digestion & absorption of carbohydrates
TRANSCRIPT
Digestion and absorption of carbohydrates
Dr Rohini C sane
Professor
Department of Biochemistry
DYP Medical College ,Ebene
NO ENERGY REQUIRED DOWN HILL –HIGH CONC TO LOW CONC
TRANSPORT DOWN HILL ( HIGH CONTRATION TO LOW CONCENTRATION )ALONG CONCENTRATION GRADIENT (NO ENERGY REQUIRED ,MEDIATION OF CARRIER PROTEINS,PING PONG MODEL ) FRUCTOSE ,& MANNOSE GLUT -5-BRUSH BORDER ( GLUCOSE , GALACTOSE CAN USE )SODIUM DEPENDENT TRANSPORTER GLUT -2 PORTAL CIRCULATION –BEING TRANSPORTED TO LIVER INSULIN REGULATE GLUCOSE TRANSPORT IN MUSCLE & ADIPOSE TISSUE
Na+ K+ pump –maintenance of high k & low Na INTRACELLULARLY –NERVE IMPULSE PROPOGATION INTRACELLULAR HIGH POTASSIUM CONC NEEDED FOR OPTIMAL GLYCOLYSIS ( PYRUVATE KINASE DEPENDENT ON K )& PROTEIN BIOSYNTHESIS
ABSORPTION OF SUGAR TAKES PLACE IN DUODENUM & UPPER JEJUNUM
Na +k + pump3 Na+ (IN )+2 K+ (OUT ) +ATP
+ 3 Na+ (OUT )+2 K+ ( IN)+ADP + PI QUABAIN & DIGITOXIN –INHIBITORS DIGITOXIN—TREATMENT OF CONGESTIVE
CARDIAC FAILURE & IMPROVES CARDIAC CONTACTILITY QUABAIN (AFRICAN SHRUB )—HUNTING ARROWS –
ORT –ORAL REHYDRATION THERAPY –COMMON TREATMENT OF DIAARHOEA –ORAL REHYDRATION FLUID CONTAINS GLUCOSE (ENERGY)& SODIUM (OSMOSIS RETENTION OF WATER ) –SYMPORT
FRUCTOSE TRANSPOTED BY FACILITATED DIFFUSIONMEDIATED BY CARRIER & CONVERTED TO GLUCOSE
MECHANISM OF ABSORPTION OF GALACTOSE SIMILLAR TO GLUCOSE & BLOCKED BY PHLORIZIN
SODIUM DEPENDENT UNIDIRECTIONAL
TRANSPORT
SGLT- 1 SMALL INTESTINE & KIDNEY ( SGLUT -2) DEFECTIVE IN CONGENITALGLYCOSURIA
ACTIVE UPTAKE OF GLUCOSE FROM LUMEN OF INTESTINE /MOST CELLS
REABSORPTION OF GLUCOSE IN PROXIMAL TUBULE OF KIDNEY AGAINST CONCENTRATION GRADIENT
GLUCOSE TRANSPORTERS IN VARIOUS TISSUES FOR ITS UPTAKE
Glucose transporters for glucose uptake
Facilitative bidirectional transporters
TISSUE TRANSPORT
1 GLUT 1 BRAIN ,KIDNEY ,COLON ,RBC, PLACENTA
2 GLUT 2 LIVER ,PANCREAS ,INTESTINE ,KIDNEY,BETA CELLS
INTESTINAL CELLS RELEASE GLUCOSE IN CAPILLARIES (UNIPORT ,FASCILITATED DIFFUSION,PING –PONG )SENSE HIGH GLUCOSE LEVELS –RELEASE INSULIN BY BETA PANCREATIC CELLS
3 GLUT 3 BRAIN ,KIDNEY ,PLACENTA
4 GLUT 4 HEART ,SKELETAL MUSCLES ,ADIPOSE TISSUE ( INSULIN STIMULATED UPTAKE OF GLUCOSE )
ONLY TRANSPORTER UNDER CONTOL OF INSULIN IN MUSCLE & FAT CELLS CONC REDUCED IN DM –ENTRY OF GLUCOSE IN MUSCLE REDUCED
5 GLUT 5 SMALL INTESTINE ONLY TRANSPOTER FOR FRUCOSE ,IN TESTIES & SPERMS
RELATIVE RATE OF ABSORPTION OF INTESTINAL LUMEN
COMPARISON WITH GLUCOSE
1 GALACTOSE 110 (MILK –NEW BORN SORCE OF ENERGY/GALACTOSE EPIMERIZED TO GLUCOSE )
2 D-GLUCOSE 100 (SALINE + GLUCOSE )
3 D- FRUCTOSE 43
4 D -MANNOSE 20
5 D-XYLOSE 15
6 D-ARABINOSE 9
Abnormalities of carbohydrate digestion • Monosaccharides absorbed efficiently.
• Defect in disaccaridases –osmosis by undigested disaccharides ,---diarrhea ---flatulence ( UTILIZATION OF DISACCHARIDES BY BACTERIA –formation of H2/CO2/CH4 )
• Alteration in mucosa of small intestine –(observed in intestinal diseases ,drug therapy,) ---treatment restrict consumption of sucrose ,lactose
• Genetic causes –intolerance of specific disaccharide
Lactose intolerance
• Defect –lactase (congenital/acquired –sudden high intake of milk products )
• Half of world population suffers from Lactose intolerance
• More common in Africans & Asians
• Symptoms –flatulence
• Management –restrict consumption of lactose (milk)
• Curd/yeast –source of lactase
Sucrase deficiency
• 10% Eskimos of Greenland & North Americans
• RESTRICT DIETARY SUPPLEMENTATION OF SUCROSE
FLATULENCE
• INGESTION OF LEGUMINOSE SEEDS –BENGAL GRAM,BEANS ,SOYABEAN ,PEAS
• NONDIGESTABLE OLIGOSACCHARIDES BY HUMAN ENZYMES –UTILIZATION BY BACTERIA—FLATULENCE –formation of H2/CO2/CH4 )
• eg --RAFFINOSE –-OLIGOSACCHARIDES -GALACTOSE ,GLUCOSE ,FRUCTOSE
Non digestible carbohydrate • DIETARY FIBRES –CELLULOSE ,HEMICELLULOSE ,PECTIN LIGNIN,GUMS
ADVANTAGES OF DIETARY FIBRES(CELLULOSE ,HEMICELLULOSE ,LIGNIN,PECTINS)
IMPROVES GLUCOSE TOLERANCE(DIMINISHED RATE OF ABSORPTION OF GLUCOSE )
DECREASED ABSORPTION OF CHOLESTEROL FROM INTESTINE >>>>REDUCE PLASMA
CHOLESTEROL LEVELS
FIBRES BIND WITH BILE SALTS & REDUCE ENTERO HEATIC CIRCULATION >>>DEGRADATION
OF CHOLESTEROL TOBILE SALTS & ITS DISPOSAL FROM BODY IS INCREASED
PREVENTS CONSTIPATION (INCREASING BULK OF FAECES BY ABSORBING WATER )
ELEMINATES BACERIAL TOXINS (ADSORPTION OF TOXIC COMPOUNDS )
LOWER INCIDENCE OF GIT CANCER
SATIETY VALUE –SENSETION OF STOMATCH FULLNESS , SATIETY WITHOUT CONSUMPTION
OF EXCESS CALORIES
ADVERSE EFFECTS OF DIETARY FIBRES
DIGESTION & ABSORPTION OF PROTEINS ARE ADVERSLY AFFECTED
INTESTINAL ABSORPTION OF MINERALS CALCIUM ,MAGNESIUM ,PHOSPHOROUS
DECREASED
INTESTINAL BACTERIA FERMENT FIBRES CAUSING FLATULANCE
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