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
What ATPase is found on the basolateral side of the jejunum?
K-Na ATPase
What exchanger is found on the apical side of the Jejunum?
Sodium-Hydrogen exchanger
What is different in the Ileum compared to the Jejunum?
ileum has a chlorine-bicarbonate exchanger
What is the main role of the ileum?
net absorption of NaCl
What is the main role of the jejunum?
absorption of Na & bicarbonate
What do acinar cells secrete?
enzymes (CCK recs)
What do centroacinar cells secrete?
isotonic aqueous portion, modified by ductal cells
How is HCO3 secreted into pancreatic juice?
using Cl-HCO3 exchanger
What is the net effect of the pancreas?
- secretion of HCO3
- absorption of H+ (acidification of pancreatic venous blood)
What are ductal cells receptors for?
CCK, Ach + secretin, which will upregulate production
What induces the synthesis if Na+ channels in the large intestine?
aldosterone
Is K secreted or absorbed in the large intestine?
secreted
What happens to the products of carbohydrases?
products absorbed into villus blood
What happens to the products of proteases?
products absorbed into villus blood
What happens to lipases + bile salts?
products into the lacteals within villus (part of the lymphatic system)
How does glucose get reabsorbed?
facilitated diffusion (cotransported with Na+)
How do proteins get absorbed?
travel as dipeptides or tripeptides, which have been broken down by peptidase.
- travels into the epithelial cell of SI, using facilitated diffusion & sodium as a cotransporter.
How do micelles get transported across the epithelial cell of villi?
as chylomicrons
What % of the pancreas does the islets of langerhans make up?
10-30% - 500,000
What is the rest of the pancreas made of?
aciner & ductal cells - part of exocrine tissue that secrete enzymes, bicarbonate for digestion
What are the islet main secretory cells?
- beta cells (65%)
- alpha cells (20%)
- delta cells (10%)
What are other cells found in the endocrine tissue?
F cells (polypeptide cells)
E cells
Enterochromaffin cells
What do B cells secrete?
insulin
What do A cells secrete?
glucagon
What do D cells secrete?
somatostatin
What do F cells secrete?
pancreatic polypeptide
What do E cells secrete?
Ghrelin protein (stimulates hunger)
How does blood distribute via fenestrated capillaries?
small arteries enter islet core
What allows communication & control between B & A cells?
gap junction between B & A cells
What does somatostatin do?
somatostatin is a power inhibitor of glucagon & insulin secretion
What are islets innervated by?
adrenergic - sympathetic innervation
cholinergic - parasympathetic innervation
How does glucose enter the B cells?
via GLUT2
What are the 3 types of G-coupled receptors?
- B adrenergic
- Glucagon
- Somatostatin A
What does the activation of B adrenergic agonist & glucagon lead to?
upregulates - adenyl cyclase - leading to more - Exocytosis of insulin
What does activation of somatostatin A & adrenergic lead to?
down regulation of adenyl cyclase, leading to less exocytosis of insulin
What does insulin encourage?
the insertion of GLUT4 (allows for glucose uptake) in the membrane of cells
What is the name given to the conversion of glucose to glycogen?
glycogenesis
What happens to excess glucose?
it converted into adipose tissue (lipogenesis)
What 4 effects does insulin have on muscle?
- promotes glucose uptake
- promotes glycogen synthesis from glucose
- promotes glycolysis & carbohydrate oxidation
- promotes protein synthesis
What is the action of insulin on adipocytes?
- glucose converted into FA (fatty acids) - stored as triglycerides
- insulin prevents lipolysis
What are biguanide drugs?
drugs that up-regulate receptors on target tissues
What drives the mensural cycle?
the hypothalamic-pituitary gonadal axis
