Functions of Testosterone Secretion Testes produce several male

Functions of Testosterone

Secretion • Testes produce several male hormones (Androgens) – – – • • • Testosterone Dihydrotestosterone Androstenedione Testosterone – most abundant Dihydrotestosterone is the most active form Most of the testosterone also, is converted into dihydrotestosterone in the tissues Produced in Interstitial cells of Leydig Constitute 20 % of the testicular mass

Interstitial cells of Leydig

Interstitial cells of Leydig • Almost nonexistent in childhood – No testosterone secretion throughout childhood because of absence of LH • Numerous in new born babies due to HCGH • If germinal epithelium degenerates due to heat, x-rays etc ICL survive and still produce testosterone.

Testosterone • Responsible for distinguishing masculine characteristics • HCGH stimulated intrauterine secretion→ Development of male fetus • No testosterone throughout childhood • Near puberty LH from anterior pituitary → gradually increasing levels of testosterone • Declined secretion after 50 years of age • Secretion continues throughout life

Stages of testosterone secretin

Intrauterine functions • Secreted from genital ridge or developing testes due to HCGH • Y chromosome causes secretion of testosterone from the genital ridge • X chromosome causes secretion of estrogen from the genital ridge • Simply presence or absence is responsible for male or female external genitalia in the fetus.

BASIC INTRACELLULAR MECHANISM OF ACTION OF TESTOSTERONE § • • • Testosterone 5α-reductase Dihydrotestosterone binds with a cytoplasmic “receptor protein” --cell nucleus-- nuclear protein -- DNA-RNA transcription-- within 30 minutes-- RNA polymerase activated –Increase in cellular proteins—DNA increase afer several days

Development of male fetus • Intrauterine testosterone responsible for development of – – Penis & Scrotum Prostate gland Seminal vesicles Wolffian duct system give rise to male tubular system • Testosterone suppresses development of female genital organs • Müllerian duct system disappears

Descent of testes • Testes develop from the genital ridge in the genital region • Testes descend into scrotum through inguinal canal • Testosterone required for this descent • Cryptorchidism may be treated with administration of testosterone in neonates

Functions at puberty • Enlargement – Penis – Scrotum – Testes • Development of secondary sex characters of male – Apparent differences of male from female

Distribution of hair • Growth of hair – – On face (beard & mustaches) Over the pubis Along the linea alba Usually on the chest, legs and other parts of the body • Baldness – Genetic back ground – High testosterone level – ↑↑Testosterone even in female can cause baldness Baldness

Voice • Testosterone causes – Enlargement of larynx – Hypertrophy of laryngeal mucosa and vocal cords – Initially cracking voice – Later voice changes into typical masculine voice

Skin • • • ↑ thickness of the skin ↑ruggedness of SC tissue ↑ rate of secretion of sebaceous glands ↑ secretion on the face → Acne very common after puberty Acne disappear due to gradual adaptation of sebaceous glands and skin

Proteins • Powerful anabolic hormone • Deposition of protein in muscles • Deposition of protein in nonmuscular tissues as well • Male musculature is 50 % more than female • Athletes use synthetic androgens to improve muscular performance • May be used in elderly people to improve muscle strength

Bones • • ↑Deposition of protein in bones ↑matrix as well as calcium deposition ↑ thickness and strength of the bones Male bones are much more stronger than female ↑ growth in length of the bone near puberty Disappearance of epiphyseal cartilage Eunuchs have more height than normal male or female

Special changes in pelvis • • • Narrow pelvic outlet Elongated and Funnel shaped pelvis More load bearing type Female pelvis is broad and ovoid If testosterone is absent the male pelvis is also female like

BMR & RBC count • ↑ BMR • More oxygen consumption in male compared to female • BMR 15 % more than female • May be an indirect effect of protein anabolism caused by testosterone • ↑O 2 consumption → relative hypoxia → renal erythropoietic factor → ↑erythropoiesis • ↑ RBC count may be due to direct effect on erythropoiesis

Water and electrolytes • All the steroid can – ↑ Na+ and other electrolytes reabsorption from the kidney tubules – Secondary reabsorption of water

Regulation of Testosterone secretion and reproductive functions

Hypothalamo hypophyseal feedback control • Hypothalamic hormone – Gonadotropin releasing hormone (Gn. RH) • Hypophyseal gonadotrophic hormones – Follicle stimulating hormone (FSH) • Controls spermatogenesis – Luteinizing hormone (LH) • Also called as Interstitial Cells Stimulating Hormone (ICSH) • Stimulates testosterone secretion

Hypothalamo hypophyseal feedback control • Gn. RH – – – 10 AA peptide Arcuate nuclei of hypothalamus Nerve endings in median eminence Hypothalamo-hypophyseal portal vessels Intermittent (cyclic) release of Gn. RH • A few minutes release after every 1 -3 hours • Variations in frequency of release • Variations in quantity released in each cycle – LH secretion has similar cyclic release – LHRH

Hypothalamo hypophyseal feedback control • LH and FSH – Glycoprotein in nature – Produced by gonadotropes in adenohypophysis – LH cyclic release according to cyclic fluctuations of Gn. RH- exactly follows – FSH also increases or decreases with the fluctuations in Gn. RH- more slowly – Gn. RH also called as LH-releasing hormone (LHRH) – Without Gn. RH no secretion of LH & FSH

Regulation of testosterone secretion • • • Interstitial cells of Leydig LH stimulates secretion of testosterone ICL present in new born babies Absent throughout childhood At puberty when LH secretion starts ICL develop again • Testosterone has negative feed back effect on LH secretion

Negative feedback control • ↑Testosterone inhibits – Hypothalamus – arcuate nuclei →↓ Gn. RH – Adenohypophysis – gonadotropes →↓ LH & FSH • ↓ Testosterone stimulates – Hypothalamus – arcuate nuclei → ↑ Gn. RH – Adenohypophysis – gonadotropes →↑ LH & FSH

Regulation of spermatogenesis • FSH –receptors in Sertoli cells – Cells enlarge – Produce substances necessary for spermatogenesis – Testosterone also increases spermatogenic activity – Sertoli cells produce hormone “Inhibin” • A glycoprotein • Has been extracted from the Sertoli cells – Inhibin inhibits FSH and Gn. RH

Hypothalamo hypophyseal feedback control

Psychic element • Different signals from different part of the brain affect Hypothalamic release of Gn. RH • Psychic factors from limbic system greatly affect the hypothalamic secretion of Gn. RH – Hence secretion of LH and FSH

Puberty • Gradual onset of secretion of sex hormones and the reproductive life • Before puberty – – No secretion of Gn. RH No secretion of LH & FSH No testosterone and spermatogenesis Hypothalamus is hypersensitive to smallest amount of circulating sex hormones – This hypersensitivity gradually reduces – Or maturation process of limbic system or hypothalamus → onset of puberty

Adult sexual life and male climacteric • After puberty LH & FSH are produced throughout life • After late 40 s or 50 s there is reduction in testosterone level • The decrease in sexual functions in elderly male is called male climacteric. • Sometimes symptoms like female menopause (hot flushes, psychic sensation of dyspnea, irritability, fatigue, anxiety etc) may need treatment with testosterone

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