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Lab 16. Male Reproductive Tract
Functionally, the principal structures of the male reproductive system are:
Gametes are produced in the testis within long, twisted seminiferous tubules which make up the bulk of the organ. The process of gamete production and maturation is called spermatogenesis. The primitive sex cells of spermatogonia are diploid and divide mitotically to produce large numbers of differentiated daughter cells called primary spermatocytes and undergo meiosis (reduction division, or maturation division). The resulting cells, secondary spermatocytes, have half the somatic chromosome number, but each chromosome is still composed of two chromatids. The secondary spermatocytes rapidly enter prophase, and the chromatids finally separate, producing haploid daughter cells called spermatids. The spermatids undergo spermiogenesis, i.e., morphological transformations resulting in spermatozoa without further cell division.
The endocrine cells of the testis called Leydig or interstitial cells, are in clusters of various sizes between the seminiferous tubules. Their secretion, testosterone, influences spermatogenesis as well as all male secondary sex characteristics. In the genital tract, it promotes development and controls the secretory activity of the duct system and its associated glands.
At the mediastinum testis, the seminiferous tubules end as narrow, short, straight tubules (tubuli recti) lined with columnar Sertoli-like cells and these tubules enter the rete testis, a labyrinth of channels. Here sperm passing from the tubules come to a network of large, irregular spaces lined with cuboidal or squamous epithelium. The rete testis opens into the 10 or 15 ductili efferentes.
The surface of the testis not covered with mesothelium is the region of the mediastinum testis where the seminiferous tubules converge to become excretory ducts and where blood vessels and nerves enter the gland. Most of the slides were cut near the mediastinum so that the epithelium-lined labyrinthine channels of the rete testis may be seen in the dense collagenous C.T. In some slides, particularly in #94 odd, seminiferous tubules can be seen opening into (or becoming) tubuli recti lined with columnar epithelium; these are very short, and the epithelium soon becomes the squamous to cuboidal epithelium of the rete testis.
Connective tissue septa penetrate into the testis in a pattern radiating from the mediastinum to the tunica albuginea, dividing it into about 250 conical spaces called lobules. Each lobule is tightly packed with a few (14) long, twisted seminiferous tubules which are U-shaped in the sense that both ends Open into tubuli recti. The outer covering of the seminiferous tubules consists of specialized limiting membrane covered by closely packed and circularly oriented flattened cells which are small, modified smooth muscle elements (myoid cells); there is also abundant ground substance and fine fibrillar elements between these cells. Within the tubules, the sex cells and Sertoli cells constitute the seminiferous epithelium. The cell boundaries of the various cells are not clearly seen in histological sections, except near the edge of the lumen, and the various cells in the seminiferous epithelium are identified by differences in nuclear morphology and localization. First find Sertoli cells. Their nuclei are usually oval and located midway between the limiting membrane and the lumen. They are pale-staining with prominent, often acidophilic nucleoli and their nuclear membrane may be deeply infolded at one or two points. E.M. studies have shown these cells to have a slender pillar-like shape with irregular outlines due to compression by adjacent cells. Sertoli cells may have an exocrine function since they secrete androgen-binding proteins into the lumen of the tubules. They are generally thought to contribute to the biochemical maturation of spermatozoa which, at one stage of spermiogenesis, can be seen in groups just above Sertoli cell nuclei. Find such groups in your section.
The duct system of the male reproductive tract begins at the mediastinum testes (hilus) and consists of the ductuli efferentes, the epididymis, the vas deferens with its ampulla, and the ejaculatory duct. The epithelial lining of the duct is secretory and in some regions absorptive and under the control of androgens. A large fraction of the fluid leaving the testis with spermatozoa is reabsorbed by the epithelia of the ductuli efferentes and the upper portion of the epididymis. Spermatozoa leaving the testis appear morphologically complete but are unable to fertilize eggs. Further maturation takes place as they pass slowly through the epididymis (several weeks).
The ductuli efferentes are 10 to 15 small coiled ducts with a few layers of smooth muscle in their walls. The epithelial lining of the ductules is pseudostratified ciliated and consists of alternating groups of columnar and cuboidal cells. The convoluted ductules empty into a single larger tube, the ductus epididymis. This is an extremely long (4-6 meters) tortuous tube with a thin muscle coat. An outer fibrous tunic binds the whole mass to form the epididymis. The duct is lined with pseudostratified columnar epithelium consisting of rounded-basal cells and tall columnar cells with stereocilia. The epididymis is divided into head, body, and tail, the duct being smallest and most convoluted in the head where reabsorption of fluids predominates. Towards the tail, the duct gradually straightens and enlarges, acquiring a thicker muscular coat that becomes continuous with the vas deferens. Spermatozoa are stored in the body and tail, however the ionic medium maintained by the epithelium is such that they are non-motile and conserve stored energy.
The vas deferens (ductus deferens) is a tube with an extremely thick muscular wall. It is bound by C.T. with blood vessels, nerves and lymphatics to form the spermatic cord which passes from the scrotum into the abdominal cavity. The lumen of the vas deferens has an irregular outline due to longitudinal folds of the mucosa, and it is lined by a pseudostratified epithelium that is lower than that of the ductus epididymis. Some cells have stereocilia, but the latter tend to disappear toward the ampulla. The ampulla is a fusiform dilation of the vas in the abdominal cavity, just before it receives the duct of the seminal vesicle. The muscle coat becomes thinner and the lumen larger, and the longitudinal folds of mucosa are tall and intricately branched to form a network of partitions. The epithelium is clearly secretory with glandular outpocketings extending deep into the muscle layer. After receiving the duct of the seminal vesicle, the vas is reduced in diameter and becomes the ejaculatory duct which empties into the prostatic urethra. There are numerous folds and glandular pockets, but these are less prominent than in the ampulla; the epithelium is simple or pseudostratified columnar, becoming transitional near the urethra.
With the scanning lens, locate a group of tubules with a much taller, very regular epithelium near the large dilated ductules; this is the beginning of the coiled ductus epididymis lined with a pseudostratified columnar epithelium with stereocilia. A layer of smooth muscle cells, 2 or 3 layers thick, is apposed to the basement membrane of this epithelium.
Examine slide #99. In even-numbered boxes (from an adult), the lumen contents consist mainly of desquaminated, dying cells. The epithelium appears cuboidal or even squamous and mucosal folds have been flattened out so that only a few remain. This gland reflects a decline of androgen levels. However, sperm are present in the lumen. In odd-numbered boxes (from a 15 year old boy), the epithelium is pseudostratified, and the mucosal folds are large and abundant. Identify the smooth muscle in the tube walls.
The Prostate Gland
As the urethra leaves the bladder, its lumen becomes U-shaped. At this point many tubulo-alveolar glands surround and open into the urethra; these glands are embedded in fibro-muscular tissue and constitute the prostate gland. The glands are in three groups: the short mucosal glands directly beneath the opening throughout the urethral epithelium, a few submucosal glands with relatively short excretory ducts, and the large main prostatic glands with long ducts embedded deep in the connective tissue and making up the bulk of the prostate.
As the urethra emerges from the prostate, it pierces the fasciae of the urogenital diaphragm. This is the "membranous" urethra. It then becomes surrounded with erectile tissue which consists of a network of large irregular venous sinuses in connective tissue. This is the "cavernous" part of the urethra. Many small serous and mucous glands open into the urethra.
The erectile tissue immediately surrounding the urethra is the corpus cavernosum urethrae, or corpus spongiosum. In the penis, this body becomes smaller in diameter, and there is an adjacent, much larger body of erectile tissue called the corpus cavernosum. The blood spaces of these cavernous bodies are supplied by highly coiled arteries which uncoil and allow a rapid passage of large volumes of blood to fill and distend the sinuses and cause erection of the penis. These sinuses are venous channels and do not serve for exchanges or phagocytosis; they should not be confused with sinusoids.
The large corpus cavernosum is surrounded by a dense, fibrous capsule which sends in medial septa, giving the structure a bi-lobed appearance in cross-section. The fibrous capsule limits expansion of the corpus cavernosum, and provides the turgidity which occurs when the blood spaces are filled. Examine the structure of its erectile tissue and note that the spaces are larger towards the central, deeper region. Compare with the corpus cavernosum around the urethra, where the sizes of the sinuses tend to be more uniform. The cavernous bodies are supplied and drained by the numerous vessels seen at their periphery.