A The tree testosterone reaches the target organ (T) hypothalamus and (ii) the anterior pituitary}

more available) but again spring into action at the time of puberty (because now the pituitary LH is available). There after, the Leyden cells continue to function till death although the activity progressively declines at old age Chemistry, biosynthesis Testosterone is a steroid hormone without any side chain attached to the C17 position. it is thus a C19 structure (for comparison, cholesterol is C27; bile acid C24; progesterone, corticosteroids are C21; estrogen is C18). Fig. 6. 9.4. (for DHEA see fig. 643) Cholesterol is the starting material. Cholesterol may be obtained from (he blood or may be synthesized by the Leyden cells from acetate (fig. 695) Fig.6.9.5. Major steps of biosynthesis of testicular hormone in Lending cells See also table G 4 1 = androgens N G Some androslenedione can escape into the blood and may become precursor of estrogen man Fate of testosterone After its formation, testosterone combines with a protein of plasma, called Testosterone binding globulin1 (TBG, also written, more desirably, as TeBG) and the hormone circulates in the blood in this combined form Of the circulating testosterone in blood, befoul 96% occurs in combined form (combined usually with TeBG but small amount of testosterone combines with plasma albumin also) and only about 2% is free TeBG is almost identical with ABP [androgen binding protein) secreted by the cells of Stolid. In the target cells (i e. accessory set organs, brain, liver skeletal muscles, skin) the following events happen. A The tree testosterone reaches the target organ (T) hypothalamus and (ii) the anterior pituitary} - enters within the call and performs its functions. No conversion of testosterone to dihydrotestosterone is necessary B. in some other larger organs (accessory seen organs, that is prostate, seminal vesicle, epididymis. penis and skin) the free testosterone enters the call D converted into dihydrotestosterone by en enzyme called 5 a reduces, and all the actions or the target organs are due to dihydrotestosterone For these organs, therefore, the testosterone can be viewed as the prohormone and dehydrates osterone the final hormone C In still some other area, (notably in the brain of rodents), testosterone is converted into estrogen within the Celts and actions are due to the estrogen thus formed Conversion of Testosterone into estrogen (estradiol) also occurs in man. Plasma concentrate ion of testosterone in young adult men is about 700 ng/100 ml. The concentration declines as age advances Ultimately most of the testosterone is converted by the liver into androsterone and etiocholanolone conjugates with glucuronic acid excreted via urine as glucuroindes In some tissues, testosterone is converted into estrogen Actions of testosterone For descriptive purposes, and these can be divided into two broad groups. (A)0n sex organs, secondary sex characteristics and sex behavior.. (B) On metabolism (extra genital) On the send organs I. In the fetus (a) Testosterone, as already stated, begins to be formed at around 7th week of intrauterine life Prior to the 7th week, in every fetus, both the Wolfing and Mullerian ducts e«i&l [From the Wolffian duels, epididymis, vas and seminal vesicles develop, whereasthe Mullerian duct gives rise to vagina, uterus and the Fallopian tubes] If test tosterone begins to appear, the Multerian duct system disappears and the male accessory organs appear Absence of testosterone thus causes development of the Mullerian duet into the accessory female sex organs and disappearance of the Wolffian duct. Mark, that, this means that if there is no sex hormone (i.e. . in absence of both female as well male sex hormone), the fetus develops the female sex organs (see Turner's syndrome. T 6.1.2. 1.) This means that every fetus left to itself will become a female gender unless testosterone is present from the 7th week of intrauterine life [in the Varshnava (a Hindu sect) doctrine, one fundamental teaching is that all human beings are basically females the maidenhood is merely imposed upon) This is called sex differentiation Testosterone is responsible for the say differentiation of male fetus (b) Towards the later part of muautenne lite, the exposure of the hypothalamus and some other parts of the brain testosterone in the male foelus is one of the fundamental causes of male sex behavior in adult life If the above mentioned exposure occurs, something, (the nature of which is unknown), happens and as a result, at puberty the boy begins to be attracted by the girls If the fetus is female and its mother receives testosterone (say for some treatment purposes), there rest a chance That in adult life she (i.e. the female fetus of today) would be sexually attracted to a female (homosexuals) Exposure of some parts of brain to testosterone in fetal life, therefore, determines the sexual behavior in adult life. II. In puberty (a) Testosterone causes growth of the external genitalia and accessory sex organs in the pubertal age. (b) it also causes the appearance of secondary sex characters in boys, i e . (i) beard, moustache, hairs on the chest and abdomen, as well as axillaries and pubic hairs, (ii) linear growth, (iii) muscular growth, (iv) deepening of the voice and (v) the male psyche. III. In full adults (a) Testosterone causes maintenance of the accessory sex organs (b) Testosterone also is responsible for the development of sebaceous glands and acne vegans. As during early youth, androgen secretion is maximum, acne vegans is seen very frequently in adolescents and young adults IV. Testosterone is necessary for spermatogens