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Dr.Sajida Lec: 9
The male reproductive system
Consists of the paired testes, the reproductive tract and the external genitalia.
Anatomy
The testis composed of 900 coiled seminiferous tubules, each average more
than 5 meters length in which the sperms are found. Between the
seminiferous tubules are the interstitial cells of leydig for synthesis of
testosterone. The sperms pass from the seminiferous tubules to the
epididymis which is coiled and about 6 meters length, this leads to the vas
deferens which enlarges into the ampulla before entering into the prostate
gland. The seminal vesicles are two, one located on each side of the ampulla,
empties into the prostatic end of the ampulla and the contents from the
ampulla and seminal vesicles pass into the ejaculatory duct leading to
urethra.
The testes serve three main functions:
1- Production of gametes.
2- Secretion of hormones that cause differentiation of the brain and
reproductive tract during fetal and neonatal development, maintain the
structure and function of the reproductive tract, it promotes the
development of sexual characteristics.
3- Feedback regulation of the hypothalamus –pituitary hormones
secretion.
The seminiferous tubules are lined with sertoli cells and the spermatogonia.
The sertoli cells are linked by tight junctional complexes to form the sertoli
cells barrier which limits the movement of fluid and nutrients between
interstitial space of the testis and the lumen of seminiferous tubules, lipid
soluble substances such as steroids (androgen) are able to traverse the barrier
and enter the lumen of the seminiferous tubules, the barrier prevent the
penetration of immunoglobulin that might interfere with the development of
spermatozoa.
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Sertoli cells have many functions:
1- Provision of nutrients to germ cells.
2- Synthesis of multiple proteins that are secreted into the luminal fluid
including caeruloplasmin, acidic glycoprotein and transferrin.
3- Synthesis of estrogen.
4- Production of androgens binding protein (ABP).
5- Phagocytosis of damaged germ cells.
6- Synthesis and secretion of inhibin.
Inhibin
Is a protein that selectively inhibits the synthesis and secretion of FSH by the
pituitary gonadotropes.
Androgen binding protein
Is protein that binds androgens. It is found both in the luminal fluid and
plasma. ABP is concentrated in the luminal fluid and in the epididymis and
its role is to carry testosterone within the sertoli cells and from the testis to
the epididymis in order to maintain high testosterone concentration.
Estrogen
The principle estrogens in the plasma of adult males are estradiol and
estrone, only 10%-20% of the circulatory estrogens are synthesized by
sertoli cells in the testis, the remainder originate through the extra gonadal
conversion of testosterone and androstenedione.
Interstitial cells of leydig
The principal function of leydig cells is to produce androgens. Leydig cells
begin to secrete androgens during the 7
th
week of fetal life in response to
hCG (human chorionic gonadotropin) which is produced by the placenta.
During childhood when gonadotropin secretion is low, the leydig cells
regress. When plasma LH levels rise again at puberty, the leydig cells
differentiate again and secrete steroids.
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Androgen
Androgenic steroid hormones are the male sex hormones, their function are:
1- Differentiation of the male reproductive tract and brain during fetal
life.
2- Stimulation of the testis descend during the last three months of
gestation.
3- Stimulation, maturation and maintenance of reproductive tract.
4- Maintenance of spermatogenesis in adult testis.
5- Negative feedback regulation of LH secretion by the pituitary.
Androgens also stimulate development of male secondary sex
characters including:
1- Growth of facial, chest, axillary and pubic hair as well as hair
recession and balding.
2- Hypertrophy of the laryngeal mucosa causing enlargement of the
larynx and deepening of the voice.
3- Development of increased musculature due to increased protein
deposition and nitrogen retention.
4- Enhancement of linear growth through stimulation of bone growth.
5- Androgens are very potent anabolic hormone that accelerate
metabolism.
6- Increase thickness of skin over entire body and increase the rate
sebaceous glands result in (acne).
7- Increase the total quantity of bone matrix and cause calcium retention,
it causes narrowing of pelvic outlet and causes funnel like shape
pelvis and increases strength of pelvis for load bearing.
8- Testosterone increases RBC count so adult male have 700000 RBCs
more than in female.
9- Testosterone causes sodium reabsorption from kidney tubules.
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