Hirschsprung's disease results from absence of ganglionic cells in the myenteric and submucosal plexuses of the distal colon. What is the physiological consequence of agangliosis?

• A The aganglionic segment is tonically contracted (fails to relax) due to unopposed smooth muscle contraction without inhibitory neuronal input, causing functional obstruction ✓
• B The aganglionic segment is permanently dilated and hypomotile due to lack of peristalsis
• C The proximal normally ganglionated bowel dilates; the aganglionic segment is atrophied and thin-walled
• D Absent ganglia reduce secretion of VIP, causing hypersecretion of mucus and diarrhea in the aganglionic segment

Explanation

The myenteric plexus (Auerbach's) contains inhibitory neurons (predominantly VIP- and NO-releasing neurons) that coordinate peristaltic relaxation. In Hirschsprung's disease, absence of these ganglionic neurons means the aganglionic bowel segment cannot relax — it remains tonically contracted. This creates a functional obstruction. The normally innervated proximal bowel dilates due to the obstruction, creating the 'megacolon' proximal to the aganglionic segment. Importantly, it is the narrow aganglionic segment (not the dilated bowel) that is the pathological zone requiring surgical resection.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.