Flashcards in Lecture 8- COPY Deck (30):
1
contents of saliva
EMSL
Electrolytes: hypotonic high HCO3-
Mucins: lubricate bolus and enhance chewing action
Salivary amylase: initiates digestions
Lactoferrin: lysozyme with anti-bacterial action
2
major roles of the stomach
- reservoir
- adjust osmolality of conents
- antrum= grinding
- pylorus= regulates the size of particles
- secretion of acid
3
Gastric motility
1. relaxation of fundus
2. contraction of body and antrum
3. pylorus contracts= to limit exit of chyme
4. mixing by retrupulsion
4
what is required for normal gastric emptying
in tact antrum, pylorus duodenum
normal vagal function
normal hormonal function
(positive feedback from duodenum)
5
what causes delayed gastric emptying
diabetic gastroparesis
- due to autonomic neuropathy
- leads to variable rate of glucose absorption
- upper abdominal discomfort
drugs that delay gastric emptying
- eg anti-cholinergic drugs
6
what causes rapid gastric emptying
after gastric surgery
- "dumping syndrome" = nausea, vomiting, cramping, diarrhoea
- food moves too quickly from stomach to duodenm so are not completely digested
- undigested particles result in hyperosmolar chyme in small bowel
- this causes a rapid fluid shift into the gut causing intestinal distension=pain
- diarrhoea due to osmotic effect
drugs that speed up gastric eptying
- eg metaclopramide
7
what are the 4 types of cells in the stomach
parietal cells
ECL cell
G cell
D cell
8
what is the role of gastric acid in the stomach
- sterilise
- digestion (denatures proteins)
- helps with absorption of b12 and iron
9
what is achlorhydria
absent or low gastric acid
can be a result of pernicious anaemia
10
what kind of pump is in the parietal cells
H+/K+ ATPase proton pump
11
how do the proton pumps in parietal cells work
- H+ is actively pumped out of cells and into the stomach
- in exchange K+ enters the cell
- HCO3- is formed in the cell and transported out into the bloodstream
- in exchange Cl- enters the cell
- HCl formed
12
what reaction happens in the bloodstream with HCO3-
H2O + CO2 H+ + HCO3-
13
why does Cl- enter the cel after HCO3- moves out
to keep the pH and osmolarity in equilibrium
14
what happens when the parietal cell secretes HCl
the tubulovesicles fuse with canaliculus
increased SA and numbers of H+/K+ ATPase
increased acid secretion into gut lumen
15
what are the protection of the gastric mucosa from acid
mucus layer
bicarbonate secretion
16
autocrine
molecule that targets itself
17
paracrine
targets adjacent cells
18
endocrine
released into circulation to target distant cells
19
where are ecl cells located and what do they secrete
located in body of stomach
secrete histamine
20
what does histamine do
paracrine
stimulates acid secretion from adjacent parietal cells
21
what releases Ach
vagus nerve and enteric neurons
22
what does Ach stimulate
1. parietal cells to stimulate HCl
2. ECL cells to release histamine--> stimulates parietal
3. G cells to release gastrin --> stimulates parietal and ECL
23
where are D cells located
in the antrum of the stomach
24
what do D cells do
secrete somatostatin which is paracrine and endocrine
- inhibit acid secretion by acting on adjacent G cells and inhibiting gastrin release
25
what do G cells do
secrete gastrin which is an endocrine hormone
stimuates acid secretion indirectly via ECL cells
goes into circulation and binds to ECL cells which secrete histamine which stimulates parietal cells to release HCl
26
where are G cells located
in the antrum of thes tomach
27
what is the cepahlic phase
initiated by the thought, sight , smell of food
mediated by the vagus nerve through neurotransmitter Ach which directly stimulates the parietal cell to release HCl
28
what is the gastric phase
distension of both the body and the antrum causes acid secretion mediated by the vagus nerve
protein in the antrum (mainly breakdown products eg aas) stimulates G cells to secrete gastrin
29
what is the intestinal phas
inhibition of acid secretion
- HCl in antrum causes D cells to release somatostatin which inhibits V cells from releasing gastrin
Also HCl in duodenum stimulates S cells to release secretin which inihibits gastric acid and gastric emptying and stimulates pancreatic HCO3- secretion to neuralise acid
Partially digested fats and proteins in the duodenum stimulate CCK which inhibits gastric acid and gastric emptying
30