Sertoli Cells:They are tall, columnar cells representing the main cell type of the germinal epithelium until puberty, after which they comprise only about 10% of the cells lining the S.T, in elderly men they decrease in number, sertoli cells are not affected by any of the factors that injure the sensitive germinal epithelium (e.g. they do not degenerate when they are exposed to the normal body temperature & can therefore survive in the undescended testis.
Sertoli cells are sited on the basement membrane of the S.T.
Microscopically the sertoli cells have an irregular apex extending into the lumen of the S.T, their nuclei are irregular in shape but tend to be oval with long axis at right angle to the basement membrane, the nuclei have vesicular chromatin pattern & prominent nucleolus.
The sertoli cells are characterized by irregular outline with many cytoplasmic extensions which make with those from nearby cells form a meshwork of cytoplasm, this meshwork encloses the developing cells of the germinal epithelium & forms tight junctions which roughly divide the S.T lining epithelium into basal & luminal compartments, the spermatogonia & preleptotene spermatocytes occupy the basal & adluminal compartment while the remaining primary & secondary spermatocytes & spermatids are located in the adluminal compartment. Other forms of intercellular junctions between the sertoli cells including gap junctions & desmosomes could been seen.
Sertoli cells cytoplasm is eosinophilic & finely granular, it may contain lipid vacuoles.
By E/M abundant endoplasmic reticulum usually found in the cytoplasmic processes interdigitating between the developing germinal cells while ribosomes, lipid vacuoles, microfilaments & microtubules are common in the area of the cytoplasm close to the developing spermatids.
Functions of sertoli cells:Sertoli cells have supportive, phagocytic & secretory functions:
Supportive function includes provision of nutrients to the developing germinal epithelium by their cytoplasmic processes & transport of waste products of spermiogenesis process to the blood & lymphatic vascular systems surrounding the S.T.
Sertoli cells phagocytoze any residual cytoplasm produced by maturating cells during spermatogenesis.
Secretory function varies with sexual maturation stage, in the prepubertal stage they secrete substances preventing meotic division of the germinal epithelial cells while in mature testis they secrete androgen-binding protein (ABP) which binds to the testosterone hormone produced outside the S.T, this hormone is required for normal germ cell maturation.
The interstitial tissue lying between the S.T is a loose network of fibrocollagenous tissue composed of:
Collagen fibers associated with macrophage & mast cells.
Blood &lymphatic vessels.
Clumps of interstitial or "Leydig cells".
Leydig cells:They are most common in the tubular interstitium, they can be found occasionally in the mediastinum of testis, epididymis or even in the spermatic cord.
Leydig cells synthesize testosterone, these cells have round vesicular nuclei with one or two nucleoli.
Most of leydig cells are round or polygonal in shape but some are small & spindle- shaped which are thought to be immature form.
They have eosinophilic cytoplasm containing lipase & oxidative enzymes & number of steroid- dehydrogenase.
Characteristic feature of these cells is "Reik's crystalloid" which are intracytoplasmic eosinophilic masses not seen before puberty but increase in number during the years of sexual maturity.
The Rete Testis:Is a complex arrangement of interconnecting channels located at the mediastinum of testis. The spermatozoon formed in the S.T loops, pass to the terminal portions &then via few short straight tubules, they reach to the rete testis, both straight tubules & rete testis are lined by simple cuboidal or low columnar epithelium bearing microvilli on their luminal surface .
Efferent Ductules:Channels of the rete testis fused to form efferent ductules which emerge from the upper end of the mediastinum to penetrat the tunica albuginea then enter the head of the epididymis, here they are gradually emerge to become a single tube called (epididymal duct).The efferent ductules are lined by a mixed undulating epithelium of tall ciliated columnar cells & non ciliated cuboidal or low columnar cells with microvilli on their luminal surface, the cilia beats towards the epididymis & propel the spermatozoa onward while the non ciliated cells absorb some of the testicular fluid which is the transport medium for the immature spermatozoa, the efferent ductules are highly convoluted & have a narrow sheath of smooth muscle fibers +elastic fibers, contraction of this muscle fibers enhance the progression of the spermatozoa.
The epididymal duct is formed by the fusion of the efferent ductules, this duct is a single highly convoluted tube about 5 meter long embedded in a loose vascular supporting stroma consisting of fibroblasts, collagen fibers & glycosaminoglycan matrix, it is surrounded by dense capsule to form a comma- shaped body called "epididymis" (i.e. duct +stroma+ capsule).
Epididymis is divided into (head, body, &tail regions), the efferent ductules enter the head while the distal end of the epididymis emerges at the tail region to become the vas deferens, the epididymal duct is highly convoluted & it is all contained within the epididymis.
In the cross sections of the epididymal duct, the wall consists of 3 components:
The lining epithelium is pseudostratified tall columnar epithelium bearing very long atypical microvilli which are immotile called "stereocilia" because they do not contain the microtubules & not function like the cilia.The cells posses lysosomes, RER & prominent Golgi & they have absorptive, phagocytic & secretory functions:
Absorption of testicular fluid.
Phagocytosis of degenerated spermatozoa.
Secretion of glycoproteins which play a role in the maturation of the spermatozoa.
Small basal rounded cells lie on the basement membrane.
The entire epididymal duct is surrounded by a narrow sheath of circular SMF, but in the tail region there is longitudinal layer internal to the circular layer & other outer longitudinal layer, all of the muscle layers are thickened at the tail where the epididymal duct emerges to become the vas deferens.
Vas Deferens:Is a straight tube running vertically upward behind the epididymis within the spermatic cord, the vas deferens has a thick muscular wall composed of middle circular layer with outer & inner longitudinal layers, internal to the inner layer there is fibroelastic lamina propria covered by columnar epithelium similar to that of the epididymis but thrown into longitudinal folds, this produce small stellate lumen, contraction of thick muscular wall move the spermatozoa. forward.
Each vas deferens has a dilatation called "ampulla" where the muscle layer become thinner & the folds are branched & taller at distal end of the ampulla, the vas deferens joined the short duct from the seminal vesicle.
Seminal Vesicle:Each S.V is highly convoluted & unbranched tubular diverticulum of the vas deferens, the S.V is a coiled tube surrounded by an inner circular & outer longitudinal smooth muscle fibers.
The mucosa is composed of fibroelastic lamina propria covered by epithelial cells, the mucosa is thrown into tall narrow complicated folds covered by non- ciliated tall columnar epithelium & some few basal rounded cells lie at the basement membrane, the tall cells have a characteristic secretory vacuoles near their luminal surface +RER, the complex mucosal folds increase the surface area for secretion thus about 70% to 80% of the ejaculate is a thick creamy secretion produced by the S.V, contraction of smooth muscle fibers propels the accumulated secretions into the ejaculatory ducts.
Ejaculatory duct:Is (1 cm long) duct lined by tall columnar epithelium & small rounded cells, there is no SMF in its wall, the Rt. & Lt. ducts run through the prostatic gland & pen in the prostatic urethra.
Male Reproductive System PAGE 5
Lecture 2 Dr. Muna Zuhair