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
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
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