Physiology of Pregnancy and Lactation Flashcards
What name is given to the zygote immediately prior to becoming a blastocyst?
Morula
What are the two main parts of the blastocyst?
Inner cell mass - develops into foetus
Trophoblast - implants into uterine wall and becomes foetal portion of placenta
During what days of gestation does the embryo implant into the uterus?
5-8 days: blastocyst attaches to lining of uterus.
How do the trophoblastic cells penetrate the endometrium?
- cords of trophoblastic cells penetrate the endometrium
- These tunnel deeper and carve out a hole for the blastocyst
- implantation finishes when the blastocyst is completely buried in the endometrium - DAY 12
Placenta is derived from both trophoblast and decidual tissue. TRUE/FALSE?
TRUE
=> both foetal and maternal tissue
Describe how the placenta develops
- Trophoblasts differentiate into multinucleate cells
- invade decidua and break down capillaries
=> form cavities filled with maternal blood - Embryo sends capillaries into trophoblast projections to form “placental villi”
- Each villus contains foetal capillaries separated from maternal blood by a thin layer of tissue – no direct contact of foetal and maternal blood
What can be exchanged between foetal and maternal blood in the placenta?
respiratory gases
nutrients
metabolites
** largely down diffusion gradient **
When does the placenta become functional during pregnancy, and what other structure becomes functional at this point?
Placenta (and foetal heart) functional by 5th week of pregnancy
How is the early embryo delivered nutrients?
- HCG signals corpus luteum to continue secreting progesterone
- Progesterone stimulates maternal cells to concentrate glycogen, proteins and lipids for diffusion
Describe how circulation in the placenta works as a physiological arterio-venous shunt?
- hair-like projections (villi) into uterine wall.
- increases contact area between uterus and placenta
=> more nutrients and waste materials can be exchanged - Circulation within the intervillous space acts partly as an arteriovenous shunt.
Explain how the placenta plays the role of the foetal lungs?
O2 diffuses from maternal -> foetal circulation down concentration gradient
CO2 follows reverse conc gradient (due to partial pressure being elevated in foetal blood)
O2 saturated blood returns to fetus via umbilical vein
Maternal O2-poor blood, flows back into uterine veins.
Foetal haemoglobin is higher than that of adults. TRUE/FALSE?
TRUE
- Higher Hb conc. in fetal blood
- 50% more than adults
- it also has a higher affinity for O2
How do water and electrolytes get into the placenta from the mother?
- Water diffuses along osmotic gradient
- electrolytes follow water (iron and Ca2+ can only go from MOTHER -> CHILD)
How is glucose transported into the placenta and when is the most glucose required for the foetus during pregnancy?
- simplified transport into placenta
- glucose = main energy source for foetus
- high glucose need in 3rd trimester
How do the majority of waste products exit the foetus back into the placenta?
- diffusion based on concentration gradient
What prescription and non-prescription drugs can cross the placenta?
- Teratogens e.g. valproate, carbamazepine, tetracycline
- Alcohol, nicotine, heroin, cocaine, caffeine
Why is HCG important in pregnancy?
- promotes Corpus Luteum to remain and produce hormones (Progesterone and Oestrogen)
- Has an effect on the testes of male fetus - development of sex organs
Why is Human Placental Lactogen (or Human Chorionic Somatomammotropin) needed in pregnancy?
- produced from ~ week 5 of pregnancy
- growth hormone-like effects: protein tissue formation.
- decreases insulin sensitivity in mother => more glucose to foetus
- breast development.
What is progesterone release responsible for during pregnancy?
- development of decidual cells
- decreases uterus contractility
- preparation for lactation
What is the role of oestrogen in pregnancy?
- enlargement of uterus
- breast development
- relaxation of ligments
What are estriol levels used to indicate in pregnancy?
estriol level - indicator of vitality of fetus
What other hormonal changes can occur in pregnancy and what complications can these cause?
- increased Aldosterone
=> salt and water retention
=> increased BP - Increased Cortisol
=>oedema and insulin resistance
=> Gestational Diabetes
The placenta and baby demand higher Ca2+ levels during pregnancy. What complication can this cause in the mother?
Hyperparathyroidism
What cardiovascular adaptations may a pregnant woman experience?
- Increased cardiac output (30 -50% more)
- CO decreases in last 8 weeks
- CO increases 30% more during labour
- Heart rate increases (90bpm) => Increase CO.
- Blood pressure drops during 2nd trimester (uteroplacental circ. expands and peripheral resistance decreases)
- vasodilation occurs
What haematological changes can be experienced by a mother in pregnancy?
- plasma volume increases with CO (50%)
- RBC erythropoesis increases
- Hb is decreased by dilution (large PV)
- Iron requirements increases (baby needs a lot of iron => mother may require supplements)
What respiratory changes occur in a mother when she is pregnant?
- progesterone signals to brain to lower CO2 levels
- O2 levels are increased (RR and Tidal vol increase) to meet demands of both mother and baby (20% more than normal)
Explain how the urinary system of a pregnant mother is affected?
- GFR and renal plasma flow increase
- Increased re-absorption of ions and water (oedema)
- Slight increase of urine formation
- Postural changes affect renal functions
- upright position DOWN
- supine position UP
- lateral position during sleep VERY UP
What is pre-eclampsia?
pregnancy induced hypertension + proteinuria
What signs other than increased blood pressure and proteinuria may be seen in pre-eclampsia?
Kidney function decline
=> salt and water retention
=> oedema formation (esp hands and face)
=> Renal blood flow and GFR decreases
Pre-eclampsia is more common in what groups of women?
- pre-existing hypertension
- diabetes
- autoimmune diseases (eg lupus)
- renal disease
- FHx of pre-eclampsia
- obesity
- multiple gestation (twins or multiple birth).
What is the most significant risk factor for pre-eclampsia?
having had pre-eclampsia previously.
What is Eclampsia?
- EXTREME pre-eclampsia (lethal without Tx)
Symptoms:
- vascular spasms
- extreme hypertension
- chronic seizures
- coma
How is eclampsia normally treated?
- vasodilators
- cesarean section (best Tx is to get the baby OUT)
How many kilograms does the average mother put on during pregnancy?
11kg (5kg foetus and 6kg mother)
How are the average 11kg split up into different components of maternal weight gain during pregnancy?
Foetus - 3.5kg Extra-embryonic fluid/tissue - 2kg Uterus - 1kg Breasts - 1kg Body Fluid - 2.5kg Fat accumulation - 1kg
what should a pregnant mother be eating more of during pregnancy in relation to metabolism and nutrition for the foetus?
- 250 - 300 extra kcal/day for mother
- Extra protein intake - 30g/day
- At end of pregnancy - fetal glucose requirements higher => need to account for this
What are the two different stages of metabolism that a mother experiences during pregnancy?
1st - 20th week - mother´s ANABOLIC phase:
- small nutritional demands of the foetus
21 - 40 week (esp. last trimester):
- high metabolic demands of the fetus
- accelerated starvation of the mother
What usually happens during the mother’s anabolic metabolism phase of pregnancy?
- normal/increased sensitivity to insulin
- lower plasma glucose
- lipogenesis, glycogen stores increases
- growth of breasts/ uterus /weight gain
What occurs during the mothers catabolic metabolism phase of pregnancy?
- maternal insulin resistance
- increased transport of nutrients through placental membrane
- lipolysis
What specific nutritional needs are important in pregnancy?
- Folic acid (folate) - reduces risk of neural tube defects
- Vitamin D supplements
- High protein diet, higher energy uptake
- Iron supplements may be required
- B - vitamins - erythropoesis
Why should folic acid ideally be taken BEFORE pregnancy begins?
- it is taken to prevent neural tube defects
BUT often neural tube has formed BEFORE patient knows they are pregnant
Describe how the uterus becomes more “excitable” towards the end of pregnancy?
- Oestrogen:Progesterone ratio INCREASES
=> oestrogen increases contractility and oxytocin receptors on uterus - Oxytocin (posterior pituitary)
=> increases contractions and excitability
=> stimulates placenta to make prostaglandins - Foetal hormones: oxytocin, adrenal gland, prostaglandin (control timing of labour)
- Mechanical stretch of uterine muscles increases contractility
- Stretch of the cervix also stimulate uterine contractions
What are Braxton Hicks contractions?
Small contractions that do NOT indicate labour
- these increase toward the end of pregnancy
Describe how stretching of the cervix causes positive feedback?
stretch of the cervix by fetal head
=> increases contractility
=> causes further oxytocin release
How may a woman engage abdominal muscle contractions during labour?
- Strong uterine contraction / pain from birth canal cause neurogenic reflexes from spinal cord
=> Induce intense abdominal muscle contractions
What are the 3 stages of Labour?
1st stage: cervical dilation (8-24 hours).
2nd stage: passage through birth canal (few min to 120 mins).
3rd stage: expulsion of placenta.
How are the means to lactate developed in the mother during pregnancy?
Oestrogen = stimulates growth of ductile system
Progesterone: development of lobule-alveolar system
Prolactin stimulates milk production (steady rise in levels wk 5 – birth).
Why can milk only normally be produced AFTER women give birth?
Oestrogen and Progesterone inhibit milk production
=> At birth sudden drop in both
How soon after birth does prolactin stimulate milk production and what are the contents of the first milk produced?
- 1-7 days after birth, prolactin induces high milk production.
- Stimulates colostrum (low volume, no fat)
What does the baby do to allow milk ejection from the mother’s breast?
- suckling on mechanoreceptors in nipple
- this sends signal to higher brain centres to allow production of oxytocin (for smooth muscle contraction) and prolactin (for milk production)
Why may a post-partum haemorrhage occur after the delivery of the placenta?
If the womb doesn’t contract down after placenta is delivered (to condense surface area and vasculature)
then haemorrhage is likely to occur
