Plate 82 Testis I

The male reproductive system consists of the paired testes, epididymides, and genital ducts, as well as accessory reproductive glands and the penis. The functions of the testis are the production of sperm and the synthesis and secretion of androgens, especially testosterone. The events of cell division that lead to the mature sperm involve both normal cell division, mitosis, and reduction division, meiosis, to yield a haploid chromosome number and haploid DNA content. Androgen secretion by the testis begins early in fetal development and is essential for continued normal development of the male fetus. At puberty, androgen secretion resumes and is responsible for initiation and maintenance of sperm production (spermatogenesis), secretion by accessory sex glands (e.g., prostate and seminal vesicle), and development of secondary sex characteristics.

Figure 1, testis, monkey, H&E x65.

This section of the testis shows the seminiferous tubules and the tunica albugĂ­nea (TA), the capsule of the organ. Extending from the very thick capsule are connective tissue septa (S) that divide the organ into compartments. Each compartment contains several seminiferous tubules and represents a lobule (L). Blood vessels (BV) are present within the inner portion of the capsule, the part referred to as the tunica vasculosa, and in the connective tissue septa.

The seminiferous tubules are convoluted; thus, the profiles they present in a section are variable in appearance. Not infrequently, the wall of a tubule is sectioned tangen-tially, thus obscuring the lumen and revealing what appears to be a solid mass of cells (X).

Figure 2, testis, monkey, H&E x400.

Examination at higher magnification, as in this figure, reveals a population of interstitial cells that occur in small clusters and lie in the space between adjoining tubules. They consist mostly of Leydig cells (LC), the chief source of testosterone in the male. They are readily identified by virtue of their location and by their small round nucleus and eosinophilic cytoplasm. Macrophages are also found, in close association with the Leydig cells, but in lesser number. They are, however, difficult to identify in H&E sections.

A layer of closely apposed squamous cells forms a sheath-like investment around the tubule epithelium of each seminiferous tubule. In man, several layers of cells invest the tubule epithelium. The cells of this peritubular investment exhibit myoid features and account for the slow peristaltic activity of the tubules. Peripheral to the myoid layer is a broad lymphatic channel that occupies an extensive space between the tubules. In routine histologic sections, however, the lymphatic channels are usually collapsed and, thus, unrecognizable. The cellular elements that surround the tubule epithelium are generally referred to as a lamina propria (LP) or as a boundary tissue. As a lamina propria, it is atypical. It is not a loose connective tissue. Indeed, under normal circumstances, lymphocytes and other cell types related to the immune system are conspicuously absent.

Examination of the tubule epithelium reveals two kinds of cells: a proliferating population of spermatogenic cells and a nonproliferating population, the sustentacula!-, or Sertoli, cells. The Sertoli cells are considerably fewer and can be recognized by their elongate, pale-staining nuclei (Sn)

and conspicuous nucleolus. The Sertoli cell cytoplasm extends from the periphery of the tubule to the lumen.

The spermatogenic cells consist of successive generations arranged in concentric layers. Thus, the spermatogonia (Sg) are found at the periphery. The spermatocytes (Sc), most of which have large round nuclei with a distinctive chromatin pattern (because of their chromatin material being reorganized), come to lie above the spermatogonia. The spermatid population (Sp) consists of one or two generations and occupies the site closest to the lumen. The tubules in this figure have been identified according to their stage of development. The tubule at the upper right can be identified as stage VI. At this stage, the mature population of spermatids (identified by their dark-blue heads and eosinophilic threadlike fiagella protruding into the lumen) are in the process of being released (spermiogenesis). The younger generation of spermatids is composed of round cells and exhibits round nuclei. Moving clockwise, the tubule indicated as stage VII is slightly more advanced. The mature spermatids are now gone. Progressing to stage VIII, the tubule at the bottom of the micrograph reveals that the spermatid population is undergoing a change in nuclear shape. Note the tapered nuclei (arrows). Further maturation of the spermatids is reflected in the tubule at the top of the micrograph, stage XI. Finally, the tubule marked stage II, on the left, reveals slightly greater maturation of the luminal spermatids, and with the start of the new cycle (stage I), a newly formed spermatid population is now present. By examining the spermatid population and assessing the number of generations present (i.e., one or two) and the degree of maturation, it is possible with the aid of a chart to approximate the stage of a tubule.

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