bio1120_human_sex_hormones 2/25/04
BIOL 1120 REEDER
SEX HORMONES AND OTHER REPRODUCTIVE PROCESSES
Male Sex Hormones: as a group, the male sex hormones are termed androgens and they include substances
produced by the adrenal cortices and the testes. Among the androgens, testosterone is by far the most important.
It is produced and secreted by interstitial cells of the testes under the influence of LH (also called ICSH in the
male). Although FSH stimulates primary spermatocytes to undergo meiosis in process of spermatogenesis, sperm
cells do not mature completely unless testosterone is present.
Testosterone is also responsible for secondary sexual characteristics which include:
1) Enlargement of penis, scrotum, prostate gland, seminal vesicles, Cowper's gland, and the testes.
2) Increased growth of body hair, particularly on face, chest, axilla (underarms), and pubic region.
3) Enlargement of larynx and thickening of vocal cords, accompanied by development of a lower-pitched
voice.
4) Thickening of the skin.
5) Increased muscular growth accompanied by development of broader shoulders.
6) Thickening and strengthening of bones.
To summarize, under influence of FSH, the testes of a male child first begin to produce sperm cells, and under
influence of LH, the interstitial cells produce and secrete testosterone; GRH (release hormone) from
hypothalamus influences the release of FSH and LH from anterior pituitary.
Puberty: secondary characteristics begin to appear between ages 10 and 11 with gamete production beginning
between ages 15 and 17 average.
The concentration of testosterone in the male body is regulated so that it remains relatively constant from day to
day (Negative-feedback System). As concentration of testosterone in blood increases, hypothalamus becomes
inhibited, thereby stimulation of anterior pituitary is decreased. As pituitary's secretion of LH is decreased, the
amount of testosterone is reduced also, and vice-versa.
Female Sex Hormones: The hypothalamus releases GRH which in turn stimulates anterior pituitary to release
FSH and LH (gonadotropins). Although several different female sex hormones are secreted by various tissues,
including the ovaries, adrenal cortices, placenta and embryonic tissues (during pregnancy), these hormones
belong to two major groups that are referred to as the estrogens and progesterones.
The primary source of estrogen (in nonpregnant female) is the ovaries, and it corresponds in its effects to
testosterone in the male. Development and maintenance of secondary sexual characteristics by estrogen include:
1) Enlargement of vagina, uterus, uterine tubes, ovaries, and external reproductive organs.
2) Growth of the breasts and development of ductile system of mammary glands.
3) Increased deposition of adipose tissue in subcutaneous layer particularly in breasts, thighs, and buttocks.
4) Increased vascularization (blood vessel growth) of the skin.
Other changes that occur in female at puberty seem to be related to androgen concentration secreted by the
adrenal cortices and ovaries. These are increased growth of hair in pubic and axillary regions. On the other hand,
the development of the female skeletal configuration, which includes narrow shoulders and broad hips, seems to
be related to a lack of androgen.
Puberty: secondary sexual characteristics begin to appear between ages 8 and 9 due to androgen release (pubic
and axillary hair, breast size increases noticeably); at age 12, menarche occurs with the first ovulation at 6-9
months later.
The ovaries are the primary source of the gestatory hormone progesterone (in a nonpregnant female). The effects
of this hormone are related mainly to changes that occur in the uterus during the rhythmic reproduction cycles
(preparation of the endometrium for implantation of a fertilized ovum and the mammary glands for milk
secretion)
