how spermatogenesis takes place and how are the sperms transported also explain hormonal control
Paired testes
are male reproductive organs (gonads).
Scrotum:
Shortly after
birth the testes descent from abdominal cavity into the scrotum (a leather
pouch for arrous) which hangs between the thighs. The temperature inside the
scrotum is about 34°C composed to 36°C core temperature. Lower temperature is
necessary for active sperm production and survival. Muscles elevate or lower
the testes, depending on outside air temperature.
Testis:
Each testis
contains over eight hundred tightly coiled seminiferous tubules which produce
thousands of sperms each second in healthy young man. The walls of the
seminiferous tubules are lined with two types of cells.
(1)
Spermatogenic cells which give rise to sperms and
(2)
Sustentacular cells which nourish the sperm and also secrete a fluid (also
hormone inhibin) into the tubules to provide a liquid medium for the sperm.
Between
seminiferous tubules are clusters of endocrime cells called interstitial cells
(leydig cells) that secrete the male sex hormone the testosterone.
Duct system:
A system of
tubes carries the sperm that the testes produce to the penis. Seminiferous
tubules merge into a network of tiny tubules called the rete testis which
merges into a coiled tube called epididymis which has three functions:
(1) It stores
sperms until they are mature and ready to be ejaculated.
(2) It contains
smooth muscle that helps propel the sperm toward the penis by peristaltic
contractions and
(3) It serves as
a duct system for sperm to pas from the testis to the ductus deferens which is
dilated continuation of epididymis. Continuing upward after leaving the
scrotum, ductus deferens passes through lower part of abdominal wall via
inguinal canal. The ductus deferens then passes around the urinary bladder and
enlarges to form ampulla. The ampulla stores some sperms until they are
ejaculated. Distal to the ampulla the ductus deferens becomes the ejaculatory
duct. The urethra is the final section of reproductive duct system.
Accessory
glands:
They add their
secretions to the sperm as they are propelled through the ducts. Paired seminal
vesicles secrete water, fructose, prostaglandins and vitamin C. This secretion
provides an eargy source for the motile sperm and helps to neutralize the
natural protective acidity of vagina (pH of vagina is about 3 to 4 , but sperm mutility and fertility are enhanced when it increases to
about 6). The prostate gland secretes water, enzymes, cholesterol, buffering
salts and phospholipids.
Bulbourethral
glands secrete a clear alkaline fluid that lubricates the urethra to facilitate
the ejaculation of semen and lubricates the penis prior to sexual intercourse. The
fluid that results from the combination of sperm and glandular secretions is
semen. Penis carries urine through urethra to outside during urination. It also
transports semen through urethra during ejaculation.
Penis contains strands
of erectile tissue corporex cavernosa and corpus spongiosum. Tip of Penis is
covered by prepuse.
Hormonal control
of male organs:
Male sex
hormones are collectively called androgens. Interstitial cells produce male sex
hormones testosterone. When level of testosterone in the blood decreases, the hypothalamus
is stimulated to secrete GnRH (Gonadotropin releasing hormone). GnRH stimulates
the secretion of FSH (follicle stimulating hormone) and LH (luteinizing
hormone) into blood stream. FSH causes spermatogenetic cells in the
seminiferous tubules to initate spermatogenesis and LH stimulates the
intersticial cells to secrete testosterone. The cycle is complete when
testosterone inhibits the secretion of LH and another hormone inhibin is
secreted. Inhibin inhibits the secretion of FSH from anterior pituitary. This
cycle maintains a constant rate of spermatogenesis.
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