Scrotum is a dual-chambered protuberance of skin and muscle, which contains the testes, epididymis and lower end of the spermatic cords. It can be considered as an outpouching of the lower part of anterior abdominal wall containing the above structures. It is divided into two segments by a central septum.
The scrotum is an extension of the perineum and is located between the penis and anus. It is homologous to labia majora in females.
Structure of scrotum:
The wall of the scrotum is made up of numerous layers. These are;
- Skin: Skin of scrotum is thin, wrinkled and pigmented. It forms a single pouch around the entire surface. In the middle, there is a slightly raised ridge, which indicates the fusion of the tow lateral labioscrotal swellings. In females, the lateral swellings remain separate and form the labia majora.
- Superficial fascia: The superficial fascia of scrotum is continuous with the fatty and membranous layers of fascia of anterior abdominal wall. The fatty layer in this region is replaced by a smooth muscle known as dartos muscle, which is innervated by sympathetic nerve fibers. It is primarily responsible for wrinkling of the skin.
The membranous layer of fascia in the scrotal region is known as Colle’s fascia. It is continuous in front with the Scarpa’s fascia (membranous layer of fascia of anterior abdominal wall).
Both layers of superficial fascia contribute to the median partition, which crosses the scrotum and separates the testes from each other.
- Spermatic fasciae: The lie beneath the superficial fascia and are derived from the three layers of anterior abdominal wall. These are;
- External spermatic fascia: Derived from the aponeuorsis of external oblique muscle.
- Cremasteric fascia: Derived from the internal oblique muscle. This fascia contains both the connective tissue and muscle fibers, which form the cremaster muscle.
- Internal spermatic fascia: Derived from the fascia transversalis.
- Tunica vaginalis: It lies within the three spermatic fasciae, covering the anterior, medial and lateral surfaces of each testis. The tunica vaginalis is in fact the lower expanded part of processus vaginalis, from which it is shut off just before birth. The tunica vaginalis is thus a closed sac, which is invaginated from behind by the testis on each side.
Blood supply of scrotum:
Scrotum receives its blood supply from anterior scrotal artery (a branch of the deep external pudendal artery) and posterior scrotal artery (a branch of the internal pudendal artery). The venous blood drains through the testicular veins into the inferior vena cave.
Nerve supply to scrotum:
Nerve supply to scrotum is rather abundant. It receives the following nerves.
- Anterior and Posterior scrotal nerves
- Genital branch of genitofemoral nerve (supplies the cremaster muscle)
- Perineal branches of posterior femoral cutaneous nerve
Lymph drainage of scrotum:
Lymph from the skin, fasciae and tunica vaginalis of scrotum drains into the superficial inguinal lymph nodes. It must be kept in mind that the lymph from testes and epididymis (structures contained within scrotum) drains into the para-aortic lymph nodes at the level of first lumbar vertebra. This is because during development, testes migrate from high up on the posterior abdominal wall.
Functions of scrotum:
The primary function of scrotum is to provide a cooler environment to the testes. For spermatogenesis to occur, the testes must be present at a temperature slightly lower than the rest of the body.
The cremaster muscle has a role in controlling the temperature. It can shrink the scrotum to move the testes near the abdomen or it can dilate the scrotum to move the testes away from abdomen. Temperature will rise when scrotum is near the abdomen and it will drop in the other case.
An additional function of scrotum appears to be the protection of testes and providing enough time for spermatozoa to mature before discharge. It has been suggested that if testes were situated within the abdominal cavity, they would be subject to regular changes in abdominal pressure created by contraction and relaxation of abdominal muscles. This squeezing and relaxing would result in more rapid emptying of the testes, thus not giving enough time for spermatozoa to mature.