glands secrete nutrients into the uterine cavity, helping to prepare the lining for the
arrival of the fertilized egg. If the egg is fertilized, the embryo produces human
chorionic gonadotropin (HCG). Thehuman chorionic gonadotropin signals the corpus
luteum to continue to supply progesterone to maintain the uterine lining. Continuous
levels of progesterone prevent the release of FSH and ovulation ceases.
c. Additional Information.
(1) The length of the menstrual cycle is highly variable. It may be as short
as 21 days or as long as 39 days.
(2) Only one interval is fairly constant in all females, the time from ovulation
to the beginning of menses, which is almost always 14-15 days.
(3) The menstrual cycle usually ends when or before a woman reaches her
fifties. This is known as menopause.
Ovulation is the release of an egg cell from a mature ovarian follicle (see figure
1-5 for ovulation). Ovulation is stimulated by hormones from the anterior pituitary gland,
which apparently causes the mature follicle to swell rapidly and eventually rupture.
When this happens, the follicular fluid, accompanied by the egg cell, oozes outward
from the surface of the ovary and enters the peritoneal cavity. After it is expelled from
the ovary, the egg cell and one or two layers of follicular cells surrounding it are usually
propelled to the opening of a nearby uterine tube. If the cell is not fertilized by union of
a sperm cell within a relatively short time, it will degenerate.
As mentioned in paragraph 1-6c(3), menopause is the cessation of menstruation.
This usually occurs in women between the ages of 45 and 50. Some women may reach
menopause before the age of 45 and some after the age of 50. In common use,
menopause generally means cessation of regular menstruation. Ovulation may occur
sporadically or may cease abruptly. Periods may end suddenly, may become scanty or
irregular, or may be intermittently heavy before ceasing altogether. Markedly
diminished ovarian activity, that is, significantly decreased estrogen production and
cessation of ovulation, causes menopause.
Section II. THE MALE REPRODUCTIVE SYSTEM
a. The male reproductive tract consists of external genitals and internal organs.
These organs are located in the pelvic cavity (see figure 1-8). The male's reproductive
system begins to develop in response to testosterone during early fetal life. Essentially