Page 91 - 86 human physiology part-2

Chapter 16

Cervix Clinical Application:
Pelvic inflammatory disease (PID) is a
The cervix (from Latin "neck") is the lower, narrow portion widespread infection that originates in
of the uterus where it joins with the top end of the vagina. the vagina and uterus and spreads to
Where they join together forms an almost 90 degree curve. It is the uterine tubes, ovaries, and
cylindrical or conical in shape and protrudes through the upper ultimately the pelvic peritoneum. This
anterior vaginal wall. Approximately half its length is visible condition, which occurs in about 10%
with appropriate medical equipment; the remainder lies above of women is usually caused by
the vagina beyond view. It is occasionally called "cervix uteri", chlamydial or gonorrheal infection,
or "neck of the uterus". other bacteria infecting the vagina
may be involved as well. Signs and
During menstruation, the cervix stretches open slightly to symptoms include tenderness of the
allow the endometrium to be shed. This stretching is believed to lower abdomen, fever, and a vaginal
be part of the cramping pain that many women experience. discharge. Even a single episode of
Evidence for this is given by the fact that some women's cramps PID can cause infertility, due to
subside or disappear after their first vaginal birth because the scarring that blocks the uterine tubes.
cervical opening has widened. Therefore, patients are immediately
given broad-spectrum antibiotics
The portion projecting into the vagina is referred to as the whenever PID is suspected.
portio vaginalis or ectocervix. On average, the ectocervix is three cm long and two and a half cm wide.
It has a convex, elliptical surface and is divided into anterior and posterior lips. The ectocervix's
opening is called the external os. The size and shape of the external os and the ectocervix varies widely
with age, hormonal state, and whether the woman has had a vaginal birth. In women who have not had
a vaginal birth the external os appears as a small, circular opening. In women who have had a vaginal
birth, the ectocervix appears bulkier and the external os appears wider, more slit-like and gaping.

The passageway between the external os and the uterine cavity is referred to as the endocervical
canal. It varies widely in length and width, along with the cervix overall. Flattened anterior to
posterior, the endocervical canal measures seven to eight mm at its widest in reproductive-aged
women. The endocervical canal terminates at the internal os which is the opening of the cervix inside
the uterine cavity.

During childbirth, contractions of the uterus will dilate the cervix up to 10 cm in diameter to allow
the child to pass through. During orgasm, the cervix convulses and the external os dilates.

Uterus

The uterus is shaped like an upside-down pear, with a thick lining and muscular walls. Located
near the floor of the pelvic cavity, it is hollow to allow a blastocyte, or fertilized egg, to implant and
grow. It also allows for the inner lining of the uterus to build up until a fertilized egg is implanted, or it
is sloughed off during menses.

The uterus contains some of the strongest muscles in the female body. These muscles are able to
expand and contract to accommodate a growing fetus and then help push the baby out during labor.
These muscles also contract rhythmically during an orgasm in a wave like action. It is thought that this
is to help push or guide the sperm up the uterus to the fallopian tubes where fertilization may be
possible.

306 | Human Physiology