Antidiuretic hormone (ADH), vasopressin).
(a) Blood pressure. If large amounts of ADH are injected into an
animal, the arterial pressure rises appreciably.
(b) Renal tubule effect. This hormone increases the permeability of the
collecting tubules to water. Without ADH (diabetes insipidus), a person will lose large
amounts of water from the body fluids, but retain the electrolytes. In the presence of
ADH, a person keeps most of the water in the body, but loses more electrolytes. ADH
keeps the body fluid diluted and a lack of this hormone concentrates the body fluids.
(a) Contraction of uterus. Oxytocin in sufficient quantity causes the
uterus to contract and is, therefore, responsible to a large degree for initiating labor and
(b) Milk ejection. Suckling stimulates the release of oxytocin which, in
turn, starts the flow of milk.
a. Ovaries (Female). The ovaries, located in the pelvic cavity, secrete
estrogens and progesterone. Estrogens are also secreted by the adrenal cortex and,
during pregnancy, in very large amounts by the placenta.
(1) The main function of estrogens is to promote cellular proliferation and
growth of the sexual organs and other reproductive tissues. Estrogens cause the
endometrium (lining of the uterus) to thicken, and they play an essential role in the
regulation of the menstrual cycle. Estrogens produce the secondary sex characteristics
of females: enlargement of the uterus and vagina, growth of pubic hair, development of
mammary glands, development of the pelvic girdle, and deposition of fat in the mons
pubis and labia majora.
(2) Progesterone is secreted by the corpus luteum, and during pregnancy,
by the placenta. The corpus luteum is a glandular mass formed in an ovary when a
follicle discharges its ovum. If the ovum is impregnated, the corpus luteum increases in
size and lasts for several months. Without pregnancy, the corpus luteum actively
secretes for only about 14 days. The function of progesterone is primarily to provide
adequate nutrients for an embryo if it should begin to develop. During pregnancy, it
maintains the placenta, prevents further ovulation, enlarges the breasts, and stimulates
the development of milk-secreting cells in the mammary glands.