In the fetal circulation, which ventricle ejects the larger share of the combined ventricular output, and why?
- A Right ventricle, because most of its output flows through the ductus arteriosus to the descending aorta and placenta ✓
- B Left ventricle, because it receives the well-oxygenated stream from the ductus venosus
- C Both ventricles contribute equally, since the fetal circulation is a strict parallel circuit
- D Right ventricle, because it faces systemic vascular resistance through the closed ductus venosus
Correct answer: A. Right ventricle, because most of its output flows through the ductus arteriosus to the descending aorta and placenta
Explanation
In the fetus the right ventricle handles roughly 55 to 60 percent of the combined ventricular output. Only a small fraction of its output enters the high-resistance pulmonary bed; the rest passes down the ductus arteriosus into the descending aorta toward the low-resistance placenta, keeping RV load high. The left ventricle receives the better-oxygenated IVC stream but ejects only about 40 percent of combined output, mostly to head and upper body.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
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