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Male Reproductive System

Male Reproductive System

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Male Reproductive System

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  1. Male Reproductive System • Sexual reproduction and development • Male reproductive anatomy • Puberty and climacteric • Sperm and semen • Male sexual response 27-

  2. Essence of Sex • Reproduction • one property of a living thing • great variety of methods • Sexual reproduction • each offspring has 2 parents and receives genetic material from both • provides genetic diversity • foundation for survival and evolution of species 27-

  3. Two Sexes • Male and female gametes (sex cells) combine their genes to form a fertilized egg (zygote) • one gamete has motility (sperm) • parent producing sperm considered male • has Y chromosome • other gamete (egg or ovum) contains nutrients for developing zygote • parent producing eggs considered female • in mammals female also provides shelter for developing fetus (uterus and placenta) 27-

  4. Overview of Reproductive System • Primary sex organs • produce gametes (testes or ovaries) • Secondary sex organs • male - ducts, glands, penis deliver sperm cells • female - uterine tubes, uterus and vagina receive sperm and nourish developing fetus • Secondary sex characteristics • develop at puberty to attract a mate • pubic, axillary and facial hair, scent glands, body morphology and low-pitched voice in males 27-

  5. Role of Sex Chromosomes • Our cells contain 23 pairs of chromosomes • 22 pairs of autosomes • 1 pair of sex chromosomes (XY males: XX females) • males produce 50% Y carrying sperm and 50% X carrying • all eggs carry the X chromosome • Sex of child determined by type of sperm that fertilizes mother’s egg 27-

  6. Hormones and Sex Differentiation • Gonads begin to develop at 6 weeks • 2 sets of ducts • mesonephric ducts develop into male reproductive system or • paramesonephric ducts (müllerian ducts) develop into female reproductive tract • SRY gene (Sex-determining Region of Y gene) • in males, codes for a protein that causes development of testes → • secrete testosterone • secrete müllerian-inhibiting factor → degenerates paramesonephric ducts • Female development occurs in absence of hormones 27-

  7. Embryonic Development • External genitals of both sexes begin as a • genital tubercle • becomes glans of penis or • clitoris • pair of urogenital folds • enclose urethra of male or • form labia minora • a pair of labioscrotal folds • scrotum or • labia majora 27-

  8. Embryonic Development 27-

  9. Androgen-Insensitivity Syndrome • Genetically male (XY) • Testosterone secreted • target cells lack receptors for hormone • No masculizing effects occur 27-

  10. Development of External Genitalia 27-

  11. Development of External Genitalia • All 8 week old fetuses have same 3 structures • by end of week 9, begin to show sexual differentiation • distinctly male or female by end of week 12 27-

  12. Descent of Testes • Begin development near kidney • gubernaculum (cordlike structure containing muscle) extends from gonad to abdominopelvic floor • it shortens, guides testes to scrotum • vaginal process • peritoneum develops fold; extends into scrotum • create inguinal canal, pass through abdominal wall • Descent begins in weeks 6-10, finished by 28 • 3% born with undescended testes (cryptorchidism) • Location outside pelvic cavity essential for low temperatures needed for sperm production 27-

  13. Descent of Testis 27-

  14. Boundaries of Male Perineum 27-

  15. Male Reproductive System 27-

  16. Scrotum • Pouch holding testes • divided into 2 compartments by median septum • Spermatic cord travels up from scrotum to pass through inguinal canal • contains testicular artery, vein, nerve and lymphatics 27-

  17. Testicular Thermoregulation • Sperm not produced at core body temperature • cremaster muscle = pulls testes close to body • dartos muscle • wrinkles skin reducing surface area of scrotum • lifts it upwards • pampiniform plexus = veins ascending near testicular artery • countercurrent heat exchanger cools arterial blood entering testis 27-

  18. Male Inguinal and Scrotal Region 27-

  19. Countercurrent Heat Exchanger 27-

  20. Testes • Oval organ, 4 cm long x 2.5 cm in diameter • covered anteriorly by tunica vaginalis • Tunica albuginea • white fibrous capsule on testes • Septa divide testes into compartments containing seminiferous tubules • each tubule lined with a thick germinal epithelium for sperm • interstitial cells between tubules - testosterone • Sustentacular cells • promote sperm cell development 27-

  21. Blood-testis barrier • Formed by tight junctions between sustentacular cells -- separating sperm from immune system 27-

  22. Testis and Associated Structures • Seminiferous tubules drain into rete testis • Low BP of testicular artery results in poor O2 supply • sperm develop very large mitochondria helping them survive hypoxic environment of female reproductive tract • Testicular veins drain to inferior vena cava 27-

  23. Spermatic Ducts • Efferent ductules • 12 small ciliated ducts collecting sperm from rete testes and transporting it to epididymis • Epididymis (head, body and tail) • 6 m long coiled duct adhering to posterior of testis • site of sperm maturation and storage (fertile for 60 days) • Ductus deferens (peristalsis during orgasm) • muscular tube 45 cm long passing up from scrotum through inguinal canal to posterior surface of bladder • Ejaculatory duct • 2 cm duct formed from ductus deferens and seminal vesicle and passing through prostate to empty into urethra 27-

  24. Male Duct System 27-

  25. Male Urethra • Regions: prostatic, membranous and penile --- totals 20 cm long 27-

  26. Accessory Glands • Seminal vesicles • posterior to bladder • empty into ejaculatory duct • Prostate gland • below bladder, surrounds urethra and ejaculatory duct • 2 x 4 x 3 cm • Bulbourethral glands • near bulb of penis • empty into penile urethra • lubricating fluid 27-

  27. Penis • Internal root, shaft, and glans • external portion 4 in. long when flaccid • skin over shaft loosely attached allows expansion • extends over glans as prepuce (foreskin) • 3 cylindrical bodies of erectile tissue • corpus spongiosum along ventral side of penis • encloses penile urethra • ends as a dilated bulb ensheathed by bulbospongiosus muscle • corpora cavernosa • diverge like arms of a Y • each crus attaches to pubic arch covered with ischiocavernosus muscle 27-

  28. Anatomy of Penis Fig. 27.12 a and b 27-

  29. Puberty and Climacteric • Reproductive system remains dormant for years after birth • surge of pituitary gonadotropins begins development • 10-12 in most boys; 8-10 in most girls • Puberty • period from onset of gonadotropin secretion until first menstrual period or first ejaculation of viable sperm • Adolescence • ends when person attains full adult height 27-

  30. Brain-Testicular Axis • Hypothalamus produces GnRH • Stimulates anterior pituitary (gonadotrope cells) to secrete • LH • stimulates interstitial cells to produce testosterone • FSH • stimulates sustentacular cells to secrete androgen-binding protein that interacts with testosterone to stimulate spermatogenesis 27-

  31. Other Effects of Testosterone • Enlargement of secondary sexual organs • penis, testes, scrotum, ducts, glands and muscle mass enlarge • hair, scent and sebaceous glands develop • stimulates erythropoiesis and libido • During adulthood, testosterone sustains libido, spermatogenesis and reproductive tract 27-

  32. Hormones and Brain-Testicular Axis 27-

  33. Aging and Sexual Function • Decline in testosterone secretion • peak secretion at 7 mg/day at age 20 • declines to 1/5 of that by age 80 • Rise in FSH and LH secretion after age 50 produces male climacteric (menopause) • mood changes, hot flashes and “illusions of suffocation” • Erectile dysfunction • 20% of men in 60s; 50% of those in 80s 27-

  34. Mitosis and Meiosis • Mitosis produces two genetically identical daughter cells (for tissue repair, embryonic growth) • Meiosis produces gametes • for sexual reproduction • keeps chromosome number constant from generation to generation after fertilization • 2 cell divisions (only one replication of DNA) • meiosis I separates homologous chromosome pairs into 2 haploid cells • meiosis II separates duplicated sister chromatids into 4 haploid cells 27-

  35. Meiosis 27-

  36. Spermatogenesis • Spermatogonia produce 2 kinds of daughter cells • type A remain outside blood-testis barrier and produce more daughter cells until death • type B differentiate into primary spermatocytes • cells must pass through BTB to move inward toward lumen - new tight junctions form behind these cells • meiosis I → 2 secondary spermatocytes • meiosis II → 4 spermatids 27-

  37. Spermatogenesis • Blood-testis barrier is formed by tight junctions between and basement membrane under sustentacular cells. 27-

  38. Spermiogenesis • Changes that transform spermatids into spermatozoa • discarding excess cytoplasm and growing tails 27-

  39. Spermatozoon • Head is pear-shaped front end • 4 to 5 microns long structure containing the nucleus, acrosome and basal body of the tail flagella • nucleus contains haploid set of chromosomes • acrosome contains enzymes that penetrate the egg • basal body • Tail is divided into 3 regions • midpiece contains mitochondria around axoneme of the flagella (produce ATP for flagellar movement) • principal piece is axoneme surrounded by fibers • endpiece is very narrow tip of flagella 27-

  40. Spermatozoon 27-

  41. Semen or Seminal Fluid • 2-5 mL of fluid expelled during orgasm • 60% seminal vesicle fluid, 30% prostatic, 10% sperm • normal sperm count 50-120 million/mL • Other components of semen • fructose - energy for sperm motility • fibrinogen causes clotting • enzymes convert fibrinogen to fibrin • fibrinolysin liquefies semen within 30 minutes • prostaglandins stimulate female peristaltic contractions • spermine is a base stabilizing sperm pH at 7.2 to 7.6 27-

  42. Male Sexual Response - Anatomy • Arteries of penis • dorsal and deep arteries(brs. of internal pudendal) • deep artery supplies lacunae of corpora cavernosa • dilation fills lacunae causing an erection • normal penile blood supply comes from dorsal a. • Nerves of penis • abundance of tactile, pressure and temperature receptors • dorsal nerve of penis and internal pudendal nerves lead to integrating center in sacral spinal cord • both autonomic and somatic motor fibers carry impulses from integrating center to penis 27-

  43. Excitement and Plateau • Excitement is characterized by vasocongestion of genitals, myotonia, and increases in heart rate, BP, and pulmonary ventilation • Initiated by many different erotic stimuli • Erection of penis is due to parasympathetic triggering of nitric oxide (NO) secretion • dilation of deep arteries and filling of lacunae with blood • Erection is maintained during plateau phase 27-

  44. Sexual Response • Parasympathetic signals produce an erection with direct stimulation of penis or perineal organs 27-

  45. Orgasm and Ejaculation • Climax (orgasm) is 15 second reaction that includes the discharge of semen (ejaculation) • Ejaculation • emission = sympathetic nervous system propels sperm through ducts as glandular secretions are added • expulsion = semen in urethra activates muscular contractions that lead to expulsion • Ejaculation and orgasm are not the same • can occur separately 27-

  46. Resolution • Sympathetic signals constrict internal pudendal artery and reduce blood flow to penis • penis becomes soft and flaccid (detumescence) • Cardiovascular and respiratory responses return to normal • Refractory period (10 minutes to few hours) 27-

  47. How Viagra Prolongs Erection 27-