TESTES

1. Testes
Testes, the male gonads have two important
functions,
Production of gametes.
Synthesis of male sex hormones.
Location
In the human male, the testes are located within
the scrotal sace outside the body wall to
maintain the lower temperature necessary for
efficient sperm production.
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2. Structure
• The testes are paired ovoid bodies
covered by white fibrous connective
tissue.
• The testes is composed of up to 900
coiled seminifreous tubules, which form
sperm,and interstital cells of Leydig which
secrete testosterone.
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3. Hormones of Testes
• Male sex hormones secreted by testes are
collectively called Androgens.
• These are as follows,
• Testosterone (Principle androgen)
• Dihydrotestosterone.
• Androstenodione.
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4. Chemistry and biosynthesis of Testosterone.
Testosterone is a steroid chemically, consists of 19
carbon atoms, which is synthesized from cholesterol.
Sites of secretion
1.In fetus.
By genital ridges under the influence of male
chromosomes. (Y-chromosome) .After the 7th week of
intrauterine life,testosterone is produced by the fetal
testes under the influence of HCGH from the placenta.
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5. 2.After birth/adult. (Leydig cells)
A) None-existant in childhood.
B) Abundant in adult males after puberity.
Transport in Plasma.
• 65% of testosterone is bound to gonadal steroid
binding globulin (SBG) (Beta-globulin)
• 33% is bound with albumin.
• 2% in free form.
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6. Conversion in target cells.
Testoterone in target cells is converted into,
• Dihydrotestosterone.
• 5-alpha androstanediol.
Degradation and excretion of
testoeronr.
Testosterone that is not up taken by target cells is
converted by the liver into androsterone and
dehydroepiandrosterone and is conjugated as
glucuronides or sulfates.
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7. The conjugated products of degraded testosterone are
excreted in bile or in urine.
Mechanism of action.
Testosterone acts through gene mediator action.
Actions of Testosterone.
1. Effect on the male reproductive system.
During intrauterine life testosterone is secreted by the
genital ridge.Later on it is secreted by the placenta.At
this stage it causes the development of male sex organs
including the penis,scrotum prostate, seminal vesicle
and male genital duct.
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8. In adults testosterone is secreted by the Leydig
cells of the testes.This hormone causes the
enlargement of the male sexual organs.
• 2.Effects on secondary sex
characteristics.
Body Hairs.
• Testosterone causes increased hair growth,
• Over pubis,male patern is convex,
• On face,chest and on back.
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9. Baldness.
Decreased growth of hairs on top of the head.
Voice.
It causes hypertrophy of the laryngeal mucosa and
enlargement of the larynx.
Skin.
Increases skin thickness,secretion of sebaceous
gland and acne.
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10. 3.Effect on Testes.
Increases spermatogenesis in somniferous
tubules.
4. Effect on protein metabolism.
Testosterone increases protein synthesis, causes
positive nitrogen balance and decreases blood
urea level.
5. Effect on muscles.
Increases muscle development due to increase
protein synthesis.
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11. 6.Effect on Bone.
– Increases thickness of bones.
– Increases total quantity of bone matrice.
– Increases the deposition of calcium salts in bones.
7.Effect on male pelvis.
Increases the length of the male pelvis and makes it
funnel shaped.
8.Effect on BMR.
Increases the BMR (12-16%) due to increased
protein formation.
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12. 9.Effect on RBCs.
Increases the RBC`s count due to increase
metabolic rate.
10.Effect on water and electrolyte
balance.
Increases the water and sodium reabsorption in
distal tubules of kidneys.
11.Effect on CNS.
Increases the libido by directly acting on CNS.
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13. Regulation of Testosterone
The principle of sexual function in both males
and females depends upon the secretion of
gonado trophin releasing hormone (GnRH) by
the hypothalamus.This hormone (GnRH)
stimulates the anterior pituitary gland to secrete
two other hormones called gonadotropic
hormone, FSH and LH.LH is the primary
stimulus for the secretion of testosterone by the
testes.
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14. Psychic and nervous stimuli
GnRH(secreted by hypothalamus
Stimulates anterior pituitary gland
Secretes LH and FSH
Stimulates Leydig cells of testes
Secretes testosterone
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15. Negative feed back Inhibition
When there is an increased plasma level
of testosterone, there is negative feedback
inhibition of GnRH from the hypothalamus.
It decreases the secretion of LH from the
anterior pituitary gland ,inhibition the
secretion of testosterone by the Leydig
cells of the testes.
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