Question

How does the structure & function of the circulatory system in a fetal mammal differ from that of the adult mammal?

a. Where is fetal blood oxygenated and what is the pathway of oxygenated blood to the fetal heart?

b. How does the structure of the fetal heart and the blood flow through the fetal heart differ from the adult?

Answer 1

The structural and functional differences in circulatory system of fetal mammal from that of adult mammal is diagrammatically represented above which is self-explanatory.

(a) The source of oxygenated blood is not the lung but the placenta. Gaseous exchange takes place here. Oxygenated blood from the placenta comes to the fetus through the umbilical vein, which joins the left branch of the portal vein. A small portion of this blood passes through the substance of the liver to the inferior vena cava, but the greater part passes direct to the inferior vena cava through the ductus venosus. The oxygenated blood reaches the right atrium through the inferior vena cava.

(b) The structural differences of fetal heart are:

• Foramen ovale which connects right atrium to left atrium
• Ductus arteriosus which bypasses pulmonary circulation and circulates greater part of blood of right ventricle to the aorta

The blood flow through the fetal heart differ as follows:

• The oxygen rich blood reaching the right atrium from inferior vena cava is directed (greater part) by valve of inferior vena cava to the left atrium via foramen ovale. The remaining part get mixed up with deoxgenated blood reaching right atrium from superior vena cava and goes to right ventricle.
• The greater part of blood reaching right ventricle bypasses pulmonary circulation via ductus arteriosus to reach the aorta. The remaining part enters pulmonary circulation via pulmonary arteries.