What effect does the parasympathetic branch have on the fetal heart rate?

What effect does the parasympathetic branch have on the fetal heart rate?

• A. Increases fetal heart rate
• B. Decreases fetal heart rate via vagal response
• C. Has no effect on heart rate
• D. Increases fetal movement

Answer: (B)

The parasympathetic system slows the fetal heart rate. It achieves this through the vagus nerve releasing acetylcholine onto the heart’s pacemaker and conduction pathways (SA and AV nodes). Activation of muscarinic receptors (M2) increases potassium conductance and hyperpolarizes the cells, reducing the rate of spontaneous depolarization and slowing AV conduction. The net effect is a decreased heart rate, i.e., a vagal (parasympathetic) bradycardic response.

The parasympathetic system slows the fetal heart rate. It achieves this through the vagus nerve releasing acetylcholine onto the heart’s pacemaker and conduction pathways (SA and AV nodes). Activation of muscarinic receptors (M2) increases potassium conductance and hyperpolarizes the cells, reducing the rate of spontaneous depolarization and slowing AV conduction. The net effect is a decreased heart rate, i.e., a vagal (parasympathetic) bradycardic response.