The secondary sexual characteristics of the male are those features designed to
One ovum is released per menstrual cycle.
The development of a germinal cell takes place within a follicle, a fluid-filled
cavity within the ovary.
At midperiod, the mature ovum is expelled from the follicle onto the surface of the
ovary and is then picked up by the uterine tube. (para 9-14b)
Initially, the cells of the ovary that form the follicle secrete the hormones called
estrogens. After the ovum has been expelled from the follicle, the resulting cavity is
filled with a yellowish material known as the corpus luteum, which secretes primarily
progesterone. This hormone prepares the uterus for pregnancy. Thus, during the first
half of the menstrual period estrogens are secreted, during the second half of the
The secondary sex organs of the female serve to transport and care for the ovum
and to develop the embryo and fetus.
The uterine tube picks up the free ovum when it is expelled from the follicle of the
ovary. The ovum stays in the uterine tube to await fertilization. If it is fertilized, it goes
through the initial stages of development as an embryo, which then passes on to the
uterus. If it is not fertilized within 3 to 5 days, its stored food is exhausted and it dies.
The embryo continues its development within the uterus, whose inner lining is
known as the endometrium. This inner lining contains uterine glands and blood vessels.
To receive the early embryo, the endometrium is developed. If there is no embryo
present at the end of the menstrual cycle, the endometrium breaks down. Thus, a
"flow" of blood and cellular elements occurs in a process known as menstruation.
When the embryo passes into the uterus from the uterine tube, it "burrows" into
the endometrium. Later, the fluid-filled amniotic sac surrounds the embryo. The
embryo floats free, surrounded by amniotic fluid. The embryo has an umbilical cord that
originates in the center of its anterior abdomen. This cord is attached to the wall of the
uterus by a special structure known as the placenta.
The circular muscle tissue in the cervix holds the opening closed until time for
parturition, when the musculature dilates to form an opening for the passage of the