25 The Reproductive System

1. 25 The Reproductive System

2. Section 1: The Male Reproductive System Learning Outcomes 25.1 Describe the components of the testes and outline their embryological and fetal development. 25.2 Summarize the events of meiosis in the production of spermatozoa, and describe the functional anatomy of a mature spermatozoon. 25.3 Explain meiosis and early spermiogenesis within the seminiferous tubules.

3. Section 1: The Male Reproductive System Learning Outcomes 25.4 Explain the roles played by the male reproductive tract and accessory glands in the functional maturation, nourishment, storage, and transport of spermatozoa. 25.5 Describe the structures and functions of the penis. 25.6 Explain the roles of regulatory hormones and testosterone in the establishment and maintenance of male sexual function.

4. Section 1: The Male Reproductive System Reproductive components (male and female) Gonads (gone, seed, generation) Reproductive organs that produce gametes and hormones Accessory glands and organs Secrete fluids into reproductive system or other excretory ducts Perineal structures (external genitalia)

5. Section 1: The Male Reproductive System Overview of male reproductive system Testis Gonad producing spermatozoa or sperm Male reproductive tract Transports semen (sperm with secretions of accessory glands)

6. Section 1: The Male Reproductive System Overview of male reproductive system (continued) Accessory organs Ductus deferens (conducts sperm from epididymis to prostate gland) Seminal glands (secrete fluid forming bulk semen volume) Prostate gland (secretes fluid and enzymes) Urethra (conducts semen to exterior) Epididymis (site of sperm maturation) External genitalia Penis (deposits sperm into vagina) Scrotum (surrounds testes)

7. Figure 25 Section 1 An overview of the components of the male reproductive system Gonads Accessory Organs Ductus deferens (conducts spermbetween the epididymis and prostategland) Testis (produces sperm andhormones) Seminal glands (secrete fluid that makes up much of the volume of semen) External Genitalia Penis (contains erectile tissue,deposits sperm in the vagina of thefemale, and produces pleasurablesensations during sexual activities) Prostate gland (secretes fluid andenzymes) Urethra (conducts semen to the exterior) Scrotum (surrounds the testes) Epididymis (site of sperm maturation)

8. Module 25.1: Principal structures of male reproductive system Pathway of sperm Testes Epididymis Ductus deferens Ejaculatory duct Seminal vesicle Urethra Prostate gland Bulbo-urethral glands

9. Module 25.1: Principal structures of male reproductive system Animation: Male Reproductive System Movie Animation: Male Reproductive System

10. Figure 25.1 1 A sagittal section showing the principal structures ofthe male reproductive system Ureter Urinarybladder Pubic symphysis Seminalgland Rectum Urethra Prostate gland Ductus deferens Ejaculatory duct Penis Epididymis Bulbo-urethral gland Anus Testis Scrotum

11. Figure 25.1 2 The positional changes involvedin the descent of a testis Birth Late in fetal development, hormonescause the connective tissue band tocontract, pulling each testis throughthe abdominal musculature into thescrotum. 3 months The connective tissue bands donot get longer as the fetus grows.As a result, the relative positionof the testes change as the bodyenlarges. 2 months The testes form inside the bodycavity adjacent to the kidneys. Developingtestis Connectivetissue band Testis 5 mm Scrotum 5 mm 5 mm

12. Module 25.1: Principal structures of male reproductive system Scrotum and associated structures Scrotal cavities (house testes) Separated by scrotal septum (marked by raised raphe) Dartos muscle Elevates testes and wrinkles scrotal surface Cremaster muscle Pulls testes closer to body during sexual arousal or cold

13. Module 25.1: Principal structures of male reproductive system Scrotum and associated structures (continued) Spermatic cords Extend between testes and abdominopelvic cavity Each contains layers of fascia and muscle enclosing: Ductus deferens Blood vessels Nerves Lymphatic vessels Superficial inguinal ring (entrance to inguinal canal) Inguinal canal (extends from body cavity into scrotum) Inguinal hernias (protrusions through canal)

14. Figure 25.1 3 Dissection view showing superficial and deeperfeatures of the scrotum, testes, and related structures Inguinal canal Inguinal ligament Superficial inguinal ring Nerve Spermaticcords Artery Cremaster muscle Venous plexus Ductus deferens Scrotal septum Scrotum containing thedartos muscle Scrotal cavity Raphe

15. Module 25.1: Principal structures of male reproductive system Testes Tunica albuginea Outer capsule continuous with septa subdividing testes into lobules Seminiferous tubules Coiled tubules within lobules (total length ~1/2 mile/testis) Site of sperm production Rete testis (collecting area outside of lobules) Efferent ductules (lead from rete testis to epididymis)

16. Figure 25.1 4 A horizontal section through thescrotum showing the internalorganization of the testes Efferent ductule Epididymis Ductus deferens Mesothelium liningthe scrotal cavity Scrotum Skin Tunica albuginea Dartos muscle Superficial fascia Cremaster muscle Septa Scrotal cavity Seminiferous tubule Rete testis Rete testis

17. Module 25.1 Review a. Name the male reproductive structures. b. Identify the complex network of channels that is connected to the seminiferous tubules. c. On a warm day, would the cremaster muscle be contracted or relaxed? Why?

18. Module 25.2: Sperm Spermatogenesis (sperm production) Mitosis and cell division Somatic cells produce two daughter cells containing 23 identical chromosome pairs (= diploid) In seminiferous tubules, stem cells undergo mitosis Meiosis Two cycles of cell division (meiosis I and II) Produces four haploid (haplo, single) cells each with 23 individual chromosomes During fertilization, 23 paired chromosomes regained with 23 paternal and 23 maternal associated (= synapsis)

19. Module 25.2: Sperm Spermatogenesis (sperm production) (continued) Spermiogenesis (differentiation of immature male gametes into physically mature spermatozoa) Animation: Spermatogenesis Oogenesis

20. Figure 25.2 1 – 2 The events in mitosis and meiosis The fates of three representativechromosomes during mitosisand cell division Mitosis Stem cell Chromosomes Chromosomeduplication Daughtercells 2Cell enteringmeiosis Chromosomesof daughter cell 2 1Stem cell Chromosomesof daughter cell 1 The fates of three representative chromosomes during meiosis I and II Meiosis Daughtercell 2 Chromosomes Meiosis I Chromosomeduplication, synapsis,and tetrad formation Tetrad Meiosis II 2 3 4 1 2 3 4 1 Gametes Chromosomes of gametes

21. Figure 25.2 3

22. Module 25.2: Sperm Spermatozoon structure Lacks many intracellular structures/organelles Acrosomal cap (enzyme-containing compartment) Head (contains nucleus with densely-packed chromosomes) Neck (contains both centrioles from original spermatid) Middle piece (contains mitochondria) ATP generation for flagellum movement Tail (flagellum) Whiplike organelle that moves sperm Only flagellum in body

23. Figure 25.2 4 Structure of a Spermatozoon Acrosomal cap Head Neck Middle piece Tail (flagellum)

24. Module 25.2 Review a. Define spermatogenesis. b. How many spermatozoa will eventually be produced from each primary spermatocyte? c. Describe the functional anatomy of a typical spermatozoon.

25. Module 25.3: Seminiferous tubules Seminiferous tubules Organized into lobules Often segments of tubule seen in cross section Spermatogenesis and spermiogenesis occur inside tubules and take ~9 weeks Each segment at different stage so tubule continuously producing spermatozoa

26. Figure 25.3 1 – 2 The histology of the testis A light micrograph of a horizontalsection through a testis Retetestis Seminiferoustubules Septa Testis LM  26 A view of several sectionsthrough a single seminiferoustubule Seminiferous tubulecontaining spermatidsbeginning spermiogenesis Seminiferous tubulecontaining spermatidscompleting spermiogenesis Seminiferous tubulescontaining spermatozoaabout to be released intothe lumen LM  450 Sectional view of a coiled seminiferous tubule

27. Module 25.3: Seminiferous tubules Seminiferous tubule structure Cells Spermatogonia (earliest developmental stage) Spermatocytes (primary and secondary) Undergoing meiosis Spermatids (undergoing spermiogenesis) Lastly undergo spermiation Turning into spermatozoa and entering lumen Nurse cells Create blood–testis barrier, protecting seminiferous tubules Attached to developing sperm cells

28. Module 25.3: Seminiferous tubules Seminiferous tubule structure (continued) Tissues Surrounded by delicate connective tissue capsule Areolar tissue fills spaces between tubules Also includes blood vessels and interstitial cells Interstitial cells secrete androgens Layers Basal compartment (contains spermatogonia) Luminal compartment (where meiosis and spermatogenesis occur)

29. Figure 25.3 3 – 5 A diagrammatic section through aseminiferous tubule showing the structureof the tubule and surrounding structures Nurse cellnucleus Capillary Spermatid Dividingspermatocytes Lumen Fibroblast Spermatogonium Connectivetissue capsule Interstitial cell Areolar tissue Spermatozoa A diagrammatic section of aseminiferous tubule showingthe cells involved in the variousstages of spermiogenesis Spermatids beginningspermiogenesis Spermatids completingspermiogenesis Initial spermiogenesis Secondaryspermatocyte Secondary spermatocytein meiosis II Primaryspermatocytepreparing for meiosis I Luminal compartment Connectivetissue capsule Nurse cell Spermatogonium Interstitial cells Basal compartment A diagrammatic section of aseminiferous tubule showing thelocation of the blood-testis barrier Luminalcompartment Nurse cell nucleus Level of blood–testis barrier Basalcompartment

30. Module 25.3 Review a. What is the function of interstitial cells? b. What is the role of nurse cells? c. List the order of development for a spermatid.

31. Module 25.4: Male reproductive tract and glands Activation of spermatozoa Spermatozoa released from testes are physically mature But immobile and incapable of fertilizing an oocyte Other parts of male reproductive system aid in functional maturing and activation Capacitation Spermatozoa become mobile when in contact with seminal gland secretions Spermatozoa become capable of fertilization when exposed to female reproductive tract

32. Module 25.4: Male reproductive tract and glands Male reproductive tract Epididymis (epi, on, + didymos, twin) Coiled tube bound to posterior border of each testis Lined with pseudostratified columnar epithelium With long stereocilia that increase surface area Sperm undergo functional maturation here for ~2 weeks Three parts Head (receives spermatozoa from efferent ductules) Body (extends inferiorly) Tail (transitions into ductus deferens)

33. Figure 25.4 2 – 3 Epitheliumof epididymis Spermatozoa inlumen of epididymis The structure of the epididymus A diagrammatic view of the structureof the epididymus Spermatic cord Regions of the Epididymis The head of the epididymisreceives spermatozoa from the efferent ductules. Efferent ductules Stereocilia The body of the epididymisextends inferiorly along the posterior margin of the testis. Rete testis Seminiferoustubule Near the inferior border of thetestis, the number of coilsdecreases, marking the startof the tail. The tail recurvesand ascends to its connectionwith the ductus deferens. Testis Ductus deferens Epididymis LM  240 Tunicaalbuginea A photomicrograph showing thepseudostratified columnar epitheliallining of the epididymis Scrotal cavity

34. Module 25.4: Male reproductive tract and glands Male reproductive tract (continued) Ductus deferens (or vas deferens) Passes through inguinal canal as part of spermatic cord Transports and stores (for several months) spermatozoa Ampulla (distal portion posterior side of bladder) Ejaculatory duct (from ductus deferens to urethra)

35. Figure 25.4 1 A diagrammatic posterior view showing the urinary bladder,prostate gland, and other structures of the male reproductive system Ureter Urinarybladder Ductus deferens Seminal gland Ampulla Ejaculatory duct Prostate gland Prostatic urethra Urogenital diaphragm Bulbo-urethral glands

36. Module 25.4: Male reproductive tract and glands Male accessory glands Seminal glands (also called seminal vesicles) Contribute ~60% of semen Secretion ejected by smooth muscle lining gland Stimulates flagellum movement in spermatozoa First step of capacitation Prostate gland (encircles proximal urethra) Contributes 20%–30% of semen Contains seminalplasmin (antibiotic for male tract) Bulbo-urethral glands Secrete alkaline mucus for lubrication and pH buffer

37. Module 25.4 Review a. Define semen. b. What are the functions of the secretion of the bulbo-urethral glands? c. Trace the ductal pathway from the epididymis to the urethra.

38. Module 25.5: Penis Penis (conducts urine to exterior and semen to female vagina during intercourse) Root (fixed portion attached to body wall) Body or shaft (movable, tubular part) Glans or head (expanded end around urethral opening) Neck (between shaft and glans) Prepuce (foreskin) Smegma (waxy secretion)

39. Figure 25.5 1 The penis and adjacent structures Pubic symphysis Root of penis Membranous urethra Bulb of penis Body (shaft) of penis Right crus of penis Ischial ramus Neck Corpus spongiosum Corpora cavernosa Glans of penis Scrotum External urethral orifice

40. Figure 25.5 3 A diagrammatic view of the male reproductive tract providing a three-dimensional perspective on therelationships among the glands and passageways Seminalgland Ductusdeferens Prostate gland Opening ofejaculatoryduct Prostaticurethra Bulbo-urethralgland Membranousurethra Opening frombulbo-urethral gland Root of penis Corpus spongiosum Corpus cavernosum Penile urethra Glans External urethralorifice Prepuce

41. Module 25.5: Penis Penis layers (superficial to deep) Outer skin (similar to scrotum) Dermis has smooth muscle continuous with dartos Underlying areolar tissue allows skin to move Elastic tissue (encircling internal structures) Erectile tissue (well-vascularized tissue causing erection) In resting state, arterial branches constricted Corpora cavernosa (2, dorsal side) Corpus spongiosum (around penile urethra)

42. Figure 25.5 2 A cross section through thebody of the penis Superficial and deepdorsal veins of penis Tissue Layers of the Penis Skin Dermis Areolar tissue Dense network of elastic fibers Corpora cavernosa Deep arteryof penis Corpus spongiosum Erectile tissues Urethra

43. Module 25.5: Penis Three major sexual activity phases Arousal Erotic thoughts or stimulation increase parasympathetic stimulation through pelvic nerves Release of nitric oxide causes erection by arterial dilation Bulbo-urethral glands secrete to lubricate penis tip Emission (formation and movement of semen internally) Sympathetic stimulation causes contractions of ductus deferens ampullae and other accessory glands

44. Module 25.5: Penis Three major sexual activity phases (continued) Ejaculation (male orgasm) Bulbocavernosus muscles (at base) push semen toward external urethral orifice Ischiocavernosus muscles (along sides) stiffen erect penis

45. Module 25.5: Penis Impotence Inability to achieve or maintain erection Various causes Vascular changes Neural commands Psychological factors Viagra and Cialis inactivate enzymes that degrade nitric oxide (NO) Small amounts of NO can then produce erection

46. Module 25.5 Review a. Name the three columns of erectile tissue in the penis. b. List the three physiological phases of male sexual activity. c. An inability to contract the ischiocavernosus and bulbospongiosus muscles would interfere with which phase of male sexual activity?

47. Module 25.6: Hormonal control of male reproductive function Hypothalamus Gonadotropin-releasing hormone (GnRH) stimulates release from anterior pituitary Anterior pituitary Luteinizing hormone (LH) Stimulates testosterone secretion from interstitial cells Testosterone effects Maintain libido and associated behaviors Stimulation of bone and muscle growth Maintenance of secondary sexual characteristics Maintenance of accessory glands

48. Module 25.6: Hormonal control of male reproductive function Anterior pituitary (continued) Follicle-stimulating hormone (FSH) Stimulates nurse cells Promote spermatogenesis Secrete androgen-binding protein (ABP) Stimulates maturation of spermatids Secrete inhibin to feed back to anterior pituitary

49. Module 25.6: Hormonal control of male reproductive function Dihydrotestosterone (DHT) Converted form of testosterone in some tissues ~10% circulating levels of testosterone Can bind to same receptors Some organs bind DHT mainly

50. Module 25.6 Review a. Identify important regulatory hormones in the establishment and maintenance of male sexual function. b. Identify the sources of hormones that control male reproductive functions. c. What effect would low FSH levels have on sperm production?