Physiology of Pregnancy Flashcards
Where does fertilisation occur?
Ampulla
After fertilisation what happens?
Fertilised ovum progressively divides and differentiates into a blastocyst as it moves from site of fertilisation in the upper oviduct to the site of implantation in the uterus
At what gestational age is the blastocyst transported to the uterus?
3-5 days
What happens to the blastocyst at 5-8 days?
Blastocyst attaches to the lining of the uterus and the inner cells develop into an embryo and outer cells burrow into the uterine wall
What do the cells that burrow into the uterine wall become?
Placenta
Describe how the placenta forms
- Cords of trophoblastic cells penetrate into the endometrium
- Maternal capillaries respond to form the decidual layer and placental bed
- Boundaries between the trophoblastic tissue disintegrate
When is implantation complete?
Day 12
Is there any contact between maternal and foetal blood?
No - thin layer of tissue
When is the placenta functional?
Week 5
What hormone keeps the placenta alive?
hCG - signals the corpus luteum to continue secreting progesterone which in turn stimulates decidual cells to concentrate glycogen, proteins and lipids
What increases the contact area of the placenta?
Villi
What acts as a shunt in the placenta?
Circulation in the intervillous space
State the factors that allow oxygen transportation to the baby
- Foetal Hb has increased ability to carry oxygen
- Higher Hb concentration in foetus (50% more than adults)
- Bohr effect
What is the bohr effect?
Foetal Hb can carry more oxygen in low pCO2 than high pCO2
State four mechanisms by which nutrients and waste can be exchanged between mum and baby
Passive/active transport
Simple diffusion
Osmosis
Simplified transport
What is the main energy source to the foetus?
Glucose - simplified transport
Define teratogens
Drugs that can cross the placental barrier and are detrimental to the foetus
Name some teratogens
Thalidomide Carbamazepine Tetracycline Alcohol Nicotine Caffeine
Which ions can only go from mother to child?
Iron and calcium
When does water exchange stop increasing?
35 weeks
State the purpose of hCG
Prevents involution of the corpus luteum in the first 12 weeks of pregnancy (stimulates progesterone and oestrogen)
Describe the normal trend of hCG
Levels double every 48 hours
In pathology what happens to hCG
Ectopic - static
Failing - falls usually >50%
Molar - extremely high
What are the side effects of hCG?
Nausea and vomiting
When does hCG levels start to fall?
12-14 weeks
State the purpose of HPL
Growth hormone like effects - protein tissue formation
Decreases insulin sensitivity (increase glucose to foetus)
Breast development
When is HPL produced?
From week 5 when the placenta and foetal heart develop
Describe the role of progesterone in pregnancy
Rises throughout
Development of decidual cells
Decreases uterine contraction
Prepares breast for lactation
Describe the role of oestrogen in pregnancy
Oestradiol rises throughout pregnancy
Enlargement of uterus
Breast development
Relaxation of ligaments for labour
What pathology can hCG/HPL cause in the mum?
Hyperthyroidism
What pathology can calcium demands cause in the mum?
Hyperparathyroidism
What pathology can corticotrophin releasing hormone cause in the mum?
Increase ACTH causes increased aldosterone and cortisol which can cause
- hypertension
- oedema
- insulin resistance (gestational diabetes)
What happens to cardiac output in pregnancy?
Increases due to demands of uteroplacental circulation
In the last 8 weeks of pregnancy what does cardiac output depend on?
Body position
At what gestational age does increase in cardiac output peak?
24 weeks
What are the signs of physiological cardiovascular changes in pregnancy?
ECG changes
Functional/flow murmurs
Heart sounds
What will happen to heart rate during pregnancy?
Increases up to 90bpm
What happens to blood pressure in pregnancy?
Drops in the 2nd trimester as uteroplacental circulation expands and peripheral resistance decreases
Why do pregnant women often need iron supplement?
Erythropoesis increases as plasma volume increases so Hb is decreased by dilution and iron requirements increase
How much iron is required in the second trimester?
6-7mg/day
State the values for anaemia in first and 2nd/3rd trimester?
Outwith pregnancy 120-160g/L
First - <110g/L
Second/third <105g/L
What effect does progesterone have on respiration?
Signals the brain to lower CO2 and there is an increase in CO2 sensitivity
What factors causes lower levels of carbon dioxide?
Progesterone
Oxygen consumption increase
Growing uterus
Describe the effect of lower carbon dioxide levels
- Increased respiratory rate
- tidal and minute volume increase
- pCO2 decreases
- vital capacity and pO2 do not change
What renal changes occur in pregnancy?
GFR and renal plasma flow increases
Increased re-absorption of ions and water
Increased urine formation
What substance drives the re-absorption of ions and water?
Steroids and aldosterone
What external factor impacts renal function?
Posture - upright reduces, supine increases and lateral lying significantly increases
In general how do pregnancy values compare to normal values for renal/liver function?
Lower
How can pregnancy be describe haematologically?
Hypercoaguable state - helps to reduce risk of haemorrhage
What contribute to maternal weight gain?
Foetus Amniotic fluid Uterus Breasts Plasma volume Fat accumulation
How many extra calories a day should a pregnant lady eat?
200
Describe phase 1 of pregnancy metabolism
Anabolic Phase week 1-20
Small nutritional demands from the foetus
What factors contribute to phase one maternal metabolism?
Normal/increased insulin sensitivity
Lower plasma glucose
Increased lipogenesis
Growth of breast and uterus
Describe phase 2 of pregnancy metabolism
Higher metabolic demand and accelerated starvation of the mother if intake is not regular
What factors contribute to phase 2 maternal metabolism
Maternal insulin resistance
Increased transport of nutrients through placental membrane
Lipolysis
State five nutritional needs of women during pregnancy
- folic acid
- vitamin D
- high protein diet
- iron supplements
- B vitamins
Define lactation
Producing and releasing milk
How do oestrogen and progesterone impact lactation?
Oestrogen - growth of ductile system
Progesterone - development of lobular-alveolar system
Both inhibit lactation so decrease after birth
Describe the role of prolactin in lactation
Stimulates milk production, steady rise in levels from week 5. 1-7 days after birth prolactin induces high milk production and stimulates colostrum
What is the let-down reflex?
- Receptors in nipple stimulated
- Impulses propagated to spinal cord
- Stimulation of hypothalamic nuclei
- Oxytocin released
- Milk ejected
What is colostrum?
High protein and immunoglobulins but no fat and low in volume
