Lecture 25- Monday, March 8 , 2010h
GIT Structure, Functions, Regulation
There are sertain regions in which the musculature is striated (eg the pharynx, upper
1/3 of the esophagus, external anal sphincter, mouth). From below the upper 1/3 of
the esophagus to the internal anal sphincter is smooth muscle enteric innervation.
Propulsion (Flow) in the Gut:
Establishment of gradients of pressure results from the coordinated
contraction of the muscular elements of the wall of the GIT (mostly
o Segmentation: rings of contraction which divide the gut into
sausage like sections. Very effectice mixing movement mixing
contents back and forth.
o Peristalsis: analogy: taking a tube of toothpaste, squeezing it down
so that toothpaste comes out of the tube you are acting like a
Variations in resistance
o Normally very little or no resistance.
o Used to be thought that sphincters regulate the flow of contents
through tubes. One way valves control movement from one organ
to another, close to prevent reflux back into the organ it came
-Normally, flow is slow, aboral and meets little/no resistance.
Phases of Deglutition (swallowing)
-Is accomplished through a complex series of highly coordinated muscular
movements aimed at building up pressure, temporarily sealing off of
compartments to prevent dissipation of pressure, and decreasing resistance. -All of deglutition occurs with the mass of food you ingested moving from the oral
cavity into the stomach.
Oral phase pharyngeal phase esophageal phase
-Transport of bolus (masticated, insalivated mass of food) from anterior to posterior
portion of mouth. This involves a series of reflexes coordinated in DEGLUTITION
CENTRE in medulla oblongata
-Transport from anterior mouth to pharynx.
Cortical vs Medullary Centres
see picture above
-“Voluntary” (ability to initiate)
-Deglutition Center (“involuntary” reflexes coordinate movement)
-Cortical Center to Medullary Center
Under involuntary control, consists of
a) a series of protective reflexes, initiated by stimulation of afferent fibres in the
pharynx, organized in Deglutition Centre, closing off nasal, oral, and laryngeal
cavities, preventing misdirection of the bolus. Simultaneously, respiration is briefly
b) transfer to esophagus, as pharyngeal muscles contract and Upper Esophageal
-Where the respiratory and digestive systems cross.
-What needs to happen:
Passages into the nose, mouth, trachea blocked
Apnea added measure of safety, stop breathing.
UES (upper esophageal sphincter) relaxes
Pharynx muscles contract
Epiglottis covering the glottis secondary process, not that important Upper Esophageal Sphincter
-Corresponds to muscle- Cricopharyngeus. Must be activated neurally by the Somatic
Fibres of the Vagus Nerve are what innervates it.
-CLOSURE of the sphinct