Small Intestine Flashcards
Anatomical components small intestine, function
- duodenum
- jejunum
- ileum
- primary site digestion/absorption
ileocecal valve: contents of ileum can push through valve. cecal contents close flaps, prevent reverse
ileocecal sphincter: neuronal/hormonal control. ileal distention = relaxation. gastrin inhibits sphincter
Motility: Differentiate between segmentation and the migrating mobility complex and state the function and control mechanism(s) for each
segmentation: ensures thorough mixing during chyme processing during meal. altering contractions/relaxations. initiated by distention of duodenum, presence of gastrin, PSNS input. helps move chyme
migrating mobility complex: moves luminal contents along small intestine in btw meals. begins at duodenal-gastric jxn. weak peristaltic contractions that travel short distance. 2 hours from small –> large
Secretions: Identify the secretions of the small intestine and discuss their function and control mechanism(s).
mucosal epithelium secretes 1.5 L of aqueous salt/mucus “succus entericus” which lubricates, protects mucosa, H2O needed for hydrolysis.
stimulus for succus entericus production is presence luminal chyme
Digestion: Outline the steps involved in the digestion of protein, fats and carbohydrates in the small intestine.
fats: completely hydrolyzed by pancreatic lipase. MG and FFA = absorbable
proteins: reduced to small peptide chains by pancreatic proteolytic enzymes. further hydrolysis by aminopeptidases in epithelial brush border before absorption
carbs: broken to DS and some MS. further hydrolyzed by disaccharideses in epithelial brush border
Absorption: Describe the specific adaptations of the small intestine lumen to increase surface area. Explain why a large surface area is important.
circular folds on inner surface increase SA x 3
villi extend into lumen, increase SA x 10
brush border increase x20
Absorption: Describe the steps involved in the absorption of proteins, fats and carbohydrates in the small intestine. Explain the relevance of secondary active transport.
carb- disaccharidases in brush border hydrolyze DS into glucose, galactose, fructose.
glucose/galactose absorbed via secondary active transport. cotransporter with Na+ ions, passively diffuse into interstitial fluid through channel, enter capillary
fructose passively diffuses through epithelial cells by facilitated diffusion
protein
- endogenous: digested enzymes, proteins from epithelial cells sloughed, plasma proteins leaked into GI
peptide fragments hydrolyzed by aminopeptidases in brush border, absorbed via secondary active transport with Na+ ions. enter capillaries
fats
micelles deliver GA and FFA to brush border. digested fat diffuse into cell. bile salts/lecithin/cholesterol free again
MG and FFA combined to form TGA, aggregate with lipoproteins = chylomicrons, Exocytosed
enter central lacteal of lymphatic system
Absorption: Explain how water is absorbed and the importance of active Na+ uptake in this process
h2o absorbed in small intesinte
active pumping Na into interstitium
osmotic pressure attracts water from lumen
hydrostatic pressure moves water into capillaries
Absorption: Describe how calcium and iron absorption differ from the three main nutrients.
iron: ferrous iron (2+) easily absorbed
- phosphate molecules can bind to iron, prevent abs
- vit C enhance abs by increasing Fe2+
actively transported into epithelial cells
iron needed to RBC production enters blood, rest remains found ferritin in epithelial cell
Ca: absorption regulated at site active transport Ca2+ into epithelium
- brush border ca2+ active transport enhanced by vit 2
Absorption: Describe how the GI tract maintains acid-base balance and the complications of diarrhea
intestinal absorption ensures inos are recycled
loss electrolytes in large quantities produce imbalance
vomiting = loss stomach acid, = metabolic alkalosis
diarrhea = loss HCO3- in feces, = metabolic acidosis
also, rapid exit of chyme, decrease absorption time - malnutrition, dehydration, acid-base imbalance
