Thorax 5 - Foetal Circulation Flashcards
Since there is no mixing of blood between mother and foetus, how are nutrients transferred from mother to baby and waste products vice versa?
Via the placenta
How many umbilical vessels are there?
1 vein, 2 arteries
What do the umbilical arteries become upon birth?
Medial umbilical ligaments
What does the umbilical vein become upon birth?
Ligamentum teres
List the flow of blood in the foetal heart from the inferior vena cava.
IVC —> Right Atrium —> Foramen ovale —> Left Atrium —> Left Ventricle —> Aorta
How does the foramen ovale close?
Pressure in the left atrium rises at birth, forcing the septum premum into the septum secundum and closing the foramen ovale
What is the name given to the vessel that allows blood coming from the SVC to bypass the pulmonary circulation?
Ductus arteriosus
What is the name given to the vessel that allows blood to bypass the hepatic system?
Ductos venosus
How does ductus arteriosus close?
Oxygen - potent constrictor
Prostaglandin levels fall
If closure of the ductus arteriosus doesn’t ensue, what must be administered?
Prostaglandin inhibitors
An overview: describe in relative detail the path blood takes from entering the foetus from the mother to emptying back to the placenta.
Oxygenated blood enters the foetus through the umbilical vein. It bypasses the liver via the ductus venosus and moves into the IVC where it combines with deoxygenated blood. Joined by deoxygenated blood from the SVC, it enters the RA and the majority of blood is shunted through the foramen ovale (due to the pressure in the RA being greater than the pressure in the LA). The minority that passes into the RV makes its way into the aorta via the ductus arteriosus, connecting the PT to the aorta. Deoxygenated blood returns to the placenta via the umbilical arteries, originating from the internal iliac near the bladder.
How long after birth does it take for the ductus arteriosus to constrict and transform into the ligamentum arteriosus?
10-15 hours
What is the first thing that happens to the CVS upon taking a first breath?
Increased alveolar O2 pressure causes vasodilation of the pulmonary vessels
How do the umbilical arteries and vein constrict?
Obstetrical clamping
What type of tissue does the placenta consist of?
Foetal tissue
The membrane between the maternal and foetal circulations is very thin endothelium of the foetal capillaries. What are they solely covered by?
Syncytiotrophoblast
How is a very low pressure system, which allows vast diffusion of material into the foetal villi, achieved?
Maternal capillaries break down and maternal blood bathes the foetal microvilli directly
Is there any mixing of maternal and foetal blood?
NO
Why is hepatic circulation to the liver restricted in the foetus?
Nutrients are already modified by the maternal liver before reaching the foetus via the placenta
What produces prostaglandins?
The placenta
What are some associated issues with patent foramen ovale?
Asymptomatic, however if a thrombus passes into the RA, it is unlikely to end up as a PE in the pulmonary circulation and instead will pass into the LA and later, the systemic circulation through the patent foramen ovale
What are some associated issues with patent ductus arteriosus?
Aortic pressure > PT pressure –> left to right shunt (blood will flow back into the PT –> pulmonary hypertension or congestive cardiac failure
What is a classic sign of patent ductus arteriosus?
Continuous ‘machinery’ murmur
