Lecture 11 Flashcards
What is pyloric sphincter?
Doorway to small intestine
Function of pyloric sphincter?
Regulates movement of contents
3 main parts of stomach (top to bottom)?
Fundus, body, antrum
What does body of stomach secrete?
Mucous, pepsinogen, HCl
What does antrum secrete?
Mucous, pepsinogen, gastrin
What is chyme?
Partially digested food
What is secretion of intrinsic factor essential for?
Absorption of vitamin B12
What does the muscularis mucosa enable during mechanical digestion?
Food to be churned to ensure optimal coverage from secretions
What part of stomach has thicker muscle wall?
Antrum (stronger contractions)
Function of peptic (chief) cell?
Secrete pepsinogen (inactive form of pepsin)
Function of parietal (oxyntic) cells?
Secrete HCl (and intrinsic factor)
Function of goblet (neck) cells?
Secrete mucous (for good lubrication to mix contents)
Function of G cells?
Secrete gastrin
Function of enterochromaffin (mast like) cells?
Secrete histamine
Function of D cells?
Secrete somatostatin
Where are most parietal cells located in stomach?
Body (not antrum - most of pepsin has acted on contents by this stage)
Function of pepsin?
Breaks down proteins, only in acidic environment (converted from pepsinogen by HCl)
Function of gastric lipase?
Breaks down fat at higher pH (5-6)
Formation of acid in parietal cell?
CO2 from bloodstream produces carbonic acid which is broken down to protons and bicarbonate ions. Protons are transported out into lumen by pump, subsequent transport of Cl- ions
What prevents leakage of gastric juice onto underlying tissue?
Tight junctions between mucosal epithelial cells and lumen of stomach
What does mucous secreted by epithelial/goblet cells with higher pH do?
Provides localised neutralisation and physical barrier to acid
What do prostaglandins do?
Increase mucosal thickness and stimulate bicarbonate production (inhibits proton pump activity)
Gastric secretion phases?
Cephalic phase (increased)
Gastric phase (increased)
Intestinal phase (decreased)
What is cephalic phase stimulated by?
Sight, smell, taste, though of food/decrease in blood glucose
What occurs during cephalic phase?
Nerve impulses to medulla cause parasympathetic neurones via vagus nerves to increase HCl and pepsin
Gastrin secretion promoted in antrum which stimulates further HCl and pepsin secretion
What is gastric phase stimulated by?
Stomach digestion due to presence of food
What occurs during gastric phase?
Stomach digestion triggers parasympathetic reflex leading to further HCl, pepsin and gastrin secretions
What is intestinal phase stimulated by?
Digested proteins/fats/low pH in duodenum
What occurs during intestinal phase?
Secretion decreased by:
Neuronal impulses sent to medulla which decrease parasympathetic stimulation of gastric glands (enterogastric reflex)
Local reflexes in gut wall
Release of hormones secretin, gastric inhibitory peptide and cholecystokinin via bloodstream to gastric glands
Role of somatostatin (paracrine agent)?
Involved in HCl inhibition - released in response to increased HCl concentration
