Descent Of The Testes

Toward the end of the second month, the urogenital mesentery attaches the testis and mesonephros to the posterior abdominal wall (Fig. 14.3 A). With degeneration of the mesonephros the attachment serves as a mesentery for the gonad (Fig. 14.28B). Caudally it becomes ligamentous and is known as the caudal genital ligament (Fig. 14.40A). Also extending from the caudal pole of the testis is a mesenchymal condensation rich in extracellular matrices, the guber-naculum (Fig. 14.40). Prior to descent of the testis, this band of mesenchyme terminates in the inguinal region between the differentiating internal and external abdominal oblique muscles. Later, as the testis begins to descend toward the inguinal ring, an extra-abdominal portion of the gubernaculum forms and grows from the inguinal region toward the scrotal swellings. When the testis passes through the inguinal canal, this extra-abdominal portion contacts the scrotal floor (the gubernaculum forms in females also, but in normal cases it remains rudimentary).

Factors controlling descent of the testis are not entirely clear. It appears, however, that outgrowth of the extra-abdominal portion of the gubernaculum produces intra-abdominal migration, that an increase in intra-abdominal pressure due to organ growth produces passage through the inguinal canal, and that regression of the extra-abdominal portion of the gubernaculum completes movement of the testis into the scrotum. Normally, the testes reach the inguinal region by approximately 12 weeks gestation, migrate through the inguinal canal by 28 weeks, and reach the scrotum by 33 weeks (Fig. 14.40). The process is influenced by hormones, including androgens and MIS. During descent, blood supply to the testis from the aorta is retained, and testicular vessels extend from their original lumbar position to the testis in the scrotum.

Independently from descent of the testis, the peritoneum of the abdominal cavity forms an evagination on each side of the midline into the ventral abdominal wall. This evagination, the processus vaginalis, follows the course of the gubernaculum testis into the scrotal swellings (Fig. 14.40B). Hence the processus vaginalis, accompanied by the muscular and fascial layers of the body wall, evaginates into the scrotal swelling, forming the inguinal canal (Fig. 14.41).

The testis descends through the inguinal ring and over the rim of the pubic bone and is present in the scrotum at birth. The testis is then covered by a reflected fold of the processus vaginalis (Fig. 14.40D). The peritoneal layer covering the testis is the visceral layer of the tunica vaginalis; the remainder of the peritoneal sac forms the parietal layer of the tunica vaginalis (Fig. 14.40D). The narrow canal connecting the lumen of the vaginal process with the peritoneal cavity is obliterated at birth or shortly thereafter.

In addition to being covered by peritoneal layers derived from the processus vaginalis, the testis becomes ensheathed in layers derived from the anterior abdominal wall through which it passes. Thus, the transversalis fascia forms the internal spermatic fascia, the internal abdominal oblique muscle gives rise to the cremasteric fascia and muscle, and the external abdominal oblique

Fascia The Peritoneal Cavity

Figure 14.40 Descent of the testis. A. During the second month. B. In the middle of the third month. Peritoneum lining the coelomic cavity evaginates into the scrotal swelling, where it forms the vaginal process (tunica vaginalis). C. In the seventh month. D. Shortly after birth. E. Scanning electron micrograph of a mouse embryo showing the primitive gonad (C), mesonephric duct (arrowheads), and gubernaculum (arrows).

Figure 14.40 Descent of the testis. A. During the second month. B. In the middle of the third month. Peritoneum lining the coelomic cavity evaginates into the scrotal swelling, where it forms the vaginal process (tunica vaginalis). C. In the seventh month. D. Shortly after birth. E. Scanning electron micrograph of a mouse embryo showing the primitive gonad (C), mesonephric duct (arrowheads), and gubernaculum (arrows).

Abdominal musculature

Cremastei fascia an

Epididym deferen muscle

Ductus

Abdominal musculature

Cremastei fascia an

Epididym deferen muscle

Ductus

Ligamentum Gubernaculum

Gubernaculum

Figure 14.41 A. Testis, epididymis, ductus deferens, and various layers of the abdominal wall that surround the testis in the scrotum. B. Vaginal process in open communication with the peritoneal cavity. In such a case, portions of the intestinal loops often descend toward and occasionally into the scrotum, causing an inguinal hernia. C. Hydrocele.

Epididymis

Hydrocele Ductus deferens

Epididymis

Hydrocele Ductus deferens

Gubernaculum

Figure 14.41 A. Testis, epididymis, ductus deferens, and various layers of the abdominal wall that surround the testis in the scrotum. B. Vaginal process in open communication with the peritoneal cavity. In such a case, portions of the intestinal loops often descend toward and occasionally into the scrotum, causing an inguinal hernia. C. Hydrocele.

muscle forms the external spermatic fascia (Fig. 14.41 A). The transversus abdominis muscle does not contribute a layer, since it arches over this region and does not cover the path of migration.

CLINICAL CORRELATES Hernias and Cryptorchism

The connection between the abdominal cavity and the processus vaginalis in the scrotal sac normally closes in the first year after birth (Fig. 14.40D). If this passageway remains open, intestinal loops may descend into the scrotum, causing a congenital inguinal hernia. (Fig, 14.41 B). Sometimes obliteration of this passageway is irregular, leaving small cysts along its course. Later these cysts may secrete fluid, forming a hydrocele of the testis and/or spermatic cord (Fig. 14,41 C).

In 97% of male newborns, testes are present in the scrotum before birth. In most of the remainder, descent will be completed during the first 3 months postnatally. However, in less than 1% of infants, one or both testes fail to descend. The condition is called cryptorchidism and may be caused by decreased androgen (testosterone) production. The undescended testes fail to produce mature spermatozoa and the condition is associated with a 3% to 5% incidence of renal anomalies.

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Pregnancy Diet Plan

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The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.

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