Foetal and Neonatal Physiology

Question 1

what 4 things make the amount of PO2 ok for babies (30mmHg vs 50mmHg)

Answer 1

1) foetal red cell content
2) greater concentration of Hb
3) foetal Hb
4) the Bhor Effect

Question 2

describe foetal red cell content

Answer 2

this has DPG within the RBC but no binding sites on the Hb. Hb saturation curve is therefore displaced to the left .

Question 3

describe the greater concentration of Hb

Answer 3

the foetal red cells have more Hb present and the count is higher making the total Hb concentration in foetal blood about 50% greater than in maternal blood

Question 4

describe the foetal Hb (HbF)

Answer 4

HbF exhibits a low affinity for 2,3-DPG, resulting in a higher binding affinity for O2. this increased O2 binding affinity is relative to that of adult Hb (HbA) is due to HbF having 2 alpha/gamma dimers as opposed to the 2 alpha/beta sites of HbA. the HbA beta subunits are essential for forming the 2,3- DPG binding site altered in HbF gamma subunits- as 2,3-DPG has difficulty linking to HbF, it functions like Hb unaffected by DPG

Question 5

describe the Bhor Effect in relation to foetal blood

Answer 5

foetal blood has high CO2 tension present and after gaseous exchange makes the foetal blood alkalinise and shifts the Hb saturation curve to the left. maternal blood gets loaded with CO2 and is therefore acidified , with the Hb saturation curve being displaced to the right. the double bhor effect means that o2 is more likely to come off maternal blood and attach to foetal blood. at any given PCO2 foetal blood contains more O2. the net result is that sufficient transport of oxygen occurs despite the lower than lung partial pressure gradient

Question 6

describe co2 partial pressures and diffusing through the placenta

Answer 6

progesterone makes the mother hyperventilate to vent off co2 so that the pCO2 is about 38-29mmHg while foetal blood pCO2 is about 40-41mmHg which is enough for adequate CO2 exit through the placenta into maternal blood

Question 7

who do nutrients get to the foetus

Answer 7

these enter by facilitated diffusion through the placenta into the foetal circulation. foetal blood glucose is about 20-30% lower than maternal blood glucose and this is adequate for the transport of glucose into the foetus. most other substances have carrier proteins in the placental villi membranes. the foetus also absorbs large amounts of calcium, iron and phosphate for bone and blood formation

Question 8

why is there excretion into maternal blood

Answer 8

has the foetus has no functioning kidneys, urea and any other nitrogen metabolism products diffuse into the maternal blood

Question 9

how does water absorption occur in the placenta

Answer 9

the placenta in common with most biological membranes can transport water from mother towards the foetus in the absence of an osmotic gradient. there is absorption through amniotic membranes of water as well as throguh the placenta

Question 10

small amounts of amniotic fluid are ingested- what happens to it?

Answer 10

it is mixed with GI secretions to form a fluid called meconium that is present in the GI tract. there is also urination and utero as renal mechanisms begin to function in the foetus and dilute urine is excreted into amniotic fluid. kidney function continues to develop until 2-3 months after birth

Question 11

what happens to maternal blood volume during late pregnancy

Answer 11

maternal blood volume increases by 2-3 likes which will compensate for any blood loss (normally 500ml) during birth. the mother also produces colostrum or fate-free milk. after birth, lactation develops and prolactin concentrations in the maternal blood oscillate between weeks 0-36. on birth, lost placental oestrogen and progesterone disinhibits prolactin and milk production is copious

Question 12

what happens to the lungs with and then after the first breath

Answer 12

at birth the expansion of the lungs requires a first breath to generate an intracellular pressure of 40cm H2O, 30 or 4o times thermal intrapleural pressure. with each breath the lung pressure required changes so that after 40 minutes, breathing is normal. there can be resp distress if there is little surfactant produced

Question 13

what vascular changes occur at birth

Answer 13

lung peripheral resistance, principally the pulmonary circulation falls and systemic circulation peripheral resistance is higher causing left arterial pressure to exceed right atrial pressure by a small amount. there is therefore blood flow from the left to the right atrium. this is enough to close the foramen ovale which adheres to tissue closes. aorta pressure rises and there is flow from the aorta into the pulmonary artery. this direction change in flow leads to the wall of the ductus arteriosus constricting and then closing.

Question 14

what problems can there be after birth for baby (hint: fluid balance, liver function, metabolism)

Answer 14

underdeveloped kidney function can lead to dehydration of the infant, rarely over hydration
peripheral oedema because of inability to form proteins in sufficient quantity. gluconeogenosis is deficient so blood glucose concentrations can be low. blood coagulation is poor.
BMR twice as great as adults and cardiac output and minute ventilation volume are twice adult rates on a weight corrected basis. because of the larger surface area to body mass, ratio heat is easily lost and temp regulation remains poor

Question 15

what nutritional needs are there for the baby

Answer 15

calcium ion for bone deposition
iron for haemoglobin formation
vitamin C for bone and cartilage formation

Question 16

what problems are there for premature babies

Answer 16

temperature control- need for incubators
poor absorption of fat
poor calcium and vit D intake
respiratory diseases: caused by lack of surfactant, but oxygen therapy leads to retrolental fibroplasia. there is inhibited growth of BVs because of high O2 tension and then uncontrolled growth when O2 therapy is stopped leading to BVs and then fibrous tissue growth, blocking light to the retina

Question 17

describe lactation

Answer 17

after birth and prior to weaning, babies are reliant on maternal milk. immediately after birth and the removal of the placenta, maternal oestrogen and progesterone concentrations fall, as does prolactin. however every time the baby suckles, prolactin concentrations rise and initiate milk flow. milk production falls in volume after 7-8 months. milk ejection is a combination of production through prolactin stimulation but there is little no flow. flow requires the action of oxytocin which stimulate the myo-epithlial cells in the breast to contract and to squeeze out the milk.

Question 18

how do periods start again after giving birth

Answer 18

eventually periodically high concentrations of prolactin no longer inhibit hypothalamic secretion of gondatrophin releasing hormones and therefore LH and FSH. over time, failure of prolactin to do this leads to lifting of the inhibition and LH and FSH reinstate the monthly cycle.