Ans. c (Inulin) (Ref. Ganong.-23rd/Ch. 38. 26th/pg. 105).Substances Used to Measure GFRIn addition to the requirement that it be freely filtered and neither reabsorbed nor secreted in the tubules, a substance suitable for measuring the GFR should be nontoxic and not metabolized by the body. Inulin, a polymer of fructose with a molecular weight of 5200 that is found in dahlia tubers, meets these criteria in humans and most animals and is extensively used to measure GFR. Radioisotopes such as 51Cr-EDTA are also used, but inulin remains the standard substance. In practice, a loading dose of inulin is administered intravenously, followed by a sustaining infusion to keep the arterial plasma level constant. After the inulin has equilibrated with body fluids, an accurately timed urine specimen is collected and a plasma sample obtained halfway through the collection. Plasma and urinary inulin concentrations are determined and the clearance calculated. The GFR in a healthy person of average size is approximately 125 mL/min.CLASSIFICATION OF IMPORTANT SUGARS AldosesKetosesTrioses (C3H6O3)GlyceroseDihydroxyacetoneTetroses (C4H8O4)ErythroseErythrulosePentoses (C5Hl0O5)RiboseRibuloseHexoses (C6H12O6)GlucoseFructoseHexoses of Physiologic ImportanceSugarSourceImportanceClinical significanceD-GlucoseFruit juices. Hydrolysis of starch, cane sugar, maltose and lactoseThe "sugar" of the body. The sugar carried by blood, and the principal one used by the tissuesPresent in the urine (glycosuria) in diabetes mellitus owing to raised blood glucose (hyperglycemia)D-fructoseFruit juices. Honey,Hydrolysis of cane sugar and of insulin (from the Jerusalem artichoke)Can be changed to glucose in the liver and so used in the bodyHereditary fructose intolerance leads to fructose accumulation and hypoglycemiaD-GalactoseHydrolysis of lactoseCan be changed to glucose in the liver and metabolized. Synthesized in the mammary gland to make the lactose of milk. A constituent of glycolipids and glycoproteinsFailure to metabolize leads to galactosemia and cataractD-Mann- OseHydrolysis of plant mannans and gumsA constituent of many glycoproteins Pentoses of Physiologic ImportanceSugarWhere foundBiochemical importance D-RiboseNucleic acidsStructural elements of nucleic acids and coenzymes, eg, ATP, NAD, NADP, flavoproteins. Ribose phosphates are intermediates in pentose phosphate pathway D-RibuloseFormed in metabolic processRibulose phosphate is an intermediate in pentose phosphate pathway D-ArabinoseGum arabic. Plum and cherry gumsConstituent of glycoproteins D-XyloseWood gums, proteoglycans, glycosaminoglycansConstituent of glycoproteins D-LyxoseHeart muscleA constituent of a lyxoflavin isolated from human heart muscle L-XyluloseIntermediate in uronic acid pathwayFound in urine in essential pentosuria DisaccharidesSugarSourceClinical significanceMaltoseDigestion by amylase or hydrolysis to starch.Germinating cereals and malt LactoseMilk, may occur in urine during pregnancy.In lactase deficiency, malabsorption leads to diarrhoea and flatulenceSucroseCane, and beet sugar. Sorghum.Pineapple carrot roots.In sucrase deficiency, malabsorption leads to diarrhoea and flatulenceTrehaloseFungi and yeasts.The major sugar of insect hemolymphGlucose Is one of the main hexoses absorbed from GIT, derived principally from dietary STARCH.