Lecture 26- Wednesday, March 10 , 2010th
Lower Esophageal Sphincter
No visible enlargement of curcular muscle.
Anatomically insignificant, functionally very important.
Relaxation= Neurogenic- Local release of NANC
PICTURE AT SLIDE 56
LES – lowermost 4 cm of the esophagus, straddling the diaphragm.
When swallowing is not occurring, the sphincter is in a state of tone, and its walls are
in firm apposition. The tone is largely myogenic, but under neural and hormonal
Relaxation of the LES is reflex, initiated during swallowing and mediated by vagal
efferent fibres releasing ACh, which activate inhibitory enteric neurons which release
a NANC transmitter, causing muscle tone decrease. Note: the LES has an intrathoracic segment (subject to –ve pressure) and an
intraabdominal segment (subject to +ve pressure), and the pressures within
these segments vary with phases of respiration.
The presence of an intraabdominal segment of the LES assists the sphincter in
maintaining an effective barrier between the stomach and esophagus: if the
intraabdominal pressure is raised, the pressure of both the terminal segment and the
intragastric contents is raised equally, so that there is no effective change in the
gradient of pressure between stomach and esophagus.
PICTURE AT SLIDE 59
1. INTRINSIC PHYSIOLOGIC SPHINCTER
2. Assisted by presence of an INTRAABDOMINAL SEGMENT
Incompetent LES- sphincter fails to close
“Heartburn” (PYROSIS): burning sensation, radiating upwards in the chest towards
the neck, due to acid reflux into esophagus
PICTURE IN SLIDE 62
Motor Functions of the Stomach
1. Temporary Storage- 1-3 L of contents in the course of a single meal
2. Physical Disruption and Mixing of Contents- Semi Liquid Consistency= CHYME
3. Propulsion into Duodenum- Regulated
Proximal Region- Thin walled
Distal Region- Thick walled
Large doses of Gastrin will have an effect on LES, but only in very large doses.
Therefore Gastrin does not play a role in modulation of LES. Progesterone has been
known to relax the sphincter.
Accomodation of a Meal Intergastric pressure= -5 mmHg
When you take in a meal, only the proximal region expands. Increase in volume not
accompanied by any significant increase in intragastic pressure called Receptive
Relaxation. This receptive relaxation is restricted to the proximal stomach only.
Receptive Relaxation is part of the deglutition r