2. GI response to a meal Flashcards
(25 cards)
MAJOR function of the GI tract
Extract water, nutrients and electrolytes from food and to expel undigested residue as feces
Most signs of GI disease are related to the passage of a meal through the gut and are manifested by:
An abnormal response to a meal
Four major functions of the gut
- secretion
- digestion
- absorption
- motility
* communication and integration among these is important* think MADS
Function of the pharynx
food transfer to esophagus
Function of upper esophageal sphincter (UES)
- allows entry of food from esophagus
- protects airway from swallowed material and gastric reflux
Function of the esophagus
- transport bolus from pharynx to esophagus
- clears material refluxed from stomach
Function of LES
- one of the most important sphincters*
- protects esophagus from gastric reflux
- allows entry of food into stomach
- relaxation is induced by swallowing and decreased basal tone
Function of the stomach
Receives and stores food mixes it with gastric secretions, breaks it into small particles, and delivers the resulting chyme to duodenum
What do the fundus and body do/secrete?
- store food
- secrete H+, mucus, bicarb, pepsinogen, lipase
- tonic force an emptying
What does the antrum do/secrete?
- grinds, mixes, empties
- secretes mucus and bicarb, gastrin
What does the pylorus do/secrete?
- prevents food particles >2mm from leaving
- regulates emptying of stomach
- secrets mucus and bicarb
Gastric emptying
- stomach only empties when intragastric pressure exceed duodenal pressure and pyloric resistance
- influenced by physical and chemical composition of a meal, food type, pH and osmolarity
Receptive relaxation
when a bolus of food passes into the stomach the fundus relaxes, allowing gastric smooth muscle to reset to a longer resting length without an increase in intragastric pressure as ingesta accumulates
- this is accomplished by vagal inhibition of periodic fundic contractions
What are the three phases of gastric secretion?
- cephalic - presence of seeing food stimulates salivation and gastric secretion (prepares stomach)
- gastric - presence of food in the stomach stimulates acid secretion
- intestinal - presence of food in the intestines inhibits secretion of acid
Acid is secreted by the _____ cell
parietal
Pepsinogen is secreted by the ___ cell
chief
What two things stimulate acid and pepsinogen secretion during the gastric phase?
- vasovagal reflex
2. endocrine release of gastrin
A ___ meal has NO effect on gastrin secretion
CHO (protein only)
Three mechanisms of communication mediated responses in the GI tract
- endocrine
- neurocrine
- endocrine
What three things stimulate the parietal cell to secrete acid?
Ach, gastrin (from G cell) and histamine (from enterochromaffin-like cells) bind their own receptor and interact with the others
Somatostatin
- produced from D cell
- inhibits gastrin secretion by g cell, stimulated by presence of acid in the antrum (paracrine)
Why does gastric acid not digest the gastric mucosa?
- Epithelial cells secrete mucus and bicarb (which gets trapped in mucus layer) to buffer the acid
- pepsin is also secreted as pepsinogen
What delays gastric emptying?
protein, calories (fat), acid, hypertonic/hypotonic meals (pH hostile to duodenum - want isotonic)
By what mechanism is gastric emptying delayed in the presence of protein?
Protein broken down to peptides and AA, which stimulate receptors in duodenal mucosa to release CCK - binds receptors in stomach and delays to control rate of energy delivery to duodenum
