Lec: 14 Dr.Sajida
Human chronic gonadotropins
It is secreted by syncytial trophoblast cells, the secretion of this hormone can
be measured in blood by 8-9 days after ovulation, its detection in urine is
used as a test of pregnancy, the secretion increases rapidly to reach a
maximum about 10-12 weeks after ovulation, it begins to decrease to the
lower level by 16-20 weeks of pregnancy and continue at this level to the
remainder of pregnancy.
Functions:
1- It prevents the normal involution of corpus luteum at the end of the
female monthly cycle.
2- Causes the corpus luteum to secrete estrogen and progesterone, this
maintains the decidual nature of the endometrium, the corpus luteum
involutes by 13-17 week of gestation.
3- It also stimulates testosterone secretion in the testis during pregnancy
so male sex organs developed and testis descend in the scrotum.
Human chronic somatotropin (Human chronic lactogen)
Secreted by the placenta by the 5
th
week of pregnancy and its secretion
increase in direct proportion to the weight of placenta.
Functions:
1- Mobilizing fat for energy.
2- Stabilizing plasma glucose at relatively high levels (GH like effect).
3- Facilitating development of the breast.
Other hormonal factors
1- The anterior pituitary enlarges by 50% and increase production of
corticotropin, thyrotropin and prolactin, while FSH and LH decrease.
2- Increase secretion of glucocorticoids and aldosterone.
3- Mother’s thyroid increases by 50% and increase secretion of thyroxin.
4- Parathyroid increase especially in calcium deficient mothers.
5- Relaxation secreted by the corpus luteum, ovary and the placenta.
6- Increase secretion of vasopressin by posterior pituitary.
Other changes during pregnancy
1- The breast enlarges and develop mature glandular structure.
2- Body weight: increases by 12.5 Kg. Most of gain occur in the last two
trimesters due to fluid retaining hormones and increase desire for
food.
3- Nutrition: a number of nutritional deficiencies occur as calcium,
phosphate and vitamins because they are not absorbed from her diet.
During the last months of pregnancy shortly before birth of baby,
Vitamin K is added to prevent hemorrhage particularly brain damage.
4- B.M.R: increase by 15% during later half of pregnancy as
consequences of increase secretion of thyroxin, adrenocorticoid and
sex hormones.
Changes in circulatory system
The cardiac output is increased by 30-40% above normal by the 27
th
week of
pregnancy then fall to little above by the last 8 weeks of pregnancy.
The maternal blood volume increase 30% above normal shortly before term,
this because of the increase in red blood cells count by erythropoietin
hormone secreted from kidneys and increase fluid retention by aldosterone
and estrogen.
Respiration
The total amount of oxygen used by the mother is increased by 20% above
normal shortly before delivery, therefore; minute ventilation increase by
50% because progesterone increase the sensitivity of respiratory system to
CO2, respiratory rate is increased so PCO2 is decreased.
Renal changes
The rate of urinary formation is increased because of increase load of
excretory products, reabsorptive capacity for sodium and chloride, H2O is
increased by 50%, GFR increased by 50%.
Parturition
A normal human pregnancy lasts 40 weeks, parturition means delivery of the
infant followed by the placenta. Parturition is produced by strong rhythmical
contractions of the myometrium.
What are the mechanisms control the event of parturition?
1- The autonomic neurons to the uterus are of little importance in
parturition since anesthetizing them does not interfere with delivery.
2- The smooth muscle cells of the myometrium have inherent
rhythmicity and are capable of autonomous contraction, which are
facilitated as the muscle is stretched by the growing fetus, especially
twins burn 19 days earlier than single child.
3- The pregnant uterus near term and during labor secrets several
prostaglandins that are profound stimulators of uterine smooth
muscles contraction.
Oxytocin
One of the hormones secreted by the posterior pituitary which is potent
uterine muscle stimulant. It is not only acts directly on uterine smooth
muscle but also stimulates it to synthesize prostaglandins.
Oxytocin is released as a result of input to the hypothalamus from receptors
in the uterus, particularly in the cervix. During pregnancy the number of
oxytocin receptor in the uterus is increased mainly as a result of estrogen
stimulation.
Throughout pregnancy progesterone exerts an essential powerful inhibitory
effect upon uterine contraction by decreasing the sensitivity to estrogen,
oxytocin and prostaglandin.
Progesterone seems to play a major role in beginning parturition. As the
placenta ages, the rate of progesterone secretion remain constant or decrease
from the 7
th
week of pregnancy, while estrogen secretion increased.
The fetus’s pituitary secrete oxytocin that excites the uterus, in addition the
fetal membrane secrete prostaglandin in high concentrations at time of labor,
this increases the intensity of uterine contraction.
These factors once started, the uterine contraction exert a positive feedback
effect upon themselves via both local facilitation of inherent uterine and
reflex stimulation of oxytocin secretion.
Lactation
The anterior pituitary cells secretes PRL and this influenced by many
hormones. They are inhibited by dopamine which is secreted by the
hypothalamus. They are stimulated by prolactin releasing factors which is
also secreted by the hypothalamus and reaches the anterior pituitary by the
portal vessels. Estrogen also act on the anterior pituitary to stimulate PRL
secretion.
Under the inhibitory influence of dopamine, PRL secretion is low before
puberty, it then increase at puberty stimulated by the increased estrogen.
There is large secretion bursts of PRL during each nursing. The episodic
pulses of PRL are signals to the breast to maintain milk production.
The reflexes mediating the PRL bursts are initiated by afferent input to the
hypothalamus.
سيتم اكمال بقية هذا الموضوع في ملحق باالعتماد على التسجيل
Ejection of milk
When the baby suckles the nipple the breast nerve signals transmitted to the
spinal cord and then to the hypothalamus cause oxytocin secretion which
result in contraction of myoepithelial cells surrounding the alveoli and
secretion of milk.
Generalized sympathetic stimulation inhibits oxytocin secretion and milk
ejection (fear, sadness, ……. Etc.)
Suppression of sexual cycle during nursing
In about half of nursing mothers. Ovarian cycle and ovulation stop until few
weeks after cessation of lactation and is thought that the same signal from
the breast to the hypothalamus that increase prolactin secretion
inhibit GNRH secretion and this in turn inhibit FSH and LH. After
several months of lactation in half lactating mother, the pituitary
begin again to secrete FSH and LH and the ovarian cycle returns.