Physiology of Pregnancy Flashcards
Which two hormones are mostly responsible for the anatomical and physiological changes occurring in pregnancy?
Oestrogen and progesterone
The fertilised ovum divides and differentiates into ? as it moves from the site of fertilisation in the ? to the site of implantation in the ?
- a blastocyst 2. ampulla of the Fallopian tube 3. endometrium of the uterus
What days post-fertilisation does the a) transport of the blastocyst to the uterus and b) blastocyst attaching to the lining of the uterus take place?
a) 3-5 b) 5-8
Describe what happens to each of the following: a) inner cell mass of the blastocyst? b) outer (trophoblast) cells of the blastocyst?
a) become the foetus b) become the foetal part of the placenta
When does an embryo become a foetus?
After 8 weeks
At around day 8, trophoblast cells start to produce what hormone? What is the purpose of this?
They start to produce beta hCG to inform the corpus luteum that there has been a successfully implanted pregnancy and that it should continue secreting oestrogen and progesterone to stop the growth of any more follicles
When the blastocyst adheres to the endometrial lining, what do the trophoblast cells do?
They begin to penetrate the endometrium, carving out a hole for the blastocyst
By what day post-fertilisation is the blastocyst completely implanted in the endometrium?
Day 12
The placenta is derived from what?
Both trophoblast (foetal) and decidual (maternal) tissue
Trophoblast cells (chorion) differentiate into what?
Synctiotrophoblasts - multinucleate cells
What is the role of synctiotrophoblasts? What happens next?
Invade the decidua and break down capillaries to form cavities filled with maternal blood. The developing embryo then sends capillaries into these projections to form the placental villi.
Each placental villus contains what?
Foetal capillaries separated from maternal blood by a thin layer of tissue
The placenta and foetal heart are largely functional by when?
Week 5
Progesterone stimulates decidual cells to concentrate what?
Glycogen, proteins and lipids
The circulation within the intervillous space of the placenta acts partially as what?
An arteriovenous shunt
The placenta plays the role of what foetal organ?
Lungs
Gas exchange via the placenta takes place between which two blood supplies?
Maternal, oxygen rich blood and umbilical mixed arterial and venous blood which is oxygen poor
Following gas exchange via the placenta, which vessel a) returns oxygen rich blood to the foetus? b) returns oxygen poor blood to the mother?
a) umbilical vein b) uterine vein
What are the roles of beta hCG?
Prevents involution of the corpus luteum and has an effect on development of the sex organs of the foetus
Human placental lactogen is produced from what gestation? What is its main role?
Week 5 - decreases insulin sensitivity in the mother to allow more glucose to be available for the foetus
What are the main roles of progesterone in pregnancy?
Development of decidual cells, decreases uterine contractility, preparation for lactation
What are the main roles of oestrogen in pregnancy?
Enlargement of the uterus, breast development, relaxation of ligaments
Which specific oestrogen hormone is an indicator of the viability of a foetus?
Oestriol
CRH produced by the placenta causes maternal production of which hormone? This causes production of which further hormones?
ACTH - aldosterone and cortisol
What is the outcome of excess maternal production of a) aldosterone? b) cortisol?
a) hypertension b) oedema, insulin resistance and gestational diabetes
HCG and HC thyrotropin produced by the placenta causes what maternal outcome?
Hyperthyroidism
The placenta has increased demands of which electrolyte? This leads to what condition in the mother?
Ca++ / hyperparathyoidism
Describe what happens to the cardiovascular system to compensate for the increased blood volume in pregnancy?
Increased heart rate, which causes increased cardiac output
Describe what happens to cardiac output in pregnancy?
Beginning at week 6 and peaking at week 24, the cardiac output is increased by 30-50%. The CO decreases in the last 8 weeks as it is sensitive to body position, and then increases again by 30% in labour.
Describe some physiological changes in pregnancy that might be audible on auscultation of the heart?
3rd heart sound and splitting of S1
What happens to blood pressure in pregnancy normally?
It normally decreases in the 2nd trimester, and then returns to normal in the 3rd trimester
Why does blood pressure decrease in the 2nd trimester of pregnancy?
Progesterone causes vessels to vasodilate, decreasing peripheral resistance
What happens to blood pressure in a multiple pregnancy?
It drops even more in the 2nd trimester
In pregnancy, the uterus presses on the pelvic veins - what are some consequences of this?
Varicose veins and swelling of the lower limbs/ankles
What happens with regards to blood when lying down? What can help this?
The uterus presses on the IVC which decreases venous return to the right atrium and leads to hypotension / a sideline position or placing a pillow under the hip can help
Explain how there is physiological anaemia in pregnancy?
Plasma volume increases by 50%, while erythropoiesis increases by 25% meaning that Hb is diluted
By how much do iron requirements increase in pregnancy because of physiological anaemia?
6-7mg/day by 2nd trimester
Describe how pregnancy is a hypercoagulable state?
Oestrogen promotes blood clotting by increasing fibrinogen, activity of coagulation co-factors and platelet aggregation.
What is the purpose of pregnancy being a hypercoagulable state? What is the risk of this?
To minimise bleeding after deliver / VTE
What are the two factors which contribute to changes in the respiratory system in pregnancy?
Increasing progesterone levels and also the enlarging uterus compressing the diaphragm
In terms of respiratory function, progesterone signals the brain to do what?
Lower CO2 levels
Describe the 3 main respiratory changes that occur in pregnancy?
Increased RR, increased tidal and minute volume, decreased pCO2
What are two respiratory factors which do not change in pregnancy?
Vital capacity and pO2
What acid-base balance problem occurs physiologically in pregnancy?
Respiratory alkalosis
What happens to O2 consumption in pregnancy?
Increases
Describe the renal changes that occur in pregnancy?
Because there is increased plasma volume, there is increased renal plasma flow and hence increased GFR. This, combined with the compression of the bladder with the uterus explains why pregnant women have an increased urinary frequency.
Glomerular filtration rate and renal plasma flow increases peak when?
Weeks 16-24
What is the average weight gain in pregnancy? How many extra calories should be ingested each day? How much extra protein should be ingested each day?
24lbs (around 10kilos) / 250-300kcal / 30g
At the end of pregnancy, foetal glucose should be what? Maternal glucose should be what?
5mg/kg/min / 2.5mg/kg/min
Describe the two phases of maternal metabolism in pregnancy?
Weeks 1-20 is the anabolic phase, weeks 21-40 are the catabolic phase
Describe what happens during the anabolic phase of metabolism in pregnancy?
Reasonably low demands of the foetus, normal/increased sensitivity to insulin leads to lower plasma glucose levels, lipogenesis and glycogenesis occur
Describe what happens during the catabolic phase of metabolism in pregnancy?
High demands of the foetus, insulin resistance to make more glucose available for the foetus, lipolysis, increased transport of nutrients through the placenta
Insulin resistance in pregnancy is caused by which hormones?
HCL, cortisol and growth hormone
Describe the roles of oestrogen and progesterone at the onset of labour?
Oestrogen increases uterine contractility while progesterone decreases it - hence at the onset of labour, the oestrogen: progesterone ratio increases
What hormone (produced by the mother and foetus) is most responsible for increasing uterine contractions and excitability at labour? Where is this produced in the mother?
Oxytocin / posterior pituitary gland
What effect do mechanical stretch of both the cervix and uterine body have on labour?
Stretch of these structures increases contractility of the uterus
What are the roles of oxytocin?
Stimulates the uterus to contract, and stimulates the placenta to produce prostaglandins
What are the roles of prostaglandins in labour?
Stimulate more vigorous contractions of the uterus and positive feedback results in production of further prostaglandins and more oxytocin
Briefly describe the 3 stages of labour?
1st - cervical dilatation (8-24 hours) / 2nd - passage through the birth canal (few min-120 min) / 3rd - expulsion of the placenta
What are the roles of oestrogen and progesterone with regards to producing and releasing breast milk?
Oestrogen allows growth of the ductile system while progesterone allows development of the lobule-alveolar system
What happens to levels of oestrogen and progesterone after delivery of a baby? Why?
They decrease, since they inhibit the production of breast milk
What hormone stimulates breast milk production? When does this get produced?
Prolactin - steady rise in levels from week 5 - delivery
Prolactin stimulates colostrum to be produced when? Describe the components of this?
The first 24-72 hours following birth / low volume, no fat, high in immunoglobulins
What hormone is responsible for milk being ejected from the nipple?
Oxytocin
In the milk let-down reflex, what two things trigger the production of oxytocin from the posterior pituitary and production of prolactin (i.e. release of its inhibition) from the anterior pituitary gland?
Sound of child’s cry or stimulation from receptors in the nipple
