The stomach Flashcards
What are the functions of the stomach?
Ingestion Mechanical processing Digestion Secretion Absorption Excretion
Name some notable compounds absorbed in the stomach.
Alcohol
NSAIDS
Describe the muscular layers of the stomach, starting with the most luminal.
Oblique layer overlying mucosa Circular layer Longitudinal layer
Describe the secretions and functional motility of the cardia (and lower oesophageal sphincter).
Mucous, HCO3-
Prevention of reflux, entry of food, regulation of belching.
Describe the secretions and functional motility of the fundus and body.
H+, intrinsic factor, mucous, HCO3-, pepsinogens, lipase
Reservoir, tonic force during emptying
Describe the secretions and functional motility of the antrum and pylorus.
Mucous, HCO3-
Mixing, grinding, sieving, regulation of emptying
How does accomodation work?
Accommodation depends on stretch sensors signalling via the vagus: descending signals (again via the vagus) then act on the enteric nervous system, resulting in relaxation and dilatation of the fundus and body of the stomach, allowing up to about 1 litre of food to be stored in the stomach with very little rise in pressure.
What is the effect of a vagotomy on accomodation?
It doesn’t work any more!
How small do particles in the stomach have to be to pass through the pyloric sphincter?
<1-2mm
What is the response of the duodenum to the delivery of acid, amino acids, and lipids?
The secretion of hormones CCK, secretin GIP which decrease gastric motility.
Also negative feedback from the duodenum via the enteric nervous system.
What kind of cells can be found lining gastric pits?
Mucous cells - also secrete HCO3-
Parietal cells - also called oxyntic cells: secrete HCl and instrinsic factor (fundus and body)
G cell - secrete gastrin (into bloodstream) mainly antrum and pylorus
Chief cells - also call peptic cells, secrete pepsinogen
With which protein may gastrin share receptors?
CCK-PZ (C-terminal 5AA the same). Gastrin receptor also called CCK-B receptor.
What stimulates the release of gastrin?
Luminal proteins/ AAs
Parasympathetic input (cephalic, and in response to stretch) mediated by gastrin-releasing peptide hormones.
What inhibits the release of gastrin?
Luminal H+
What are the main actions of gastrin?
Stimulate acid secretion
Promote mucosal growth
From which cells is somatostatin released?
D cells of stomach, duodenum and pancreas.
What stimulates the release of somatostatin?
Luminal H+
What inhibits the release of somatostatin?
ACh
What are the actions of somatostatin?
Acts on G cells to inhibit release of gastrin
Also inhibits release of CCK and secretin
What is the function of the bicarbonate and mucous secretions?
To protect the epithlium from acid.
What is the function of instrinsic factor?
Binds to cobalamin (B12) in the ileum and facilites uptake.
What stimulates the secretion of pepsinogens?
ACh, H+, secretin, gastrin, CCK
How do pepsinogens become active?
Cleave spontaneously at low pH (<5, fast if <3) and also cleaved by pepsin (autolysis).
Describe the function of pepsin(s)
Endoproteases
Preference for aromatic AAs or large side chains
Optimum pH 2-3
Denatured above 5-7 (once they reach the small bowel)
Describe the function of gastric lipase.
Cleaves the outer fatty acids - leaves diacyl gylcerol
pH optimum = 4
Stable in stomach but denatured by pancreatic proteases
List possible causes of vomiting.
Vagal afferents - in response to irritants in or around bowel
Psychogenic (pain, revulsion, fear etc)
Motion sickness/labrynthine disorders
Drugs/toxins with direct effect
Pregnancy
What is retching?
Involuntary contractions of the diaphragm and abdominal wall muscles.
Which part of the stomach may become displaced into the thorax during vomiting?
Cardia
