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26 Cards in this Set
- Front
- Back
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What has broken down enough for absorption?
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Fats --> mono, diglycerides, FA
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Which molec still need to be broke down more?
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Polysac-> disac -->need to still be broken down to monosac
Ptns -> small peptides ---> need to be broken to aa, di and tri-peptides |
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What characterizes all of the intestinal muscosa?
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Crypts
Villi (both in the lamina propria) |
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What do the cells in the crypt do?
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Secrete large amounts (3L/day) of ALKALINE fluid (SUCCUS ENTERICUS) into the lumen (that's all they can do, can't digest)
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Where do crypt cells go?
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Divide and migrate up along the villi and are shed at the tip of the villus
->covering is replaced every 3-5 days |
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What do villi do?
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ABSORB nutrients and fluid (don't secrete fluid)
SYNTHESIZE enzymes, retain them in brush border (.: completing digestion) |
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Which enz are synthesized in the villi and what do they do?
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Enterokinase: activation of trypsinogen to trypsin
Amylase: Breaks carbs down to disac Lipase: If some lipids aren't digested yet Aminopeptidase and Dipeptidases can break down residual ptns toaa and di/tri peptides DISSACHARASES |
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What does the colonic secretion consist of?
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small volume of alkaline, isotonic fluid
mucin to lubricate feces, no digestive enzymes bacteria |
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Describe the secretions in SI.
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Crypts: succus entericus
Volume: 3L/day Isotonic: Na+, K+, Cl-, **HCO3- pH: 7.5-9 No enzymes!!! |
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Why doesn't the colon secrete any digestive enz?
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All digestion and secretion must be completed in the small intestine
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what is daily intake of water and solids?
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Water (2000mL)
Solids (500g) |
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What is the daily output?
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Solids: 50 g (includes 30% bacteria, 30% undigested fiber, 10-20% lipids, 10-20% inorganic matter)
Water: 100 ml |
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How much is ingested compared to secretions?
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2L ingested
7L secreted throughout the body Total of 9L absorbed by the GI ->Small intestine: 7L -> Colon: 2L |
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What else is reabsorbed from the lumen of the GIT?
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Ions
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Describe protein reabsorption
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50g as enzymes
30g as cells Total: 80g of ptn/day these ptns are broken into aa and enter the aa pool to be reutilized |
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What is most of the absorption in the GIT?
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Reabsorption
->circulation btw the plasma and lumen of GIT |
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What are the sites of exchange characterized by?
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1) Large surface areas
2) Intimate contact with blood vessels ->NO absorption in mouth, esophagus or stomach |
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Which is the only GI organ that is essential to life?
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Small intestine, mostly in proximal SI
Where bulk of absorption takes place Inner surface of SI = 600x outer surface area of SI |
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Why does the inner surface of the SI have such a large area?
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Has many circular fold (inc surface area 3x)
Has villi (inc SA 30x) Has microvilli (inc SA 600x) ->have more area then required, could remove half of SI and still have efficient absorption |
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Describe the villus
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Outside in: columnar epithelium, capillary network, lacteal
Have arterial supply Venous drain Lymph vessels |
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What are the postprandial blood flow and the lymph flow?
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Postprandial: 1-2L/min (to intestine, very fast)
Lymph: 1-2ml/min (slow) ->absorption takes place very rapidly from the eithelial cell to cap |
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What is absorbed in the following areas:duodenum, jejunum, ileum?
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Proximal: carbs, proteins, Na, H2O
Ileum: bile acids, B12 |
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What limits absorption?
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->Need adequate digestion: activated enz, pH, ions
->Adequate site for absorption (ex: distal ileum required for VitB12 absorption) ->Adequate transit time for absorption ->Adequate co-factors (co-lipase, bile salts), transporters |
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how much carbs get absorbed?
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99% of intake
-60% from starch -30% from sucrose -6% from lactose |
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how much protein get absorbed?
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92% of intake
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how much fat gets absorbed
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95% of intake
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