Function of the Stomach Flashcards
Name the 4 basic functions of the stomach.
- Receive food (short term storage)
- Mechanically disrupt food
- Continue digestion (via proteases)
- Disinfect (antibacterial properties)
What name is given to the point where the contents of the oesophagus empty into the stomach?
Cardia
What name is given to the part of the stomach which forms a bulge above the level of the opening of the oesophagus?
Fundus
What name is given to the strong ring of smooth muscle at the end of the pyloric canal which lets food pass from the stomach to the duodenum?
Pylorus
What type of epithlia is found in the stomach?
Simple columnar
What is the orad stomach?
The fundus and 1/2 of the body of the stomach
Describe why vagally mediated receptive relaxation is important in order for the stomach to perform its food receiving function.
It allows food to enter the stomach without raising intra-gastric pressure too much. This therefore prevents reflux of stomach contents during swallowing.
NOTE: it is gastric mucosal folds (rugae) allow distension
What do parietal cells produce?
HCL and intrinsic factor (a glycoprotein necessary for the absorption of vitamin B12 (cobalamin) later on in the ileum of the small intestine)
What do G cells produce?
Gastrin
What do enterochromaffin cells produce?
Histamine
What do chief cells produce?
Pepsinogen
What do D cells produce?
Somatostatin
What do mucus cells produce?
Mucus
What cell type is the cardia predominantly?
Mucus cells
What cell type is the fundus/body predominantly?
Mucus cells, Parietal cells (HCL), Chief cells (Pepsinogen)
What cell type is the pylorus predominantly?
G cells (Gastrin), D cells (Somatostatin)
Describe how stomach secretions of HCL are controlled.
Parietal cells are stimulated by:
- Gastrin
- Histamine
- Ach (from vagus nerve)
Parietal cells are inhibited by:
- Somatostatin
Describe how stomach secretions of gastrin are controlled.
G cells are stimulated by:
- Peptides/amino acids
- Ach (from vagus nerve)
- Gastrin-releasing peptide (GRP) (from vagus nerve)
G cells are inhibited by:
- Somatostatin
Describe how somatostatin is released.
When food leaves the stomach the pH drops. The low pH activates D cells. These cells release somatostatin.
The reduced stomach distension also reduces the vagal activity.
Describe how HCL is produced.
Lololol good luck
- Hydrogen ions are generated within the parietal cell from dissociation of water.
- The hydroxyl ions formed in this process rapidly combine with carbon dioxide to form bicarbonate ion, a reaction cataylzed by carbonic anhydrase.
- Bicarbonate is transported out of the basolateral membrane in exchange for chloride. (via anion transporter)
- The outflow of bicarbonate into blood results in a slight elevation of blood pH known as the “alkaline tide”. This process serves to maintain intracellular pH in the parietal cell.
- Chloride and potassium ions are transported into the lumen of the cell by conductance channels. (Potassium via the proton pump)
- Hydrogen ion is pumped out of the cell into the lumen, in exchange for potassium through the action of the proton pump; potassium is thus effectively recycled.
- Hydrogen ions and chloride ions join inside the stomach
YAY
Name the 3 stages of digestion.
- Cephalic
- Gastric
- Intestinal
What is meant by the cephalic phase of digestion?
The cephalic phase of gastric secretion occurs even before food enters the stomach. It results from the sight, smell, thought, or taste of food which parasympathetically stimuli the stomach via the vagus nerve in preparation for receiving the food.
What is meant by the gastric phase of digestion?
The gastric phase is a period in which swallowed food activates gastric activity in the stomach.
- Distension of the stomach stimulates the vagus nerve
- Presence of amino acids stimulate G cells
- Food acts as a buffer and removes inhibition on gastrin production
What is meant by the intestinal phase of digestion?
The intestinal phase occurs in the duodenum as a response to the arriving chyme.
- Chyme initially stimulates gastin secretion
- However, soon this is overtaken by inhibition of G cells
Name 2 substances which protect the stomach from digesting itself.
- Mucus
- HCO3- release (NOTE: epithelial surfaces are kept at a higher pH)
(also don’t forget stem cells)
Name 2 stomach defences.
- High turnover of epithelial cells
2. Prostaglandins (maintain mucosal blood flow supplying epithelium with nutrients)
Name 3 things that breach stomach defences.
- Alcohol
- Helicobactor pylori
- NSAIDS (inhibit prostaglandins)
What might be used to relieve symptoms of acid reflux, or gastroesophageal reflux disease (GERD)?
- Proton pump inhibitors
- H2 blockers (Reduce histamine effects)
