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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