In the fetal circulation, the ductus venosus shunts blood from the umbilical vein directly to the inferior vena cava. Which valve-like structure regulates this shunt, and through which foramen does oxygenated blood preferentially pass to reach the left heart?

• A The sphincter of the ductus venosus (inlet sphincter) regulates flow; foramen ovale directs IVC blood to left atrium ✓
• B Sphincter of Oddi regulates ductus venosus; ductus arteriosus connects to left heart
• C Portal sinus valves regulate ductus venosus; pulmonary foramen connects RA to LA
• D No sphincter — ductus venosus is passive; blood flows to left heart through the ductus arteriosus

Explanation

The ductus venosus has an inlet sphincter (a muscular zone at its origin from the umbilical vein) that regulates the proportion of umbilical venous blood bypassing the hepatic sinusoids. The well-oxygenated blood from the IVC (including ductus venosus flow) is preferentially directed by the crista dividens (valve of IVC / eustachian valve in RA) through the foramen ovale into the left atrium, then to the left ventricle and ascending aorta, perfusing the brain and coronary arteries. The ductus arteriosus connects the pulmonary artery to the descending aorta (right-to-left shunt), bypassing the lungs.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.