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Male Reproductive System


  The male reproductive system consists of the testes, ductuli efferentes,  epididymides,  vasa deferentia,  seminal vesicles,  prostate gland, bulbourethral glands and penis.

Low power view of testisTriangle_3D.gif (907 bytes)Large version of Fig. 1 Low power view of testis

Male gametes (sperm) and male sex hormones (mainly testosterone) are produced in the testis.  Figure 1 shows a low magnification view of a section through the testis. Numerous profiles of seminiferous tubules are seen, most of them cut more or less in cross section. The epithelium of the seminiferous tubules is an indistinct stratified cuboidal, and is composed of the gametogenic cells in various stages of development. The earliest stages (spermatogonia) are found closest to the periphery, the later stages are found progressively toward the lumen. Sperm (also called spermatozoa) can sometimes be seen along the luminal part of the epithelium or in the centre of the lumen. (Don’t try to identify cell types at this magnification). The boundary of each seminiferous tubule profile is fairly well demarkated. This reddish border consists of the basement membrane and the surrounding connective tissue (considered as the lamina propria; in humans it has contractile myoid cells rather than typical fibroblasts). Between the seminiferous tubules is a loose connective tissue. In this interstitial tissue are found the interstitial cells of Leydig (or Leydig cells), which produce testosterone. (Don’t try to find them at this magnification). The testis is surrounded by a thick fibrous capsule called the tunica albiguinea (not visible in Figure 1).

High power view of a seminiferous tubuleTriangle_3D.gif (907 bytes)Large version of Fig. 2 Seminiferous tubule

A higher power view of part of a seminiferous tubule cut in a longitudinal section is shown in Figure 2. Spermatogonia are found right along the basement membrane. Spermatogonia are the stem cells. They can divide by mitosis to produce more spermatogonia (type A spermatogonia) or they can become committed to differentiating into primary spermatocytes (type B spermatogonia). Type A spermatogonia stain more darkly and have an ovoid nucleus with finely granular chromatin. Type B are paler-staining, generally with more spherical nuclei and more condensed chromatin. (You are not required to distinguish the different types of spermatogonia.)

Committed spermatogonia will differentiate to become a primary spermatocyte. Primary spermatocytes undergo the first meiotic division. They are the largest cells of the spermatogenic series, with large nuclei exhibiting various stages of meiosis I. They lie more centrally than the spermatogonia.

When a primary spermatocyte completes the first meiotic division, it gives rise to two secondary spermatocytes. Secondary spermatocytes complete the second meiotic division, each one giving rise to two spermatids. Secondary spermatocytes are smaller than primary spermatocytes but also contain meiotic figures. However, they are almost never seen. Whereas primary spermatocytes take about three weeks to complete meiosis I, secondary spermatocytes complete meiosis II within a few hours. Therefore generally only spermatids are seen on the luminal side of primary spermatocytes.

Spermatids are much smaller than primary spermatocytes, have no meiotic figures, and lie the most centrally. Spermatids are genetically complete, that is, they contain the exact genetic information that the sperm will carry. However, they undergo a great morphological change, during a process called spermiogenesis, in which they change into motile, flagellated cells. Early spermatids are round, whereas later stages look more and more like sperm. (Figure 2 shows early spermatids only).

Spermiogenesis

Spermiogenesis is the process undergone by spermatids to become motile, flagellated cells. In the first stage (Golgi phase), pro-acrosomal granules begin to accumulate in the Golgi complex and  coalesce within a membrane-lined acrosomal vesicle adjacent to the nuclear envelope. The location of this vesicle determines the anterior pole of the sperm.  The centrioles migrate to the posterior pole, and the distal centriole aligns itself at right angles to the plasma membrane. The distal centriole initiates the formation of the flagellar axoneme. 

The acrosomal vesicle then spreads out to cover the anterior half of the nucleus (cap phase).  The acrosomal vesicle and nucleus become further condensed, and the nuclear envelope thickens and loses its pores.  The acrosome contains enzymes, including hyaluronidase, neuramidase, acid phosphatase and a trypsin-like protease.  

The spermatid then reorients itself to face toward the base of the seminiferous tubules, with its head deeply embedded in a Sertoli cell (acrosome phase). The nucleus becomes elongated and condensed; it  and the acrosome become closely apposed and lie immediately adjacent to the anterior plasma membrane. The acrosome and nucleus will form the head of the sperm.  The cytoplasm is deisplaced posteriorly.  The cytoplasmic microtubules become organized into a cylindrical sheath, the manchette, that extends from the posterior rim of the acrosome to the posterior pole of the spermatid.  

The centrioles move back to the posterior surface of the nucleus and become modified to form a connecting piece or neck.  Nine coarse fibres develop from the cenrioles attached to the nucleus and extend into the tail as the outer dense fibres peripheral to the microtubules of the axoneme. The plasma membrane moves posteriorly to cover the growing  flagellum.  The manchette disappears. The mitochondria aggregate around the proximal part of the flagellum as a helically-wrapped sheath, forming a thickened region called the middle piece.  Distal to this, a fibrous sheath surrounds the axoneme and extends nearly to the end of the flagelllum, forming the principal piece.  

During the last stage, the maturation stage, excess cytoplasm is pinched off as the residual body which is phagocytized by Sertoli cells.  The intercellular bridges remain attached to the residual bodies, and the sperm become independent of one another.  

Sertoli Cells

Sertoli cells are found in the seminiferous tubules but are not part of the spermatogenic series. They are sometimes called "nurse" cells because of their role in serving the spermatogenic cells. Sertoli cells are long, pyramidal cells that sit on the basement membrane and can extend all the way to the lumen. Their many processes surround the spermatogenic cells. However, usually only their nuclei are visible in the light microscope (sometimes – rarely – you can see a bit of cytoplasm). Their nuclei are pale, elongated, often triangular, and have a dark, prominent nucleolus. Often you will see a number of Sertoli cell nuclei in a row.

The major roles of  Sertoli cells are (1) the support, protection and nutrition of spermatogenic cells, (2) phagocytosis and (3) secretion. The cytoplasmic ramifications of  Sertoli cells provide physical support to the network of cytoplasmic bridges of the spermatogenic cells. Sertoli cells form the ''blood-testis barrier'' that divides the seminiferous tubules into a basal compartment (with spermatogonia) and an adluminal compartment (other cells of spermatogenic series). The basal compartment has free access to the blood; the adluminal compartment, and the rest of the excurrent ducts, are protected from blood-borne products and differ from blood plasma in their ionic, amino acid, protein and carbohydrate compositon. This arrangement protects developing sperm from immunogenic attack. The haploid germ cells develop after the individual becomes immunologically competent and would therefore be recognized as foreign by the immune system.  Adjacent Sertoli cells are bound together by occluding junctions, gap junctions and cytoplasmic specializations involving sER cisternae and actin filament bundles. To let early spermatocytes past this barrier to reach the adluminal compartment, Sertoli cells form new junctional complexes below newly-formed spermatocytes, while the ones above break down.  The cells in the adluminal compartment depend on Sertoli cells for the exchange of nutrients and metabolites.

The main phagocytic function of Sertoli cells is the removal of residual bodies.  They secrete a fluid that facilitates the passage of sperm into the genital ducts. They also secrete an androgen-binding protein (ABP) that concentrates testosterone in the tubule lumen; high levels are needed for the normal development of sperm.  The also secrete inhibin to regulate spermatogenesis. Inhibin inhibits the synthesis and release of follicle-stimulating hormone from  the anterior pituitary. 

Leydig Cells

Leydig cells are the steroidogenic cells of the testis.  They are found singly or in clusters in the connective tissue between the seminiferous tubules.  They are large cells with extensive eosinic cytoplasm and variable numbers of lipid vacuoles.  Ultrastructurally they are typical steroid-secreting cells.  Their major product is testosterone.  

A few Leydig cells can be seen in the interstitial space (I) in Figure 2 but are not in very clear focus.

Leydig cells in interstitial spaceTriangle_3D.gif (907 bytes)Large version of Fig. 3 Leydig cells

Figure 3 shows the interstitial space lying between three seminiferous tubule profiles. A cluster of Leydig cells occupies this space. These cells are large with an eosinophilic, vacuolated cytoplasm and a round nucleus. The cells within the tubules can also be identified. Cytoplasm can be discerned in some of the Sertoli cells, especially the labelled one at the top right.

Immature testisTriangle_3D.gif (907 bytes)Large version of Fig. 4 Immature testis

Figure 4 shows a section through an immature testis. This testis has seminiferous cords, essentially without lumina, rather than seminiferous tubules. Most of the cells are pre-Sertoli cells. The only spermatogenic cells present are spermatogonia, these are large cells usually near the periphery. They will not begin to multiply and differentiate until puberty. No Leydig cells are visible in the interstitial spaces in this section, occasionally one can see a few, partially differentiated Leydig cells.

Low power view of the rete testisTriangle_3D.gif (907 bytes)

Large version of Fig. 5 Rete testisFigure 5 shows a low power view of the rete testis, lying in the mediastinum testis. The mediastinum is the thickened, posterior portion of the tunica albiguinea which envelops the testis. The rete is an anastomosing channel system (lined with simple cuboidal epithelium) within the mediastinum. The seminiferous tubules form a loop whose ends enter the mediastinum. For a very short distance, they become straight and are called tubuli recti. The tubuli recti (not discernible in all sections) are lined only with Sertoli cells and open into the rete. A few seminiferous tubules are visible on the upper right of Figure 5. Blood vessels and lynphatics also pass through the mediastinum.

Fifteen to twenty tubules, the ductuli efferenti link the rete testis with the epididymis, a long (4-6 m) coiled tube that lies on the posterior surface of the testis. The ductuli efferentes are lined with a single layer of epithelial cells, some of which are tall, columnar and ciliated (help move sperm), and some of which are short and non-ciliated (resorb fluid). Basal cells, thought to be stem cells, are also present. The epithelium of the ductuli efferentes has a very scalloped appearance. This a useful feature for identification. The ductuli efferentes are surrounded by a small layer of smooth muscle, which helps move sperm to the epididymis, and they lie in connective tissue.

Large version of Fig. 6 Ductuli efferentesLow power view of the dutuli efferentesTriangle_3D.gif (907 bytes)

Figure 6 shows a low power view of the dutuli efferentes. The irregular surface of their epithelium is evident even at this magnification.

Large version of Fig. 7 High power view ductuli efferentesHigh power view of ductuli efferentesTriangle_3D.gif (907 bytes)

Figure 7 shows a high power view of a ductus efferens. The uneven epithelium and the smooth muscle surrounding it are evident. Fluid (pink-staining) and sperm can often be seen in the lumina of the ductuli efferentes.

Low power view of the epididymisTriangle_3D.gif (907 bytes)

Large version of Fig. 8 EpididymisFigure 8 shows a low power view of the epididymis. This is a single tube, but it is highly coiled, so you see many profiles, which often are more or less circular. Usually fluid and sperm (the latter only at high magnifications) can be seen in the lumina. In contrast to the ductuli efferentes, the inner surface of the epididymis appears very smooth. This is a useful distinguishing feature of the epididymis. Another is the presence of long stereocilia (not really cilia at all but modified microvilli), which can be seen in all the profiles of Figure 8. The epithelium is pseudostratified, having tall principal cells and short basal cells (of course all sit on the basement membrane). The basal cells are similar to those of the ductuli efferentes. The principal cells bear the stereocilia. They secrete the glycocalyx of the sperm, and may be a source of steroids for sperm maturation. They resorb fluid and phagocytize residual bodies missed by the Sertoli cells as well as degenerate sperm. It is during their passage through the epididymis that sperm become motile and acquire the capacity to fertilize eggs. The height of the epithelium (principal cells) decreases going from the head through the body and tail of the epididymis.

The head and body of the epididymis are surrounded by a circular layer of smooth muscle which moves sperm along by peristalsis. The tail, which acts as a reservoir for mature sperm, has three, much thicker layers of smooth muscle: an inner and outer longitudinal layer surrounding a middle circular layer. During ejaculation, intense contractions of these layers force the sperm into the vas deferens. The smooth muscle surrounding the profiles in Figure 8 (showing head of epididymis) stains more intensely than the surrounding connective tissue.

High power view of the epididymisTriangle_3D.gif (907 bytes)Large version of Fig. 9 High power of epididymis

Figure 9 shows a high power view of the epididymis. Note the tall epithelium with stereocilia, the smooth inner contour, and the smooth muscle surrounding the profiles of epididymis. A mass of fluid and sperm is visible in the lumen.

The vas deferens is the terminal part of the excurrent duct system. This very long tube takes the scenic route from the epididymis to the prostate gland. Upon entering the prostate gland it is called an ejaculatory duct and joins the prostatic urethra.

Low power view of the spermatic cord with vas deferensTriangle_3D.gif (907 bytes)Large version of Fig. 10 spermatic cord

Figure 10 shows a low power view of the spermatic cord containing the vas deferens. At this magnification, the smooth muscle of the muscularis is prominent. (The muscularis has 3 layers of SM: long., circ., long.). The epithelium (not distinguishable at this magnification) is pseudostratified, similar to but generally lower than that of the epididymis. The distribution of stereocilia is also variable. The epithelium is surrounded by a moderately compact lamina propria. The lumen of the vas deferens is irregular, this is thought to be an effect of the contraction of the muscularis during fixation of tissue. Beyond the muscularis, the adventitia blends with the connective tissue of the spermatic cord. Blood vessels and nerve bundles can be seen in the spermatic cord.

High power view of vas deferens mucosaTriangle_3D.gif (907 bytes)Large version of Fig. 11 Vas deferens mucosa

A high power view of the mucosa of the vas deferens, showing pseudostratified columnar epithelium with stereocilia and collagenous lamina propria, is seen in Figure 11. A bit of smooth muscle from the muscularis is also visible.

Large version of Fig. 12 Vessesls & nerves of spermaticVessels and nerves of spermatic cordTriangle_3D.gif (907 bytes)

The blood vessels and nerves of the spermatic cord can be seen in Figure 12. Many of the vessels are veins of the pampiniform plexus. These veins are atypical in having a thick muscularis with an inner longitudinal and outer circular layer. (Remember blood vessels usually only have one circular muscle layer in their muscularis, relatively thick in arteries and thin in veins). Fortunately, we are not concerned with distinguishing the blood vessels in the spermatic cord. Part of the wall of the vas deferens can be seen at the left of Figure 12.

The seminal vesicle is an elongated sac, an outpocketing of the vas deferens just before the vas enters the prostate to become the ejaculatory duct. It is highly convoluted, so even though it is just one sac, several profiles are generally visible in a section. Its mucosa has complex primary folds and many secondary folds and terriary, which branch and interconnect. The lamina propria extends into the core of the folds. The epithelium is pseudostratified, (generally very) low columnar. It has basal cells and taller, non-ciliated cells. The basal cells are not very abundant, so that the epithelium could be mistaken for simple cuboidal or low columnar. The muscularis has an inner circular and outer longitudinal layer. It is sometimes hard to discern due to the convolutions of the seminal vesicle. The seminal vesicle produces a viscous fluid that contains nutrients for sperm.

Low power view of the seminal vesicleTriangle_3D.gif (907 bytes)Large version of Fig. 13 Seminal vesicle

Figure 13 shows a low power view of the seminal vesicle. One profile and part of another are visible. The complex folds of the mucosa are distinguishable. Secretory product is seen in the lumina. At this magnification, it is hard to distinguish the mucosa from the muscularis.

Large version of Fig. 14 High power seminal vesicleHigh power view of mucosal folds of seminal vesicleTriangle_3D.gif (907 bytes)

A high power view of mucosal folds of the seminal vesicle is shown in Figure 14. The low pseudostratified epithelium and the lamina propria core of the folds is evident. Secretory product is seen in the lumina. (All of the "lumina" produced by the folding of the mucosa are continuous with the lumen of the seminal vesicle).

Wall of seminal vesicleTriangle_3D.gif (907 bytes)

In Figure 15, the wall of the seminal vesicle is shown quite clearly (not the case in all sections), with an inner circular and outer longitudinal muscle layer in the muscularis. Some smooth muscle fibers extend into the lamina propria. The folds of the mucosa are visible at the left.Large version of Fig. 15 Wall of seminal vesicle

The prostate consists of 30 – 50 tubuloalveolar glands surrounding the prostatic urethra in three concentric layers. The glands either empty directly into the urethra or enter via ducts. The ducts are quite similar to the secretory portions in appearance and we are not concerned with distinguishing between the two. The epithelium is quite variable, it can be pseudostratified, or simple columnar or cuboidal, sometimes squamous. The stroma of the prostate is fibroelastic, with numerous smooth muscle bundles running all through it. Contraction of this smooth muscle expels the contents of the prostate during ejaculation.

[In a section straight through the middle of the prostate gland, you would see the U-shaped urethra. Lying between the arms of the U and opening into the urethra would be a elongated sac, the utriculus (vaginalis). This is the remnant of the Mullerian duct which would have given rise to the female genital ducts in a female. On either side of the utriculus would be the ejaculatory ducts, arising from the vas deferens as they enter the prostate. The ejaculatory ducts eventually enter the urethra as they course through the prostate. Very few of the slides in our collection show these structures, most are sectioned through parts of the prostate that contain only glands.]

Large version of Fig. 16 Prostate glandLow power view of the prostate glandTriangle_3D.gif (907 bytes)

Figure 16 shows a low power view of the prostate gland. Irregularly-shaped glands of various sizes are lie in the stroma. The smooth muscle bundles that run between the glands, with no particular organization, stain more deeply than the connective tissue of the stroma.

High power view of prostate glandTriangle_3D.gif (907 bytes)

Large version of Fig. 17 High power of prostate glandFigure 17 shows a high power view of the prostatic stroma and parts of several glands. The smooth muscle in the stroma is evident. As is often the case, the lumina of the glands are irregular. The epithelium of these glands is pseudostratified.

Large version of Fig. 18 Prostate gland with concretionsProstate gland with concretionsTriangle_3D.gif (907 bytes)

The prostate gland produces much of the seminal fluid, and includes in its secretions acid phosphatase, fibrinolysin and citric acid. Pink-staining secretions are frequently seen in the lumina of the glands. Prostatic concretions, also called corpora amylacea, are frequently found in the glands of older men. They result from the precipitation of secretory material around cell fragments, and can become calcified. Figure 18 shows a section of a prostate from an older man. Concretions are visible in 3 of the glands.

The penis is the terminal part of the reproductive system and the urinary system. It consiststs of two dorsal erectile bodies, called corpora cavernosa, and one smaller, ventral erectile body, called the corpus spongiosum (or corpus cavernosum urethrae). The urethra runs through the corpus spongiosum. The three erectile bodies are held together by a connective tissue sheath called the tunica albiguinea, which forms a capsule around each one. (The capsules between the two corpora cavernosa meet in the midline to form the medial septum, which becomes attenuated near the tip of the penis.) The capsules around the two corpora cavernosa are very dense, and cause them to become very rigid when they fill with blood during an erection. The capsule around the corpus spongiosum is thinner and more elastic, so it does not become as rigid as the other two bodies. This prevents the urethra from becoming occluded during an erection. The corpus spongiosum expands at the tip of the penis to form the glans. The corpora cavernosa end at the base of the glans. Surrounding the three encapsulated erectile bodies is very loose connective tissue, called Buck’s fascia or deep penile fascia, which in turn is surrounded by the dermis and epidermis of thin skin. Because of the loose CT, the skin moves easily over the underlying stuctures.

In the specimens in our collection, the sections of the penis were made close to the base, when the crura bearing the corpora cavernosa, and the root bearing the corpus spongiosum, are still approaching each other. Thus, these structures are much farther apart (separated by more connective tissue), than in the sections typically shown in histology textbooks. Even at low power, it is not be possible to have more than one body (corpus cavernosum or corpus spongiosum) in the field of view.

Large version of Fig. 19 Corpus cavernosumLow power view of a corpus cavernosumTriangle_3D.gif (907 bytes)

Figure 19 shows a low power view of a corpus cavernosum. Numerous blood filled sinuses are evident. The dense connective tissue of the tunica albiguinea capsule is visible on the left.

Low power view of the urethra in the corpus spongiosumLarge version of Fig. 20 Corpus spongiosumTriangle_3D.gif (907 bytes)

Figure 20 shows a low power view of the urethra in the corpus spongiosum. No blood sinuses are visible in the field of view. The urethra is lying in the connective tissue of the corpus spongiosum. It is not possible to distinguish the epithelium at this magnification. The penile urethra is lined with pseudostratified or stratified columnar epithelium, this gives way to stratified squamous as it approaches the external orifice. The urethra has numerous invaginations of the mucosa called lacunae or Morgagni. Although they are not discernible at this magnification, single or groups of mucous cells are distributed in the epithelium of the lacunae. Branched tubular mucous glands, the glands of Littré, open into the lacunae. (Quite often, the single cells or groups of mucous cells in the lacunae are also called glands of Littré). 

 

High power view of groups of mucous cells in some lacunae of MorgagniTriangle_3D.gif (907 bytes)

HMLITTRE_sm.gif (27475 bytes)Figure 21 shows a high power view of groups of mucous cells in some lacunae of Morgagni.  These cells are paler than the surrounding epithelial cells.  Also visible is a lacuna cut tangentially so that it looks like an isolated cluster of epithelial cells. 

 

 

 

 

High power view of two tubular glands of LittréTriangle_3D.gif (907 bytes)

HMLITTRE2_sm.gif (28569 bytes)Figure 22 shows a high power view of two tubular glands of Littré.  All the cells are mucous secreting and the glands open into lacunae (not visible but  toward the top of the field of view).  Sometimes, due to the plane of sectioning, glands of Littré will appear as isolated clusters of cells.  

 

 

 

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