Gastrointestinal tract secretions Flashcards
How many litres is absorbed by the small intestine?
9 litres
How does the GI tract regulate the ECF volume?
Na+ is taken up by GI tract
What are the 3 main functions of the stomach?
- secretion
- motor - regulate food intake, mixing chyme, decrease food size
- humoral - gastrin, somatostatin
What are proximal secretions?
- HCI
- Pepsinogen (cleaved into pepsin (protease))
- intrinsic factor
- mucins/bicarbonate ions
What are distal secretions?
- gastrin
- somatostatin
- pepsinogens
How many litres does the mucosal layer of the stomach secretory cells?
2L/day
What is basal secretions rich in?
rich in H+
What are the different cells & their secretions in the oxyntic glands?
- Epithelial cells - HCO3
- Mucous neck cells - mucus
- Parietal cells - HCI, intrinsic factor
- Chief cells - pepsinogen
How is the pyloric glands different from the oncotic glands?
pyloric glands don’t contain parietal cells
What does intrinsic factor absorb?
Vitamin B12
Describe resting parietal cells
- cytoplasmic pool of tubulovesicular membrane in apical side
- contain acid secreting H, K-ATPase
Describe the cytoskeletal changes when a parietal becomes active
- fusion of tubulovesicular & canalicular membranes]- 50-100x increase in surface area
- microvilli appearance
- insertion of H, K-ATPase pump, K+ + Cl- channels
What is the major function of parietal cells?
gastric acid secretion
What channels are found on the apical side of a parietal cell?
- H-K ATPase
- chloride channel
(HCl secretion)
What channels are found on the basolateral side of a parietal cell?
- Na-K ATPase
- HCO3 & Cl channel
What stimulates ATPase releasing HCl acid?
the release of acetylcholine via the vagus nerve
What do ECL cells release?
histamine, stimulating the H2 receptor, stimulating the H-K ATPase
What can stimulate H+?
Histamine (ECL), ACh (vagus), gastrin (G cells)
What inhibits gastrin?
low pH, therefore downregulating H+ secretions
What similarity do SI & LI structures have?
- crypts of Leinerkuhn (SI - microvilli)
- absorpb fluid & electrolytes via villus cells/surface epithelia respectively
What do crypt epithelial cells secrete?
fluid & electrolytes (Protective-bacteria/toxins)
What is the difference in net absorption/secretion between the small & large intestine?
small - absorbs K+
large - secretes K+
Is paracellular movement passive or active?
passive - determined by tight junctions
Do the crypts cells secrete or absorb?
secrete
Do the surface cells secrete or absorb?
absorb
What can activate a chloride channel?
cAMP
What does the Na+K+Cl- cotransporter bring?
brings ions into cell from blood
What ATPase is in the intestine?
K-Na ATPase