Fetal adaptations for birth

Question 1

basic intrauterine environment

Answer 1

warm
ready food source
ready oxygen supply
automatic waste filtration
long nap times

Question 2

where does in utero gas exchange occur

Answer 2

via the placenta

Question 3

gas exchange via placenta mother to foetus

Answer 3

low resistance
large proportion of combined cardiac output and facilitates gas exchange
maternal blood PO2 is higher than fatal
oxygen readily diffuses across to the foetus

Question 4

gas exchange via placenta foetus to mother

Answer 4

fetus produces high levels of CO2
diffuses easily across placenta to maternal circulation as maternal levels are lower
increased maternal expiration of CO2 via maternal lungs

Question 5

how is foetal haemoglobin different to adult haemoglobin

Answer 5

has 2 alpha and 2 gamma chains
higher affinity for oxygen
delivers bound oxygen to foetal tissues that have low partial pressure
enhanced release of oxygen to foetal tissues
50% more haemoglobin in foetal blood
curve shifts left

Question 6

where is foetal blood oxygenated

Answer 6

as gas exchange is predominantly via the placenta foetal circulation bypasses the foetal lungs as not necessary for gas exchange

Question 7

fetal circulation

Answer 7

high right side pressure: high pulmonary vascular resistance, hypoxaemia- pulmonary vasoconstriction

blood flows across 3 shunts right to left
foramen ovale
ductus arteriosus
ductus venosus

Question 8

ductus venosus

Answer 8

helps blood bypass the liver and delivers highly oxygenated blood back to the inferior vena cava

Question 9

ductus arterioles and foramen ovale

Answer 9

help shunt oxygenated blood away from pulmonary circulation to brain and system circulation

Question 10

first few breaths for baby

Answer 10

Change in circulation occur within first few breaths as infants makes a transition to extrauterine life. Photo of baby in first 1-2 minutes of life
Look at colour of baby – pink lips and tongue, rest cyanosed as lower oxygen saturation in utero – remember description of your case – blue hands and feet; takes several hours for peripheral circulation to make full transition

Question 11

what are the circulatory changes at birth

Answer 11

lower pulmonary vascular resistance
higher systemic pressure
foramen ovale, one way flap closes

Question 12

in utero, foramen ovale significance

Answer 12

blood bypasses by shunting right atrium to left atrium across foramen ovale. Small amount will go to right ventricle and pulmonary artery but shunts away from lungs through ductus arteriosus to aorta

Question 13

what causes the lower pulmonary vascular resistance

Answer 13

Gas exchange at lungs produces rise in PO2 causing vasodilatation of pulmonary vasculature;

Question 14

foramen ovale closing

Answer 14

The reversal in interatrial pressure gradient causing a valve over the foramen ovale to close
– causing a functional closure.

Question 15

reversal in pressure gradient affect on ductus arteriosus

Answer 15

Similarly the reversal in pressure gradient between pulmonary artery and aorta causes flow to reverse through the ductus arteriosus. The loss of placental PGE2 and the increased aortic PO2 triggered by respiration also triggers contraction of the ductus arteriosus – causing a functional closure of ductus arteriosus. This will anatomically close over several days to weeks

Question 16

fetal lungs prior to birth

Answer 16

filled with amniotic fluid

Question 17

fetal lungs at birth

Answer 17

infant needs to replace lung fluid with air and establish resting lung volume
onset of labour causes surge in glucocorticoids, catecholamines and ADH causing secretion of lung fluid to be switched off
main way baby clears lung fluid is through crying

Question 18

surface tension and surfactant

Answer 18

Surfactant is produced from Type 2 pneumocytes

From 30-32 weeks gestation

Helps to lower surface tension and increase compliance

Stimulated by surge in maternal glucocorticoid hormones and thyroid hormones

Question 19

with and without surfactant

Answer 19

Question 20

thermoregulation

Answer 20

large surface area
wet
small

heat is lost by: radiation, convection, conduction, evaporation

Question 21

how to keep body temperature constant

Answer 21

heat production= heat loss

Question 22

brown adipose tissue and non-shivering thermogenesis

Answer 22

increase in heat production not associated with muscle activity
Brown fat highly specialised
colour due to increased mitochondria
High vascularised
Rich beta sympathetic innervation
Increase in lipase activity and free fatty acid production
Can double metabolic heat production during cold exposure

Question 23

different between brown adipose tissue and white adipose tissue

Answer 23

BAT stores few small lipid droplets
larger density of mitochondria to turn fat into heat to regulate body temperature
highly vascularised
well innervated by sympathetic nervous system which regulates rate of heat generation

Question 24

where is BAT located in neonates

Answer 24

interscapular region as well as around the clavicles, heart, aorta, trachea, kidney and pancreas.

Question 25

what has been proposed by WHO on how to best manage thermoregulation

Answer 25

the warm chain

Question 26

what is the warm chain

Answer 26

warm delivery room
immediate drying
skin to skin contact
breast feeding
bathing and weight postponed
clothing newborn
mother and baby together
warm transportation
warm resuscitation
training and awareness raising

Question 27

fetal nutrition

Answer 27

receives nutrients in utero via placenta
transplacental transport of glucose from maternal circulation
cutting of cord disrupts the steady supple of glucose and nutrients
neonate must rapidly adapt its metabolism to survive in extrauterine environment

Question 28

glucose and amino acid transport

Answer 28

glucose diffuses and rate of diffusion depends on concentration in maternal blood stream
amino acids transported across placenta by active transport

Question 29

glucose homeostasis prior to birth

Answer 29

cortisol helps triggers the storage of glycogen in the liver. In addition, when maternal glucose supply is good, insulin triggers storage of glucose not required for growth as fat. A normal fetus stores around 500g of fat (15% body weight). There are sufficient energy supplies to last the term infant 2-3 days post- birth.
However pre-term infants will not have as extensive an energy store. In addition, glucose homeostasis controls are not as well-developed.

Question 30

glucose homeostasis upon birth

Answer 30

the neonate must begin to provide its own energy sources and there is usually a drop in plasma glucose concentration at birth. It does this initially through triggering the release of its glycogen stores – although these deplete in the first 12 h post-birth

At birth the baby has to switch from a state of net glucose uptake to independent glucose metabolism

Question 31

phosphoenolpyruvate carboxykinase activity

Answer 31

PEPCK activity increases allowing onset of hepatic gluconeogenesis
allows lactate recycling to start tot provide support to energy generation
allows adrenaline-induced release of fatty acids to be used to further support neonates energy requirements

Question 32

when does gluconeogenesis start after birth

Answer 32

2 hours and peaks at 12 hours

Question 33

why is gluconeogenesis not active immediately after birth

Answer 33

low activity of cytosolic phosphoenolpyruvate carboxykinase (PEPCK)
the rate-limiting enzyme of this metabolic pathway (fig.2). Liver PEPCK gene and cytosolic enzyme activity increases markedly after birth in response to the decrease in the plasma insulin/glucagon molar ratio.

Question 34

12 hours after birth

Answer 34

Ketogenesis begins, which helps to provide an alternative fuel to glucose for some tissues, and helps ensure cerebral glucose supply. Very high rates – may account for around 25% of BMR in neonates

Question 35

cortisol in fetal maturation

Answer 35

Lung maturation – anatomy and surfactant
Clearance of lung fluid Increased β receptor density Gut functional maturation Maturation of thyroid axis Regulate catecholamine release
Control energy substrate metabolism
Increased Glomerular filtration rate and increased Na+ reabsorption in distal convoluted tubule

Question 36

catecholamines in fetal maturation

Answer 36

Blood pressure regulation, Surfactant release, Clearance of lung fluid,
Glycogenolysis, Thermogenesis

Question 37

thyroid hormones in fetal maturation

Answer 37

Clearance of lung fluid, Blood Pressure regulation, Thermogenesis, CNS
maturation

Question 38

prematurity and fetal adaptation

Answer 38

no fat stores
little glycogen
no surfactant
persistence of fetal circulation