physiology of the stomach 2 Flashcards
what coordinates contraction and relaxation of the muscle in stomach wall
the myenteric plexus which receives input from ANS
does parasympathetic stimulation increase or decrease motility
increases
does sympathetic stimulation increase or decrease motility
decrease
what does the muscularis allow
food to be churned - particularly in antrum where muscle wall is thicker
what does food mix with to produce
mixes with gastric juice to produce chyme
where does chyme travel to
chyme passes through pyloric sphincter to duodenum
what breaks down protein in the stomach
pepsin
how is pepsin produced and activated
it is converted from pepsinogen by HCl
only active in acid environment
what does gastric lipase do
breaks down fat at a higher pH
what does gastric pepsin do
initiate protein digestion in the stomach
hydrolyses proteins to polypeptides and amino acids which stimulate acid production
when does pepsin become activated/deactivated
it is inactivated at high ph (6+) but can be reactivated upon re-acidification
when does salivary amylase act on carbohydrate
if pH is around 6 (mouth), so its far less active in acidic environment of stomach
what determines the force of contraction and amount of gastric emptying
neuronal and hormonal input to the antral smooth muscle
what increases antral contraction
distension of stomach
increased gastrin levels
what influences rate of gastric emptying
physical and chemical nature of stomach/intestine content
what does stomach emptying involve
- contraction of lower oesophageal sphincter
- contraction of gastric muscularis
- relaxation of pyloric sphincter
what inhibits gastric emptying
called the enterogastric reflex
- the distension of the duodenum
- presence of fat
- increased HCl
what does the enterogastric reflex prevent
too much chyme entering the duodenum all at once and aids digestion/absorption
what are the implications of the enterogastric reflex on oral drug absorption
high fat meal delays entry to the duodenum
what happens if you eat a larger meal
a longer digestive phase
what is the effect of high fat content
fat in duodenum causes fundus to relax, lowering intragastric pressure
increases feeling of fullness for longer than low fat meal of same energy content, influences intake at next meal
what is absorbed from stomach
- water
- electrolytes
- alcohol
- some drugs
when does absorption properly start
when contents reach small intestine where food is acted upon by products of pancreas, liver, gallbladder
what is the major source of variability in gastric absorption of drugs
the presence of food in the stomach
what is an ulcer
erosion of the mucosal layer with leads to inflammation and damage to underlying tissue
what are the main causes of gastric ulcers
- H pylori infection most common
- NSAID use (2nd most common)
- smoking, caffeine etc can contribute
how can gastric ulcers be managed
- explanation and reassurance
- drug therapy (control of acid production)
- eradication of H pylori
