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Other Terms: Testicle, Testis (Orchis), Orchis, Testicule, Testikel
The testes are two organs that provide a site for production and maturation of sperm; they are suspended in the scrotum by the spermatic cords. At an early period of fetal life the testes are contained in the abdominal cavity, behind the peritoneum. Before birth they descend to the inguinal canal, along which they pass with the spermatic cord, and, emerging at the subcutaneous inguinal ring, they descend into the scrotum, becoming invested in their course by coverings derived from the serous, muscular, and fibrous layers of the abdominal wall, as well as by the scrotum. The testes are suspended in the scrotum by the spermatic cords, the left testis hanging somewhat lower than the right. The average dimensions of the testis are from 4 to 5 cm in length, 2.5 cm in breadth, and 3 cm in the antero-posterior diameter; its weight varies from 10.5 to 14 gm. Each testis is of an oval form, compressed laterally, and having an oblique position in the scrotum; the upper extremity is directed anterior and a little lateral; the lower, posterior and a little medial; the anterior convex border looks anterior and inferior, the posterior or straight border, to which the cord is attached,posterior and superior. The anterior border and lateral surfaces, as well as both extremities of the organ, are convex, free, smooth, and invested by the visceral layer of the tunica vaginalis. The posterior border, to which the cord is attached, receives only a partial investment from that membrane. Lying upon the lateral edge of this posterior border is a long, narrow, flattened body, name the epididymis.
The epididymis consists of a central portion of body, and upper enlarged extremity (the head), and a lower pointed extremity (the tail), which is continuous with the ductus deferens, the duct of the testis. The head is intimately connected with the upper end of the testis by means of the efferent ductules of the testis; the tail is connected with the lower end by cellular tissue, and a reflection of the tunica vaginalis. The lateral surface, head and tail of the epididymis are free and covered by the serous membrane; the body is also completely invested by it, except along its posterior border; while between the body and the testis is a pouch, named the sinus of the epididymis. The epididymis is connected to the back of the testis by a fold of the serous membrane.
Tunics of the Testes
The testis is invested by three tunics: the tunica vaginalis, tunica albuginea, and tunica vasculosa The tunica vaginalis is the serous covering of the testis. It is a pouch of serous membrane, derived from the saccus vaginalis of the peritoneum, which in the fetus preceded the descent of the testis from the abdomen into the scrotum. After its descent, that portion of the pouch which extends from the abdominal inguinal ring to near the superior part of the gland becomes obliterated; the lower portion remains as a shut sac, which invests the surface of the testis, and is reflected on to the internal surface of the scrotum; hence it may be described as consisting of a visceral and a parietal lamina. The visceral lamina covers the greater part of the testis and epididymis, connecting the latter to the testis by means of a distinct fold. From the posterior border of the gland it is reflected on to the internal surface of the scrotum. The parietal lamina is far more extensive than the visceral, extending upward for some distance anterior and on the medial side of the cord, and reaching below the testis. The inner surface of the tunica vaginalis is smooth, and covered by a layer of endothelial cells. The interval between the visceral and parietal lamina constitutes the cavity of the tunica vaginalis. The obliterated portion of the saccus vaginalis may generally be seen as a fibrocellular thread lying in the loose connective tissue around the spermatic cord; sometimes this may be traced as a distinct band from the upper end of the inguinal canal, where it is connected with the peritoneum, down to the tunica vaginalis; sometimes it gradually becomes lost on the spermatic cord. The tunica albuginea is the fibrous covering of the testis. It is a dense membrane, of a bluish-white color, composed of bundles of white fibrous tissue which interlace in every direction. It is covered by the tunica vaginalis, except at the points of attachment of the epididymis to the testis, and along its posterior border, where the spermatic vessels enter the gland. It is applied to the tunica vasculosa over the glandular substance of the testis, and, at its posterior border, is reflected into the interior of the gland, forming an incomplete vertical septum, called the mediastinum testis. The mediastinum testis extends from the superior to near the lower extremity of the gland, and is wider above than below. From its front and sides numerous imperfect septa are given off, which radiate toward the surface of the organ, and are attached to the tunica albuginea. They divide the interior of the organ into a number of incomplete spaces which are somewhat cone-shaped, being broad at their bases at the surface of the gland, and becoming narrower as they converge to the mediastinum. The mediastinum supports the vessels and duct of the testis in their passage to and from the substance of the gland. The tunica vasculosa is the vascular layer of the testis, consisting of a plexus of blood vessels, held together by delicate areolar tissue. It clothes the inner surface of the tunica albuginea and the different septa in the interior of the gland, and therefore forms and internal investment to all the spaces of which the gland is composed.
Structure of the testis
The glandular structure of the testis consists of numerous lobules. They differ in size according to their position, those in the middle of the gland being larger and longer. The lobules are conical in shape, the base being directed toward the circumference of the organ, the apex toward the mediastinum. Each lobule is contained in one of the intervals between the fibrous septa which extend between the mediastinum testis and the tunica albuginea. The seminiferous tubules are supported by loose connective tissue which contains here and there groups of “interstitial cells” containing yellow pigment granules. The tubules are pale in color in early life, but in old age they acquire a deep yellow tinge from containing much fatty matter. Each tubule consists of a basement layer formed of laminated connective tissue containing numerous elastic fibers with flattened cells between the layers and covered externally by a layer of flattened epithelioid cells. Within the basement membrane are epithelial cells arranged in several irregular layers, which are not always clearly separated, but which may be arranged in three different groups. Among these cells may be seen the spermatozoa in different stages of development. (1) Lining the basement membrane and forming the outer zone is a layer of cubical cells, with small nuclei; some of these enlarge to become spermatogonia. The nuclei of some of the spermatogonia may be seen to be in process of indirect divison, and in consequence of this daughter cells are formed, which constitute the second zone. (2) Within this first layer is to be seen a number of larger polyhedral cells, with clear nuclei, arranged in two or three layers; these are the intermediate cells or spermatocytes. Most of these cells are in a condition of meiotic division, and the cells which result from this division form those of the next layer, the spermatids. (3) The third layer of cells consists of the spermatids, and each of these, without further subdivision, becomes a spermatozoon. The spermatids are small polyhedral cells, the nucleus of each of which contains half the usual number of chromosomes. In addition to these three layers of cells others are seen, which are termed the supporting cells (cells of Sertoli). They are elongated and columnar, and project inward from the basement membrane toward the lumen of the tube, as development of the spermatozoa proceeds the latter group themselves around the inner extremities of the supporting cells. The nuclear portion of the spermatid, which is partly imbedded in the supporting cell, is differentiated to form the head of the spermatozoon, while part of the cell protoplasm forms the middle piece and the tail is produced by an outgrowth from the double centriole of the cell. Ultimately the heads are liberated and the spermatozoa are set free. In the apices of the lobules, the tubules become less convoluted, assume a nearly straight course, and unite together to form from twenty to thirty larger ducts, of about 0.5 mm in diameter, and these, from their straight course, are called straight seminiferous tubules. The straight seminiferous tubules enter the fibrous tissue of the mediastinum, and pass upward and backward, forming, in their ascent, a close network of anastomosing tubes which are merely channels in the fibrous stroma, lined by flattened epithelium, and having no proper walls; this constitutes the rete testis. At the upper end of the mediastinum, the vessels of the rete testis terminate in from fifteen to twenty ducts, the effernt ductuoles; they perforate the tunica albuginea, and carry the sperm from the testis to the epididymis. Their course is at first straight; they then become enlarged, and exceedingly convoluted, and form a series of conical masses, the coni vasculosi, which together constitute the head of the epididymis. Each cone consists of a single convoluted duct, from 15 to 20 cm in length, the diameter of which gradually decreases from the testis to the epididymis. Opposite the bases of the cones the efferent vessels open at narrow intervals into a single duct, which constitutes, by its complex convolutions, the body and tail of the epididymis. When the convolutions of this tube are unraveled, it measures upward of 6 meters in length; it increases in diameter and thickness as it approaches the ductus deferens. The convolutions are held together by fine areolar tissue, and by bands of fibrous tissue.The straight seminiferous tubules have very thin walls; like the channels of the the rete testis they are lined by a single layer of flattened epithelium. The efferent ductuoles and the tube of the epididymis have walls of considerable thickness, on account of the presence in them of muscular tissue, which is principally arranged in a circular manner. These tubes are lined by columnar ciliated epithelium.
The scrotum is a cutaneous pouch which contains the testes and parts of the spermatic cords. It is divided on its surface into two lateral portions by a ridge or raphe, which is continued forward to the under surface of the penis, and backward, along the midd line of the perineum to the anus. Of these two lateral portions the left hangs lower than the right, to correspond with the greater length of the left spermatic cord. Its external aspect varies under different circumstances; thus, under the influence of warmth, and in old and debilitated persons, it becomes elongated and flaccid; but under the influence of cold, and in the young and robust, it is short, corrugated, and closely applied to the testes. The skin of the scrotum is very elastic and capable of great distension, and on account of the looseness and amount of subcutaneous tissue, the scrotum becomes greatly enlarged in cases of edema, to which this part is especially liable as a result of its dependent position.
Vessels and nerves
The arteries supplying the coverings of the testes are: the superficial and deep external pudendal branches of the femoral, the superficial perineal branch of the internal pudendal, and the cremasteric branch from the inferior epigastric. The veins follow the course of the corresponding arteries.
The lymphatics end in the inguinal lymph glands.
The nerves are the ilioinguinal and lumboinguinal branches of the lumbar plexus, the two superficial perineal branches of the internal pudendal nerve, and the pudendal branch of the posterior femoral cutaneous nerve.
The spermatic cord extends from the abdominal inguinal ring, where the structures of which it is composed converge, to the back part of the testis. In the abdominal wall the cord passes obliquely along the inguinal canal, lying at first beneath the internal obliques, and upon the fascia transversalis; but nearer the pubis, it rests upon the inguinal and lacunar ligaments, having the aponeurosis of the external obliques in front of it, and the inguinal falx behind it. It then escapes at the subcutaneous ring, and descends nearly vertically into the scrotum. The left cord is rather longer than the right, consequently the left testis hangs somewhat lower than the right. The spermatic cord is composed of arteries, veins, lymphatics, nerves, and the excretory duct of the testis. These structures are connected together by areolar tissue, and invested by the layers brought down by the testis in its descent.
Vessels and nerves
The arteries of the cord are the internal and external spermatics and the artery to the ductus deferens. The internal spermatic artery, a branch of the abdominal aorta, escapes from the abdomen at the abdominal inguinal ring, and accompanies the other constituents of the spermatic cord along the inguinal canal and through the subcutaneous inguinal ring into the scrotum. It then descends to the testis, and, becoming tortuous, divides into several branches, two or three of which accompany the ductus deferens and supply the epididymis, anastomosing with the artery of the ductus deferens; the others supply the substance of the testis. The external spermatic artery is a branch of the inferior epigastric artery. It accompanies the spermatic cord and supplies the coverings of the cord, anastomosing with the internal spermatic artery. The artery of the ductus deferens, a branch of the superior vesical, is a long, slender vessel, which accompanies the ductus deferens, ramifying upon its coats, and anastomosing with the internal spermatic artery near the testis. The spermatic veins emerge from the back of the testis, and receive tributaries from the epididymis; they unite and form a convoluted plexus, which forms the chief mass of the cord. The vessels composing this plexus are very numerous, and ascend along the cord in front of the ductus deferens; below the subcutaneous inguinal ring they unite to form three or four veins, which pass along the inguinal canal, and, entering the abdomen through the abdominal inguinal ring, coalesce to form two veins. These again unite to form a single vein, which opens on the right side into the inferior vena cava, and an acute angle, and on the left side into the left renal vein, at a right angle.
The lymphatic vessels of the reproductive organs.The Lymphatic Vessels of the Testes consist of two sets, superficial and deep, the former commencing on the surface of the tunica vaginalis, the latter in the epididymis and body of the testis. They form four to eight collecting trunks which ascend with the spermatic veins in the spermatic cord and along the front of the Psoas major to the level where the spermatic vessels cross the ureter and end in the lateral and preaortic groups of lumbar glands.
The nerves are the spermatic plexus from the sympathetic, joined by filaments from the pelvic plexus which accompany the artery of the ductus deferens.