Digestion and Absoprtion - BRS

Lipid Digestion and Absorption

1. Must first be converted into fatty acids, monoglycerides, and cholesterol by lingual lipases, gastric lipases, and pancreatic lipases (pancreatic lipase, cholsterol ester hydrolase and phospholipase A20. CCK released slows gastric emptying. 2. Micelles are formed with bile salts in the lumen 3. Absorption into lumen, and products of digestion are re-esterified to tri-glycerides, cholesterol ester, and phospholipids, and with apolipoproteins, form chylomicrons. 4. Chylomicrons are transported out of the intestinal cells by exocytosis into lymph vessels and added to the bloodstream via the thoracic duct.

Calcium Absorption

Absorption requires the active form of vitamin D, 1,25-dihydroxycholecalciferol, produced in the kidney. This induces the synthesis of intestinal Calcium binding protein, calbindin.

Digestion of proteins into their absorbable forms are by these enzymes

Endopeptidases, exopeptidases, pepsin, pancreatic proteases such as trypsin, chemotrypsin, elastase, carboxypeptidases A and B. Pancreatic proteases must be activated first into their active forms.

Abetalipoproteinemia

Failure to synthesize apoprotein B, inability to form chylomicrons

Absorption of Vitamins

Fat soluble vitamins are incorporated into micelles and absorbed along with other lipids. Water-soluble vitamins are absorbed by sodium dependent cotransport mechanisms Vitamin B12 is absorbed in the ileum and requires intrinsic factor (secreted by Parietal cells), usually absorbed by Bacteroides (microbiology) Pathology: if there is no intrinsic factor to allow for ileal absorption, the patient may develop Pernicious anemia, which will require supplementation of B12.

Absorption of proteins into the cells are via _________

Free amino acids are absorbed by Na/Amino acid cotransport, with four separate carriers for neutral, acidic, basic and imino amino acids for facilitated diffusion into the bloodstream. Dipeptides and tripeptides are absorbed by H+ dependent cotransport, converted to amino acids by cytoplasmic peptidases and transported into the blood by facilitated diffusion.

The gradient for absorption of NaCl is created by

Na-K+ pump

Glucose and galactose are absorbed into the lumen via ________ and absorbed into the bloodstream by ______

Na/Glucose cotransport into cells (SLGT1) Facilitated diffusion via GLUT2

Proteins are digested into _______ before absorption into cells

amino acids, dipeptides and tripeptides

Carbohydrates must first be digested into _____ to be absorbed

monosaccharides

Vibrio Cholerae

stimulates chloride secretion ADP is permanently attached to Gs protein, activating the chloride channels permanently. Secretory diarrhea is created by chloride secretion, and sodium and water following it.

K Absorption and Secretion

Absorbed in the small intestine by passive diffusion K+ is actively secreted in the colon, and is stimulated by aldosterone *Excessive loss K in diarrheal fluid causes hypokalemia

Absorption of NaCl

Absorption of NaCl moves into intestinal cells via Passive diffusion Na-glucose or Na-amino acid cotransport* Na-Cl cotransport Na-H exchange* *most important in SI Absorption of NaCl moves into colon cells via Passive diffusion (stimulated by aldosterone Chloride absorption accompanies sodium absorption by: Passive diffusion Na-Cl cotransport Cl-HCO3- exchange

Hypersecretion of gastrin

Duodenal pH is increased, inactivating pancreatic lipase

With the exception of vitamin B12 and bile acids, where is the majority of nutrients absorbed?

Brush border of the small intestine

Bacterial Overgrowth

Deconjugation of bile acids and early absorption in the upper small intestine.

Ileal resection

Depletion of the bile acid pool because bile acids do not recirculate into the liver

Secretion of Water and Electrolytes

Secretory mechanisms are located in the crypts Chloride is the primary ion secreted in the intestinal lumen (H in the stomach). It is transported in the chloride channels. Na is secreted passively by following chloride. Water will follow sodium and chloride to maintain isosmotic conditions.

Iron

absorbed as heme iron or as free Fe2+. Heme iron is degraded and free Fe2+ is release, binding to apoferritin. The Free Fe2+ circulates in the blood bound to transferrin, which is transported from the small intestine to storage sites in the liver, from the liver to bone marrow for hemoglobin synthesis. Pathology: Iron deficiency anemia

Fructose is absorbed via ______

facilitated diffusion

Absorption of Water

secondary to solute absorption isosmotic in small intestine and gallbladder Colon permeability to water is lower than in the small intestine, and feces may be hypertonic

Malabsorption of Lipids leads to ____

steatorrhea