Phgy 210 – Gastric System 3

Phgy 210 – Gastric System 3 - 19:38 o o...

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Phgy 210 – Gastric System 3 19:38 What if the bolus gets stuck in the esophagus? Secondary peristalsis : o Initiated by local distension. o May be mediated by enteric reflexes (short reflexes) or by long (vagal)  reflexes. o Local distension activates sensory fibers as well. The output will be  mediated back to the esophagus by the vagus. This is the  vago-vagal  reflex o Not one peristaltic wave as primary peristalsis. Involves both short and  long reflexes. May be several secondary peristaltic waves until objective is  attained (ie, dislodge the blocked bolus). The LES is in the last 4cm of the esophagus. Half of it is above the diaphragm,  and half is below the diaphragm. The LES has no visible enlargement of circular  muscle. Between the top and the lower end of the sphincter, there is a huge  difference of pH (pH = 7 to pH = 2!) The closure of the sphincter is myogenic. Tonically contracted. On the other  hand, the relaxation is neurogenic. It results from the local release of NANC. Also  vagus involvement.  The relaxation of LES is part of the deglutition reflexes. This makes sense. You  want the food to go down… So from the pharyngeal receptors, activation of the deglutition centre. From there:  Vagal somatic nerves activate directly the skeletal muscle (UES) Vagal autonomic activate indirectly the ENS, which then activates o Smooth muscles in the lower esophagus o Lead to the relaxation of LES In normal conditions, the 2 cm of LES reside in the abdominal cavity. The  100mmHg will therefore not lead to regurgitation. 
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