Histology of Male Reproductive System

1. Histology of Male Reproductive System Petek Korkusuz MD PhD

3. Aim • To learn histological structure and the histophysiology of male reproductive organs

4. Learning Goals • To learn the histology and histophysiology of two testes • To learn the histology and histophysiology of the genital ducts • To learn the histology and histophysiology of the associated glands: • Paired seminal vesicles • Single prostate glands • Bulbourethral (Cowper) glands • To learn the histology and histophysiology of the penis

5. Male Genital System • Two testes..formation of spermatozoa&synthesis, release and storage of testosterone • Genital ducts • Associated glands..formation of noncellular portion of semen • Paired seminal vesicles • Single prostate glands • Bulbourethral (Cowper) glands • Penis...delivery of semen to female reproductive system

6. Testes • Paired oval organs, located in the scrotum (approx 4x3x3cm) • Testes develop retroperitoneally, carry a peritoneal outpouching while descending in scrotum: tunica vaginalis • Tunica albuginea (irregular dense connective tissue) surrounds each testis • Tunica vasculosa (highly vascular loose connective tissue) located immediately deep to TA forms the vascular capsule.

7. Testes • The posterior aspect of TA is thickened to form mediastinum testis. • The connective tissue septa radiate from MT to subdivide each testis into approx 250 pyramid shaped lobuli testis. • Each lobule has 1-4 blindly ending seminiferous tubules • Richly vascularized and innervated loose connective tissue derived from TV surrounds STs. • Interstitial cells of Leydig make groups within this CT.

8. Testes • Seminiferous epithelium of STs produces spermatozoa. • Spermatozoa enter tubuli recti that connect the open end of each ST to rete testis (labyrinthine spaces within MT). • Spermatozoa leave the RT through ductuli efferentes (10-20 short tubules) which fuse with epididymis.

9. Testes: vascular supply • The vascular supply of each testis is derived from testicular artery descending with testis into scrotum with ductus deferens (vas deferens) • The TA give branches before piercing the capsule to form intratesticular elts. • Testicular capillary beds are collected into pampiniform plexus of veins which are wrapped around the testicular artery • Artey, veins and the ductus deferens form the spermatic cord. • PP blood is cooler than TA; reduce the arterial blood temperature ...form a countercurrent heat exchange system. Testes temp is kept lower (35 oC)...spermatozoa develop normally

10. Seminiferous tubules • 30-70 cm long, 150-250 m in diameter highly convoluted tubules (total1000 STs in two testes, total length 0.5 km) • Tunica propria (slender CT) and thick seminiferous (germinal) epithelium make the wall of ST • A basal lamina separates SE and the TP • TP contains type 1 collagen bundles housing several layers of fibroblasts (myoid cells in aimals not humans). • There are spermatogenic cells and the Sertoli cells within the SE. Seminiferous tubules, some of which are outlined, and groups of pale-stained interstitial (Leydig) cells (arrowheads). Pararosaniline—toluidine blue (PT) stain.

11. Sertoli cells • Tall columnar cells, with a basal clear oval nucleus and complex infoldings at the apical and lateral cell membranes • Contain cytoplasmic inclusions crystalloids of Charcot-Böttcher with unknown function • Cell cytoplasm is filled with SER, has many mitochondria and a well developed Golgi apparatus. • Lat. cell membranes of adjacent Sertoli cells form occluding junctions subdividing the lumen of the ST into narrower basal and the wider adluminal compartments. • The ZOs of Sertoli cells establish a blood-testis barrier that isolates the adluminal compartment from CT influences thereby protecting the developing gametes from the immune systeme.

12. Blood-testis barrier • Sertoli cells form the blood-testis barrier. • Basal compartment comprises the interstitial space and the spaces occupied by the spermatogonia. • Adluminal compartment comprises the tubule lumen and the intercellular spaces down to the level of the occluding junctions (OJ). In this compartment are spermatocytes, spermatids, and spermatozoa. • Cytoplasmic residual bodies from spermatids undergo phagocytosis by the Sertoli cells and are digested by lysosomal enzymes. • Myoid cells surround the seminiferous epithelium.

13. Sertoli cells function in: • supporting the developing spermatogenic cells; • establishing the blood-testis barrier; • phagocytosis of cytoplasm shed by developing spermatogenic cells; • manufacturing the following substances: androgen binding protein, antimullerian hormone, inhibin, testicular transferrin, and a fructose-rich medium.

14. Spermatogenic cells • Most of the cells composing the thick seminiferous epithelium are spermatogenic cells in various stages of maturation. Spermatogonia, are located in the basal compartment, • Primary spermatocytes, secondary spermatocytes, spermatids,spermatozoaoccupy the adluminal compartment. • Spermatogonia are diploid cells that undergo mitotic division to form more spermatogonia, primary spermatocytes, which migrate from the basal into the adluminal compartment.

15. Spermatogenesis • Primary spermatocytes enter the firstmeiotic division to form secondary spermatocytes, which undergo the second meiotic division to form haploid cells known as spermatids. • Spermatids are transformed into spermatozoa by shedding of much of their cytoplasm, rearrangement of their organelles, and formation of flagella.

16. Part of the wall of a seminiferous tubule. Several cells of the spermatogenic lineage are present: aspermatogonium, primary spermatocytes, and young and late spermatids. The approximate limits of a Sertoli cell holding several spermatids are delineated. H&E stain. High magnification.

17. Spermatocytes and spermatids in the epithelium of a seminiferous tubule. The tubule is covered by myoid cells..

18. Spermatids • Electron micrograph of a mouse spermatid. In the center is the nucleus, covered by the acrosome. The flagellum can be seen emerging in the lower region below the nucleus. A cylindrical bundle of microtubules, the manchette, limits the nucleus laterally. (Courtesy of KR Porter.)

19. The maturation process (spermatid....spermatozoa) • Spermatocytogenesis: spermatogonia differentiate into primary spermatocytes • Meiosis: reduction division whereby diploid primary spermatocytes reduce their chromosome complement, forming haploid spermatids • Spermiogenesis: transformation of spermatids into spermatozoa (sperm)

20. Spermatogenesis • Diagram showing the clonal nature of the germ cells. Only the initial spermatogonia divide and produce separate daughter cells. • Once committed to differentiation, the cells of all subsequent divisions stay connected by intercellular cytoplasmic bridges. • Only after they are separated from the residual bodies can the spermatozoa be considered isolated cells.

21. Spermiogenesis • The principal changes occurring in spermatids during spermiogenesis are demonstrated. • The basic structural feature of the spermatozoon is the head, which consists primarily of condensed nuclear chromatin. • The reduced volume of the nucleus affords the sperm greater mobility and may protect the genome from damage while in transit to the egg. • The rest of the spermatozoon is structurally arranged to promote motility. • Bottom: The structure of a mature spermatozoon.

22. Spermatozoon • Spermatidsdiscard much of their cytoplasm and form a flagellum to become transformed into spermatozoa, a process known as spermiogenesis. • Spermatozoa (sperm)are long cells (~65 μm), composed of a head, housing the nucleus, and a tail, which accounts for most of its length • Tailof the spermatozoon is subdivided into four regions:neck, middle piece, principal piece, and end piece. The plasmalemma of theheadis continuous with the tail’s plasma membrane.

23. Spermatozoon • Neck (~5 μm long) connects the head to the remainder of the tail. It is composed of the cylindrical arrangement of the nine columns of the connecting piece that encircles the two centrioles, one of which is usually fragmented. The posterior aspects of the columnar densities are continuous with the nine outer dense fibers. • Middle piece (~5 μm long) is located between the neck and the principal piece. It is characterized by the presence of the mitochondrial sheath, which encircles the outer dense fibers and the centralmost axoneme. The middle piece stops at the annulus. Two of the nine outer dense fibers terminate at the annulus; the remaining seven continue into the principal piece.

24. Spermatozoon Principal piece(~45 μm long) is the longest segment of the tail and extends from the annulus to the end piece. The axoneme of the principal piece is continuous with that of the middle piece. Surrounding the axoneme are the seven outer dense fibers that are continuous with those of the middle piece and are surrounded, in turn, by the fibrous sheath. End piece(~5 μm long) is composed of the central axoneme surrounded by plasmalemma. The axoneme is disorganized in the last 0.5 to 1.0 μm.

25. Spermatozoon • Scanning electron micrograph of a spermatozoon in the uterine cavity of a rodent. The tufts are ciliated epithelial cells. x2,000.

26. Leydig cells • Luteinizing hormone (LH), a gonadotropin released from the anterior pituitary gland, binds to LH receptors on the Leydig cells, activating adenylate cyclase to form cyclic adenosine monophosphate (cAMP). Activation of protein kinases of the Leydig cells by cAMP induces inactive cholesterol esterases to become active and cleave free cholesterol from intracellular lipid droplets. The first step in the pathway of testosterone synthesis is also LH-sensitive because LH activates cholesterol desmolase, the enzyme that converts free cholesterol into pregnenolone. • The various products of the synthetic pathway are shuttled between the smooth endoplasmic reticulum and mitochondria until testosterone, the male hormone, is formed and is ultimately released by these cells.

27. Leydig cells • Epithelium of seminiferous tubules surrounded by myoid cells. The spaces between the tubules contain connective tissue, blood and lymphatic vessels, and interstitial cells.

28. Leydig cells Interstitial cells and cells of the seminiferous epithelium. H&E stain. High magnification.

29. Leydig cells • Electron micrograph of a section of an interstitial cell. There is abundant smooth endoplasmic reticulum as well as mitochondria. Medium magnification.

30. Hormonal relationships • Because blood testosterone levels are not sufficient to initiate and maintain spermatogenesis, FSH induces Sertoli cells to synthesize and release androgen-binding protein (ABP). ABP binds testosterone, thereby preventing the hormone from leaving the region of the seminiferous tubule and elevating the testosterone levels in the local environment sufficiently to sustain spermatogenesis.

31. Hormonal relationships • Release of LH is inhibited by increased levels of testosterone and dihydrotestosterone, whereas release of FSH is inhibited by the hormone inhibin, which is produced by Sertoli cells. • Testosterone is also required for the normal functioning of the seminal vesicles, prostate, and bulbourethral glands as well as for the appearance and maintenance of the male secondary sexual characteristics. The cells that require testosterone possess 5α-reductase, the enzyme that converts testosterone to its more active form, dihydrotestosterone.

32. Hypophyseal control of male reproduction • Luteinizing hormone (LH) acts on the Leydig cells, • Follicle-stimulating hormone (FSH) acts on the seminiferous tubules. A testicular hormone, inhibin, inhibits FSH secretion in the pituitary.

33. Intratesticular genital ducts • Tubuli recti • Rete testis • Connect seminiferous tubules to epididymis

34. Tubuli recti • Short, straight tubules delivering spermatozoa from the seminiferous tubules into rete testis. • Lined by Sertoli cells in their first half near the ST • Formed by seminiferous epithelium, lined by a simple cuboidal epithelium in their second half near the rete testis • Cuboidal cells have short stubby microvilli and most have a single flagellum

35. Rete testis • Consists of labyrinthine spaces lined by a simple cuboidal epithelium within the mediastinum testis. • Cuboidal cells resemble those of tubuli recti; have numerous short microvilli with a single flagellum • Immature spermatozoa pass from tubuli recti into rete testis

36. Ductuli efferentes • 10-20 short tubules that drain spermatozoa from the rete testis andpierce the tunica albuginea of testis to conduct the sperm to epididymis • Simple epithelium contains noncilliated cuboidal cells or cilliated columnar cells • Cillia of the columnar cells move the spermatozoa toward the epididimis • Cuboidal cells having many lysososomes and apical plasmolemmal invaginations are responsible of endocytosis (resorb most of the luminal fluid) • Epithelium sits on a BL that separates it from the thin loose CT wall of each ductule • CT is surrounded by a thin layer of circularly arranged smooth muscle.

37. Extra testicular genital ducts • Epididymis • Ductus deferens • Ductus ejaculatorius

38. Epididymis • Secrete numeruous factors that facilitate the maturation of spermatozoa; but spermatozoa cannot fertilize a secondary oocyte untill they undergo capacitation; a process trigered by secretions produced in female genital system. • Is a thin, long (4-6 m), highly convoluted tubule consisting of a head, body and tail. • The lumen is lined by pseudostratified epithelium composed of two cell types: short basal cells with round nuclei functioning as stem cells and the tall principal cells with basally located oval nuclei and stereocillia, resorbing the luminal fluid and manifacturing glycerophosphocholine (a glycoprotein that inhibits spermatozoon capacitation preventing spermatozoon from fertilizing a secondary oocyte untill the sperm enters the female genital tract) • Epith is separated from the underlying loose coonective tissue by a BL • Circularly arranged smooth muscle cells surround the CT layer. Peristaltic contractions of this layer help conduct the spermatozoa to the ductus deferens.

39. Epididymis • Highly coiled ductus epididymidis, sectioned several times. • Its wall is made of a pseudostratified columnar epithelium surrounded by connective tissue and smooth muscle. • Inset: Higher magnification of the epithelial cells with their long microvilli (stereocilia).

40. Ductus deferens (Vas deferens) • Each DF is a thick walled muscular tube with a small irregular lumen that conveys the spermatozoa from the tail of the epididimis to the ejaculatory duct. • Mucosa formed by pseudostratified columnar epithelium(principal cells are shorter) with stereocilia and a lamina propria. • Thick outer wall is formed of smooth muscle (three layers:inner outer longitudunal middle circular) and collagen fibers (blue). • SML isinvested by a thin layer of fibroelastic connective tissue

41. Extra testicular genital ducts • The dilated terminus of each ductus deferens is known as ampulla • As the ampula approaches the prostate gland it is joined by seminal vesicle. • The continuation of the junction of the ampulla with the seminal vesicle is known as ejaculatory duct.

42. Ejaculatory duct • Ampulla of ductus deferens joins the seminal vesicle to form ejaculatory duct; which then enters the prostate gland and opens in the prostatic urethra at the colliculus seminalis. • Is a short straight tubule • Lumen is lined by simple columnar epithelium • Subepithelial CT is folded • Has no smooth muscle in its wall.

43. Accessory genital glands • Paired seminal vesicle • Single prostate gland • Paired bulbourethral glands

44. Seminal vesicles • About 15 cm long highly tubular structures located between post aspect of the neck of the bladder and the prostate gland; and join the ampulla of the ductus deferens just above the prostate gland • Its mucosa is highly convoluted forming labyrinth-like cul-de-sacs that are observed to open into a central lumen. • Lumen is lined by a pseudustartified columnar epithelium (short basal cells and low columnar) • Each columnar cell cell-with numerous short microvilli and a single flagellum • Subepithelial fibroelastic CT is surrounded by inner circular outer longitudinal smooth muscle coat • SM is surrounded by fibroelastic CT again • This gland produces a viscose yellow fructose rich seminal fluid that makes 70% of the volume of the semen. It is the source of the enery for the spermatozoa. • The characteristic pale yellow colour of semen is due to the lipochrome pigment released by seminal vesicles

45. Seminal vesicles • Tortuous tubular gland with a much-folded mucosa gives the impression that the gland consists of many tubules.

46. Prostate • Is the largest of the accessory glands, is pierced by the urethra and the ejaculatory ducts. • Slender capsule is composed of a richly vascularized, dense irregular dense connective tissue interspersed with smooth muscle cells. • Connective tissue stroma of the gland is derived from the capsule and is, therefore, also enriched by smooth muscle fibers in addition to their normal connective tissue cells. • Is a conglomeration of 30 to 50 individual compound tubuloalveolar glands, • is arranged in three discrete, concentric layersmucosal, submucosal, and main.

47. Prostate • Mucosal glands are closest to the urethra and thus are the shortest of the glands • Submucosal glands are peripheral to the mucosal glands and are consequently larger than the mucosal glands. • Largest and most numerous of the glands are the peripheralmost main glands, which compose the bulk of the prostate. • Lumina of the tubuloalveolar glands frequently house round to oval prostatic concretions (corpora amylacea), composed of calcified glycoproteins, whose numbers increase with a person’s age.

48. Prostate • Distribution of its glands in 3 zones. The gland ducts open into the urethra.

49. Prostate • Section of the central region of the prostate showing the prostatic urethra and tubuloalveolar glands surrounded by connective tissue and smooth muscle.

50. Prostate • Components of prostate gland are lined by a simple to pseudustratified to columnar epihelium; surrounded by connective tissue and smooth muscle.