Foetal Adaptations to Birth Flashcards
Intrauterine environment - how is it different from outside world?
What is the basic direction of gas exchange across the placenta.
O2 + nutrients = from maternal blood –> into intervillous spaces –> into chorionic villi –> foetal blood
CO2 = from foetal blood –> into chorionic villi –> into intervillous space –> into maternal blood
Describe how O2 & nutrients are exchanged occurs across the placenta.
O2 & nutrients diffuse from spiral arteries (maternal blood) -> across trophoblast memb -> into branches of umbilical vein/chorionic vein (within placental villi) -> then flows into umbilical vein -> then through umbilical cord to foetal circulation O2 & nutrients distributed to heart, brain & all foetal organs & tissues
Describe how CO2 is exchanged occurs across the placenta.
CO2 & other waste products from foetus body -> umbilical arteries (x2) -> branches of umbilical artery/chorionic artery (within placental villi) -> across trophoblast memb -> through uterine veins (maternal blood)
How does O2 transport occur - what facilitates it?
-Placenta has low resistance
-Maternal blood PO2 is higher than foetal -> so O2 readily diffuses across to foetus = pressure gradient set up
How does CO2 transport occur - what facilitates it?
-Placenta has low resistance
-Foetal blood PCO2 is higher than maternal -> so CO2 readily diffuses across to mother = pressure gradient set up
What else assists in the movement of CO2 across placenta?
Haldane effect = the increased capacity of deoxy blood to carry CO2 compared to oxygenated blood
-As foetal blood absorbs O2 to form oxyhaemoglobin – it has reduced affinity for CO2 – so releases this CO2 to mother
-Whereas waste products e.g., urea, uric acid, creatinine – diffuse passively due to conc grads – from foetal to maternal blood
How is foetal haemoglobin different from adult haemoglobin -> describe process involved?
-Foetal = x2 alpha + x2 gamma chains
-Adult = x2 alpha + x2 beta chains
-Foetal Hb = has higher affinity for O2 (so is shifted to left on oxyhaemoglobin dissociation curve) - more readily binds/associated O2 - higher O2 carrying capacity
-Adult Hb = has lower affinity for O2 (so curve is further to right) - more readily dissociates O2 - lower O2 carrying capacity
–> more 2,3-DPG at placenta - beta chains (in HbA) bind to 2,3-DPG more readily than alpha (= stabilises deoxygenated Hb by allosteric binding & facilitates O2 release at tissue)
–> so 2,3-DPG enables more O2 release from HbA at placenta - to HbF - so HbF can then deliver O2 to foetal tissues
(as HbF is unaffected by 2,3-DPG)
Why is foetal haemoglobin (HbF) different from adult haemoglobin (HbA)?
Foetal arterial oxygen pressures are lower than adult arterial oxygen pressures
–> so HbF requires the ability to associate with more O2 (as there is less of it!)
Describe foetal circulation (& shunts involved)?
- Blood from placenta –> flows to umbilical vein (oxygenated blood)
- Ductus venosus shunts blood from umbilical vein to inferior vena cava
- Inferior vena cava flows to right side of heart – RA
- Blood will bypass lungs (as lungs are filled with fluid not air – so pressure is too high to get blood to flow to them – need pressure gradient) by:
- Foramen ovale –> shunts blood from RA to LA (as right side of heart has higher pressure than left)***
- Flows down to LV
- Up aorta
- Down descending aorta
- Joins up with umbilical artery (deoxygenated blood)
- –> to placenta
*** Another shunt – called ductus arteriosus:
-As some blood flows from RA -> RV
–> so shunt moves blood up pulmonary artery & to the aorta (this bit is the shunt) –> to aorta –> down descending aorta –> joins up with umbilical artery –> to placenta
Name the 3 shunts in foetal circulation & where they shunt blood from & to.
-Foramen ovale - shunts blood from RA to LA
-Ductus arteriosus - shunts blood up pulmonary artery & to aorta
-Ductus venosus - shunts blood from umbilical vein to inferior vena cava
What facilitates the movement of blood from right to left side of heart?
*Higher pressure on right side compared to left
-High pulmonary vascular resistance
-Hypoxaemia – pulmonary vasoconstriction
Why are the lungs bypassed in foetal circulation?
As lungs are filled with fluid not air – so pressure is too high to get blood to flow to them – need pressure gradient
What occurs at birth to baby’s circulation - simple description?
-Change in circulation occurs in first few breaths as infants makes a transition to extrauterine life
–> this occurs as umbilical cord is cut
-Pink lips & tongue, rest cyanosed (blue) as lower oxygen saturation in utero – takes several hours for peripheral circulation to make full transition
Give the process of the circulatory changes at birth.
-Circulatory changes – once umbilical cord is cut –> then gas exchange is no longer from placenta
-First breaths transforms circulation in infant
Inflation of lungs reduces pulmonary vascular pressure
-Gas exchange at lungs = rise in PO2
–> causes vasodilatation of pulmonary vasculature (factor causing higher pressure in right side than left – enabling blood shunts)
–> significantly reduces pulmonary vascular resistance (factor causing higher pressure in right side than left – enabling blood shunts)
-Reversal in interatrial pressure gradient causing a valve over foramen ovale to close = functional closure – leaves fossa ovalis (small depression)
-Reversal in pressure gradient between pulmonary artery & aorta causes flow to reverse through ductus arteriosus
-Loss of placental PGE2 & the increased aortic PO2 triggered by respiration also triggers contraction of ductus arteriosus – causing a functional closure of ductus arteriosus = forms ligamentum arteriosum
-Ductus venosus closes = forms ligamentum venosum
Why is it easier for foetus to breath compared to newborn?
-Pulmonary compliance = measure of lung expandability
-Foetus - lungs filled w/ fluid - compliance w/ fluid is higher
-Newborn - lungs are uninflated - compliance w/ air is much lower
=> so is much harder for lungs of newborn to expand
–> so need much higher pressure to have same change in vol (compared to in foetus)
What is the foetal adaptations for birth to assist in breathing?
-Surfactant is produced by Type 2 pneumocytes
–> stimulated by surge in maternal glucocorticoid hormones & thyroid hormones = cortisol! - which increases no. of type 2 pneumocytes & increase in enzymes that make surfactant
–> @ around 30-32 weeks gestation
–> lowers surface tension (at the newly formed air-water interface) & increases pulmonary compliance (makes it easier to expand lungs)
Why do babies lose heat rapidly once they are born?
-Large SA ratio (SA:Vol) - including proportionately bigger head
-Wet
-Small
-Naked
-Poor thermal insulation by adipose tissue
-Can’t shiver to make heat, or move to warmer envs or put clothes on themselves
What is the foetal adaptation to birth to assist keeping warm?
= Brown adipose tissue (BAT) production - enabling non-shivering thermogenesis
-Production of brown adipose tissue (BAT) prior to birth – (@ ~26 weeks gestation)
-BAT – found centrally – in intrascapular region & around clavicles, heart, aorta, trachea, kidney & pancreas
-BAT – has inc amount of mitochondria, is highly vascularised & is well innervated by sympathetic NS
–> Mitochondria = convert fat into heat
–> Highly vascularised & well innervated by symp NS = regulates rate of heat generation
-Also has increased lipase activity & free fatty acid production
==» So BAT - can double metabolic heat production during cold exposure
How to newborns get their nutritional supply immediately after birth?
Glucagon, catecholamine & cortisol – help mobilise glycogen
-Decreased plasma glucose conc
= triggers increase in glucagon & adrenaline
-> these hormones promote glycogenolysis (glycogen -> glucose)
-Adrenaline – also inhibits insulin secretion & stimulates glucagon release from pancreatic islets
-Adrenaline & glucagon = promote lipolysis – providing fatty acids
How do newborn get their nutritional supply 12 hours after birth -> once glycogen supply has run out?
PEPCK (enzyme) activity increases (due to decreased plasma glu conc – but doesn’t immediately increase – hence the previous process taking place 1st) – enables onset of gluconeogenesis
-Cortisol promotes lipolysis = glycerol
-Cortisol promotes gluconeogenesis of non-carb substrates = fatty acids & AAs & glycerol = forms glucose (& can also be used to store more glycogen)
-So glycogen can again undergo glycogenolysis
–> = glucose
*
-Cori cycle forms lactate which can then undergo gluconeogenesis (promoted by cortisol) or convert to glycogen stores (then undergo glycogenolysis)
–> Cori cycle also converts glucose back to lactate (so Cori cycle recycles)
How do newborns get their nutritional supply 12 hours after birth?
-Ketogenesis = production of ketone bodies – by breaking down fatty acids & (ketogenic) AAs
-So same processes as above – fatty acids & AAs can either undergo gluconeogenesis or be converted to glycogen (& later undergo glycogenolysis to form glucose)
-Lactate Cori cycle still occurring
But now fatty acids (& AAs?) can undergo B-oxidation
= this is where fatty acids are converted into acetyl CoA in mitochondria of liver
-x2 of these acetyl-CoA molecules are combined -> forming ketone bodies
-Ketone bodies are used to supply energy to brain, heart & skeletal muscles
Summarise the importance (i.e., the roles) of endocrine hormones in foetal maturation.
