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19- Hirschsprung's Disease_Questions only.docx

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McGill University
PHGY 313
Russell Jones

PHGY 313 Hirschsprung's Disease Symptoms: Infants pass very little meconium and distended abdomen. Obstruction recurs and excessive vomiting can occur. Surgery must be done to remove the distal large bowel to cure the condition. Note: meconium has no smell since babies are sterile. 1. Why is the defect in this disease? Why is the child abdomen distended and why had he passed no meconium? This is a congenital disease that is associates with Down's Syndrome and chromosomal deletions. There is a loss of intramural ganglion cells (excitatory and inhibitory) in the myenteric and submucosal plexi. The lumen is made of smooth muscle so it is tonically contracted and narrow, obstructing the flow of feces. There is a build up of matter behind it, distending the proximal colon (creating a megacolon). The internal anal sphincter doesn't relax. 2. What did the biopsy reveal? Expand on the innervation of the intestine and the function of the enteric nervous system. The biopsy reveals an absence of ganglion cells to the area of the colon. An elevated level of acetylcholinesterase also indicates an abnormality of the cholinergic innervation. Intrinsic inervation: ACh, CP (+), VIP, NO (-) Extrinsic innervation is by both sympathetic (+,-) and parasympathetic (+). The sympathetic system stimulates motility if it synapses directly on the muscle, but inhibits it via an interneuron. 3. How does this abnormality affect the motility of the intestine? Expand on the different types of bowel movements and how are they generated. An absence of intramural plexus nerves disrupts the coordinated propulsive activity of the colon leading to severe constipation. The parasympathetic nerves synapse directly on the muscle and cause contraction though, but there is no interneuron to provide the inhibition. The sympathetic nerves thus cannot act to inhibit the cholinergic nerves of the plexus, and effective relaxation of circular muscle is lost. Tonic contraction of smooth muscle in the aganglionic segment occurs. PHGY 313  Mixing in the colon results in the formation and reformation of sacs, known has haustration.  Propulsion involves peristalsis or sequential haustration. Can technically be either direction and are slow, 5-10cm/h.  Food has two effects: o Indigestable compounds such as fibre provoke distension and stimulate pro
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