Stomach Flashcards
What are the 3 key functions of the stomach?
- Digestion of macronutrients - chemically and mechanically
- Storage reservoir
- Immunological protection - acid destroys ingested pathogens
Stomach mucosa is lined with columnar epithelia. They also invaginate into what?
Gastric pits.
Gastric pits contain specialist exocrine and endocrine cells.
What do the fundus and body of the stomach secrete?
Gastric acid (HCL, Mucous, Pepsinogen).
Cardia part of stomach and pyloric canal only secrete mucus.
What does the pyloric Antrum secrete?
Gastrin
How does the stomach differ to other parts of the digestive tract?
It has an extra oblique layer of smooth muscle inside circular layer - aids mechanical digestion.
Explain rugae and their significance.
Empty state - mucosa and submucosa are in folds called rugae.
After eating, rugae are stretched and become flat.
Rugae allows stomach to take its reservoir function.
What border does the Z line represent?
Epithelial Border between oesophagus and stomach.
Below Z line = simple columnar
Above Z line = stratified squamous
Contrast the oesophageal epithelium and the stomach lining.
Oesophageal epithelium - light pink. Function as wear and tear lining.
Stomach lining - bright red. resistant to low pH
Millions of gastric pits line the stomach, which are pores in stomach mucosa containing gastric glands. What do gastric glands house?
Functional secretory cells of stomach.
Secrete gastric juice, mucous, paracrine signalling molecules and hormones.
Describe the cells present in gastric glands.
- Mucous cells
- Parietal cells
- Chief cells
- G cells
- Enterochromaffin-like cells (ECL), D-cells, Gastric stem cells
Describe mucous cells.
Mucous cells - many present. Secrete bicarbonate rich mucous, protecting stomach lining. Keeps pH next to lining near to 7 (combats acidic environment). Also protects stomach lining from active lipase and proteases (which may interfere with lipid bilayer and membranous transporters).
Describe parietal cells.
Parietal cells - acid secreting cells. Quiescent until activated. Activation causes tubovesicles fuse with apical surface to make canalicular surface with high SA for secretion. Many mitochondria for membrane transport. Secrete intrinsic factor (GP for B12 absorption - lack of can cause pernicious anaemia).
What are the function of HCL?
- kill ingested pathogens
- Activate protease zymogens
- Alter protein structure to help digestion.
Describe chief cells
Produce protease zymogen (pepsinogen) and lipase (gastric lipase). Pepsinogen activated to pepsin in HCl presence (gastric lumen). Pepsin then breaks dietary proteins into peptide chains. Gastric lipase digests fats by removing fatty acid from triglyceride molecule.
Why do chief cells secrete pepsinogen as an inactive zymogen?
To prevent autodigestion of themselves.