst • No Pregnancy • Menses Figure 26-13: The menstrual cycle

  36. The Ovarian Cycle:Early Follicular Phase; make ESTROGEN ESTROGEN LH FSH

  37. Early follicular phase; FSH stimulates follicles! Negative feedback on hypothalamus and pituitary gland. Stops FSH and LH secretions. You don’t want to stimulate too many follicles! Figure 26-14a,b: Hormonal control of the menstrual cycle

  38. Late Follicular Phase • Granulosa cells will now produce • Inhibin • Progesterone • More estrogen • LH surge! • Meiosis completes the first meiotic division • Egg (secondary oocyte) • First polar body (degrades)

  39. Late Follicular Phase Estrogen + feedback on granulosa cells. You can make estrogen without FSH from the anterior pituitary! Estrogen helps the endometrium thicken. Figure 26-14a,b: Hormonal control of the menstrual cycle

  40. Ovulation • 16-24 hours after LH surge; the mature follicle secretes collagenase • Egg breaks out of the follicle • The egg “awaits” fertilization in the fallopian tube. • The follicle “leftovers”, differentiate into the corpus luteum.

  41. Early to Mid-Luteal Phase • Corpus Luteum produces • Progesterone (dominates) • Estrogen somewhat increases • Endometrium prepares for a fertilized egg (blastocyst) • Lipid and glycogen stores • Mucus • increase in temperature

  42. Figure 26-14c, d: Hormonal control of the menstrual cycle

  43. Late-Luteal Phase and Menstruation • Corpus luteum: 12 day life span • Apoptosis; programmed death • Estrogen/progesterone levels fall • Thickened endometrium cannot be maintained • Menses occurs about 2 days after corpus luteum degeneration.

  44. Figure 26-14c, d: Hormonal control of the menstrual cycle

  45. FERTILIZATION- corpus luteum maintained • No menses; you miss your period.

  46. Fertilization usually occurs in oviducts. • Developing embryo arrives in the uterus after several days and implants in the lining of the endometrium.

  47. Fertilization: Union of Male & Female Chromosomes • Sperm capacitation • Its final maturation process. • Occurs in the female reproductive tract Figure 26-16b: Fertilization

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