Physiology of Pregnancy and Lactation Flashcards
What part of the blastocyst develops into the placenta?
Trophoblast = accomplishes implantation and develops into foetal portions of placenta
What happens to the fertilised ovum as it moves from the site of fertilisation to the site of implantation?
Progressively divides and differentiates into a blastocyst
Where does fertilisation occur?
In the ampulla of the fallopian tube
What happens to the blastocyst between days 3-5?
Transported into uterus
When does the blastocyst attach to the lining of the uterus?
From days 5-8
What do the different cells of the blastocyst develop into?
Inner cells = embryo
Outer cells = burrow into uterine wall and become placenta
What happens when the blastocyst adheres to the endometrial lining?
Cords of trophoblastic cells begin to penetrate the endometrium
What carves a hole in the endometrium for the blastocyst to adhere to?
Advancing cords of trophoblastic cells = tunnel deeper into endometrium
What happens to the boundaries between cells in advancing trophoblastic tissue?
The boundaries disintegrate
What is the fate of the blastocyst at the end of implantation?
It is completely buried in the endometrium = occurs by day 12
What is the placenta derived from?
Trophoblastic and decidual tissue
What do trophoblastic chorion cells differentiate into?
Multinucleate cells called syncytotrophoblasts = invade decidua and break down capillaries to form cavities filled with maternal blood
How are placental villi formed?
Developing embryo sends capillaries into the syncytotrophoblast projections
What does each placental villi contain?
Foetal capillaries separated from maternal blood by a thin layer of tissue = no direct contact between foetal and maternal blood
What kind of exchange exists between the mother and foetus?
2 way exchange = largely down diffusion gradient
When are the placenta and foetal heart functional from?
By the fifth week of pregnancy
What does HCG signal the corpus luteum to do?
Continue secreting progesterone = stimulates decidual cells to concentrate glycogen, proteins and lipids
What is the purpose of the placental villi?
Increase contact between uterus and placenta = more nutrients and waste products cane be exchanged
Where do blood vessels from the embryo develop?
In the placental villi = thin membrane separates embryonic villous blood from maternal blood in intervillous space
What does the circulation within the intervillous space act as?
An AV shunt
How does the placenta act as the foetal lungs?
Respiratory function makes supply of oxygen and removal of carbon dioxide possible
Where does exchange of oxygen take place in the placenta?
Between maternal oxygen-rich blood and umbilical oxygen-poor blood
What direction does oxygen move in during placental exchange?
From maternal into foetal circulation system = carbon dioxide moves in the opposite direction
What happens to blood once oxygen exchange has occurred within the placenta?
Foetal oxygen-enriched blood returns to foetus via umbilical vein
Maternal oxygen-depleted blood flows back into uterine veins
What facilitates foetal oxygen supply?
Foetal Hb = increased ability to carry oxygen
Higher Hb concentration = 50% higher than adults
Bohr effect
How does the Bohr effect facilitate foetal oxygen supply?
Foetal Hb can carry more oxygen in low pCo2 than in high pCO2
How is water transported in the placenta?
Diffuses into placenta along osmotic gradient = exchange increases during pregnancy up to 35th week (3.5L/day)
How are electrolytes transported in the placenta?
Follow water = iron and calcium only go from mother to child
How does glucose pass into the placenta?
By simplified transport = high demand in third trimester
How do fatty acids move in the placenta?
Via diffusion
What is diffusion of waste products based on?
Concentration gradient
How much are drugs (other than alcohol) implicated in congenital malformations?
Responsible for 3% of all congenital malformations
What is the function of HCG?
Peaks at 10 weeks gestation = prevents involution of corpus luteum, causes development of male sexual organs
What is the function of human placental lactogen (HPL)?
Produced from 5th week and increases as pregnancy goes on = GH-like effect causing protein tissue formation, decreases insulin sensitivity in mother, involved in breast development
What is the function of progesterone?
Increases as pregnancy goes on = development of decidual cells, decreases uterine contractility, preparation for lactation
What are the functions of oestrogens?
Enlargement of uterus, breast development, relaxation of ligaments
How do HCG levels change in a singleton early pregnancy?
Serum levels double every 48hrs
What conditions can HCG levels be useful for diagnosis?
Ectopic pregnancy = static or slow rising levels
Failing pregnancy = falling levels
Ongoing viable pregnancy = doubling/>60% rise
What are the side effects of HCG?
Nausea and vomiting
When may high levels of HCG occur?
In multiple or molar pregnancies
When do HCG levels begin to fall?
From 12-14 weeks gestation
Why does cardiac output increase during pregnancy?
Due to the demands of the uteroplacental circulation
How does the cardiac output change during pregnancy?
Increases to 30-50% above normal = begins in week 6 and peaks at week 24
Decreases in last 8 weeks = uterus compresses IVC
Increases 30% more during labour
What are some normal CV changes that occur during pregnancy?
ECG changes, functional murmurs and heart sounds
What happens to maternal heart rate during pregnancy?
Increases up to 90 beats per minute
How does blood pressure change during pregnancy?
Drops during 2nd trimester = uteroplacental circulation expands and peripheral resistance decreases
What are the CV changes that occur during a multiple pregnancy?
Cardiac output increases by more and BP drops by more than would occur during a singleton pregnancy
What haematologic changes occur during pregnancy?
Plasma volume increases proportionally with cardiac output (50% increase)
Erythropoesis increases by 25%
What effect do the haematologic changes that occur during pregnancy have on haemoglobin?
Decreases Hb by dilution = decreases blood viscosity
How do iron requirements change during pregnancy?
Increase = 6-7 mg/day needed in second half of pregnancy = may need iron supplements
What causes lung changes during pregnancy?
Increases in progesterone and the enlarging uterus interfering with lung function
How does progesterone affect CO2 level?
Signals brain to lower CO2 levels
Why does oxygen consumption increase during pregnancy?
Increases up to 20% above normal to meet metabolic needs of mother, foetus and placenta
What changes occur to lower CO2 levels?
Respiratory rate increases, tidal and minute volumes increase, pCO2 increases slightly
What changes occur in the urinary system during pregnancy?
GFR and renal plasma flow increase by up to 30-50% = peaks at 16-24 weeks gestation
Increased reabsorption of ions and water
Slight increase in urine formation
How do postural changes during pregnancy affect renal function?
Decrease in function if upright
Increase in function if supine
Significant increase in function when in lateral position during sleep
What is pre-eclampsia?
Pregnancy induced hypertension and proteinuria
What are some signs of pre-eclampsia?
Increasing BP since 20 weeks gestation
Decrease in renal blood flow and GFR
Oedema = salt and water retention
What causes oedema in pre-eclampsia?
Decline in renal function
What are the risk factors for pre-eclampsia?
Pre-existing hypertension, diabetes, autoimmune disease, renal disease, family history, obesity, twins/multiple births
What are the features of eclampsia?
Lethal without treatment = vascular spasms, extreme hypertension, chronic seizures, coma
How is eclampsia treated?
C-section and vasodilators
What is the usual maternal weight gain during pregnancy?
Average is 11kg = can be as much as 30kg
What contributes to maternal weight gain during pregnancy?
Foetus = 3.5kg Extra-embryonic fluid and tissues = 2kg Uterus = 1kg Breasts = 1kg Body fluid = 2.5kg Fat accumulation = 1kg
How much should calorie intake increase by during pregnancy?
200 extra kcal/day = 85% for foetal metabolism, 15% stored as maternal fat
How does protein intake need to change during pregnancy?
Extra protein intake required = 30g/day
When is the anabolic phase of pregnancy?
Weeks 1-20 = anabolic metabolism of mother, quite small nutritional demands of conceptus
When is the catabolic phase of pregnancy?
Weeks 21-40 = especially high during 3rd trimester, high metabolic needs of foetus, accelerated starvation of mother
What changes occur during the anabolic phase of pregnancy?
Normal/increased sensitivity to insulin
Lower plasma glucose level
Lipogenesis and increased glycogen stores
Growth of breasts and uterus, and weight gain
What changes occur during the catabolic phase of pregnancy?
Maternal insulin resistance
Increased transport of nutrients through placental membrane
Lipolysis
What causes insulin resistance?
HPL, cortisol and GH
What are the special nutritional needs of pregnancy?
Folic acid = reduces risk of neural tube defects
High protein diet
Vitamin D and iron supplements
B vitamins = erythropoesis
What happens to the uterus towards the end of pregnancy?
Becomes progressively more excitable
What causes increased uterine excitability?
Alteration of oestrogen:progesterone ratio
Oxytocin = also increases contractions
How do foetal hormones influence labour?
Control timing of labour
What effect does stretch of pelvic organs during labour have?
Mechanical stretch of uterine muscles increases contractility
Stretch of cervix stimulates uterine contractions
When do Braxton Hicks contractions occur?
Increase towards end of pregnancy
How does positive feedback influence onset of labour?
Stretch of cervix by foetal head increases contractility and causes further oxytocin release
What effect do string uterine contractions and pain from birth canal during labour have?
Cause neurogenic reflexes from spinal cord that induce abdominal muscle contractions
What are the stages of labour?
1st stage = cervical dilation (8-24hrs)
2nd stage = passes through birth canal (up to 120mins)
3rd stage = expulsion of placenta
How do oestrogen and progesterone aid lactation?
Oestrogen = growth of ductile system Progesterone = development of lobule-alveolar system
What effect do oestrogen and progesterone have on milk production?
Inhibit milk production = drop suddenly at birth
What hormone stimulates milk production?
Prolactin = steady rise in levels from week 5 to birth
When does prolactin induce high milk production?
1-7 days after birth = also stimulates colostrum (low volume, no fat)
What are the components of the milk let-down reflex?
Sucking stimulus and oxytocin
What occurs in the milk let-down reflex?
Receptors in nipples stimulated
Impulses propagated to spinal cord
Stimulation of hypothalamic nuclei
Oxytocin released and milk ejected
