Stomach Physiology Flashcards
What cells are present in gastric pits?
- Neck cells
- Parietal cells
- Chief cells
- G-cells
What is the purpose of the stomach?
- Store food
- Disinfect food
- Breakdown food into chyme
What do parietal cells do?
- Produce H+
- Proton pumps (in canaliculi) expel H+ against its conc gradient
- OH- reacts with CO2 and bicarbonate ions are secreted into the blood
What stimulates parietal cells to produce acid?
- ACh
- Gastrin
- Histamine
Tell me about ACh.
- Released from postganglionic parasympathetic neurones
- Acts on muscarinic receptors on parietal cells
- Release is stimulated by gastric distension
What binds to muscarinic receptors on parietal cells?
ACh
Tell me about Gastrin.
- Released from G cells
- Secretion is stimulated by presence of peptides and ACh from intrinsic neurones
- Secretion is inhibited by low gastric pH
What is secreted by G cells?
Gastrin
Gastric distension stimulates release of ___________.
ACh
Tell me about Histamine.
- Released from mast cells
- Binds to H2 surface receptors on parietal cells
- Stimulates acid secretion via secondary messenger pathway (cAMP)
- Works as an amplifier as mast cells are stimulated by Gastrin and ACh
What is released from mast cells?
Histamine
What binds to H2 receptors?
Histamine
Where are H2 receptors located?
Parietal cells
What are the three phases of gastric secretion?
- Cephalic phase
- Gastric phase
- Intestinal phase
What happens in the Cephalic phase?
- Sight and smell of food and swallowing activates the PNS
- ACh is released
- ACh act directly on parietal cells and via histamine to increase acid production
Where can muscarinic receptors be found?
Parietal cells
What happens in the gastric phase?
- Distension of the stomach further stimulates ACh release
- Food acts as a buffer, causing pH to rise
- Rise in pH dis-inhibits gastrin production
- Breakdown of proteins into peptides further stimulates gastrin release
- Increased acid production
What happens in the intestinal phase?
- Chyme leaving the stomach stimulates the release of CCK and gastric inhibitory peptide
- They antagonise Gastrin
- No food to act as buffer, pH falls
- Low pH inhibits Gastrin, acid production decreases
What inhibits acid secretion?
CCK
Gastric inhibitory peptide
What do neck cells secrete?
Mucus
Outline the stomachs defences
- Thick, sticky mucus is secreted by neck cells to protect gastric musoca
- Surface epithelial cells secrete HCO3-
- H+ ions react with amine groups on the mucus or HCO3- and become neutralised
Describe the properties of the mucus.
- Thick, sticky and basic
- Forms an I stirred layer that ions cannot easily move through
What stimulates mucus and HCO3- secretion?
Prostaglandins
What inhibits production of prostaglandins?
NSAIDs
