Download Lecture #13 Sex Differentiation

Lecture #13 Sex Differentiation
1. Which parent determines sex?
2. From what embryonic tissue, do the gonads develop from?
3. When does sexual differentiation occur in embryonic life? A. Describe male
sexual differentiation. B. Describe female differentiation.
4. What are some factors that may be involved in testis differentiation?
5. Since the 6th week is crucial for sexual development, there is a chance
that things don’t go right. What are some example of disorders of sex
differentiation with normal chromosomal complement? With an abnormal
complement?
6. The CNS plays an important role in sex differentiation. Please describe the
effects of neonatal androgens on the CNS in males and females.
Answers to Lecture #13
1. The father through an X or Y sperm will determine sex of the fetus.
2. The primordia of the gonads and gondal ducts arise from a thickening of
mesodermal tissue. Anatomically, this occurs below the kidney primordial.
The tissue is undifferentiated and can give rise to either male or female
genitalia depending on specific stimuli.
3. Sex Differentiation occurs at the 6th week of development.
a. In the male, the Y chromosome will code for the H-Y antigen which
will stimulate the bipotential gonad to differentiate into a testis.
The testis will start to secrete testosterone from the Leydig cells.
The Wolferian ducts develop into the male secondary sex organs.
The Mullerian ducts regress under the influence of Mullerian
Inhibiting Substance (MIS) secreted by Sertoli cells. The
testosterone will convert into dihydrotesterone (DIT) which will
induce male external genital differentiation.
b. In the female, there is no sex responsible gene (SRY). The default
for the bipotential gonad is to become an ovary. In the absence of
MIS and T, the Wolffian ducts regress and the Mullerian ducts
become the female secondary sex organs and external genitalia.
4. Some factors involved may include H-Y antigen, testis determining factor
(TSF), the “Zinc Finger” protein on Y and several other Y – chromosomal
genes.
5. A. With normal complement of chromosomes, pseudohermaphroditism
may occur. In the female, this may occur because of abnormal levels of
androgens in the mother, a virilizing adrenal or ovarian tumor or
treatment with androgens and progestins. In the male, this may occur
with androgen resistance, defective testicular development, congenital
steroid enzyme deficiency.
B. With an abnormal complement, we may see Ovarian dysgenesis (XO) or
Turner’s Syndrome in women or Seminiferous tubule dysgenesis or
Klinefelter’s Syndrome (XXY) in men. In women may see superfemales (XXX
or even XXXX) and men supermales XYY (I checked on this – it does exist).
Or in the rarest case, we see true hermaphrodites who are mosaics and have
both functional sets of sex organs.
6. In males, androgen stimulate presence of larger (than females) nucleus of
the pre-optic area (SDN-POA) in the hypothalamus, a larger spinal nucleus
of the bulbocavernosus muscle and male sexual behavior.
In female, androgens are still important because they stimulate the
development of smaller SDN-POA and SNB muscles. Female sex behavior
will also appear including lordosis.