Gastric Physiology 4/12/23 Flashcards
4 Key cell types in Stomach
Mucous
Parietal
Chief cells
Enterendocrine cells
What cells secrete Gastric acid?
Parietal cells
What type of acid is Gastric acid?
Hydrochloric acid
How are H+ ions taken out of Parietal cells?
Via active transport
What type of stimulation turns on Gastric acid secretion in the Cephalic stage?
Parasympathetic
Which Neurotransmitter is released during Stimulation of Gastric acid secretin during the cephalic phase?
Acetylcholine
What causes the Cephalic phase of Gastric acid secretion to begin?
Sight, Smell and taste of food
Chewing
What two things does Acetylcholine do in the cephalic phase?
Acts directly on parietal cells
ACh triggers release of gastrin and histamine
Second phase of Gastric acid secretion name?
Gastric phase
How much HCl does the average human produce per day
2 litres/day
What is released during the Gastric phase?
Gastrin
What does the release of Gastrin trigger to be released?
Histamine
What does Protein in the stomach trigger the release of?
Gastrin
How does increased proteins in the Lumen cause more parietal cell activity?
Acts as a buffer, mops up H+ ions
Decreases secretion of somatostatin
What is Somatostatin?
Protein that reduces Gastrin secretion
What causes Gastric acid secretion to turn off in the Gastric Phase?
Low luminal pH
What causes gastric acid secretion to turn off in the intestinal phase (4)
Duodenal distension
Low luminal pH
Presence of Amino acids and fatty acids
What is released in the intestinal phase?
Enterogastrones
Two enterogastrones released in Gastric acid secretion? What do they do?
Secretin (Inhibits gastrin release promotes somatostatin release)
Cholecystokinin (CCK)
Summary of Gastric acid release:
Name for 1 Neurotransmitter
Name for 1 hormone
Name for 2 Paracrine factors
Name for 2 Entetrogastrones
ACH
Gastrin
Histamine + somatostatin
Secretin + CCK
What is an Ulcer?
Breach of a mucousal surface
Causes of Peptic ulcers (4)
Helicobacter Pylori
Drugs (NSAIDS)
Chemical irritants- alcohol, bile salts and dietary factors
Gastrinoma
4 Ways Gastric Mucosa defends itself?
Alkaline Mucus
Tight junctions
Replacement of damaged cells
Feedback loops
How does Helicobacter pylori cause reduced mucosal defence?
Splits urea into CO2+ Ammonia
Produces Ammonium
Ammonium secretes proteases and phospholipases which damage gastric epithelium
What does NSAIDs stand for?
Non-Steroidal anti inflammatory drugs
What do NSAIDs inhibit? What does this do?
Inhibits cyclo-oxygenase 1
Reduces mucosal defence
What do Bile salts do to mucosal layer?
Strip it away
Reducing mucosal defence
What is the therapy called for Helicobacter pylori?
Triple Therapy
consists of 1 proton pump inhibitor and 2 antibiotics
Examples of 3 proton pump inhibitors?
Omeprazole
Lansoprazole
Esomeprazole
H2 Histamine receptor antagonist two examples?
Cimetidine
Ranitidine
What do Chief cells produce in the Stomach?
Which is the inactive form of?
Pepsinogen
Pepsin
What nervous system mediates pepsinogen release? What neurotransmitter is involved?
Enteric nervous system
Acetylcholine
What is Pepsin?
What else stimulates the conversion of Pepsinogen –> pepsin?
Protease
HCl
What pH is the conversion of pepsinogen to pepsin most effective?
pH<2
What protease stimulates the conversion of pepsinogen-pepsin? What is this process called?
Pepsin
Positive feedback loop
What causes the irreversible inactivation of pepsin?
Where?
HCO3-
Small intestine
Is Pepsin essential?
What percentage of total protein digestion does it account for?
Not essential
app 20% of total protein digestion
What is Empty stomach volume
What is the Maximum stomach capacity?
Empty~50mL
Eating~1.5L
What mediates Receptive relaxation in the Stomach?:
Nervous system
Nerve(1)
Neurotransmitters (2)
Parasympathetic (Enteric nerve plexuses)
Vagus nerve
Nitric oxide and Serotonin
Part of stomach where most powerful contraction during peristalsis occurs?
Gastric antrum
What determines the frequency of peristaltic waves and where is it? Average frequency of Electrical rhythms?
Pacemaker in Muscularis propria
3/minute
Strength of peristaltic contractions increased by what two factors?
Gastrin
Gastric distension
What 5 factors is the Strength of peristaltic contractions decreased by?
Increased duodenal luminal fat
Increased Duodenal osmolarity
Decreased Luminal pH
Increased Sympathetic NS action
Decreased Parasympathetic NS action
What is Gastroparesis
Delayed gastric emptying
