Chapter 27— The Male Reproductive System

1. Chapter 27— The Male Reproductive System

2. Ch. 27 Study Guide Read pp. 1048-1050 of section 27.1 before prenatal hormones and sexual differentiation section; also read sections 27.2-27.4 (pp.1053-1067) Comprehend Terminology (those in bold) Study-- Figure questions, Think About It questions, and Before You Go On (section-ending) questions Do end-of-chapter questions: Testing Your Recall— 2-20 True or False– 1-9 Testing Your Comprehension– 3, 4

3. Said an ovum one night to a sperm, “You’re a very attractive young germ. Come join me, my sweet, let our nuclei meetAnd in nine months we’ll both come to term.”--Isaac Asimov

4. 27.2. Male Reproductive Anatomy—A. The Spermatic Ducts and the Accessory Glands

5. § A. Sperm’s journey • Testes– sperm-producing organs; inside the scrotum (skin-covered sac) • Routes (spermatic ducts) the sperm travel: A-Testes  B-Efferent ductules  C-Epididymis D-Ductus deferens E-Ejaculatory duct  F-Urethra  Exterior Fig. 27.11b

6. Anterior/posterior view? Urinary bladder Ureter 2. Prostate gland 1. Seminal vesicle 3. Bulbourethral gland E D F Penis C B A Glans penis

7. § Spermatic Ducts Include-- • 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 (vas) 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 Fig. 27.9, 27.11

8. § Male Urethra • Three Regions: prostatic, membranous and penile urethra--- totals 20 cm long (Fig. 20.11b) • Function • It serves both urinary and reproductive roles • It cannot pass urine and semen simultaneously

9. Ampulla Seminal vesicle Prostate gland Ejaculatory duct A Bulbourethral gland B Ductus deferens Efferent ductules Testis Epididymis C 27-9

10. § Accessory Glands-A • Sperm is supported by semen from accessory sex glands-- • including the seminal vesicles, prostate gland, and bulbourethral glands

11. § Accessory Glands-B • Seminal vesicles (paired) • posterior to bladder • Yellowish alkaline secretion empties into ejaculatory duct; constitute 60% of the semen • Containing fructose, sugars, ascorbic acid, a coagulating enzyme, prostaglandins, proseminogelin • Prostate gland (single) • below bladder, surrounds urethra and ejaculatory duct; digital rectal examination • 2 x 4 x 3 cm; thin, acidic milky secretion; 30% of the semen • Plays a role in activating sperm, containing citrate (a nutrient), serine protease

12. § Accessory Glands-C • Bulbourethral glands (paired; Cowper’s glands) • near bulb of penis • empty into penile urethra • neutralize urine • lubricating fluid secreted during sexual arousal

13. 27.2. Male Reproductive Anatomy—B. The Scrotum & Testicular Thermoregulation

14. § Scrotum • Perineum– Fig. 27.6 • Pouch (scrotum) holding testes • divided into 2 compartments by ______ which is external marked byperineal raphe • Spermatic cords– paired structures consisting of layers of CT and muscle enclosing ductus deferens, blood and lymphatic vessels, and testicular nerves. • Location– each spermatic cord begins at the entrance to the In-________ canal Fig. 27.7

15. Fig. 27.6--The male perineum 27-15

17. § Testicular Thermoregulation • Sperm cannot be produced at core body temperature (too warm): • 1. pampiniform plexus = near testicular artery, a network of veins– forming countercurrent heat exchangerthatcools arterial blood entering testis by 1-2 degree Celsius (Fig. 27.8) • When Cold: • 2. cremaster muscle = pulls testes close to body when cold • 3. dartos muscle-- • Contracts and scrotum becomes taut • wrinkles skin reducing surface area of scrotum

19. 27.2. Male Reproductive Anatomy—C. Testes

20. § Testes (Fig. 27.10 a-b)-A Dimension-- Oval organ; 3 cm (anterior to posterior) x 2.5 cm (wide) x 4 cm (long) Each testis is surrounded by two tunics: (From outermost and moving in) • Its anterior and lateral surfaces are covered by tunica vaginalis • Tunica albuginea– testis itself has a white fibrous capsule

22. Review spermatic ducts  

23. § Testes (Fig. 27.10 a-b)-B • Septa divide testes into 250-300wedge-shaped lobules containing seminiferous tubules(where sperm are produced) • each tubule lined with a thick germinal epithelium (several layers of germ cells) for sperm production • Tall Sertoli (sustentacular) cells; function? • Between the seminiferous tubules are interstitial (Leydig) cells, the source of testosterone Fig. 27.10 and X

24. See next slide for details of germ and sustentacular cells

25. Stages of sperm maturation:  Lumen of seminiferous tubule Spermatozoon Tight junctions --see next slide Spermatids Secondary spermatocyte Primary spermatocyte Sertoli cell Spermatogonium

26. § Blood-testis barrier of testes • (Structures) Formed by tight junctions between sustentacular (Sertoli) cells -- separating sperm from blood and immune systems • (Functions) Prevents proteins and other large molecules in the blood and intercellular fluid from getting to the germ cells

27. § Blood circulation to/from the testis • Sperm’s transportation inside the testes--Seminiferous tubules drain into rete testis which is embedded in the capsule on the posterior side • Testicular arteries– arise from the abdominal aorta; low BP of testicular artery results in poor O2 supply • sperm develop very large __________ helping them also survive hypoxic environment of female reproductive tract • Pampiniform plexus of veins and then testicular veins-- the right one drains to inferior vena cava; the left one drains into the left renal vein

28. 27.2. Male Reproductive Anatomy—D. The Penis

29. § Penis (Fig. 27.11, 27.12) • Internal root; visible (external)-- 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 (1) along ventral side of penis • encloses penile urethra • at distal end, fill the entire glans • corpora cavernosa (2) • On each side; separated by a median septum • Each is ensheathed in a fibrous tunica albuginea • diverge like arms of a Y • each arm, called crus, attaches to pubic arch covered with ischiocavernosus muscle

32. 27.3. Sperm and Semen—A. Spermatogenesis

33. § Spermatogenesis--A • Def. of spermatogenesis– The production of sperm cells through a series of mitotic and meiotic cell divisions • Location? • How long does it take? • Microscopic examination– two important cell types (see next slide)

34. § Spermatogenesis--B • Two important cell types in seminiferous tubules • Germ cells– • In various stages of sperm development, such as spermatogonia, primary spermatocytes, secondary spermatocytes • Sustentacular (Sertoli) cells– these cells provide crucial support for spermatogenesis Figure 27.15

36. § Spermatogenesis--C • Three major stages— • Mitotic proliferation— • Spermatogonia located in the outermost layer of the seminiferous tubule, outside the blood-testis barrier (BTB) • One of the daughter cells (Type A spermatogonium) remain at the outer edge of the tubule; importance? • The other daughter cell (Type B spermatogonium) starts moving toward lumen forming 4 identical primary spermatocytes (2N)

37. § Spermatogenesis--D • Meiosis— • Each primary spermatocyte (2N) must pass through BTB (tight junction) and ultimately yield 4 spermatids (1N) • Spermiogenesis— • Spermatids become extremely specialized and motile spermatozoa • Sperm travel lightly Figure x&y, 27.16

38. A. B. Meiosis C.

39. Spermatogenesis Stages: Chromosomes: 46; 2n (diploid number; single strands) One daughter cell remains at the outer edge of the seminiferous tubule to maintain the germ cell line Spermatogonia One daughter cell moves toward the lumen to produce spermatozoa Mitosis 46; 2n (diploid number; single strands) Primary spermatocyte 46; 2n (diploid number; doubled strands) First meiotic division Meiosis Secondary spermatocyte 23; n (haploid number; double strands) Second meiotic division 23; n (haploid number; single strands) Spermatids Spermio- genesis 23; n (haploid number; Single strands) Spermatozoa

40. Figure 27.16

41. 27.3. Sperm and Semen—B. Spermatozoon

42. § The Spermatozoon--A • Two parts– the head and the tail • Head contains three structures: • A nucleus– with a haploid set of chromosomes • Acrosome– a lysosome vesicle in a thin cap; in the apical half of the head • Flagellar basal body– is nestled in an indentation at the basal end of the nucleus Fig. 27.17

44. § The Spermatozoon--B • Two parts– the head and the tail • Tail contains three regions: • Midpiece– many large mitochondria coil around the axoneme (center of the sperm) and they provide the ATP needed for the tail • Principal piece– constitutes most of the tail and provides motility for the spermatozoon • Endpiece– axoneme only; the narrowest part of the sperm Fig. 27.17

45. Figure 27.17b

46. 27.3. Sperm and Semen—C. Semen

47. § Semen (2-5 ml)--A • Def.– milky white mixture of sperm and accessory gland secretions expelled during orgasm • Functions– • provides a transport medium and nutrients (fructose mainly and also citrate and sugars) • protects and activates the sperm • overall alkalinity helps neutralize the acid environment • prostaglandins– decrease the viscosity of mucus guarding the entry of the uterus

48. § Semen--B • The clotting enzyme from the prostate activates proseminogelin (from the seminal vesicles) into seminogelin • Seminogelin sticks to the walls of the vagina, ensuring the semen doe not drain back • 20-30 minutes after ejaculation: serine protease of the prostatic fluid breaks down seminogelin and liquefies the semen (sperm now very active)

49. § Semen—C; Low sperm count? • 2-5 ml semen per ejaculation • 200 million sperm per ejaculation • 50-130 million sperm per ml • Low sperm count is < 20 million sperm per ml of semen (less than the minimal jackpot of the Powerball)