The testis is the primary sex organ (gonad) of the male a. Location. Each male has a pair of testes located within the scrotum. The scrotum is a sac suspended from the inferior end of the trunk, between the thighs. Each testis is within a separate serous cavity within the scrotum.
(1) Migration. Originally, testes develop within the posterior abdominal region of the body. However, during development, they "migrate" out of the body cavity, through the inguinal canal of the abdominal wall, and into the scrotum.
(2) Temperature control. For the production of mature sperm (spermatozoa), the testes must be at a temperature that is a few degrees lower than that of the body cavity. For this reason, the testes are located outside of the body cavity.
(a) Under cold conditions, each testis is pulled up toward the body by the cremaster muscle. At the same time, the dartos muscle of the scrotal wall contracts and thus reduces the exposed surface area and thickens the wall.
(b) Under warm conditions, these structures are "relaxed." This allows the scrotum with the testes to hang free.
(c) If a boy baby is born with undescended testes (either in the abdominal cavity or inguinal canal) and if nothing is done to bring the testes into the scrotum, he will be sterile.
b. Production of Spermatozoa. Millions of spermatozoa (male gametes) are produced by the seminiferous tubules of the testis.
SEMEN = seed
FER = to carry
In general, the secondary sex organs of the male are responsible for the transport and care of the spermatozoa.
a. Epididymis. The spermatozoa pass from the seminiferous tubules into the tubular structure known as the epididymis. The epididymis is a very long tube, but it is coiled and attached to the surface of the testis in the scrotum. As the spermatozoa pass along the length of the epididymis, they are nurtured by the secretions of the epididymal wall. During this passage through the epididymis, the spermatozoa become mature functioning gametes. They remain in the epididymis until "called for."
b. Ductus (Vas) Deferens. During sexual excitement, the spermatozoa leave the epididymis and are carried by another duct known as the ductus deferens. The ductus deferens passes through the inguinal canal, enters the body cavity, and turns into the pelvic cavity.
c. Seminal Vesicle. At the posterior surface of the prostate gland, the ductus deferens is joined by another duct called the seminal vesicle. The seminal vesicle is also a long tubular structure, but it is coiled up into a small mass at the back of the prostate gland. The seminal vesicle produces a nutrient fluid that helps to maintain the spermatozoa.
d. Ejaculatory Duct. On each side, as the ductus deferens and seminal vesicle join, they form a single tube on the same side, called the ejaculatory duct. Each ejaculatory duct, left and right, carries the seminal vesicle secretion and spermatozoa through the substance of the prostate gland. Each ejaculatory duct empties into the prostatic urethra.
e. Prostate Gland. The prostate gland is located in the pelvic cavity immediately under the urinary bladder. The urethra of the urinary system passes through the substance of the prostate gland, where it is known as the prostatic urethra. The prostate gland also adds a secretion. Altogether, the combination of secretions and spermatozoa is known as the semen.
f. Urethra. In the male, the urethra is common to both the urinary system and the reproductive system. At different times, it carries either the urine or the semen.
(1) As already mentioned, the initial part of the urethra passes through the prostate gland and is called the prostatic urethra.
(2) Immediately below the prostate gland, the urethra passes through the perineal membrane. Here, it is surrounded by the external urethral sphincter. This short section of the urethra is called the membranous urethra.
(3) That portion of the urethra passing through the penis (discussed below) is known as the penile urethra.
g. Penis. The penis is a structure attached to the pubic arch of the bony pelvis and to the underside of the perineal membrane. It is an external structure of the male genital system, which is capable of enlargement and stiffening (erection).
(1) The most favorable position for the deposit of semen (spermatozoa) is the upper recess of the vagina. This is opposite the opening of the cervix of the uterus. For this purpose, the penis is inserted into the female vagina ("sheath").
(2) Covering the glans ("head") of the penis is a fold of skin called the prepuce. In many cultures, the prepuce is removed shortly after birth in the procedure called circumcision. At the base of the glans, there are glands that secrete a lipid-like material called smegma. Thus, there is a need for continual cleanliness.
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