Fetal Circulation Flashcards
What are the reasons for the different circulation in a foetus?
Lungs are non functioning and the digestive system is not fully functioning so it has a restricted hepatic circulation
What are the three shunts/by-passes of foetal circulation to avoid the lungs and liver
- By-pass of hepatic circulation,
- By-pass of pulmonary circulation via foramen ovale,
- By-pass of pulmonary circulation via ductus arteriosus (blood vessel that connects PA to aorta)
What is the function of the placenta?
Allows oxygen and nutrients to diffuse across placental barrier from mother to foetus while removing CO2 and waste from foetal circulation. Means maternal and foetal circulation never mix.
Describe what surrounds the umbilical cord and what it contains
Foetal membrane and aminon. The umbilical cord contains Wharton’s jelly which the two umbilical arteries and singular umbilical vein are embedded in.
What is the function of the umbillical vein?
Carry oxygen and nutrient rich blood from placenta. It then divides into two branches; smaller branch to liver and larger branch, called the ductus venosus which by-passes liver and drains into inferior vena cava.
90% of blood from the pulmonary trunk travels to aorta via ductus anteriosus. What happens to the other 10%
It travels to the non functioning lungs and then returns to heart via pulmonary veins to LA whithout being oxygenated
What occurs when the umbilical cord is tied and cut?
There is a loss of blood flow through the placenta, resulting in increased systemic vascular resistance and increased aortic, left ventricular and left atrial pressure.
What occurs when the baby takes its first breath
-Expansion of the lungs as alveoli open. This causes decreased pulmonary vascular resistance and reduced pulmonary arterial, right ventricular and right atrial pressures.
Describe how the foramen ovale closes
Once pulmonary circulation is established, the blood from the lungs is returned to LA causing pressure to rise in the LA. This causes the foramen ovale to be pushed rightwards and close. Structurally closed by 4 months forming fossa ovalis and falx septi.
What can arise as a consequence of non closure of foramen ovale?
Patent foramen ovale (PFO), this is usually aysymptomatic but may cause paradoxical emboli
Describe the functional closure of the ductus anteriosus
Within the first hour after birth their is constriction of the smooth muscle in the wall of ductus anteriosus which is caused by increased oxygen content of the blood and a fall in prostaglandins.
Describe the structural closure of the ductus anteriosus
Occurs between 1 and 4 months. Anatomic closure by thickening of tunica intima
Describe what occurs with patent ductus anteriosus
Postnatally aortic pressure > pulmonary trunk pressure so blood will flow into pulmonary circulation, increased pulmonary blood flow can lead to pulmonary hypertension which if untreated can lead to congestive cardiac failure
Describe the obliteration of the ductus venosus
When blood flow through umbilical vein ceases the muscle wall of ductus venosus contracts. It functionally closes within 1-3hrs, obliterates and becomes ligamentum venosum
Describe the oliteration of the umbilical vessels
Umbilical vein obliterates and becomes ligamentum teres hepatis. The distal parts of the umbilical arteries atrophy within 2-3 months and become medial umbilical ligaments.
