Learn — Reproductive system

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Embryonic testis to scrotum descent

The testis develops high on the posterior abdominal wall at about the level of the tenth thoracic segment and then migrates down through the inguinal canal into the scrotum, dragging its blood supply, nerves and lymphatic drainage with it. That journey explains three things the nurse must know: why testicular pain is felt around the umbilicus rather than in the groin, why testicular cancer spreads to the para-aortic and not the inguinal nodes, and why an undescended testis is so common in babies born early.

  • The timetable of descent: the testis lies at the level of the deep inguinal ring by about the seventh month of gestation, traverses the inguinal canal in about the seventh to eighth month, and lies in the scrotum by the ninth month — so a preterm boy is often born before the descent is complete.
  • The gubernaculum guides the descent and the processus vaginalis, a diverticulum of peritoneum, precedes it; the distal part of that process remains as the tunica vaginalis and the rest normally obliterates, so failure to obliterate leaves a congenital indirect inguinal hernia or a hydrocele of the cord.
  • As it passes through the abdominal wall the testis acquires its coverings from the layers it crosses: external spermatic fascia from the external oblique aponeurosis, cremasteric muscle and fascia from the internal oblique, and internal spermatic fascia from the fascia transversalis.
  • The scrotum keeps the testis about 2 to 3 degrees Celsius below core temperature, which spermatogenesis requires; the dartos and cremaster muscles adjust that by drawing the testis up in the cold, and the same cremaster is tested by the cremasteric reflex — stroking the inner thigh, carried by the genitofemoral nerve from L1 and L2.
  • The blood supply stays where it started: the testicular artery arises from the abdominal aorta at about the level of L2, just below the renal arteries, and lymph drains to the para-aortic (lumbar) nodes, while the scrotal skin drains to the superficial inguinal nodes — so a testicular tumour is staged by abdominal imaging and a scrotal skin lesion by feeling the groin.
  • Venous drainage differs on the two sides: the right testicular vein joins the inferior vena cava obliquely and the left joins the left renal vein at a right angle, which is why about 85 to 90% of varicoceles are left-sided and why a new left varicocele in an adult raises the question of a renal tumour obstructing that vein.
  • Cryptorchidism (undescended testis) is present in about 3% of term and up to 30% of preterm male newborns; most descend spontaneously by 3 to 6 months, and if the testis is still undescended at 6 months the child is referred for orchidopexy between about 6 and 18 months, because the germ cells are damaged by the higher temperature after that.
  • The risks of an undescended testis are infertility, torsion, trauma against the pubic bone, associated hernia and a raised risk of testicular malignancy that orchidopexy reduces but does not abolish — the operation at least places the testis where it can be examined.
  • An undescended testis must be distinguished from a retractile testis, which can be milked down into the scrotum and stays there; a retractile testis is a normal variant needing follow-up rather than surgery, and a cold room or cold hands will make a normal testis look undescended.

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