MALE REPRODUCTIVE SYSTEM
Objectives
You should be able to identify the following structures on your slides:
| Testis Epididymis Spermatic cord |
Prostate
gland Penis Clitoris |
 |
Blue Histology |
Slides
|
| D-62 | Clitoris (H&E) | |
| D-65 | Spermatic cord (H&E) | |
| D-66 | Testis (FeH) | |
| D-67 | Testis (H&E) | |
| D-69 | Epididymis (H&E) | |
| D-70 | Prostate gland (H&E) | |
| D-71 | Penis (H&E) | |
| D-72 | Seminal vesicle (H&E) |
Prologue
The male reproductive system consists of the testes and a series of ducts and glands and the penis for conveying the sperm to the female reproductive tract. Refer to the diagram at the beginning of this section in the printed syllabus for the orientation of the various slides of the male reproductive system. The testis has two functions; to produce the male gametes (sperm) and the steroid hormone testosterone. These functions are partitioned into discrete regions of the testis. Sperm are produced by the seminiferous tubules. They are passively transported out of the testes and into the epididymis on a current of fluid generated by the Sertoli cells of the seminiferous tubule and resorbed by the duct of the epididymis and the vas deferens. Testosterone is synthesized by the interstitial cells (Leydig cells) in the connective tissue surrounding the seminiferous tubules. It is picked up by local capillaries.
Most of the volume of testes is occupied by long twisted seminiferous tubules cut in various orientations. Two distinct classes of cells comprise the seminiferous epithelium of their walls; Sertoli cells and spermatogenic cells. Each Sertoli cell extends from the basement membrane to the lumen of the seminiferous tubule. The spermatogenic cells are smaller, round and stacked at different levels in the epithelium. This epithelium is considered to be stratified even though its Sertoli cells extend all of the way from the basement membrane to the surface. (Why wouldn't such an epithelium be pseudostratified?) As the cells develop they move up the epithelium, with the stem cells lying along the basement membrane and the mature sperm adjacent to the lumen of the tubule.
Spermatogonia are the mitotically-active germline cells. They lie on the basement membrane and their nuclei are oval or circular. When the cells enter into meiosis, they lift off the basement membrane and are called primary spermatocytes.
Primary spermatocytes rapidly grow in size, and their chromosomes progressively condense into densely stained strands. You can easily recognize these cells by their position in the middle layers of the epithelium and the large size of their spherical nuclei. In any one cross-section of a tubule, either one or two stages (early and late) may be seen. Primary spermatocytes finally divide (first meiotic division) to yield a pair of secondary spermatocytes.
Secondary spermatocytes have half the volume of primary spermatocytes. They divide soon after being formed. Therefore, you probably will not see this stage. The best place to look, of course, would be in a region that contains primary spermatocytes in division. These you can see. The cytoplasm becomes very eosinophilic during meiotic division, and the chromosomes cluster into a dense irregular clump.
The second meiotic division converts the secondary spermatocytes to spermatids. These small cells have small nuclei containing the haploid number of chromosomes. Spermatids occur at the top of the seminiferous epithelium. They mature into spermatozoa by cytodifferentiation without any further cell division. Spermatids show an extreme range in appearance depending on their stage of differentiation into mature sperm. Spermatids are called sperm = spermatozoa only after they are released from the epithelium. When released they peel out of their cytoplasm like you could pull your foot out of your sock. Sertoli cells hold on to that cytoplasm and phagocytize it.
Spermatogenesis occurs in waves so that in a cross-section of a tubule the cells will be synchronized into about four stages of development. This is important in order to understand in order for the appearance of seminiferous epithelium to make sense. Spermatogenic stem cells, (spermatogonia) on the basement membrane divide rarely. Occasionally one becomes committed to develop. It then divides rapidly for 16 days. The mitotic divisions are unusual in that the cytoplasm of the cells fails to completely separate (incomplete cytokinesis) so that the cells form a syncytium along the basement membrane. All of the cells are connected to one another by cytoplasmic bridges but are still called spermatogonia. The entire syncytium then lifts off of the basement membrane and the nuclei enter and proceed through meiosis in synchrony. The cells stay connected all the while until they are finally released from the epithelium as individual spermatozoa. When a syncytium leaves the basement membrane a new syncytium begins to form. Because it takes about 60 days to go to from stem cell to sperm the cells in any one region of seminiferous tubule are synchronized into about four discrete stages, 16 days apart. In some regions you will see abundant spermatogonia while in others very few. There will always be primary spermatocytes in some stage of prophase I of meiosis and sometimes two, early and late. Similarly you will always find spermatids in some stage of maturation and sometimes early and late ones.
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Slide descriptions
D-67 Testis (H&E)
Hold the slide up to your eye. Note the eosinophilic outer capsule, the tunica albuginea. What is its special function? The more purplish interior contains the seminiferous tubules. To one side you will note the cross-section of the epididymis outside the tunica albuginea. Locate these structures under low power. Note especially the many sections through seminiferous tubules, with their complex stratified epithelium.
Examine the cells of the seminiferous tubule. First identify
the Sertoli cells.
Their nuclei
are aligned with their long axis in a radial direction. You can recognize
them, using the 40X objective, by their pale-staining, large, irregular-shaped
nuclei and prominent nucleoli. However, their lateral boundaries will be difficult
to trace. Look at enough examples to be able to identify them with ease in
your section. Try to recall their various functions.
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Next, examine the spermatogenic cells. Spermatogonia may or may not be abundant, as explained above. They always lie on the basement membrane and often are flattened somewhat.
Primary spermatocytes are easy to recognize because of their large size (or more accurately the large size of their nuclei. It is difficult to discern their cytoplasm which blends in with that of the surrounding Sertoli cells.) You can actually see individual chromosomes as they condense in their nuclei (a geneticist's dream). On the basis of their degree of condensation it will be possible for you to find some regions which have both early and late primary spermatocytes layered on each other.
Spermatids show an amazing range of appearances as they differentiate, going from what look like normal (albeit small) cells to structures that look like mature sperm. Scan a dozen or so sections of tubules at high power or under oil. You can easily discern four or five different stages of spermatid development. Even the most mature-looking should be called spermatids since they do not become spermatozoa (= sperm) until they are released from the epithelium. Until they are released, spermatids have an intimate relationship with Sertoli cells, anatomically and physiologically. The maturing spermatids appear to be embedded within the apical end of the Sertoli cell (example 1, example 2, although they actually do not penetrate its cell membrane.
If you wish, you may try to find tubules with cells in meiotic division (2nd example). Search at 100 X power for areas that have unusually red cells in them. Typically the epithelium at this stage looks particularly shabby with seemingly fewer cells and gaps between them. At this magnification the metaphase plate looks like a black irregular blob within the cell. Turn to higher power and examine the dividing cells. They may be in either the first or second division of meiosis and you may see some secondary spermatocytes nearby. Can you red-hot geneticist types make a guess at the stages in the division cycle that you see? You guys may want to go to oil and look at these cells, at the various stages of chromosomal condensation in primary spermatocytes and at the range of spermatid stages. Pretty neat! Also, if you go to oil, do not forget to look at the strange nucleoli of the Sertoli cells. With their red and purple components, they will be the most complex nucleoli that you will see in this course.
Interstitial cells (of Leydig) are not too easy to find because they are scarce and jammed together between the tubules (illustration). They show up much better in the next slide.
D-66 Testis (FeH)
This section has been cut thin and stained with iron hematoxylin to bring out cytological detail. It is excellent for observing interstitial cells (= Leydig cells). These cells, lying in clusters in the connective tissue between the seminiferous tubules are the source of testosterone. They are plump, with round open nuclei and cytoplasm that looks foamy due to numerous droplets of lipid.
Use this slide to review the nuclear changes that occur during spermatogenesis. It shows especially well that seminiferous epithelium is a mosaic of patches in different stages of development. You can even find cross sections in which the left hand part of a tubule is in one stage and the right side in another. Try to find a section with two stages of primary spermatocytes (illustration)and another with two stages of spermatids (illustration). Note the variation in the numbers of spermatogonia from one stage of seminiferous epithelium to another. The epithelium in this cross section of a tubule includes many spermatogonia at 11:00 and very few at 6:00-10:00. This picture shows cells in meiosis.
D-69 Epididymis (H&E)
The epididymis is made up of two sets of ducts encased in a connective tissue capsule. A dozen or so efferent ducts drain the rete testis and coalesce into a single larger duct of the epididymis. Both types of ducts are highly convoluted. You can distinguish the two by holding the slide up to the light and noting the size of the tubules at the two ends of the epididymis (illustration). Both types of tubules are lined by pseudostratified epithelium, but of distinctive appearances (illustration).
The efferent ducts are distinguishable by the irregular contour of their lumens. The pseudostratified epithelium is composed of short secretory and tall ciliated cells. The two cell types tend to cluster to give a wavy appearance to the lumenal surface. The tubule is surrounded by a small number of poorly differentiated smooth muscle cells.
The epithelium of the duct of the epididymis is tall with a uniform thickness. It has two cell types, tall columnar cells and basal cells. The tall cells have very long, non-motile, branching cell processes, inappropriately called stereocilia, to increase the apical surface area tremendously. What is their role in the transport of sperm? Non-motile sperm are stored in this duct and in its extension called the vas deferens. You can see dense aggregations of them in some cuts through the duct of the epididymis.
The lamina propria around the duct of the epididymis has a small amount of smooth muscle, fibroblasts and capillaries. The circular arrangement of these cells is evident. As the duct proceeds down the tail of the epididymis, the amount of smooth muscle in its wall increases to finally develop a huge well organized layer where it becomes the vas deferens. Slide D-67 shows two or three cuts through the duct in the tail of the epididymis soon before it turns into the vas deferens (illustration). The amount of smooth muscle in them has increased considerably. During ejaculation the muscle layer contracts in peristaltic waves. Sperm far enough down in the epididymis or in the vas deferens will be swept along into the ejaculate. Those in the part of the duct of the epididymis with a smooth muscle layer two poorly developed to be effective will have to wait for another day (or another night or months in the case of one of your unnamed instructors).
D-65 Spermatic cord (H&E)
The spermatic cord connects the testis with the rest of the body. List to yourself the structures to be found in it. The vas deferens is characterized by the extraordinary amount of smooth muscle below the mucosa. This muscle is organized into three easily distinguished layers; inner and outer longitudinal, middle circular. The epithelium is similar to that of the duct of the epididymis, tall pseudostratified columnar. Why do you think that stereocilia continue down into the vas? The mucosa of this duct is thrown into one or several longitudinal folds, to allow the lumen to expand during ejaculation.
In addition to the vas deferens, the spermatic cord carries the vascular and neural supply to the testis, and some longitudinally disposed striated muscle fibers. The arteries are particularly prominent and arranged to form a counter current heat exchange with the veins to cool the blood before it reaches the testis (illustration). (The veins are muscular and not that easy to recognize). All of these structures are wrapped up in a dense connective tissue sheath, only partly preserved here.
D-72 Seminal vesicle (H&E)
The seminal vesicle contributes an important component of semen. It is a simple tubular gland about ten centimeters long coiled up in a corkscrew fashion. On your slides it is sectioned several times. The epithelial cells (pseudostratified columnar/cuboidal) lining it are secretory.
Three notable features of the gland are:
| 1. | The large lumen. Secretion is stored as it accumulates between ejaculations. | |
| 2. | A mucosa elaborated as an amazing and beautiful set of folds. Try to imagine what they are like in three dimensions. These convolutions greatly increase the area of the secretory epithelium. | |
| 3. | A very well developed muscularis layer in which you might distinguish an inner circular and outer longitudinal layer (illustration). |
The activity of the gland and the appearance of the epithelium are controlled by the level of testosterone in the blood and thus vary with the age of the individual. The epithelium can range from pseudostratified columnar to simple cuboidal. What would you say about the dude whom this tissue was taken from (illustration)?
D-70 Prostate gland (H&E)
The prostate is actually a large collection of glands of various sizes. They empty separately into the urethra. Secretory epithelium lines both the secretory alveoli and the ducts. The ducts have the larger cross section because it is here that the secretion is stored. The urethra has a distinctive crescent cross section because a ridge of tissue, the verumontanum, protrudes into the posterior side. The ducts of the main glands empty into the urethra at the cusps of the crescent. If you look in this region you can see sections through some of them here. As a detail of interest, but no functional significance, you can see a small lumen in the middle of the verumontanum. This is called the utriculus and it is the homologue of the uterus of the female. I'll bet you guys didn't know you had one!
Note the great amount of smooth muscle in the connective tissue between the glands, a characteristic of this organ (illustration). It can rapidly squeeze out the whole gland during ejaculation.
The glandular part of the prostate looks somewhat similar to the seminal vesicle. However, the glands are fundamentally different in morphology. The seminal vesicle is a hollow tube with elaborately fluted mucosal projections. The prostate has compound alveolar glands (remember the bunch of grapes analogy) embedded in a dense muscular connective tissue. You should convince yourself that YOU can SEE this difference before going on. The epithelium of the glands is useless for distinguishing the prostate. It also is pseudostratified columnar in young males and regresses to simple cuboidal in the elderly (please, not "old men", but "the elderly". I don't call you young squirts "sonny" or girlie or "kiddo").
Another characteristic feature of the prostate is the presence of insoluble concretions (example 2). These grow by accretion of layer upon layer of precipitated material. In section, the concretions often show rings, like the growth rings of a tree. Concretions increase in number and size with age but are considered to be a "normal" feature of the prostate, since they cause no medical problems. They can be useful at confirming the identification of a section of prostate tissue, but your slides do not have many of them, for some reason.
D-71 Penis (H&E)
Hold this slide up to the light. The penis consists of three cylindrical masses of erectile tissue. Two corpora cavernosa lie side by side. A single corpus spongiosum (= corpus cavernosum urethra) runs ventrally and contains the urethra. The urethra has the flattened, star-shaped lumen surrounded by a pseudostratified columnar epithelium with densely stained nuclei. The corpus spongiosum expands distally to form the glans penis. A dense fibrous coat, the tunica albuginea, surrounds each corpus.
The erectile tissue itself comprises a network of large, thin-walled veins (the cavernous sinuses) separated by trabeculae of connective tissue. You can see the endothelium lining the cavernous spaces and bands of smooth muscle in partitions between them (illustration). These sinuses receive arterial blood by way of arteries which open into them. The smooth muscle in the tunica media of these arteries relaxes upon parasympathetic stimulation.
Blood drains from the erectile tissue peripherally through progressively smaller channels into veins which traverse the tunica albuginea. The veins go through the tunica albuginea at an angle so that as blood distends the cylinders of erectile tissue it pinches off its exit, helping to maintain erection.
Examine the urethra. It collapses when not in use by forming a series of longitudinal folds. Note the infiltration of lymphocytes into the lamina propria here and there. This is an excellent place to examine plasma cells. Take the time to review how they look, using oil immersion, if you have the patience. Now examine the epithelium. What type is it? A scattering of mucous glands invaginates from the surface epithelium a short ways into the lamina propria. These glands of Littre are not very impressive.
One important feature of the spongiosum is that it never becomes as firmly erect as the two corpora cavernosa. It becomes engorged with blood but not rigid. This is essential, otherwise it would pinch shut the urethra. You should recall that an unyielding connective tissue capsule is necessary for erection. If not, review the mechanism of erection. You can see on your slide that the tunica albuginea of the corpus spongiosum is thinner than that of the other corpora. This is one reason that it is incapable of complete erection. Another structural difference that you can see is that the cavernous sinuses are smaller in the corpus spongiosum.
D-62 Clitoris (H&E)
The clitoris is the anatomical homologue of the more highly developed penis. Although part of the female reproductive system the clitoris is most appropriately examined at the same time as its male counterpart.
Hold the slide up to the light. The orientation may be somewhat confusing. The clitoris has been sectioned obliquely; more longitudinally than transversely and sort of parallel to the overlying skin. The apical end of the organ is to the left in the picture above. A fold of skin over the clitoris forms a "hood" homologous to the foreskin of the penis. This is why the covering epidermis seems to be located so far from the erectile tissue.
The clitoris is composed of only two columns of erectile tissue. These are homologous to the corpora cavernosa of the male penis but have the general architecture and erectile capabilities of the corpus spongiosum. Note the small, but abundant, cavernous sinuses and the relatively thin tunica albuginea, surrounding and separating the two columns of erectile tissue. The clitoris has no homologue of the corpus spongiosum. The urethra does not run in the clitoris. It reaches the surface behind the organ.