Flashcards in RR - Nutrition I Deck (131):
What is the recommended dietary allowance?
RDA - Refers to intakes needed for optimal health; it is NOT a minimum daily requirement.
Daily energy expenditure depends most importantly ...?
On the basal metabolic rate (BMR) + On postprandial thermogenesis and the degree of physical activity.
What is the respiratory exchange rate (RER)?
Also called respiratory quotient, is the rate of O2 consumption for different carbon sources.
How is daily energy expenditure calculated?
Daily energy expenditure = BMR + Postprandial thermogenesis + physical activity.
The RDA (recommended dietary allowance) represents ...?
An optimal dietary intake of nutrients that under ordinary conditions can maintain a healthy general population.
The RDA varies with ...?
3. Body weight.
5. Physiologic status.
BMR accounts for about ...% of daily energy expenditure and refers to the energy consumption of an individual at rest.
Estimation of BMR:
BMR = 24 x body weight in kg.
Besides weight, mention other factors that affect BMR:
1. Gender - Males > Females.
2. Age - Children > Adults.
3. Fever - BMR increased.
4. Thyroid function.
Energy used in digestion + absorption + distribution of nutrients.
Postprandial thermogenesis - Accounts for about ...% of daily energy expenditure.
Physical activity is variable and is expressed as an ...?
ACTIVITY FACTOR - when multiplied by the BMR equals the daily energy expenditure.
The activity factor for a sedentary person, for a moderately active person, and for a very active person is ...?
Sedentary person - 1.3.
For a moderately active person - 1.5.
For a very active person - 1.7.
RER (respiratory exchange rater or respiratory quotient) calculation:
RER = Vco2 (CO2 production)/ Vo2 (O2 consumption).
RER for carbohydrates and fats?
RERcarbs = 1.0.
RERfat = 0.7.
RER ... after a meal.
Declines after a meal as FAT replaces glucose as the major fuel.
When primarily drawing on adipose tissue to meet energy needs, to lose about 1lb, a person must expend ... calories more than are consumed.
Dietary carbohydrates with α-1,4 glycosidic linkages are digested to ...?
Monosacharrides and transported directly to the LIVER through the hepatic portal vein.
Dietary carbohydrates with β-1,4 glycosidic linkages are NOT digested but ...?
Serve other functions in the gut such as reducing cholesterol absorption and softening the stool.
Major dietary lipids?
What is the fate of the long-chain triacylglyceroles and cholesterol?
They are packaged in chylomicrons and bypass the liver by transport through the lymphatics to the subclavian vein.
What is the fate of short- and medium-chain triacylglycerols?
They are transported as FFAs directly through the portal vein to the liver.
Dietary proteins are digested to ...?
Free amino acids for the synthesis of proteins and to supply carbon skeletons for the synthesis of glucose for energy.
What does nitrogen balance tell us?
It is an indication of net synthesis (growth), loss (breakdown) or stability in bodily proteins.
Types of dietary carbohydrates?
1. Polysaccharides (eg starch).
2. Disaccharides (eg lactose, maltose, sucrose).
3. Monosaccharides (eg glucose, galactose, fructose).
4. Insoluble fiber (eg cellulose, lignin).
5. Soluble fiber (eg pectins, hemicellulose).
Starch digestion is done by ...?
Alpha-amylase is found in ...?
Saliva in the mouth and in pancreatic secretions in the small intestine.
Mechanism of alpha-amylase:
Cleaves α-1,4 linkages in starch, producing smaller molecules (eg oligosaccharides and disaccharides).
Important role of insoluble fibers:
1. Increase transit time.
2. Decrease exposure to carcinogens.
Important role of soluble fibers:
1. Increase favorable bacteria.
2. Decrease serum cholesterol level.
Composition of plant fats from oils:
1. Monosaturated and polyunsaturated, long chain.
2. Saturated, medium chain.
Composition of animal fats from adipose:
Saturated, long chain.
Composition of animal fats from muscle and organ tissues:
Polyunsaturated and monounsaturated.
Essential fatty acids:
1. Linoleic (ω-6).
2. Linolenic (ω-3).
3 functions of essential fatty acids:
1. Help maintain fluidity of cellular membranes.
2. Precursors for arachidonic acid (linoleic acid) from which the eicosanoids (eg PGs) are derived.
3. Prevent platelet aggregation (linolenic acid), which reduces the incidence of strokes and MI.
Essential fatty acids are present in high concentration in ...?
1. Fish oils.
2. Canola oil.
Deficiency of essential fatty acids results in ...?
2. Poor wound healing.
3. Hair loss.
Dietary triacylglycerols are digested primarily inthe small intestine - Role of pancreatic lipase?
Pancreatic lipase (aided by colipase) degrades triacylglycerol into 2-monoacylglycerol and FFAs.
Role of pancreatic cholesterol esterase?
Hydrolyzes cholesterol esters and releases free cholesterol.
Role of bile salts:
Form micelles for reabsorption by small intestine villi.
Cholesterol and triacylglycerols are resynthesized in the ...?
Mucosal cells after absorption.
Short- and medium-chain fatty acids are directly absorbed and released into the ...?
--> They also bypass the CARNITINE CYCLE and are used directly by the MITOCHONDRIA.
What is the composition of a nascent chylomicron?
1. Triacylglycerols - 85%.
2. Cholesteryl esters - 3%.
5. Apolipoprotein B-48.
What is the importance of apolipoprotein B-48?
Important in formation of chylomicrons and secretion into lymphatics.
What is the composition of a micelle in the intestine?
1. 2-monoacylglycerol + FFAs.
4. Free cholesterol.
The pathophysiology of malabsorption is classified as?
1. Pancreatic insufficiency.
2. Bile salt deficiency.
3. Small bowel disease.
In pancreatic insufficiency, of which nutrient is digestion unaffected?
Carbohydrates. (Fat + Proteins are affected due to lipase and trypsin deficiency)
What determines the biological value of a dietary protein?
Its content of ESSENTIAL amino acids.
Achlorhydria leads to ...?
Inability to properly digest protein (eg pernicious anemia).
Nitrogen balance - During growth?
Nitrogen balance - During surgery, recovery, and burns?
Carbohydrates have what effect on proteins?
Marasmus and Kwashiorkor?
Marasmus = Total calorie deprivation.
Kwashiorkor = Diet inadequate in protein in the presence of an adequate carbohydrate intake.
Role of thiamine:
1. In oxidative DECARBOXYLATION.
2. In pentose phosphate pathway.
Thiamine deficiency produces ...?
Role of riboflavin?
Primarily in electron transport.
Deficiency of riboflavin produces?
Glossitis + Stomatitis.
Role of niacin:
In NAD and NADP as cofactors for redox reactions.
Deficiency of niacin causes ...?
Role of pantothenic acid:
Functions in fat and carbohydrate metabolism as a component acetyl CoA and fatty acid synthase.
Deficiency of pantothenic acid?
Role of pyridoxine?
1. Transamination reactions.
2. Heme synthesis.
4. Various other amino acid conversions.
Pyridoxine deficiency produces ...?
Sideroblastic anemia + peripheral neuropathy.
Role of cobalamin?
Single carbon metabolism; deficiency produces macrocytic anemia + pernicious anemia.
Deficiency of thiamine (B1):
1. Wernicke-Korsakoff syndrome (confusion, ataxia, nystagmus, ophthalmoplegia, antegrade and retrograde amnesia).
2. Peripheral neuropathy (dry beriberi).
3. DCM (wet beriberi).
Riboflavin deficiency (B2):
1. Corneal neovascularization.
4. Angular stomatitis.
Niacin (B3) deficiency:
Pellagra - 3 "D's".
Pyridoxine deficiency (B6):
1. Sideroblastic anemia.
2. Peripheral neuropathy.
4. Lactic acidosis.
Role of folate:
Single carbon metabolism.
Role of biotin?
Sources of thiamine:
1. Enriched and whole-grain cereals.
2. Brewer's yeast.
What is the active form of thiamine?
Thiamine pyrophosphate is a cofactor for ...?
1. Dehydrogenases in oxidative decarboxylation of α-keto acids (eg pyruvate dehydrogenase conversion of pyruvate into acetyl CoA).
2. Transketolase (2-carbon transfer reactions) in the pentose phosphate pathway.
Thiamine deficiency is most commonly due to ...?
Alcoholism or undernourishment.
What do most clinical findings in thiamine deficiency reflect?
The loss of ATP from dysfunction of the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase reactions, which normally gain 2 NADH (6 ATP).
What is important to remember when giving glucose to alcoholics?
Give IV thiamine BEFORE infusion fluids with glucose.
--> If not, ACUTE thiamine deficiency may be precipitated (depleted by the pyruvate dehydrogenase reaction).
Sources of riboflavin (B2):
6. Green leafy vegetables.
Which are the active forms of riboflavin?
FAD and FMN.
FAD is a cofactor associated with ...?
Succinate dehydrogenase - Converts succinate to fumarate in the citric acid cycle.
FMN is a component of the ...?
Electron transport chain and accepts 2 hydrogen atoms (becomes FMNH2) from NADH in a reaction catalyzed by NADH dehydrogenase.
Riboflavin deficiency is usually seen in ...?
Lack of dairy products or general malnourishment.
Riboflavin deficiency symptoms:
2. Enriched and whole-grain cereals.
3. Synthesis of tryptophan-containing foods, such as milk and eggs.
Excess tryptophan is metabolized to ...?
Niacin - Supplies about 10% of the niacin RDA.
The 2 active forms of niacin are:
NAD+ and NADP+.
NAD+ reactions are primarily ...?
CATABOLIC (eg glycolysis).
NADP+ reactions are primarily anabolic or catabolic?
ANABOLIC (fatty acid synthesis).
3 causes of niacin deficiency:
2. Hartnup's disease.
3. Carcinoid syndrome.
Which diets may cause niacin deficiency?
Corn-based diets are low in tryptophan and niacin.
What happens in Hartnup's disease?
AR disease with a defect in the intestinal + renal absorption of neutral amino acids (eg tryptophan).
Why niacin deficiency in carcinoid syndrome?
Tryptophan used up in synthesizing serotonin.
--> Serotonin produces diarrhea and flushing.
MC active form of pantothenic acid is ...?
Coenzyme A - Also in fatty acid synthase.
Why pantothenic deficiency is uncommon?
Because it is present in a variety of foods.
Sources of pyridoxine:
1. Whole-grain cereals.
What is the active form of pyridoxine?
Pyridoxine is involved in ...?
TRANSAMINATION reactions (reversible conversion of amino acids to alpha-ketoacids), which are catalyzed by the transaminases ALT, AST.
Pyridoxine is a cofactor for ...?
δ-aminolevulinic acid (ALA) synthase, which catalyzes the rate-limiting reaction that converts succinyl CoA + glycine into δ-ALA in heme.
What may cause pyridoxine deficiency?
Alcoholism and INH.
--> Also UNFORTIFIED GOAT'S MILK!
Pyridoxine deficiency leads to a defect in ...?
Heme synthesis --> Sideroblastic anemia.
Pyridoxine is also involved in the synthesis of ...?
Neurotransmitters such as:
Pyridoxine is also a cofactor in the following:
1. Decarboxylation reactions (eg conversion of histidine to histamine).
2. Glycogenolysis (eg glycogen phosphorylase).
3. Deamination reactions (eg conversion of serine to pyruvate and ammonia).
4. Conversion of tryptophan to niacin.
Sources of B12:
5. Dairy products.
Function of cobalamin:
Removes the methyl group from N5-methyltetrahydrofolate to form tetrahydrofolate (FH4), which is used to synthesize dTMP from dUMP for DNA synthesis.
B12 also transfers ...?
Methyl groups to homocysteine to form methionine.
MCC of hyperhomocysteinemia:
Cobalamin is involved in which metabolism of fatty acids?
ODD-CHAIN fatty acid metabolism.
What is the end product of odd-chain fatty acid metabolism?
To what is proprionyl CoA converted?
Cobalamin is a cofactor for methylmalonyl CoA ...?
Mutase, which converts methylmalonyl CoA into succinyl CoA (ie citric acid cycle).
B12 deficiency results in accumulation of methylmalonyl CoA, which is converted to ...?
Increased proprionyl CoA proximal to the block leads to ...?
1. The spinal cord (ie subacute combined degeneration).
2. Peripheral nerves (ie peripheral neuropathy).
3. Brain (ie dementia).
Proprionyl CoA replaces acetyl CoA in ...?
Why does B12 complexes with the R factor in salive?
R factor complex prevents degradation of B12 by stomach acid.
IF is synthesized in ...?
Parietal cells located in the body and fundus of the stomach.
Which enzymes cleave off R factor, which allows B12 to complex with IF in the duodenum?
After absorption, vitB12 is bound to ...?
Transcobalamin II in the plasma and is delivered to metabolically active cells or stored in the liver (6- to 9-year supply).
Sources of folate:
1. Green leafy vegetables.
4. Whole-grain cereals.
Folate active form is ...?
Tetrahydrofolate is needed for ...?
Thymidylate synthase in DNA synthesis.
Mention a drug that inhibits thymidylate synthase?
What is the function of tetrahydrofolate (FH4)?
It receives a methylene group (-CH2-) from SERINE to produce N5, N10-methylene-tetrahydrofolate.
--> The methylene group is then transferred by thymidylate synthase to dUMP to produce dTMP for DNA synthesis.
Folate deficiency impairs DNA replication due to ...?
Shortage of PURINE nucleotides and thymine.
Folate is ingested in a ...?
Polyglutamates are converted into ...?
Monoglutamates in the jejunum by intestinal conjugase.
Which CNS drug inhibits intestinal conjugase?
Folate monoglutamate is absorbed in the ...?
Folata monoglutamate absorption is blocked by ...?
Alcohol and OCPs.
Folate is measured in the blood as ...?
Drugs causing folate deficiency: