Physiology Flashcards
What are the divisions of the stomach?
Cardia = no parietal cells
Corpus (and fundus)
Pyloric Antrum
What in the stomach increase surface area?
Gastric glands
- Mucous cells
- parietal cells
- chief cells
- endocrine cells
How much and what fluid do gastric glands make in a day?
2 Litres/day
- parietal secretion = H+ rich (stimulated)
- non-parietal secretion = Na+ rich (basal)
Which cells produce bicarbonate and mucous?
Foveolar cells = surface epithelial cells
Which cells does the corpus of stomach include?
Parietal
Chief (peptic) cells
Mucous cells
Endocrine cells
What do parietal cells release?
Acid
Intrinsic factor
What is the importance of intrinsic factor?
Necessary for the absorption of vitamin B12 (essential for brain + nervous functioning and blood formation) later in the small intestine
What do chief cells release?
Pepsinogens
What is the importance of pepsinogens?
Activated to pepsins at pH < 3
Pepsins initiate protein digestion by hydrolysing peptide bonds
Note: pepsinogen secretion parallels acid secretion
Where are mucous cells located?
In the neck of gland
What are the endocrine cells and what do they secrete?
Enterochromaffin-like cells
Secrete histamine
What cells are located in the pyloric antrum?
Chief cells
Endocrine cells
G cells
D cells
Note: No parietal cells
What do G cells secrete?
Gastrin
What is the importance of gastrin?
Stimulates the secretion of acid
What do D cells secrete?
Somatostatin
What is the importance of somatostatin?
Suppreses the release of other GI hormones
Delay gastric emptying by reducing smooth muscle contractions
What are the phases of gastric secretion?
Basal (post-prandially vs. interdigestive phase)
Cephalic (sight, smell, taste)
Gastric (stomach distension due to food)
Intestinal (protein digestion products)
Which nerve is stimulated in cephalic stage of gastric secretion and what is the effect?
Vagus nerve
Increased ACh release, causing:
- acid secretion
- histamine release
- gastrin
Decreased stimulation of D cells
- less somatostatin
Which reflex occur with the gastric phase and what is the effect?
Local enteric nervous system (ENS) reflexes
- ACh released
Vasovagal reflex
- ACh released
Ach causes:
- acid secretion
- histamine release
- gastrin
Describe the gastroduodenal mucosal defence.
Mucous HCO3- layer
- physiochemical barrier releasing HCO3-
Surface epithelial cells = mucous production
What are the role of prostaglandins?
Central role in gastric epithelial defence and repair
How do prostaglandins repair and defend gastric epithelium?
Regulate release of bicarbonate and mucus
Maintain mucosal blood flow
Cell restitution (maintain/repair)
Describe the process of prostaglandins synthesis
Phospholipids —- (phospholipase A2) —> arachidonic acid —- (COX) —–> prostaglandins
What are the reasons for NSAIDs causing peptic ulcers?
Affect COX as a result stop action of prostaglandins
Why are NSAIDs better than COX-2 inhibitors?
Cardiac issues associated with COX-2 inhibitors
Where are COX expressed/induced?
COX 1
- expressed in stomach, platelets, kidneys, endothelium
COX 2
- inducible by inflammatory stimuli
