Physiology 3120 Lecture Notes - Esophagus, Motility, Hyoid Bone

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26 Nov 2011
Human Physiology
Monday, April 5, 2010
“Gastro VII”
Esophageal Motility (cont’d)
When a swallow occurs, there is inhibition of the tonic electrical activity, so sphincter relaxes, allowing
food to pass through; hyoid bone also elevates, moving the glottis and the esophageal sphincter upwards
(represents minor component of sphincter opening)
Body of the esophagus
Peristaltic contractions in response to swallowing; very similar to the contraction pattern/wave in
the distal stomach to move food into the duodenum; in the stomach, the controlling mechanism
for peristaltic contractions was the slow wave pattern; smooth muscle cells in the esophagus do
NOT have a slow wave; vagus innervates at the top of the esophagus, and then the ENS transmits
the impulse to progressively distal portions; but in order to produce peristalsis, need to increase
the latency as you move down the esophagus (latency gets larger as you move down esophagus)
If something gets stuck, it gets dislodged by a phenomenon called secondary peristalsis; no
stimuli for swallowing beyond the oral pharynx; occurs as a result of stretch receptors being
activated by the presence of food in the esophagus, which then go on to activate the ENS, as well
as a long-loop vago-vagal reflex
Last hurdle bolus has to overcome the entrance into stomach through lower esophageal sphincter
(LES); the LES is not an anatomical sphincter that is, it looks like any other part of the
esophagus; pressure increases (i.e. has high muscle TONE) in the region of the LES, so it is
tonically closed (seems to be due to an intrinsic property of the smooth muscle cells; when the
bolus reaches it, it relaxes due to vagal activation (just as in the proximal stomach), so the
neurotransmitter is nitric oxide
Intestinal Motility (small & large)
Different types of contractile activity in the fed vs. fasted state (24-36hrs of fasting)
Fed state
Two basic types: (1) contractions which are segmental; orientated in time and space so as
NOT to produce propulsion; seems to be randomly distributed contractions that move
material back & forth; purpose is to slosh material back in forth, which will break down
the materials and constantly expose the material to fresh absorptive surface; occurs about
60% of the time; (2) contractions which are propulsive; waves of contraction that are
orientated to move material down the GI tract; only move material 1-4cm at a time; just
like distal stomach, where and when any contraction occurs is regulated by the slow
wave; occurs about 40% of the time
Any single contraction (segmental or propulsive) can be (a) tonic or phasic, (b) low or
high amplitude, or (c) concentric (occurs at the same time in a ring of tissue) or acentric
Fasted state
Volley of action potentials that slowly (takes about 15-24hrs) moves down the intestine;
this wave is called the migrating motor complex (MMC); only observed in fasted
individuals; duodenum releases a hormone called motilin (peptide hormone) in response
to prolonged fasting; the MMC’s function is basically to cleanse the intestine (not seen in
patients with high levels of some bacteria)
Digestion and Absorption (electrolytes & water)
Solute and water transport
No specific mechanism for water transport other than following solute concentrations; moves
paracellularly (between cells) and only moves in response to osmotic gradient established by
solute transport; will be much greater in the upper small intestine than distal small intestine
(most of the solute gets absorbed in upper small intestine (jejunum); solute transport in upper
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