Foetal Physiology Flashcards
Describe the structure of foetal haemoglobin.
2 alpha + 2 gamma sub units, increased affinity for oxygen.
Describe how RBC’s are produced in the foetus.
Initially RBC’s are made in the yolk sac but by 16 wks should have moved to the liver and eventually the bone marrow.
Yolk sac –> Liver –> Bone Marrow.
Describe the pathology of thalassmia.
Congenital abnormality with Hb chain- alpha or beta sub unit.
RBC’s are broken down at too quick a rate and the liver can take over again and become enlarged.
What is Hypoxic pulmonary vasoconstriciton?
Hypoxic pulmonary vasoconstriciton: in the lungs low oxygen means vasoconstriction, opposite of the rest of the body where hypoxia = vasodilation.
Describe the basic structure of foetal circulation.
1 umbilical vien, 2 umbilical arteries 3 shunts: Ductus venosus= 50% bypasses the liver Foreman ovale= RA --> LA Ductus arterosus= Pulmonary artery --> Aorta
Describe the process of foetal circulation
1) blood in through umbilical vein
2) Umbilical vein travels to liver:
- 50% goes through to build up glycogen stores
- 50% DUCTUS VENOSUS bypass the liver
3) IVC -> RA
4) RA-> LA-> LV -> Aorta
5) Any blood that goes through RV can go from pulmonary artery -> DUCTUS ARTEROSIS -> aorta
What keeps the ductus arterosus open?
DA is open by prostaglandins made by the placenta
COXi -> close duct so avoid aspirn etc
Prostaglandins -> keep open
Why is taking aspirin in pregnancy risky?
COXi can cause the DA to close.
What happens to the foetal circulation after birth?
Clam down on vessels:
Decreased temperature outside the mothers body causes the umbilical artery and vein to contract. Midwives add a clamp on too.
First breath:
Fluid is forced out of the lungs and air fills. Vasodilation of arterioles and decreased lung resistance. Less resistance in the lungs so RA
What can happen if the foetal circulation fails to swap to adult?
Failure of pulmonary resistance to fall –> ductus arteriosus stays patent –> left to right shunt–> cyanosis
Risks:
NEC
Intravascular haemorrhage
Describe the key developmental milestones of the lungs.
20wks: structures present
22-24wks: blood vessels become aligned with alveoli
24-28wks: type 2 pneumocytes begin to develop and make surfactant.
Who will be affect by RDS? & what is the treatment?
Preterms <28wks
Antenatal corticosteroids + surfactant + ventilation
What factors could cause lungs to not develop properly?
oligohydramnious: as lungs are filled with fluid
Diabetes mellitus- causes type 2 pneumocytes to develop later.
What are the common infections in preterms?
Toxoplasmosis Other: coxsackie, chickenpox, chlamydia Rubella Cytomegalovirus Herpes
Why are preterms more vunerable to cold?
Thin skin + no vernix
Describe normal mid gut development
1) loop of endoderm herniates out of abdomen as not enough space with all other structures e.g. liver
2) Rotates around superior mesenteric artery
3) by wk 12 back in abdomen
What happens if there is failure of the midgut to properly develop?
Midgut fails to return into the abdomen you can get omphalocoele or gastroschisis
How can you tell the difference between omphalocoele and gastroschsis?
Covered in amniotic sac -> omphalocoele
No amniotic sac –> gastroschsis
What causes omphalocoele &gastroschsis?
omphalocoele –> associated with trisomys
gastroschsis –> deficient weak abdominal wall.
Why might there be polyhydramnious?
Failure of the swallow reflex
The foetus swallows alot of amniotic fluid if there is a failure e.g. neurological/ gut obstruction then fliud can build up.
What is the meconium?
The first poo
What are the concerns with meconium stained fluid?
foetal distress and hypoxia
meconium aspiration syndrome
Describe energy storage in the foetus.
Energy stores are only really laid down in the last trimester as fat increases x5
What is the function of the liver in utero?
Liver produces RBC from 6-36wks
Stores glycogen
Does not yet conjugate billirubin
