Testosterone Dr. Hazrat Bilal Malakandi DPT (IPMR KMU), MSPT* (KMU)

Objectives of lecture Nature & Site of secretion of testosterone Mechanism of Production of testosterone Conversion & degradation of testosterone Functions of testosterone Regulation of testosterone

Nature –Steroid Sites of secretion –In fetus By genital ridges under influence of male chromosome Y (7 th Week) Later by fetal testis under influence of HCGTH from placenta –Leydig cells After birth

Mechanism of Production In adults –Nervous stimuli  stimulate hypothalamus which secrete Luteinizing-hormone-releasing hormone (LHRH)  stimulate ant. pituitary gland  secrete LH & FSH  stimulate Leydig cells  secrete testosterone

Cont … In fetus Human chorionic gonadotropin from placenta  causes Leydig cell formation in testis  testosterone secreted.

Conversion in target cells Testosterone in target cells is converted into –Dihydrotestosterone (more active form) –5-alpha-abdrostanediol Some actions of testosterone depend upon this conversion, while others do not.

Degradation and Excretion Testosterone that is not up taken by the target cells is degraded by liver into –Androsterone –Dehydroepiandrosterone Conjugated as –Glucoronides or –Sulphates Conjugated products of degraded testosterone are secreted in bile or in urine.

Functions of testosterone 1. In fetus –Causes development of penis, scrotum, prostate, seminal vesicle and male genital duct –Suppresses formation of female genital organs in male fetus –Causes decent of testis through inguinal canal into the scrotum during last two months of gestation.

Cont …. 2. Secondary sexual characters –Characters of body which make their appearance under influence of sex hormones at puberty are called secondary sexual characters In male they include Baldness: testosterone causes decrease hair growth on top of head, producing baldness.

Cont …. Body hairs: Testosterone causes increase hair growth –Over pubis –Upward along linea alba –On chest, face and back Voice: testosterone causes hypertrophy of laryngeal mucosa and enlargement of larynx which causes typical male bass voice.

Cont …. 3. on testis Increase spermatogenesis 4. On protein metabolism Increase protein synthesis 5. On muscles Increase muscle development due to inc. protein synthesis 6. On bones Increase bone thickness due to –Increase total quantity of bone matrix –Increase deposition of calcium salts in bone

Cont …. 7. On male pelvis Narrow pelvis outlet & lengthen it Causes it funnel shaped Increase the strength of pelvis for load bearing 8. Other functions Increase RBC count Increase Na and water reabsorption in distal tubules of kidney

Regulation of Testosterone Negative feedback inhibition –Excess testosterone secreted by leydig cells  negative feedback inhibition of LHRH secretion by hypothalamus  inhibits LH secretion by ant pituitary gland  inhibit testosterone by Leydig cells