HUMAN REPRODUCTION - THE MALE REPRODUCTIVE SYSTEM
The Scrotum - A loose out pouching of the pelvic cavity, it
contains
the testes. Internally, it is divided by a partition, the septum.
Each compartment contains a testis. The lower temperature of the scrotum
(3 F < body temp,) is necessary for the production of sperm. The
cremaster muscle regulates the distance between the pelvic cavity and
the testis, In cold weather, the muscle pulls the testes closer. In warmth,
the muscle relaxes.
The Testis develops in the upper posterior abdominal wall.
It
enters
the scrotum through the inguinal canal by 32 weeks of gestation and are fully descended at birth.
Undescended testes or cryptorchidism results in sterility but can
be
corrected by surgery just before puberty.
Sperm form in the semeniferous tubules by meiosis or
spermatogenesis. Spermatogonium (male stem cells) divide
to form primary spermatocytes. During the
first meiotic division, The primary spermatocyte divides to form two secondary
spermatocytes. Each of these cells has half the chromosome number (23)
found in the primary spermatocytes (46). The secondary spermatocytes
divide to form 4 spermatids. Each of the spermatids develops into a
spermatozoan. After leaving the testis, the sperm spend some time in the
epididymus to mature. During ejaculation, the sperm leave the epididymus
and enter the vas deferens for passage to the urethra.
Sustentacular cells in the
tubules nourish the developing sperm.
Testosterone - The principle male hormone. Clusters
of cells between the semeniferous tubules, the interstitial tissue, produces the
hormone testosterone.
1. Controls the development and growth of male sex
organs,
2. Stimulates bone growth and protein anabolism.
3. Stimulates sexual behavior, final sperm maturation
and male secondary
sex traits, e.g., muscular and skeletal growth, body hair, enlarged
thyroid
cartilage (Adam's Apple) and descent of testes just prior to birth.
Accessory Glands - Secrete the liquid portion of semen.
1. Seminal vesicles - Secrete an alkaline, viscous fluid rich in fructose
into the ejaculatory duct, This fluid increases sperm viability and
makes up about 50% of the volume of semen,
2. Prostate gland - Secretes an alkaline fluid
into prostatic urethra.
This fluid makes up 13 to 33% of semen. It contributes to sperm
motility.
3. Bulbourethral glands - Secrete mucous for
lubrication and a neutral-
izing substance for urine. Their ducts open into the spongy urethra,
Semen - Composed of the fluids of the above glands and
spermatozoa.
1. Slightly alkaline ( 7.35 to 7.5)
2. Contains an antibiotic-like substance,
seminal plasmin, which is
effective against microbes of the urethra and female reproductive
tract.
Erection of the Penis - Under the influence of the Autonomic
Nervous Svatem
1. Arteries supplying penis dilate. This
brings in a large quantity of blood to
engorge three cylindrical blood spaces.
2. The veins are compressed by the expansion of
the blood spaces so that
the arterial blood is trapped in the penis maintaining the erection.
These Events are under the control of the
Parasympathetic Nervous System.
Ejaculation of Semen
1. A smooth muscle sphincter at the base of the
urinary bladder closes
due to higher pressure in urethra from expansion of blood spaces in
penis.
This prevents urine from being expelled during ejaculation and semen
from entering the urinary bladder.
2. Arteries constrict removing pressure from
veins. The penis returns to
its flaccid state.
These events are under the control of the
Sympathetic Nervous System