Fetal circulation Flashcards
What are the 3 shunts in petal circulation?
- By pass of pulmonary circulation via Ductus arteriosus
- By pass of pulmonary circulation via Forman ovale
- By pass of the hepatic circulation (ductus venosus)
What is the function of the placenta?
• Diffusion of O2 and nutrients across the placental barrier from mother to foetus, removal of CO2 and metabolic waste
Where is the placenta usually located?
• In the fundus of the uterus
What surrounds the umbilical cord?
- Fetal membrane
- Amnion
- It contains whartons jelly
What is embedded in Wharton’s jelly?
- 2 umbilical arteries
* Single umbilical vein
What is the function of the umbilical vein?
• Carries oxygen rich and nutrient rich blood from the placenta
What are the branches of the umbilical vein?
- Smaller branch to the liver
- Ductus venosus - by passes the liver and drains into the inferior vena cava where the arterial blood mixes with venous blood from the lower limbs
Foramen ovale
• most of the blood coming through the inferior vena cava passes from the right atrium to the left atrium through the foramen ovale (–> LV –> Aorta)
Describe the flow of blood that comes from the superior vena cava
• Most will go into the right ventricle (gravity)
• Then most:
–> Pulmonary trunk –> Ductus Arteriosus –> Aorta
• 10%:
–> Pulmonary trunk –> Pulmonary arteries –> Lungs –> Pulmonary veins –> LA –> LV –> Aorta
Where does the blood in the aorta go?
- 1/3 to lower limbs, pelvis and abdomen
* 2/3 to the placenta via the internal iliac artery –> umbilical artery
Draw diagram of foetal circulation
look at diagram
What happens to the circulation postnatally?
• Shunts obliterated
• Umbilical cord is cut and tied (2cm left in case of intestine)
- loss of blood via the placenta, has to go other way
- increased systemic vascular resistance
- increased aortic, left ventricular, left arterial pressure
• First breath:
- Expansion of the lungs
- Decreased pulmonary vascular resistance
- Reduced pulmonary arterial, right ventricular, right atrial pressure
Describe the closure of foramen Ovale
- Blood from the pulmonary circulation is returned to the left atrium
- Pressure rises in the left atrium
- Valve of foramen ovale is pushed rightwards and closes the foramen
- Becomes structurally closed by 4 months –> fossa ovalis –> fall septi
Patent foramen ovale
- Usually asymptomatic
* May cause paradoxical emboli
Obliteration of Ductus arteriosus
• Functional closure (1 hour)
• constriction of smooth muscle on the wall of ductus arteriosus due to:
- increased oxygen
- fall in prostaglandins (vasodilator) and rise in bradykinin
• Structural closure (1-4 months)
- anatomical closure by thickening of tunica intima and becomes ligamentum arteriosum