Physiology- Pregnancy and Lactation Flashcards
Describe the process from fertilisation to implantation
Fertilisation Zygote Morula Blastocyst Implantation
How many days after fertilisation does the blastocyst transport into the uterus?
3-5 days
How many days after fertilisation does the blastocyst attach to the lining of the uterus?
5-8 days
What happens to the inner cells of the blastocyst?
Develop into the embryo
What happens to the outer cells of the blastocyst?
Burrow into uterine wall and become placenta
What happens when the blastocysts adheres to the endometrial lining?
Cords of trophoblastic cells begin to penetrate the endometrium
What is the trophoblast?
Surface layer of cells of the blastocyst
What do the cords of trophoblastic cells do after endometrium penetration?
Tunnel deeper, carving out a hole for the blastocyst. Boundaries between cells in the advancing trophoblastic tissue disintegrate
Where is the blastocyst when implantation is finished?
Completely buried in endometrium
By what day will the blastocyst be buried in the uterine lining?
Day 12
What is the placenta derived from?
Trophoblast and decidual tissue
Describe how cavities filled with maternal blood are formed from trophoblast cells
Cells (chorion) differentiate into multinucleate cells (syncytiotrophoblasts) which invade decidua and break down capillaries to form cavities
Describe what happens to the broken down capillaries in the forming of cavities
Developing embryo sends capillaries into the syncytiotrophoblast projections to form placental villi
Describe a placental villus
Each contains foetal capillaries separated from maternal blood by a thin layer of tissue- no direct contact between foetal and maternal blood
What type of exchange exists between mother and foetus?
2 way exchange of resp gases, nutrients, metabolites etc-largely down diffusion gradient
When are the placenta and foetal heart functional by?
5th week of pregnancy
What provides early nutrition to the embryo?
Invasion of trophoblastic cells into decidua
What does HCG signal the corpus luteum to continue secreting?
Progesterone- stimulates decidual cells to concentrate glycogen, proteins and lipids
Where do placental villi extend into?
The uterine wall
What is the purpose of placental villi?
Increases contact area between uterus and placenta & more nutrients and waste materials can be exchanged
What does circulation within the intervillous space of the placenta act as?
An arteriovenous shunt
What plays the role of the foetal lungs?
Placenta
What is contained within umbilical blood?
Mix of arterial and venous blood
What does the exchange of CO2 follow from mother to foetus?
Reversed gradient to oxygen
Partial pressure elevated in foetal blood
What does foetal, oxygen saturated blood return to the foetus via?
The umbilical vein
What does maternal, oxygen poor blood return to the mother via?
Uterine veins
What 3 factors facilitate the supply of oxygen to the foetus?
Foetal Hb: increased ability to carry O2
Higher Hb concentration in foetal blood (50% more than adults)
Bohr effect: Foetal Hb can carry more oxygen in low pCO2 than higher pCO2
What transport mechanisms do the placental exchange processes occur via?
Passive transport (without energy consumption) Simple diffusion Osmosis Simplified transport Active transport
Describe water diffusion into placenta
Osmotic gradient
Exchange increases during pregnancy up to 35th week (3.5l/day)
Describe electrolyte transport into placenta
Follow water
Iron and Ca2+ only go from mother to child
Describe glucose transport into placenta
Passes placenta via simplified transport
High quantity needed in 3rd trimester
Describe fatty acid transport into placenta
Free diffusion
Describe waste products transport into placenta
Diffusion along concentration gradient
Describe HCG changes in pregnancy
Prevents involution of corpus luteum
Effect on testes of male foetus- development of sex organs
Describe Human Chorionic Somatomammotropin changes in pregnancy
Produced from around week 5
Growth hormone-like effects: protein tissue formation
Decrease insulin sensitivity in mother: more glucose for foetus
Involved in breast development
Describe progesterone changes in pregnancy
Development of decidual cells
Decrease uterus contractility
Preparation for lactation
Describe oestrogens changes in pregnancy
Enlargement of uterus
Breast development
Relaxation of ligaments
Estriol level-indicator of foetus viability
Describe the trend in production of HCG, HCS, progesterone and oestrogens
All but HCG rise from onset at around week 5-6 to birth
HCG starts from week 0, sharply rises to week 10, sharply decreases to week 16 and then tapers down
Describe CRH changes from placenta to mother
Increased CRH in placenta leads to ACTH in mother
Changes in aldosterone control
Can lead to HT, oedema or insulin resistance (leading to GD)
Describe HCG/HC thyrotropin changes from placenta to mother
HCG/HCT in placenta, can lead to hyperthyroidism in mother
Describe the effects of the increased calcium demand of the placenta on the mother
Can lead to hyperparathyroidism
Why does the CO increase in pregnancy and from when?
Week 6-24 (30-50% increased)
Due to placental circulation, increased metabolism, thermoregulation and renal circulation changes
What cardiac changes are all normal in pregnancy?
ECH changes Functional murmurs Heart sounds HR increase up to 90 BP drops during 2nd trimester
When does the CO increase in pregnancy?
Decreases in last 8 weeks (becomes sensitive to body position, uterus compresses vena cava)
Increases 30% during labour
Why does the BP drop during 2T?
Uteroplacental circulation expands & peripheral resistance decreases
What happens to the CO with twins?
Increases more, BP drops more
What haematologic changes occur in pregnancy?
PV increases proportionally with CO (50%)
Erythropoesis (RBC) increases (25%)
Thus Hb decreased by dilution (decreasing blood viscosity)
Iron requirements increase (6-7mg/day in 2nd half pregnancy: iron supplements needed)
What respiratory changes occur in pregnancy?
Lung function changes due to progesterone increases and enlarging uterus interferes
Progesterone signals brain to lower CO2 levels (increases CO2 sensitivity in resp centres)
O2 consumption increases (20%)
What is done to lower CO2 levels in pregnancy?
RR increases
Tidal and minute volume increases (50%)
pCO2 decreases slightly
Vital capacity and pO2 don’t change
What urinary system changes occur in pregnancy?
GFR and renal plasma flow increase (30-50%, peaks 16-24wks)
Increased re-absorption of ions and water: placental steroids, aldosterone
Slight increase in urine formation
How do postural changes affect renal function?
Upright position decreases
Supine increases
Lateral position during sleep increases greatly
What is pre-eclampsia?
Pregnancy induced HT + proteinuria
What happens in pre-eclampsia?
Increasing BP since 20th week
Kidney function declines-salt and water retention (oedema, esp hands and face)
Renal blood flow and GFR decrease
In what women is pre-eclampsia more common in?
Pre-existing hypertension DM AI disease (eg lupus) Renal disease FHx of pre-eclampsia Obesity Multiple gestation
What is the most significant risk of having pre-eclampsia?
History of pre-eclampsia
What causes pre-eclampsia?
Extensive secretion of placental hormones
Immune respose to foetus
Insufficient blood supply to placenta- ischaemia
What is eclampsia?
Extreme pre-eclampsia (fatal unless treated)
How does eclampsia present?
Vascular spasms
Extreme HT
Chronic seizures and coma
How is eclampsia treated?
Vasodilators
C-section
What is the average weight gain in pregnancy?
24lbs, can be up to 75bs
Where does the extra weight in pregnancy come from?
Foetus - 7lbs Extra-embryonic fluid/tissues – 4 lbs Uterus – 2 lbs Breasts – 2 lbs Body fluid – 6 lbs Fat accumulation – 3 lbs
How many extra kcal/day should be ingested by mother and for what?
250-300 extra
85% foetal metabolism, 15% stored as maternal fat
How much extra protein should be ingested during pregnancy?
30g/day
What is the glucose need at end of pregnancy?
Foetal need 5mg/kg/min
Mother 2.5mg/kg/min
Describe the 1st-20th week in terms of metabolism?
Mother’s anabolic phase
Small nutrional demands of conceptus
Describe the 21st-40th week in terms of metabolism?
Esp last trimester
High metabolic demands of foetus
Accelerated starvation of mother
What happens during the mother’s anabolic phase?
Normal or increased sensitivity to insulin
Lower plasmatic glucose level
Lipogenesis, glycogen stores increases
Growth of breasts, uterus,weight gain
What happens during the catabolic phase (accelerated starvation)?
Maternal insulin resistance
Increased transport of nutrients through placental membrane
Lipolysis
What causes the insulin resistance in pregnancy?
HCS
Cortisol
GH
What are the special nutritional needs in pregnancy?
High protein diet, higher energy uptake
Iron supplements - 300mg ferrous sulfate
B - vitamins - erythropoesis
Folic acid (folate) - reduces risk of neural tube defects
Vitamin D3 + Ca2+ supplements
Before parturition - K vitamin (prevention of intracranial bleeding during labour)
What happens to the oestrogen:progesterone ratio at parturition?
Alters increasing excitability: progesterone inhibits contractility, oestrogen vice versa
What does oxytocin do during parturition?
Increases contractions and excitability
What do the foetal hormones oxytocin, adrenal gland hormones, and prostaglandins do during parturition?
Control timing of labour
What does cervical stretch cause the further release of?
Oxytocin
What is oestrogen’s role in lactation?
Growth of ductile system
Inhibit milk production (level drops at birth)
What is progesterone’s role in lactation?
Development of lobule-alveolar system
Inhibit milk production (level drops at birth
What is prolactin’s role in lactation?
Stimulates milk production (rise in levels week 5 to birth)
1-7 days after birth, prolactin induces high milk production
Stimulates colostrum (low volume, no fat)
What do the sucking stimulus and oxytocin do in lactation?
Initiate ‘milk let-down’ reflex
