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Actions of the following:
Secretin
CCK
G1P
GLP1 & YY
- Secretin: dec. H+, inc. panc & biliary HCO3-; S cells
- CCK: inc. pancreatic secretions (enzymes & HCO3-)
- G1P: dec. H+ & inc. insulin
- GLP1 & YY: ileal brake
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Small Intestine:
Mucosal Layers?
- Mucosa:
- villi - enterocytes & goblet cells
- crypts - paneth, stem & EEC (S, G, I, D, EC)
- Submucosa: duodenum (brunner's glands), ileum (peyer's patch)
- Muscularis Externa
- Serosa & Adventitia
-
Secretions of EEC?
- S: secretin
- G: gastrin
- I: CCK
- D: somatostatin
- EC: serotonin
-
SI sites of nutrient absorption:
duodenum
jejunum
ileum
- duodenum: Fe, Ca, K
- jejunum: carbs(d), fats & proteins (d & i)
- ileum: B12 & bile salt
-
Small Intestine amplifications?
- placae circularis
- valvulae conniventes
- villi
- microvilli (brush border)
-
Control of blood flow in Small Intestine?
- SANS: vasoconstriction
- Sensory C fibers: vasodilation; capsaicin sensitive & nociceptors
-
Carbohydrate digestion in Small Intestine:
Enzymes
- amylase(luminal): salivary & pancreatic
- maltase-glucoamylase (BB): maltose > glc
- sucrase-isomaltase (BB): sucrose > glc + frc
- lactase(BB): lactose > glc + gal
-
Carbohydrate digestion absorption transporters?
- SGLT1: glucose/galactose (lument to enterocyte)
- GLUT2: glucose/galactose (enterocyte to blood)
- GLUT5: fructose (lumen to blood)
-
Protein digestion enzymes?
- gastric: pepsin
- SI lumen: trypsin, chymotrypsin, carboxypeptidase A & B, elastase
- SI BB: amino peptidase, oligopeptidase & dipeptidyl peptidase
proline or glycine = slow digestion
-
Protein absorption? Mechanism transporters?
- absorb free aa, di & tri peptides; tris=kinetic advantage
- Luminal side:
- PEP T1: dis & tris (H+ cotransport) w/ NHE (Na/H antiporter)
- Capillary side:
- Na/K ATPase
-
Fat digestion enzymes?
- lingual lipase
- gastric lipase
- pancreatic lipase
(small intestine) - lipase & colipase (BB)
- lipoprotein lipase (chylomicron)
-
Micelle Formation
products of lipid digestion (TG & phospholipids) are emulsified (bile acids) along w/fat soluble vitamins and made into micelles
-
Fat absorption?
- micelles come into contact w/BB & FA, MG & cholesterol diffuse across membrane
- Re-esterified w/apoproteins --> chylomicrons
- Exocytosis: lacteal >> lymph vessels>> thoracic duct >> bloodstream >> liver
-
STEATORRHEA
- fat malabsorption due to:
- liver & biliary tract (impaired bile & HCO3- secretion)
- pancrease (reduced HCO3- secretion or lipase deficiency)
- endocrine (dec. chylomicron intake)
-
Beta lipoproteinemia
decrease chylomicron synthesis
-
Crohn's Disease
reduced bile acid absorption - dec. in bile pool
-
Celiac Disease
loss of intestinal surface area
-
-
Ca2+ absorption
- Ca2+ channel (luminal)
- calbindin (intracellular)
- Na/Calbindin anti transporter
- Na/K pump
-
Water Absorption
- Proximal SI: coupled w/Na-H & nutrient
- Ileum: NaCl absorption (Na/H & Cl/HCO3-)
- initially high permeability-hypertonic meal
- isosmotic in SI & gallbladder
- reduced permeability in colon, feces hypertonic
-
Na+ Absorption
- SI: Na/Glc (SGLT), Na/AA (SLC), Na/H (NHE)
- Colon: passive diffusion; aldosterone
-
Cl- Absorption
- passive diffusion (paracellular)
- Na/Cl co transport
- Cl/HCO3- exchanger
-
K+ absorption & secretion
- dietary K+ absorbed in SIK+ secreted in colon
- stimulated by aldosterone
- diarrhea - hypokalemia (over secretion)
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