The embryo continues its development within the
, whose inner lining is
known as the
m. This inner lining contains
e glands and blood
vessels. To receive the early embryo, the endometrium is d
d. If there is no
embryo present at the end of the menstrual cycle, the
m breaks down.
Thus, a "flow" of blood and cellular elements occurs in a process known as
When the embryo passes into the uterus from the uterine tube, it "burrows" into
. Later, the fluid-filled
c sac surrounds the embryo. The
embryo floats free, surrounded by
c fluid. The embryo has an
cord that originates in the center of its anterior
n. This cord is attached to the
wall of the uterus by a special structure known as the
The circular muscle tissue in the wall of the cervix holds the opening closed until
n, when the musculature d
s to form an
g for the
passage of the
n to be.
After the vagina receives the male penis, the semen is discharged into the upper
recess opposite the opening of the
x. At parturition, the vagina forms the
l through which the newborn passes to the outside.
The openings of the vagina and urethra are covered by the external
The secondary sexual characteristics of the female are those features designed
to make a female
ve to the male.
When the female bony pelvis "relaxes" for childbirth, the ligaments of the
m become quite stretchable. This increases the
s of the birth canal.
The mammary glands respond to the estrogens and progesterone with
h. Towards the end of the pregnancy, the breasts begin to form a
m. Within 2 to 3 days after the birth, the breasts begin to
secrete large quantities of
Human milk is the natural
of the newborn infant.
Accompanying nursing, for both the child and the mother, are strong
Initially after childbirth, the mammary gland secretes
most importantly of
s, which protect the infant during the first 6
s of life.