Term
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Definition
| Co-transported with sodium (secondary active transport) |
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Term
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Definition
| Results from a genetic defect in the transport protein for neutral amino acids |
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Term
| Small polypeptides (dipeptides, tripeptides) |
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Definition
| Absorbed by carrier-mediated transport and by endocytosis; Cleaved to amino acids within the absorptive cell |
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Term
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Definition
| Cotransported with hydrogen ions by secondary active transport |
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Term
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Definition
- Initiates activation of pancreatic proteases (e.g. trypsinogen -> trypsin) via proteolysis
- Secreted by duodenal epithelial cells |
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Term
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Definition
Trypsin, Chymotrypsin, Elastase, Carboxypeptidase A & B
* Only active at neutral pH |
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Term
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Definition
- Break down small peptides to free amino acids, dipeptides, and tripeptides
- Attached to surface of intestinal epithelial cells |
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Term
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Definition
- Major components: Bile salts and Bile acids
- Role: Digestion of lipids
- Secreted by: Liver |
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Term
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Definition
- Amphipathic
- Stabilize fat droplets in aqueous solution
- Inhibit lipase activity by preventing it from getting to fat drop surface
- Presence in blood directly stimulates rate of secretion of bile salts by the liver
- Reabsorbed in terminal ileum by secondary transport along w/ Na+ |
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Term
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Definition
- Less amphipathic at neutral pH d/t reduced charge and more limited solubility in water; higher pKa than bile salts
- Can diffuse directly into the enterocytes
- Presence in blood directly stimulates rate of secretion of bile salts by the liver |
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Term
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Definition
- Synthesized and converted into conjugated bile salts in the liver
- Converted to secondary bile acids by intestinal bacteria
* Conjugated bile acids can be deconjugated by intestinal bacteria & proteolytic enzymes |
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Term
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Definition
- Process of breaking up fat droplets into a suspension of fine droplets in water
- Greatly accelerates rate of lipid hydrolysis by lipases d/t large increase in SA:V of the fat droplets |
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Term
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Definition
- Function: Lipid hydrolysis
- Soluble in water --> only has access at oil/water interface
- Inhibited by bile salts |
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Term
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Definition
- Coenzyme that facilitates lipid hydrolysis by positioning lipase molecules near oil/water interface
- Facilitates trasnfer of lipid digestion products from the fat drop into a micelle
- Amphipathic: hydrophobic end inserts into fat drop; hydrophilic end binds lipase |
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Term
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Definition
- Helps remove digestion products from fat drops
- Critical role in transporting digestion products to absorptive epithelial cell (b/c micelles can diffuse across the unstirred layer of mucous) |
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Term
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Definition
- Covers mucosal surface of the absorptive epithelial cell --> increase total SA for absorption
- Contain actin & myosin
* Micelles can diffuse b/t microvilli |
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Term
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Definition
| Pass directly thru absorptive epithelial cells by diffusion and enter portal blood w/o modification |
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Term
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Definition
| Bind to lumenal membrane of enterocyte --> bind cytosolic FABP --> transported to ER for resynthesis into triglycerols |
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Term
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Definition
| Absorbed as free cholesterol but then is reesterified with fatty acids |
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Term
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Definition
- Large fat drop vesicles containing packaged complex lipids
- Amphipathic coat: phospholipids & apolipoproteins
- Diffuse into lymphatic sacs --> general circulation
* Bypass the liver |
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Term
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Definition
Amphipathic protein that directs the movement of chylomicrons
* Apolipoprotein B must be on chylomicron surface for exocytosis to occur |
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Term
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Definition
| Autosomal recessive disorder in which apolipoprotein B is absent from chylomicrons |
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Term
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Definition
- Stores and concentrates bile
- Tremendous capacity for absorption of salt and water |
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Term
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Definition
| Bile salts, Cholesterol, Phopholipids, Bicarbonate ion, Bile pigments (from Hb breakdown) |
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Term
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Definition
- Secreted in response to digestion products in the duodenum
- Stimulates hepatic secretion of bile salts
- Stimulates contraction of gall bladder smooth muscle
- Stimulates relaxation of the sphincter of Oddi |
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Term
| Enterohepatic circulation |
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Definition
| Recirculation of bile salts - bile salts and acids in the portal blood stimulates the rate of secretion of bile salts by the liver; synthesis of new bile acids is inhibited by increased portal blood bile salt concentration |
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Term
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Definition
Primary Regulators: CCK and the presence of bile salts in the portal blood
* Secretion stops d/t absence of fat digestion products in duodenum to stimulate CCK release --> sphincter closes --> prevents further release of bile salts |
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Term
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Definition
- Inhibited by the presence of bile salts in the portal blood
- Most rapid between meals |
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Term
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Definition
| Calcium binding protein that serves as an intracellular Ca++ -buffer that allows lg. amts of Ca++ to traverse cytosol while keeping free intracellular [Ca++] low |
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Term
| Calcium Absorption in the Duodenum |
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Definition
Lumenal Ca++ binds transporter on brush border membrane --> Ca++ moves down conc. gradient into epith. cell and binds to CaBP --> pumped out of cell via calcium-ATPase
*PTH and Vit D required for Ca++ absorption |
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Term
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Definition
| Promotes expression of important proteins incl. CaBP, Ca-ATPase, Ca channel, etc. |
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Term
| Role of Acid and Vitamin C in Iron Absorption |
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Definition
- Acid will help reduce iron and make it more soluble / absorbable
- Vitamin C forms a soluble complex with iron and also promotes reduction; both actions facilitate absorption |
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Term
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Definition
- Reversibly binds i/c Fe -->
* Forms a complex that buffers free i/c Fe levels
* Allows for transport of Fe across the cell
* Keeps Fe levels low enough to prevent toxicity |
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Term
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Definition
- Transmembrane protein located in basalateral membrane
- Exports Fe from the cell
- Closely assoc. w/ hephaestin |
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Term
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Definition
| Ferroxidase which oxidizes ferrous ions to ferric ions that can bind to transferrin in the blood |
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Term
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Definition
- Binds iron to form Ferritin, a protein-iron complex
- "Storage site" for intracellular Fe |
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Term
| Apoferritin and Mobilferrin Expression in Iron Deficiency |
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Definition
Apoferritin: Low expression
Mobilferrin: High expression
* This increases the amount of iron absorbed from the diet |
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Term
| Apoferritin and Mobilferrin Expression in Iron Overload |
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Definition
Apoferritin: High expression
Mobilferrin: Low expression
* This decreases the amount of iron absorbed from the diet |
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Term
| Absorption mechanisms of Water-soluble Vitamins |
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Definition
| Diffusion; Facilitated Diffusion (carrier-mediated); Secondary active transport along with Na+ |
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Term
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Definition
| Complex w/ dietary proteins -> B12 released by protein digestion in stomach -> B12 rebinds to R protein -> B12-R complex travels to small intestine -> R protein digested by proteases -> released B12 binds to Intrinsic Factor (IF) -> B12-IF binds to brush border receptor -> B12 complexes w/ Transcobalamin II and diffuses into the blood |
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Term
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Definition
- Glycoprotein found in saliva and gastric juice
- Binds to released B12 molecules in stomach -> travels to small intestine where it gets digested and B12 is released again |
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Term
| Vitamin B12 - Oral Ingestion |
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Definition
| Since B12 can also diffuse directly into epithelial cells (~1-2%), oral ingestion of B12 can prevent deficiencies where intrinsic factor is absent |
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Term
| Vitamin B12 - Intramuscular Injection |
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Definition
| Required in B12 deficiency resulting from degenerative changes to the absorptive mucosa (e.g. sprue) |
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Term
| Water reabsorption in Small Intestine |
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Definition
> 90%
- Epithelial cell tight jxns are permeable to water -> luminal contents isotonic w/ plasma
- Water absorbed passively as 'osmotically committed water' along w/ salts & digestion products |
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Term
| Standing osmotic gradient |
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Definition
- Na/K ATPase in basal-lateral membranes of absorptive cells transport Na+ into intercellular space -> Cl- & bicarbonate also transported into intercellular space -> creates a hypertonic solution near apical end -> causes osmotic flow of water into intercellular space from lumen of colon across tight jxns & also from adj. epith. cells
- Accounts for water absorption in colon as well as absorption of water from bile in the gall bladder |
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Term
| Water reabsorption in the Colon |
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Definition
- ~400ml/day
- Absorbed against osmotic pressure difference via standing osmotic gradient mechanism |
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Term
| Sodium Absorption in the Small Intestine |
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Definition
-Diffusion through channels
- Cotransport with organic solutes (glc, gal, AA, bile salts)
- Cotransport with chloride ions
- Countertransport in exchange for hydrogen ions |
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Term
| Sodium Absorption in the Large Intestine |
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Definition
- Duodenum and Jejunum: cotransported with AA and monosaccharides
- Ileum: cotransported with bile salts |
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Term
| Electrogenic Absorption of NaCl |
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Definition
- NaCl is absorbed by an electrogenic process in the colon with sodium ions moving through channels regulated by mineralocorticoids
- Adolsterone increases the number of sodium channels and enhances sodium absorption |
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Term
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Definition
| Irreversibly activates adenylate cyclase via G-protein interaction -> increased [cAMP] opens CFTR chloride channels in luminal membrane -> increases NaCl secretion, water producing diarrhea, electrolyte deficiencies |
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Term
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Definition
Passively absorbed in the small intestine via paracellular pathway (absorption of osmotically committed water in small intestine creates conc. gradient for passive absorption)
- Compromised by chronic diarrhea (decreases lumenal [K+]) |
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Term
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Definition
| K+ is secreted in the colon by passive diffusion across the cell membrane |
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