Lec: 13 Dr.Sajida
Menstruation
Menstrual blood is mainly arterial and only 25% of it is venous, it is
caused by sudden decrease in estrogen and progesterone at the end of
monthly cycle, so this will cause less stimulation of endometrium by
these hormones, followed by involution of the endometrium to about 65%
of its thickness during 24 hours before menstruation, the blood vessels
become vasopastic because of prostaglandins.
This vasospasm and the loss of hormonal stimulation result in necrosis of
endometrium, then gradually the necrotic outer layers of endometrium
separate from the uterus 48 hours after onset of menstruation.
The menstrual blood is unclottable because fibrinolysin is released with
the necrotic endometrium, the duration of menstruation is 3-5 days but
may be as short as 1 day or as long as 8 days, the average blood loss is 80
ml and within 4-7 days after menstruation the blood loss stops because
the endometrium is re-epithelized.
Regulation of female monthly cycle
GNRH is secreted from preoptic area and arcute nucleus of the
hypothalamus in pulses, one every 1-3 hours and this will result in
pulsatile secretion of LH and to lesser extent FSH.
The pulsatile secretion of GNRH is important for its function because if it
was secreted continuously, its effect on FSH and LH will be lost.
Estrogen in small amounts has strong inhibition of FSH and LH secretion,
also when progesterone is available the inhibition of estrogen increases,
while progesterone alone has a little effect.
In addition negative feedback of estrogen, progesterone and inhibin
(which is secreted by the granulosa cells of corpus luteum) inhibit FSH
secretion and to less extent LH secretion, it is believed that causes
decrease in FSH and LH at the end of monthly cycle.
Menopause
At the age of 40-45 years, menstrual cycle become less regular, until it
ceases completely, this cessation is known as menopause, the phase of
life beginning with menstrual irregulatory and termination in menopause
is known as climacteric, it involves numerous physical and emotional
changes as hot flushes, psychic sensation of dysnea, irritability,
fatigability and anxiety.
Menopause is caused primarily by ovarian failure, the ovaries lose their
ability to respond to gonadotropins, only few primordial follicles
stimulated by FSH and LH and the production of estrogen decreases.
The hypothalamus and anterior pituitary are functioning normally and
secreting greater amounts of FSH and LH because of the decrease in the
plasma estrogen and that doesn’t exert negative feedback on
gonadotropins secretion. Small amount of estrogen usually persist in
plasma beyond the menopause mainly from peripheral conversion of
adrenal androgens to estrogen, but the levels is inadequate to maintain
estrogen dependant tissues.
The breast and the genital organs gradually atrophy to a large degree with
thinning and dryness of the vaginal epithelium.
Marked decrease in bone mass and strength and osteoporosis may occur
because of bone re-absorption and can result in bone fractures.
The hot flushes is so typical of menopause accompanied by dilation of
skin arterioles, a feeling of warmth and marked sweating, also the
incidence of coronary diseases become similar in both sexes.
Female fertility
The ovum remains 24 hours capable of fertilization after it is expelled.
The sperms remain fertile in female genital tract for 72 hours, so the
fertility period in the female is 1-2 days before ovulation and up to 1 day
after ovulation.
Rhythm method of contraception
Coitus should be avoided for 4 days before calculated day of ovulation
and 3 days afterwards. If the periodicity of the cycle is 28 days, ovulation
occurs at day 14 of the cycle, if increase periodicity of the cycle is 40
days, ovulation occurs at the 26
th
day, if the periodicity of the cycle is 21
days, ovulation occurs on the 7
th
day of the cycle.
Hormonal suppression of fertility "pills"
If estrogen and progesterone are given during the first half of the sexual
cycle, it will prevent ovulation by preventing LH surge, among the
synthetic estrogen is ethinyl estradiol and mestranol. The synthetic
progesterone is norethindrone, norgestrel this medication is used from the
5
th
day of the cycle to the 21
st
day and then stopped to allow
menstruation.
Another type is called (mini pill) which contains only progesterone like
substance that doesn’t always prevent ovulation but it is effective because
it affects the composition of cervical mucous, preventing passage of
sperm through the cervix and also inhibits estrogen induced proliferation
of the endometrium making inhospitable for implantation.
Notes:
1- The combine pill contains estrogen and progesterone, the
progesterone is more extent.
2- The mini pill is given in the 1
st
day of the cycle to the end of it (in
lactating women it stops the milk secretion).
Pregnancy
Five weeks after implantation, the placenta become well established, the
fetal heart begins to pump blood.
In early pregnancy the placental membrane is thick so its permeability is
low, while late in pregnancy the placental membrane is thin and more
permeable.
The main function of placenta is to provide diffusion of food stuffs from
the mother's blood to fetus's blood and diffusion of excretory products
from the fetus back to the mother.
Diffusion of O2 through the placental membrane
The dissolved oxygen in the maternal sinuses is transported to fetal blood
by simple diffusion PO2 (partial pressure of O2) in the fetal blood is 20
mm hg and PO2 in the maternal blood is 50 mm hg.
This figure shows the comparative O2 dissociation curve for maternal Hb
and fetal Hb demonstrating that the curve for fetal Hb is shifted to the left
of that of maternal Hb, this means that at low levels PO2 in fetal blood
the fetal Hb can carry 20-50 % more oxygen.
The Hb concentration of fetal blood is 50% greater than in the mother.
Boher effect provides another factor that enhances the transport of O2 by
the fetal blood that is Hb can carry more O2 at low PCO2 than at high
PCO2 and by these three means the fetus is capable of receiving more
than adequate O2 through the placenta.
Diffusion of CO2 through the placental membrane
PCO2 of fetal blood is 2-3 mm hg higher than that of maternal blood, this
small pressure gradient is sufficient to allow adequate diffusion of CO2.
Diffusion of food stuffs through the placental membrane
Glucose is transported by facilitated diffusion and fatty acids are
transported by diffusion. Excretory products (urea, uric acid and
creatinine) diffuse in maternal blood and excreted along with excretory
products by mother.
Response of mother's body to pregnancy
Throughout pregnancy plasma concentration of estrogen remains high,
estrogen secreted by syncytial trophoblast. The daily production of
estrogen increased to about 30 times the normal toward the end of
pregnancy, the estrogen secreted by the placenta differs from that
secreted by the ovaries in:
1- Most of secreted estrogen is estriol which is weak estrogen.
2- The estrogen is formed from dehydroepiandrosterone secreted by
the mother's and fetal adrenal glands.
Function of estrogen during pregnancy
1- It stimulates the growth of uterine muscle mass which will
eventually supply the contractile forces needed for delivery of the
fetus.
2- It causes enlargement of breast and external genitalia.
3- It relaxes the pelvic ligaments of the mother.
So these three factors help the passage of the fetus through the birth
canal.
Progesterone
It is secreted by the syncetial trophoblast, increased in secretion
throughout pregnancy, in early pregnancy its concentration is higher than
estrogen to decrease contractility of the uterus, towards the end of
pregnancy increased 10 folds but estrogen overcomes the action of
progesterone.
Function of progesterone during pregnancy:
1- It increases the secretion of uterus and fallopian tube to provide
nutrition for the developing blastocyst
2- Helps estrogen to prepare mother's breast for lactation.