a. The male urethra, from 18 to 20 centimeters long, is common to both the
urinary and reproductive systems. It extends from the urethral orifice in the bladder to
the external urethral orifice at the tip of the penis and consists of three portions.
(1) The prostatic urethra, about 3 centimeters long, extends from the
urethral orifice in the bladder through the prostate gland. During coitus, secretions enter
this part from the prostate gland and also from the ejaculatory duct.
(2) The membranous urethra, about 2 centimeters long, extends from the
apex of the prostate to the bulb of the penis and perforates the perineal membrane,
about 2.5 centimeters inferior to the symphysis pubis.
(3) The cavernous urethra, about 15 centimeters long, extends from the end
of the membranous region, just below the perineal membrane, to the external urethral
orifice at the tip of the penis. It is surrounded by the corpus cavernosum of the urethra.
b. The female urethra, about 4 centimeters long, serves only in the urinary
system. It extends inferiorly from the internal urethral orifice in the bladder, perforates
the perineal membrane, and ends in the external urethral orifice located anterior to the
3-18. THE MALE REPRODUCTIVE SYSTEM
The male reproductive system consists of the gonads (testes which produce the
spermatozoa), a system of ducts and accessory glands, and the external genitalia
(penis and scrotum).
a. The Scrotum. The scrotum (figure 3-9) is an integumentary sac that contains
and supports the testes and the epididymis. It is suspended from the pubic and perineal
regions directly dorsal to the base of the penis. Essentially, it is an extension of the
abdominal wall, consisting of skin and subcutaneous tissue. A septum divides the
scrotum into the two chambers that house the testes.
b. The Testes. The testes are a pair of oval, glandular organs about 5
centimeters long, suspended in the scrotum by the spermatic cords. Each testis is
enclosed in a layer of dense, fibrous tissue from which originate fibrous sheets of tissue
that divide the testis into numerous wedge-shaped chambers (lobules). Each chamber
contains from one to three highly convoluted tubules, the seminiferous tubules. The
lining of these tubules is composed of two specialized types of cells: the spermatogenic
cells, which produce sperm, and the supportive cells (cells of Sertoli), which are thought
to provide nutrient materials for the developing sperm cells. In addition, specialized
cells (cells of Leydig) in the tissue between the tubules produce the male sex hormone
testosterone. The convoluted, seminiferous tubules from adjacent compartments join
into straight ducts that, in turn, unite with each other and form a network, the rete testis.
From 12 to 20 tiny different ducts emerge from the rete testis, penetrate its fibrous coat,
and form the beginning of the epididymis.