ENS Flashcards
Mucosa
-epithelium
-lamina propia
-muscular mucosa
Submucosa
-Aeriolar connective tissue & dense connective tissue
-Contains glands
-Contains Submucosal Plexus (or Meissner’s plexus)
Muscularis externa
-Inner circular layer
-Outer longitudinal layer
-Stomach has an additional layer called the inner oblique layer
-In between there is the Myenteric plexus (Auerbach plexus)
Serosa
Similar to mesothelium
GI motility of muscularis externa: course of ingested food
1) Food bolus enters GI tract
2) Stretches the wall of alimentary wall
3) Stretch Receptors in the muscular layer are activated:
➡️descending fibers (go to anal side)
➡️ascending fibers (go to oral side)
-Circular layer:
-Contracts and produces a constriction ring and pushes behind the bolus and pushes it forward
-Longitudinal layer:
-When it contracts it opens the lumen in front of the food
THEREFORE for the food to move down the gut, the circular muscles need to contract and longitudinal muscles need to relax.
GI motility of muscularis externa: function of ascending fibers
The ascending fibers work on the oral side of the bolus to push it forward.
The stretch receptors will stimulate the ascending fibers. Axons travel to the longitudinal muscle layer and the circular muscle layer
-Circular Muscle Layer:
-The fibers from the stretch receptors release acetylcholine + substance P to the circular muscle layer ➡️causes it to CONTRACT (by increasing cation influx)
-Longitudinal Muscle Layer:
-The fibers release vasoactive intestinal peptide (VIP) + Nitric Oxide ➡️ potassium ions to leave the cell ➡️hyperpolarization ➡️causes the muscle to RELAX
Gi motility of muscularis externa: function of descending fibers
The descending fibers work on the anal side of the bolus. When propelling the food down the gut tract, the area that is after the bolus needs to be open/relax to accept the food.
-Circular Muscle Layer
-The fibers release VIP + NO cause potassium ions to leave the cell hyperpolarization RELAX receptively open
-Descending fibers give fibers to the circular muscles downstream / anal side of the bolus. This area needs to relax to allow the bolus to move downstream
-Longitudinal Muscle Layer
-The fibers release acetylcholine +substance P to the longitudinal layer ➡️CONTRACT ➡️opens up the lumen to accept the bolus
Submucosal plexus
Stretch Receptors can stimulate the submucosal plexus as well. But the more powerful stimulators for the submucosal plexus are the chemoreceptors.
Function of chemoreceptors
Chemoreceptors release chemicals depending on the food eaten. Certain chemical substances can stimulate chemoreceptors and stimulates the submucosal plexus.
How are the chemoreceptors stimulated?
-chemical substances from food➡️ chemo receptors stimulated ➡️ active submucosal plexus➡️ stimulates gland to secrete secretions to the lumen to help digest food
-if 🩸 vessels are stimulated by chemoreceptors➡️ 🩸 vessels dilate ➡️more 🩸flow in area➡️⬆️’s absorption of substances of circulation
Short reflexes
Short reflexes are completely peripheral and only involve the local integration of sensory input with motor output.
Long reflexes
Long reflexes have afferent branches that enter the spinal cord or brain and involve the efferent branches
Ex. Enterogastric reflex, deification reflex, and vagovagal reflex
Enterogastric reflex
-Chemoreceptor/stretch receptor ➡️prevertebral ganglion (sympathetic nervous system) ➡️inhibits secretions, dilation, secretions, constriction pyloric sphincter, etc. (these are the effects of the sympathetic nervous system)
Function:
-This is an inhibitory reflex which is initiated by:
-↑↑↑ acid in the intestines
-↑↑↑ distention of stomach
-Signals from the colon and small intestine inhibit stomach
motility and stomach secretion.
-Since the rate of stomach emptying is slower, sufficient time is ensured for adequate digestion in the duodenum and small intestine.
