Foetal adaptation to birth

Question 1

What is the intrauterine environment like, why might this be problematic compared to dealing with the external world?

Answer 1

Warm environment - no need to generate their own heat
Long nap time - limited need to wake or move
Automatic waste filtration - limited need to defecate and microturition
Ready oxygen supply - no need to breathe
Ready food source - no need to eat

Question 2

How is the placenta adpated to aid in feotal gas exchange?

Answer 2

Has low resitance, so increased maternal blood flow
Maternal pO2 is higher than foetal pO2
Oxygen readily diffuses across the placenta
Also aided by increases maternal ventilation, this creates the concentration gradients needed fr=or the diffusion of Co2 and O2

Question 3

What are the key features of foetal Hb?

Answer 3

Structurally different from adults, foetal contain 2 alpha and 2 gamma chains, compared to 2 alpha and 2 beta chains.
Higher affinity for oxygen
50% more Hb in foetal blood than maternal blood
Reeadily dissociates oxygen at low pO2 at foetal tissue shown by the oxygen dissociation curve

Question 4

What is the oxygen saturation in a foetus?

Answer 4

Between 40-60%
Due to large amounts of Hb, high demand causes it to rapidly dissociate, hence require lots of foetal Hb in numbers

Question 5

How would a maternal and foetal Hb oxygen saturation curve compared?

Answer 5

Foetal curve would be shifted to the left of the maternal curve
This indicates that foetuses have a higher affinity for oxygen

Question 6

What aids the foetus for blood circulation to bypass the lungs?

Answer 6

High oulmonary vascular resistance - reduce blood flow to the lungs
Hypoxic pulmonary vasoconstriction - intrapulmonary arteries constrict due to lack of oxygen
High pressure in the right side of the heart - encourages to move down the pressure gradients into the left chambers of the heart through shunts

Question 7

What are the three embryonic shunts that allow the blood to move from the right to the left of the heart?

Answer 7

Foramen ovale - between the right and left atria
Ductus arteriosus - connects the pulmonary artery and the aorta
Ductus venosus - abdominal umbilical vein to the left portion of the inferior vena cava, substitutes blood to the heart.

Question 8

Describe the path of foetal blood circulation into the right atrium.

Answer 8

Placenta - diffusion of substances between fetal and maternal blood at the intervillous space.
Oxygenated blood returns to the foetus by the umbilical vein.
Blood may supply the liver and then be drained back out of the liver through a network of veins.
Alternativly some blood can bypass the liver by the ducuts venosus which connects the oxygenated umbilical vein to the deoxygenated inferior vena cava.
The combined blood volume can enter the right atrium
Deoxygenated blood from the superior vena cave can also enter the right atrium

Question 9

How does hypoxic pulmonary vasoconstriction occur?

Answer 9

In foetuses, lungs and alveoli are fluid filled so do not contact oxygen.
Capillaries still surround the walls of the alveoli.
The lack of oxygen in the blood vessels causes the smooth muscles of the arteriole to contract, this narrows the diameter or constricts the capillary reducing the blood flow.

Question 10

What causes the pressure in the pulomary artery to increase in the feotus?
How does this contribute to foetal blood flow?

Answer 10

Hypoxia vasoconstriction as alveoli filled with fluid.
This creates high resistance in the lungs, this increases pressure in the pulmonary artery, this has a knock on effect by increasing pressure in the right ventricle and right atria.
This causes the pressure in the right atria to be higher than the left.

Question 11

In foetal blood circulation, once blood has enters the right atria where might the blood circulate to?

Answer 11

1. very small amounts of blood may enter the right ventricles and circulate through the pulmonary system to enter the left atria, may drain from the pulmonary artert into the aorta through the doctus arteriosus.
2. Through foramen ovale directly into the left atria, drains through the left ventricle

Both will eventually drain into the arch of the aorta and into body wide circulation.

Question 12

How does foetal blood drain back into the placenta?

Answer 12

The placenta has a low resistance so high blood flow from the foetus.
The umbilical arteries are branches of the common illiac arteries, returns blood to the placenta.

Question 13

What is important about a babies first few breaths?

Answer 13

Adapts to extrauterine life.
Changes in circulation as lungs become air filled
Blood circulation no longer bypasses the lungs.
Baby often appears blue or greyish at the extremities but will have pink/red lips and face, this is normal. Coulour will quickly return to the baby within a few hours.

Question 14

When does the baby stop recieving oxygen from the mother?

Answer 14

Placenta and umbilical cord supply the baby before birth.
About ten seconds after birth the baby will start to breathe.

Question 15

How does the babies first breaths influence the pattern of circulation?

Answer 15

When air flows into the lungs it reduces the pulmonary vascular resistance, this also reduces the pressure in the right atrium
The reversal in pressure gradient between the right and left atria causes a valve over the foramen ovale to close.
Pressure changes also causes blood to flow from the arch of the aorta to the pulmonary trunk through the ductus arteriosum.
Loss of placenta PGE2 and increased aortic pO2 causes contraction and function closing of the ducuts arteriosum over a few days/weeks.
This causes the baby to have the same circulation as that seen in adults.

Question 16

How do babies clear their lungs of fluid at birth?

Answer 16

Squeezing of baby during the vaginal birth
Labours causes a rapid increase in ADH, glucocorticoids and catecholamines causing a decrease in lung fluid secretion
Main mechanism is through crying, it is unsure why babies cry at birth may be due to change in temperature or physical discomfort.

Question 17

Why is lung movement hard after birth? how do babies prepare for this in utero?

Answer 17

Harder as more pressure so more difficult to move than liquids.
Fetus will make diaphragmatic respiratory movements in utero to move fluid into and out of the lungs. This practices the neuromuscular reflexes of breathing.
The baby will start to secrete surfactant from type 2 pneumocytes into the alveoli by around 24/28 weeks in utero, this decreases surface tension so the alveoli are less likely to collapse.

Question 18

What forces must the baby overcome in order to take its first breath?

Answer 18

Low compliance of uninflated lung
Viscosity of any remaining fluid.
Surface tension created by air-water interference in the lungs

Question 19

What stimulates the production of surfactant in utero?

Answer 19

Begins at week 24/28
Most occurs at week 32, rise in circulating cortisol stimulates an increased number of type 2 pneumocytes and the enzyme that creates surfactant.

Question 20

How does pressure and area relate in the context of the alveoli?

Answer 20

If alveoli of the sam radius have equal surface tension then the smaller alveoli will have higher pressure.
This means it is more likley to deinflate and be harder to inflate

Question 21

How does surfactant benefit the lungs?

Answer 21

Reduces the surface tension
Decreases the pressure
Often more surfactant in smaller radius alveoli to further decrease the pressure
The smaller radius alveoli will inflate first.

Question 22

Why do babies get very cold very quickly?

Answer 22

Small - large surface area to volume ratio
Wet - evaporation, high latent heat of vaporisation of water.
Can not shiver - lack the skeletal muscle mass for shivering thermogenesis

Question 23

What are the four different ways that a baby can lose heat? In relation to physics?

Answer 23

Radiation - lost to environment, does not require physical contact, lost by infrared rays.
Convection - transfer to surrounding water or air, by moving particle energy
Conduction - physical contact, transfer to touching air and water, enables convection
Evaporation - energy loss during evaporation.

Question 24

What influences the rate of heat loss in a newborn?

Answer 24

The temperature gradient between the baby and the external environment.
Rate of heat loss compared to the rate in which the baby can generate heat.

Question 25

How is the baby adapted to maintain its own body temperature?

Answer 25

Large amounts of brown adipose tissue between the shoulder blades, around kidney, around heart neck and midline.
Brown adiposie tissues contains lots of mitochondria and a good vascular supply, oxidise fat to create heat.
The rate of heat generation is controlled by the sympathetic nervous system.
heats blood in the central vessels, ensures warm blood travels to extremites so keep baby warm.

Question 26

Why might a premature baby struggle to keep warm?

Answer 26

Smaller - larger SA:V
Brown adipose tissue begins to develop at week 26 and continues to develop until term, will have less BAT.
Greater evaporation heat loss, premature skin
Less fat stores
Poor vascular control of blood flow to the skin

Question 27

What is included in the WHO ‘The Warm Chain’ guidance to keep new born babies warm?

Answer 27

1. warm delivery room
2. Immediatly dry the baby
3. Skin to skin contact
4. Breast feeding
5. Postpone weighing and bathing if cold
6. Clothe the new born, particularly the head
7. Keep the mother and baby together making physical contact
8. Warm transportation
9. Warm resusitation
10. Training and awareness raising
    Performing these stepls consequentially has the greatest benefit for the neonate.

Question 28

How does nutrition change from the intra to extrauterine environment?

Answer 28

Intra uterine - glucose supply from the placenta
Extra uterine - babies metabolism must adapt to create its own glucose supply

Question 29

How are substances needed for foetal nutrition transported across the placenta?

Answer 29

GLucose - facilitated diffusion GLUT1/3
Amino acids - active transport
Fatty acids - carrier mediated transport.

Question 30

What happens prior to birth to prepare the baby for temporary fasting after birth before it learns to feed?

Answer 30

Cortisol triggers the storage of glycogen in the liver.
In sufficient maternal glucose supply, insuling may store some glucose as fat
15% of the fetus is fat by weight
These stores are normally enough to last 2-3 days post birth

Question 31

How does the neonate adapt to its nutritional demands upon birth?

Answer 31

Drop in plasma glucose triggers glucagon secretion and glycogenolysis and gluconeogenesis to supply glucose short term.

Question 32

What affect might stress on a foetus have on nutrition?

Answer 32

Stress on a feotus just before or during birth.
increased catecholamine and glucagon rlease
Decrease in insulin
Mobilisation of glycogen stores
Causes glycogen stores to depelte faster, foetus is unable to process the glucose in the blood.

Question 33

How does the fetus recieve nutrition from its own metabolic processes before it starts feeding?

Answer 33

Glucose production by gluconeogenesis starts 2 hours after birth, triggered by increased cortisol and catecholamines. Triggered by increase expression of PEPCK gene and cytosolic enzyme activity in the liver. Peaks 12hours after birth.
Hepatic glucose output by glycogenolysis, depleted within 12 hours of birth.

Question 34

What fuels are important for nutrition alongside glucose?

Answer 34

Ketone body
Lactate
Glucose can only provide 70% of the brains energy demand.
Note these are both temporary.

Question 35

How does the baby increase its levels of ketones available for energy after birth?

Answer 35

Breaks down fatty acids in the liver by B-oxidation to form ketones.

Question 36

What is the role of lactase activity in newborn?

Answer 36

Once babies are feeding and the gastrointestinal tract has started to mature due to hormones included in breast milk
Lactase will break lactose from breast milk down into glucose and galactose, can be absorbed and contribute to the baby energy supply.

Question 37

What is the role of cortisol in foetal maturation?

Answer 37

lung anatomy and surfactant
clearance of lung fluid
increased Beta receptor density. (sympathetic nervous system signalling)
Gut functional maturation
Maturation of thyroid axis
regulate catacholamine release
Control energy substrate metabolism
Increase glomerular filtration rate and Na+ absorption in the distal convoluted tubules

Question 38

What is the role of catecholamines in fetal maturation?

Answer 38

Blood pressure regulation
Surfactant release
Clearance of lung fluid
Glycogenolysis
Thermogenesis

Question 39

What is the function of thyroid hormones in foetal maturation?

Answer 39

Clearance of lung fluid
Blood pressure regulation
Thermogenesis
CNS maturation

Question 40

What are the main problems a premature baby may face?

Answer 40

Decreased surfactant and lung maturation
Decreased brown adipose tissue
Larger surface area to volume ration
No fat stores
Little glycogen
Persistence of foetal circulation
Decreased early bonding and attachment formation if requires emergency care in ICU so can’t be held by parents