The pregnant woman at term produces more
estrogen in one day, than a nonpregnant woman produces in 3
years! Estrogen is responsible for enormous changes during
The most common estrogens in the human are:
- estradiol (mostly
secreted by the ovaries),
- estrone and
- estriol (mostly secreted
by the placenta). During pregnancy, there is a large
increase in the amount of estriol in relationship to
estrone and estradiol.
The fetal adrenal glands and the placenta
interact in order to produce estrogen in appropriate amounts.
- The adrenal glands of the fetus provide
essential precursors for the production of estriol in the
placenta, therefore a living, healthy fetus and placenta
are needed to produce ideal estrogen levels. This is an
example of the "placenta/fetal unit" at work.
- The maternal liver conjugates the estriol,
and it is excreted in her urine.
- The level of urinary estriol increases
gradually until the12th week of pregnancy, and then
increases more rapidly until term. Measurement of
estriols in the maternal urine has historically been used
as an indicator of fetal and placental well being.
The fetus and
the placenta must interact for appropriate production of
TRUE or FALSE
Estrogen has so many functions during
pregnancy. The following is only a partial list, but it should
cover the most relevant. To organize these functions, they are
separated here between those that "build
tissue," and those that "change
tissue" in some other way.
Estrogen has a major role during pregnancy of building
tissue. It accomplishes this by either
increasing the size or the number of tissues, vessels, and blood
- It is responsible for the proliferation of
the uterine endometrium. This increase in the depth and
consistency of the uterine lining prepares it for
- Estrogen is a major factor in the
increased size of the uterus and thickening of the
uterine wall. During the pregnancy, the uterus increases
in size to accommodate the developing pregnancy. It does
this through hyperplasia (increase in the number
of cells), hypertrophy (increase in the size
of cells) of muscle cells, and stretching of the uterus.
- The uterus grows from 60 grams in
weight to 1200 grams (20 times it's nonpregnant
weight), with a volume increasing from 10 cc to
2-10 liters of fluid.
- In addition there is an increase in the
size of the external genitalia. The vaginal walls are
thick and easily distensible. The genitalia is also very
- Estrogen is responsible for an increased
blood, lymphatics and nerve supply to the uterus, and
throughout the body. The considerable increase in the
number and size of vessels in the uterine vascular bed
causes a decrease in the uterine vascular resistance. As
a result, blood flows to and from the uterus more freely.
- Uterine blood flow increases from
50cc per minute at 10 weeks to 500cc per minute
- Uterine veins may dilate up to 60
times larger than prepregnant states, in order to
produce adequate drainage for the large
uteroplacental blood flow.
- Estrogen also contributes to the increase
in breast size, especially the alveolar ductile tissue.
The numbers and size of ducts and lobes increase,
vascularity increases, and the nipples and areolae become
larger. Montgomery's glands appear as small elevations in
areolae. Increase ductal growth is estrogen's
responsibility, while increased lobular development is
attributed to progesterone.
responsible for the increased size of the uterus, and more blood
vessels both to and from the uterus.
TRUE or FALSE
Another function of estrogen is change
in the character of tissue.
- There is a change in composition of the
- Though there is a decrease in the
total plasma proteins, there is an increase in
serum-binding proteins. Estrogen increases the
availability of body proteins, maintains a
positive nitrogen balance and ensures there is
adequate protein for fetal growth. It also causes
increased deposition of fat.
- There is a significant increase in
the number of white blood cells in the blood,
("leukocytosis of pregnancy"), as may
occur during acute infection or inflammation.
- There is also an increase in
fibrinogen concentration and decrease in
fibrinolytic activity. As a result, blood clots
or coagulates more readily. This decreases the
risk of hemorrhage, but also increases the risk
of blood clots or thrombosis.
- There is a softening of connective and
collagen tissues. Estrogen, along with the hormone
relaxin, relaxes pelvic joints and ligaments, and
increases mobility of nipple tissue. In late pregnancy,
fibers of the cervix are swollen and loosely connected to
each other. This is the ripening that
prepares the cervix to dilate.
- Endocrine factors, including
estrogen, are also thought to be responsible for
changes in the blood vessel walls. Blood vessels
become more permeable during pregnancy. The
result is frequently leakage into dependent
tissues, or "swollen ankles."
- Estrogen causes the kidney tubules to
retain more sodium and water. This leads to a significant
increase in blood volume.
- Uterine tissue
becomes more elastic and contractile, under the influence
of estrogen. These features help the uterus accommodate
the growing fetus and prepare for the contractions that
bring about childbirth.
- Estrogen is also responsible for skin
changes (striae gravidarum, telangiectases, palmar
erythema, hyperpigmentation). Though we won't go into
detail about these changes in this module, we should note
that many of them appear due to an increased number and
size of blood vessels.
- Estrogen also causes increased acidity
(lower pH) in the vagina.
- The mechanism for lower pH is
attributed to a general increase in metabolic
activity under the influence of estrogen. The
glycogen in the vaginal epithelium breaks down
and results in increased lactic acid. The lower
pH (3.5-6) is thought to ward off infection to
some degree and alter the growth of pathogenic
bacteria in the vagina.
- There is a decrease in gastric secretion
of hydrochloric acid and pepsin under the influence of
estrogen. This leads to decreased fat absorption and
increasing digestive upsets and nausea. On the other
hand, ulcers may improve!
a decreased ability for the blood to clot in a pregnant woman.
TRUE or FALSE
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