Anatomy of the Male Reproductive System

Testis, Epididymis, and Ductus

Deferens

Testis and Scrotum

Male mammals have two testicles, which are components of both the reproductive and the endocrine system. Therefore, the two main functions of the testicles are producing sperm (approximately one million per hour) and male sex hormones (e.g., testosterone) (Fig. 4.1).

The average testicular volume is 18 cm³ per testis with normal size ranging from 12 to 30 cm³. A testicular volume of both testicles less than 15 mL is associated with infertility. It is most common for one testis to hang lower than the other. In about 85% of men, the lower hanging testis is the right one. This is due to differences in the vascular anatomical structure on the right and left sides (see below).

Testes (and epididymes) are contained within an extension of the abdomen, called scrotum. The scrotum, which is homologous to the labia majora in females, keeps the testis at a temperature of about 34.4°C, as temperatures above 36.7°C are damaging to sperm count. The temperature is regulated by blood flow and positioning of the testes toward and away from the heat of the body by contraction and relaxation of the musculus cremaster and the tunica dartos, a layer of smooth muscles under the skin of the scrotum.

Descensus testis: Many anatomical features of the adult testis reflect its developmental origin in the abdomen (Fig. 4.2). The layers of tissue enclosing each testicle are derived from the layers of the anterior abdominal wall. Parallel to the descensus testis in the embryo, the processus vaginalis peritonei protrude into the scrotum creating the cavitas serosa scroti, which is surrounded by the epiorchium (inner layer, covers the tunica albuginea) and the periorchium (outer layer). Epiorchium and periorchium together form the tunica vaginalis testis. The fascia spermatica interna, following the periorchium, arises from the fascia transversalis. It contains the cremasteric muscle which arises from the internal oblique muscle. The cremasteric muscle is covered by the fascia spermatica externa which arises from the fascia of the body. Testicles and layers of the testicles are covered by the skin of the scrotum. Below the body skin lies the tunica dartos comprizing a fibromuscular layer with hairs and pigments, but no fat (Fig. 4.3 and Table 4.1).

Clinic: Incomplete descensus testis results in cryptorchidism associated with male infertility. In cryptorchidism, in more than 95% of cases, the non-descended testicle is in an inguinal position.1 Abdominal and ectopic positions are clinically important and need gentle investigation when the inguinal canal seems to be empty (Fig. 4.4). In case of incomplete shut of the processus vaginalis peritonei, part of the intestine might protrude via the canalis inguinalis into the cavitas serosa scroti (indirect inguinal hernia).

Processus

vaginalis

Figure 4.2. descensus testis.

Anulus inguinalis

profundus superficialis

Arteria testicularis

Vas deferens

Epididymis

Testis

Figure 4.3. origin of testicle layers from body fasciae.

Periorchium

Epidiymis

Epiorchium

Peritoneum

Fascia transversalis m. obl. int. abd.

Fascia trunci externi

Skin

Processus vaginalis

m. cremaster Fascia spermatica ext.

Periorchium

Cavum scroti

Epiorchium

Tunica dartos