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Lecture 38

Digestion and Absorption

Carbohydrate Digestion must be reduced to monosaccharides to be absorbed
Complex Carbohydrates chains of sugars,usually glucose. diff complex carbs have diff links btw sugars.starch is diff than cellulose-we cannot digest cellulose.sugar in fruit is often monosaccharide,fructose or glucose
Enzymes produced in the mouth and in the pancreas. amylase converts starch into disaccharides. dissach are in the wall of the SI. disacch convert dissach into monosacch.sucrose is converted to glucose and fructose
Lactose Intolerance lactose is milk sugar-disac of glucose and gelatose. if no lactase is produced-no degestion of lactose. bacteria in LI use lactose as food source. gas and diarrhea produced
Absorption complete-all sugars totally diffusion-use glucose transporters.
Sodium Dependence glucose co-transport w/ na+ into epithelial cells.transport of glucose from epithelial cells to interstitial fluid uses a non na+ glucose transporter
Protein Digestion some in stomach,most in small intestine
Proenzymes released in protected form.acid,then pepsin,converts pepsinogen into pepsin. enterokinase in SI wall converts trypsinogen into trypsin.trypsin then converts other pancreatic proteases into active form
Peptidases both from pancreas and on SI wall.convert peptides into amino acids.some di-and tri-peptides absorbed
Absorption use amino acid transporters in mucosal wall.some use na+,cl- or no cotransporter
Sources of Protein 50% food,25% digestive enzymes,25% mucosal dietary proteins in feces
Infant Protein Absorption newborns can absorb protein directly until tight junctions form IgG in colostrum provides protection
Lipid Digestion mouth and stomach lipases umimportant.pancreatic lipases enter duodenum in an active form
Lipases convert lipids to absorb form.lipases convert trigylcerides into monoglycerides and free fatty acids
Micelles bile cells from liver emulsify MG and FFA and cholesterol. fats diffuse into mucous at brush border
Absorption MG and FFA cross and reform into TG in mucosal cells.TG and cholesterol form chylomicron. chylomicrons enter lymph,thru thoracic duct to blood
Portal Vein carries water soluble foods directly to liver.liver processes and detoxifies foods. fats causes lymph causes blood causes everywhere causes liver (eventually)
Electrolyte Absoption salts all h2o soluble leads to portal vein.SI has tight junc. salts use carries,channels,and pumps to go thru cells
Water 2000 mL/daY ingestion,7000mL/day secretions.200mL/day in stool.follows other absorption osmotically
Sodium most na+ enters through cells,energy gradient from na+ pumps on basolateral side of mucose (as in kidney).some na+ entry through leaky tight junctions
Potassium k+ enters through down concentration gradient through k+ channels K+ exchanged for na+ last electrolyte absorb.during diarrhea k+ loss too fast for k+ transport of k+ in colon.
Bicarbonate huge secretion by pancreas,buffers acids in duodenum.reab by concentration gradient in SI
Vitamins water soluble B and C vitamins rapidly absorb,rapid loss in urine.must take in b and c vitamins daily.b12 absorp needs intrinsic factor from stomach.vitamins a,d,e,k fat soluble leads to micells leads to lymph
Minerals ca2+ 30-80% absorbed-vit D dependent.ca2+ binding proteins and ca2+ ATPase inc ca2+ entry
Digestion and Absorption the breaking down of food into absorbable units and their absorption
Created by: danamarie9323



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