adaptations at birth

Question 1

what is the starting point of fetal circulation

Answer 1

at the placenta which is embedded in the uterine wall and is partly maternal and partly foetal.

Question 2

where does exchange between maternal and fetal circulations occur

Answer 2

At the placenta there is exchange of oxygen and nutrients

Question 3

how is there exchange between maternal and fetal blood if the blood does NOT mix

Answer 3

fingerlike projections capillaries push into the pool of maternal blood separated by thin membranes (placental villi) deoxygenated blood containing waste products enters umbilical cord. is high in CO2, waste, diffuses into maternal circulation. Blood from mother high in O2, nutrients, diffuses into fetal capillaries and returns to umbilical cord via umbilical vein

Question 4

how is o2 carried in the blood

Answer 4

1 - dissolved in plasma (2%)

2 - bound to Hb (98%)

Question 5

what is adult Hb composed of

Answer 5

2 alpha 2 beta polypeptide chains.

each has a haem group containing porphyrin ring and ferrous Fe2+

Question 6

when does Hb bind o2

Answer 6

when PO2 is high, binds O2 to haem group

Question 7

when does Hb release O2

Answer 7

when O2 is low, O2 will dissociate

Question 8

what is fetal Hb composed of

Answer 8

2 alpha 2 gamma polypeptide chains.

each has a haem group containing porphyrin ring and ferrous Fe2+

Question 9

what synthesises Hb early in gestational life (before 6 weeks)

Answer 9

yolk sac synthesises Hb

Question 10

what synthesises Hb in gestational life (between 8 weeks and 24wks -birth)

Answer 10

liver

Question 11

what type of Hb is made in gestation

Answer 11

Fetal Hb (2xa, 2xg)

Question 12

nearing birth (post 24weeks), what organ takes over Hb production

Answer 12

spleen

Question 13

how does Hb production change as we near birth

Answer 13

starts to be produced by spleen
fall in gamma Hb
beta Hb starts to increase. at birth, bHb shoots up, gHb nosedives down

Question 14

at birth what starts to take over production of Hb

Answer 14

bone marrow

Question 15

difference between fetal and adult Hb

Answer 15

fetal contains gamma chains, adult contain beta chains

fetal Hb = higher affinity for o2, so binds o2 at lower PO2 and is saturated at lower O2.

Question 16

what is the role of 2,3 DPG in o2 binding

Answer 16

2,3 DPG binds to deoxygenated Hb and promotes further release of the remaining O2 and it also makes it harder for O2 to bind.
shifts o2 dissociation curve to the right .’. releases 2 at higher PO2

Question 17

what is the role of 2,3 DPG in o2 binding in pregnant women

Answer 17

30% increase in 2,3 DPG so their Hb has less oxygen and allows more O2 to be offloaded at the placenta and given to the fetus
Foetal Hb doesn’t bind 2,3-DPG as well as adult Hb does, therefore this further enhances HbF affinity to oxygen as the curve is shifted to the left.

Question 18

what happens to the blood coming into the umbilical vein from the mother

Answer 18

umbilical vein travels up to the liver.
50-60% bypasses hepatic circulation and is shunted to IVC via the ductus venosus.
Rest enters the portal vein.

Question 19

how does fetal circulation bypass the lungs

Answer 19

lungs are still developing. filled with fluid. not ready for gas exchange .’. lung capillaries are vasoconstricted.’. high pressure & resistance in pulmonary artery = high pressure in the RV .’. high pressure in right atria.
.’. blood is pushed through foramen ovale and into left atrium .’. enters left ventricle and is pumped out into aorta

Question 20

how does fetal circulation stop blood in RV going to lungs

Answer 20

RV -> pumped into pulmonary artery.
ductus arteriosus connects the pulmonary artery to the aorta .’. blood entering pulmonary artery is shunted into the aorta .’. blood prevented from going to lungs

Question 21

what big events happen at birth

Answer 21

placental circulation ceases
baby starts to breathe (fluid in lung pushed out)
foramen ovale closes
ductus arteriosus closes

Question 22

how does placental circulation close after birth

Answer 22

when umbilical cord is clamped - exposed to cooler temperatures .’. vessels get constricted.
blood no longer flowing into the umbilical vein or ductus venosus so it closes over 3-10 days.
so placental circulation ceases

Question 23

how do lungs change after birth

Answer 23

as baby starts to breathe air, remaining fluid is pushed out and fills with air.
o2 -> pulmonary arterioles dilate and resistance in pulmonary circulation falls .’. increase in bf in pulmonary circulation

Question 24

what happens to foramen ovale after birth

Answer 24

lower resistance and pressure in pulmonary circulation (and RA/RV) .’. more blood flow .’. more blood return to LA .’. LA pressure increases.
.’. RA and LA pressure equalise .’. foramen ovale =pushed against interatrial septum .’.closes shunt

Question 25

what happens to ductus arteriosus after birth

Answer 25

fall in pulm. artery resistance &pressure = blood flow both ways (up aorta and up aorta) in ductus arteriosus
rise in o2 and fall in PG -> ductus arteriosus to close. once closed it is called ligamentum arteriosum

Question 26

how does umbilical artery of fetus change after birth

Answer 26

umbilical artery that comes off the internal iliac will have very little blood flowing into it as it constricts due to lo1w prostaglandins and higher oxygen tensions.
Eventually it will close off

Question 27

why may the transition to extrauterine life not be permanent

Answer 27

pulm. arterioles are v reactive and may end up reconstricting due to certain stimuli:
- hypoxia. hypercarbia, acidosis, cold
.’. rise in pulmonary venous pressure .’. right to left shunting

Question 28

what is patent ductus arteriosus

Answer 28

where ductus arteriosus fails to close after birth .’. deoxygenated blood that has just entered aorta from LV flows back into pulmonary artery and goes to lungs.
asymptomatic early on but a continuous machinery murmur can be heard.
if uncorrected can lead to congestive heart failure.

Question 29

symptoms of heart failure

Answer 29

Fast breathing, Increased work of breathing, Sweating during feeding, Poor feeding, Poor growth, Rapid pulse, Bounding pulse

Question 30

treatment of patent ductus arteriosus

Answer 30

indomethacin, Ibuprofen, (NSAID) inhibits production of prostaglandins and therefore encourages the duct to close.
surgery may be used to ligate the vessel.

Question 31

examples of atrial septal defect

Answer 31

Ostium primum, Ostium secundum defect, Sinus venosus defect, Common atrium, Patent foramen ovale

Question 32

why are neonates at increased risk of heat loss

Answer 32

high surface area to body mass ratio.

lack thermal insulation - lower % body fat, less subcutaneous fat

Question 33

mechanism for maintaining heat in neonates

Answer 33

thermogenesis - (babies cannot shiver .’. rely on non shivering thermogenesis through brown fat)
brown fat has high levels of mitochondria. proton movement down their gradient (from intermitochondrial space to matrix) is coupled to heat production.

Question 34

what is evaporation of heat

Answer 34

Heat loss through wet skin

Question 35

what is convection of heat

Answer 35

Heat loss caused by cooler air circulating around/over warm skin, esp. when exposed

Question 36

what is the conduction of heat

Answer 36

Heat loss through direct contact with a cold surface

Question 37

what is radiation of heat

Answer 37

Heat loss caused by heat radiating towards a cooler surface e.g. towards a window

Question 38

what is thermal stress

Answer 38

the energy needed to maintain a normal body temp
the colder the temperature the greater the thermal stress (bc body metabolism needs to increase in order to warm the body)

Question 39

how does body fluid compartment change before and after birth

Answer 39

before birth - most of the volume of water is extracellular. less intracellular
nearing birth - ECFV decreases and ICFV increases
by 6 months - ICFV is higher than ECFV

Question 40

how is fluid lost

Answer 40

from: respiratory tract, kidneys, stool, skin

Question 41

how much water is lost from resp tract affect fluid

Answer 41

depends on temperature, humidity of inspired gas, resp rate, tidal volume, amount of dead space will influence fluid loss