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Spermatogenesis

  1. 1. HUMAN EMBRYOLOGY 11-4-19 Dr.DEVI
  2. 2. MALE REPRODUCTIVE SYSTEM & SPERMATOGENESIS 11-04-2019
  3. 3. CONTENTS ◦Male reproductive system ◦Structure of mature spermatozoon ◦Spermatogenesis ◦Histology of male reproductive organ
  4. 4. Male reproductive 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
  5. 5. Testis • 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.
  6. 6. • 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.
  7. 7. • Each lobule has 1-4 blindly ending seminiferous tubules • Richly vascularized and innervated loose connective tissue derived from Tunica Vasculosa surrounds Seminiferous Tubules. • Interstitial cells of Leydig make groups within this CT.
  8. 8. • 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. 9. Intratesticular genital ducts • Tubuli recti • Rete testis •Connect seminiferous tubules to epididymis
  10. 10. 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
  11. 11. 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
  12. 12. Ductuli efferentes• 10-20 short tubules that drain spermatozoa from the rete testis and pierce 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) • CT is surrounded by a thin layer of circularly arranged smooth muscle.
  13. 13. Extra testicular genital ducts • Epididymis • Ductus deferens • Ductus ejaculatorius
  14. 14. Epididymis • Is a thin, long (4-6 m), highly convoluted tubule consisting of a head, body and tail, placed at the post end of the testis • 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
  15. 15. • Epithelium is separated from the underlying loose connective 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.
  16. 16. 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 is invested by a thin layer of fibroelastic connective tissue
  17. 17. 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.
  18. 18. 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.
  19. 19. Accessory genital glands • Paired seminal vesicle • Single prostate gland • Paired bulbourethral glands
  20. 20. 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 • This gland produces a fructose rich seminal fluid that makes 70% of the volume of the semen. It is the source of the enegry for the spermatozoa.
  21. 21. Prostate◦ Largest of accessory glands ◦ Surrounds the urethra ◦ Stroma contains fibromuscular tissue in which glandular tissue embedded ◦ Prostate secretes 10-30% of final ejaculates ◦ Contains acid phosphatase, fibrinolysin, prostate specific antigen ◦ Promotes mobility of sperm
  22. 22. Bulbourethral (Cowper’s) glands • Paired small (3-5 mm diam) glands located at the root of glans penis, just at the beginning of membranous urethra • Capsule contains fibroblasts, smooth and skeletal muscle cells • Capsule sends septa dividing each gland into lobules • Epith of these compound tubuloalveolar glands varies from simple cuboidal to simple columnar
  23. 23. Penis • Is composed of three columns of erectile tissue, each enclosed by its own dense, fibrous connective tissue capsule, the tunica albuginea. • Two of the columns of erectile tissue, the corpus cavernosa • Third column of erectile tissue, the corpus spongiosum, is positioned ventrally. Because the CS houses the penile portion of the urethra, it is also called the corpus cavernosum urethrae. • CS ends distally in an enlarged, bulbous portion, the glans penis (head of the penis). The tip of the glans penis is pierced by the end of the urethra as a vertical slit.
  24. 24. Seminiferous tubules- microscopic structure
  25. 25. Seminiferous tubules- microscopic structure • 30-70 cm long, 150-250, convoluted • Tunica propria (slender CT) and thick seminiferous (germinal) epithelium make the wall of ST • A basal lamina separates SE and the Tunica Propria • TP contains type 1 collagen bundles housing several layers of fibroblasts. ◦ There are spermatogenic cells and the Sertoli cells within the SE.
  26. 26. Sertoli cells ◦ Tall columnar cells, with a basal clear oval nucleus and complex infoldings at the apical and lateral cell membranes ◦ Extends from basal lamina to free surface of epithelium • Cell cytoplasm is filled with SER, has many mitochondria and a well developed Golgi apparatus. • Non dividing cells in adults
  27. 27. • Lat. cell membranes of adjacent Sertoli cells form occluding junctions subdividing the lumen of the Seminiferous Tubules into narrower basal and the wider adluminal compartments. • The Sertoli cells establish a blood-testis barrier that isolates the adluminal compartment from CT influences thereby protecting the developing gametes from the immune system.(prevents formation of sperm-specific antibodies)
  28. 28. Sertoli cells function in: • supporting the developing spermatogenic cells; • establishing the blood- testis barrier; • Provide nutrition to spermatogenic cells • 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.
  29. 29. 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,spermatozoa occupy 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.
  30. 30. spermatogenesis ◦ Formation of gametes takes place during reproductive period ◦ Spermatogonia (type A )or germ cells divide mitotically to give rise to more spermatogonia (type A & B) ◦ Spermatogonia (type B) enlarge, or undergo mitosis to form primary spermatocyte
  31. 31. ◦ Primary spermatocytes enter the first meiotic division to form secondary spermatocytes, which undergo the second meiotic division to form haploid cells known as spermatids.
  32. 32. • Spermatids are transformed into spermatozoa by shedding of much of their cytoplasm, rearrangement of their organelles, and formation of flagella. Process of transformation of a circular spermatid to spermatozoon is called spermiogenesis
  33. 33. Spermiogenesis ◦ Spermatid becomes spermatozoon ◦ Spermatogenesis including spermiogenesis requires about two months for its completion ◦ Spermatid- circular containing nucleus, Golgi apparatus, centriole & mitochondria ◦ Nucleus forms head ,Golgi apparatus forms acrosomic cap ◦ Centriole – axial filament appears to grow out of them , centriole lies in the neck, Most of the cytoplasm of spermatid is shed, cell membrane persists ◦ Mitochondria forms a sheath around axial filament in the middle piece region, Remaining axial filament elongates to form principal piece or tail
  34. 34. – 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) The maturation process (spermatid....spermatozoa)
  35. 35. Maturation and capacitation of spermatozoa ◦ When first formed in seminiferous tubules- spermatozoa is immature- incapable of fertilizing the ovum, non motile ◦ Fluid in the seminiferous tubules carries the spermatozoa from testis to epididymis ◦ Here they are stored and undergo maturation ◦ Spermatozoa acquire some motility after maturation ◦ Becomes fully motile- after ejaculation when get mixed with secretions of prostate gland and seminal vesicles
  36. 36. Spermatozoa acquire the ability to fertilize an ovum only after they have been in the female genital tract Capacitation: final step of maturation occurs in uterus or uterine tube When it comes in contact with zona pellucida, changes takes place in membrane over the acrosome and enable the release of lysosomal enzymes, this is called acrosomal reaction Zona reactions : some enzymes help in digesting the zona pellucida and in penetration of spermatozoa through it
  37. 37. Structure of Spermatozoon • Spermatids discard 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
  38. 38. ◦ Tail of the spermatozoon is subdivided into four regions: neck, middle piece, principal piece, and end piece. ◦ The plasmalemma of the head is continuous with the tail’s plasma membrane.
  39. 39. Head : ◦ Piriform in shape ◦ 4 um in length ◦ Derived from nucleus which consists of 23 highly condensed chromosomes ◦ Head is covered by a cap-like structure called acrosome (acrosomic cap/galea capitis) ◦ Acrosome contains enzymes that help in penetration of spermatozoon into the ovum during fertilization
  40. 40. ◦ The chromatin in the head is extremely condensed ◦ This makes the head highly resistant to various physical stresses
  41. 41. • Neck : • (~5 μmlong) connects the head to the remainder of the tail. • Narrow • Contains funnel shaped basal body and spherical centriole • It is composed of the cylindrical arrangement of the nine columns of the connecting piece (basal body) 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.
  42. 42. ◦ 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 central most 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.
  43. 43. 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 μmlong) is composed of the central axoneme surrounded by plasmalemma. The axoneme is disorganized in the last 0.5 to 1.0 μm.
  44. 44. Axial filament : ◦ Begins just behind the centriole ◦ Passes through middle piece and tail ◦ At the point where the middle piece joins the tail, the axial filament passes through a ring like structure called annulus ◦ The part of the axial filament which lies in the middle piece is surrounded by a spiral sheath made up of mitochondria
  45. 45. HISTOLOGY OF MALE REPRODUCTIVE SYSTEM
  46. 46. ◦ Each testis is enclosed in thick connective tissue capsule, tunica albuginea ◦ Internal to this is a vascular layer of loose connective tissue , tunica vasculosa.
  47. 47. ◦ Connective tissue septa arise from tunica albuginea , runs towards mediastinum testis dividing testis into lobules (200- 300) ◦ Each lobule has 2-3 convoluted seminiferous tubules and interstitial cells
  48. 48. ◦ ST surrounded by a layer of connective tissue – lamina propria ◦ Consists of flattened or spindle shaped myoid cells arranged in one or more layers ◦
  49. 49. Sertoli cells : ◦ Irregular ◦ Slender pyramidal cells ◦ Nuclei – ovoid, vesicular
  50. 50. ◦ Spermatogenic cells : ◦ Seen as various stages of development ◦ From basement membrane inwards – spermatogonia, pri spermatocyte, sec spermaocyte and spermatid ◦ Spermatozoa seen in the lumen
  51. 51. 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. • Produce testosterone • Large, ovoid intensely eosinophilic
  52. 52. Epididymis • Highly coiled ductus epididymidis • Its wall is made of a pseudostratified columnar epithelium surrounded by connective tissue and smooth muscle. • epithelial cells with their long microvilli (stereocilia).
  53. 53. Thank you !

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