The Wolffian duct structures may degenerate, and the external genitalia may be feminized. Testicular dysgenesis results in poor in utero development of the testes with concomitantly decreased secretion of testosterone and Müllerian regression factor. The Leydig cells, however, have normal function and result in normal secretion of testosterone, so that both male-type internal tracts and external genitalia develop. They may exhibit both male-type and female-type internal tracts because of the absence of Müllerian regression factor. Spermatogenesis is absent in these individuals, who also show increased plasma levels of FSH because of decreased Sertoli cell secretion of inhibin. The Sertoli-only syndrome refers to the situation in which only the Sertoli cells of the seminiferous tubules are present (germinal cell aplasia). Because of the excessive secretion of deoxycorticosterone by the adrenal cortex, these individuals are usually hypertensive. Normal secretion of Müllerian regression factor should also cause the degeneration of the Müllerian ducts. With 17a-hydroxylase deficiency, the testes cannot synthesize testosterone, resulting in feminization of the external genitalia and degeneration of the Wolffian ducts. The Müllerian ducts will also degenerate because of the normal effect of testicular Müllerian regression factor. In the absence of the androgen receptor, the Wolffian ducts will degenerate. With complete androgen resistance, the external genitalia are feminized, but neither the male-type nor the female-type internal tracts develop. If discovered after infancy, a female gender assignment can be supported with estrogen substitution therapy and prophylactic orchiectomy. If discovered early, a male gender assignment can be supported with administration of dihydrotestosterone to increase penis size. If left untreated, the affected individuals are generally phenotypic females until puberty, at which time increased amounts of testosterone result in virilization ("penis-at-twelve" syndrome). A congenital absence of 5α-reductase in these tissues will result in feminization. On the other hand, differentiation of the indifferent external genital slit into the penis, prostate, and scrotum does require dihydrotestosterone. In utero differentiation of the Wolffian ducts into the normal male phenotypic internal reproductive tract requires testosterone, but not dihydrotestosterone. It then passes between the two heads of the flexor carpi ulnaris and courses through the forearm deep to this muscle. The ulnar nerve crosses the elbow posterior to the medial epicondyle of the humerus. The radial nerve lies within the musculospiral groove along the back of the humerus, then passes between the brachioradialis muscle and the brachialis muscle at the elbow, lateral to the tendon of the biceps. It accompanies the radial artery in the musculospiral groove and then divides into the radial collateral artery and middle collateral artery, which cross the elbow lateral to the tendon of the biceps. The profunda brachii artery arises from the brachial artery in the proximal part of the arm. The remainder of the nerve is then renamed the lateral cutaneous nerve of the forearm, which passes the elbow lateral to the tendon of the biceps. The musculocutaneous nerve gives off all of its muscular branches to muscles in the arm. The musculocutaneous nerve does not cross the elbow. As the artery enters the forearm, it is covered by the bicipital aponeurosis, a broadening of the biceps tendon. The brachial artery is immediately medial to the tendon of the biceps brachii at the elbow.
0 kommentar(er)
