Male sex hormone-Biochemical forms and functions
Learning Objectives
At the end of the lecture the student should be able to know the
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Different male sex hormones
Site of synthesis
Functions and site of actions
Effects of these hormone
Sex Steroids
Site of synthesis
• Gonads
• Adrenal Cortex
Androgens
IMPORTANT ANDROGENS
Androstenedione
Dehydroepiandrosterone
Testosterone
Dihydrotestosterone
Androstenedione
• 19-carbon steroid hormone
• Adrenal glands and the gonads
Androstenedione
• Common precursor of male and female sex
hormones
• May be converted in peripheral tissues to
testosterone and estrogens.
Androstenedione
• Conversion of androstenedione to testosterone
requires
17β-hydroxysteroid dehydrogenase
Androstenedione
• Conversion of androstenedione to estrogen
requires
Aromatase
5-Dehydroepiandrosterone
• Major secretary steroidal product of the adrenal glands
• Dehydroepiandrosterone sulfate (DHEAS)
- The sulfated version of DHEA
- Conversion reversibly catalyzed by
sulfotransferase
Testosterone
• Secreted by testes
• The principal male sex hormone
• An anabolic steroid
Testosterone
• Development of male reproductive tissues
- Testis
- Prostate
• Promotes secondary sexual characteristics
Testosterone
• Testosterone effects can be classified as
- Virilizing
- Anabolic
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Testosterone
Anabolic effects
Growth of muscle mass and strength
Increased bone density and strength
Stimulation of linear growth
Bone maturation
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Testosterone
Androgenic effects
Male secondary sex characteristics
Maturation of the sex organs
Usually at puberty
Deepening of the voice
Growth of the beard and axillary hair
Testosterone
Prenatal Effects
• Genital virilization
• Development of prostate and seminal vesicles
Testosterone
Pubertal Effects
• Enlargement of sebaceous glands
• Pubic hair extends to thighs and up toward umbilicus
• Facial hair (sideburns, beard, moustache)
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Testosterone
Pubertal
Loss of scalp hair (Androgenetic alopecia)
Leg hair
Axillary hair
Increased muscle strength and mass
Testosterone
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Adult-type body odour
Increased oiliness of skin and hair, acne
Pubarche (appearance of pubic hair)
Axillary hair
Growth spurt, accelerated bone maturation
Hair on upper lip and sideburns
Testosterone
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Deepening of voice
Growth of the Adam's apple
Growth of spermatogenic tissue in testicles
Completion of bone maturation and termination of growth
Testosterone
Adult
Necessary for normal sperm development
Activates genes in Sertoli cells
- promote differentiation of spermatogonia
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Dihydrotestosterone
Synthesized in
Prostate gland
Testes
Hair follicles
Adrenal glands
Synthesized by
5α-reductase
Dihydrotestosterone
• DHT has greater affinity for androgen receptors than testosterone
and adrenal androgens
• More potent
• Primary contributing factor in male pattern baldness
Dihydrotestosterone
• During embryogenesis
- essential role in the formation of the male external genitalia
• In adult
• - acts as the primary androgen in the prostate and hair follicles
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