Learning Objectives - Nutrition, Metabolism, and Body Temperature Regulation
Define nutrient, essential nutrient, and calorie.
nutrient - a substance in food used by the body to promote normal growth, maintenance, and repair.
Essential Nutrients - 45 - 50 molecules cannot be made fast enough to meet the body’s needs and so must be provided by the diet.
List the six major nutrient categories. Note important sources and main cellular uses.
Grains, Vegetables, Fruits, Meat and beans, Oils Milk
Distinguish between simple and complex carbohydrate sources
Simple carbohydrates are made up of one or two sugars and are easily digested. They consist of food such as table sugar, candy and fruits. Complex carbohydrates are made up of three or more linked sugars. Complex carbs take longer to digest. Complex carbs consist of whole grains and vegetables.
Indicate the major uses of carbohydrates in the body.
Carbohydrates are used as fuel by body cells to produce ATP.
Indicate uses of fats in the body.
•help the body absorb fat-soluble vitamins
•triglycerides are the major energy fuel of hepatocytes and skeletal muscle
•phospholipids are an integral component of myelin sheaths and cellular membranes.
•Fatty deposits in adipose tissue provide
o a protective cushion around body organs
o insulating layer beneath the skin
o easy-to-store concentrated source of energy fuel.
•cholesterol is not used for energy. It is important as a stabilizing component of plasma membranes and is the precursor from which bile salts, steroid hormones, and other essential molecules are formed.
Distinguish between saturated, unsaturated, and trans fatty acid sources.
•Saturated are derived from animal products such as meat, dairy and eggs. But they are also found in some plant-based sources such as coconut, palm and palm kernel oils. These fats are solid at room temperature.
•Monounsaturated fats and polyunsaturated fats are two types of unsaturated fatty acids. They are derived from vegetables and plants.
•Most trans fats are made during food processing through partial hydrogenation of unsaturated fats.
Distinguish between nutritionally complete and incomplete proteins.
•Complete Proteins - meet all the body’s amino acid requirements for tissue maintenance and growth
•Incomplete Proteins – protein rich but low in one or more of the essential amino acids.
Indicate uses of proteins in the body.
Proteins are important structural materials of the body, including, for example, keratin in skin, collagen and elastin in connective tissues, and muscle proteins. In addition, functional proteins such as enzymes and some hormones regulate an incredible variety of body functions.
Define nitrogen balance and indicate possible causes of positive and negative nitrogen balance.
•In healthy adults the rate of protein synthesis equals the rate of protein breakdown and loss, a homeostatic state called nitrogen balance. The body is in nitrogen balance when the amount of nitrogen ingested in proteins equals the amount excreted in urine and feces.
•Positive Nitrogen Balance - when the amount of protein incorporated into tissue is greater than the amount being broken down and used for energy, the normal situation in growing children and pregnant women. A positive balance also occurs when tissues are being repaired following illness or injury.
•Negative Nitrogen Balance - protein breakdown for energy exceeds the amount of protein being incorporated into tissues. This occurs during physical and emotional stress (for example, infection, injury, or burns), or when the quality or quantity of dietary protein is poor, or during starvation.
Distinguish between fat- and water-soluble vitamins, and list the vitamins in each group.
•Watersoluble Vitamins - which include B-complex vitamins and vitamin C, are absorbed along with water from the gastrointestinal tract.
•Fat-Soluble Vitamins - (A, D, E, and K) bind to ingested lipids and are absorbed along with their digestion products
For each vitamin, list important sources, body functions, and important consequences of its deficit or excess.
Vitamin B1 (thiamine)
•Found in Lean meats, liver, legumes, peanuts, whole grains
•Coenzyme used in removing CO2 from organic compounds; required for synthesis of acetylcholine and pentose sugars
•Deficiency - Beriberi (nerve disorders, emaciation, anemia), profound fatigue
Vitamin B2 (riboflavin)
•Milk, liver, yeast, meats, enriched grains, vegetables
•Component of coenzymes FAD and FMN
•Deficiency - Dermatitis, skin lesions such as cracks at corners of mouth, blurred vision None known
Vitamin B3 (niacin)
•Nuts, poultry, fish, meats, grains
•Component of coenzyme NAD
•Deficiency - Pellagra, skin and gastrointestinal lesions, nervous disorders
•Excess - Liver damage, gout, hyperglycemia
Vitamin B5 (pantothenic acid)
•Most foods: meats, dairy products, whole grains, etc.
•Component of coenzyme A; involved in synthesis of steroids and hemoglobin
•Deficiency - Fatigue, numbness, tingling of hands and feet, neuropathy of alcoholism
Vitamin B6 (pyridoxine)
•Meats, fish, poultry, vegetables, bananas
•Coenzyme used in amino acid metabolism; required for glycogenolysis and antibody formation
•Deficiency - Irritability, convulsions, muscular twitching, anemia
•Excess - Unstable gait, numb feet, poor coordination, depressed deep tendon reflexes, nerve damage
Vitamin B9 (folic acid or folacin)
•Liver, oranges, nuts, legumes, whole grains
•Coenzyme in nucleic acid and amino acid metabolism; needed for normal neural tube development in embryos
•Deficiency - Anemia, gastrointestinal problems, spina bifida risk in newborns, neural deficits May mask signs of vitamin
•Excess - B12 deficiency while allowing its neurological damage
Vitamin B12 (cyanocobalamin)
•Meats, eggs, dairy products except butter (not found in plant foods) (also made by enteric bacteria)
•Coenzyme in nucleic acid metabolism; maturation of red blood cells
•Deficiency - Pernicious anemia, nervous system disorders (typically due to impaired absorption)
•Legumes, other vegetables, meats, liver, egg yolk
•Coenzyme in synthesis of fat, glycogen, and amino acids
•Deficiency - Scaly skin, pallor, fatigue, neuromuscular disorders, elevated cholesterol levels
Vitamin C (ascorbic acid)
•Fruits and vegetables, especially citrus fruits, strawberries, broccoli, cabbage, tomatoes, green peppers
•Used in collagen synthesis (such as for bone, cartilage, gums); antioxidant; aids in detoxification; improves iron absorption
•Deficiency - Scurvy (degene
List minerals essential for health; indicate important dietary sources and describe how each is used.
•Dairy products, dark green vegetables, legumes
•Bone and tooth formation, blood clotting, nerve and muscle function
•Deficiency - Stunted growth, possibly loss of bone mass
•Excess - Depressed neural function, muscle weakness, calcium deposit in soft tissues
Phosphorus (P) 700 Dairy products, meats,
•whole grains, nuts
•Bone and tooth formation, acid-base balance, nucleic acid synthesis
•Deficiency - Weakness, loss of minerals from bone, rickets
•Sulfur-containing proteins from many sources (meats, milk, eggs)
•Component of certain amino acids
•Deficiency - Symptoms of protein deficiency
•Meats, dairy products, many fruits and vegetables, grains
•Acid-base balance, water balance, nerve function, muscle contraction
•Deficiency - Muscular weakness, paralysis
•Excess - Muscular weakness, cardiac problems, alkalosis
•Table salt, cured meats (ham)
•Osmotic pressure, acidbase balance, gastric juice formation
•Muscle cramps, reduced appetite
•Table salt, cured meats
•Osmotic pressure, acid-base balance, water-balance, nerve function, important for pumping glucose and other nutrients
•Deficiency - Muscle cramps, reduced appetite
•Excess - Hypertension, edema
•Whole grains, green leafy vegetables
•Component of certain coenzymes in ATP formation
•Deficiency - Nervous system disturbances, tremors, muscle weakness, hypertension, sudden cardiac death
•Excess – Diarrhea
Define metabolism. Explain how catabolism and anabolism differ.
Metabolism - variety of biochemical reactions
Catabolism - degradative, tearing down
Anabolism - synthetic, building up
Define oxidation and reduction and indicate the importance of these reactions in metabolism.
Oxidation is the gain of oxygen or the loss of hydrogen
Reduction - substances gain energy
As food fuels are oxidized, their energy is transferred to a “bucket brigade” of other molecules and ultimately to ADP to form energy-rich ATP
Indicate the role of coenzymes used in cellular oxidation reactions.
REDOX enzymes require the help of a specific coenzyme, typically derived from one of the B vitamins. Although the enzymes catalyze the removal of hydrogen atoms to oxidize a substance, they cannot accept the hydrogen Their coenzymes, however, can act as hydrogen (or electron) acceptors, becoming reduced each time a substrate is oxidized.
Explain the difference between substrate-level phosphorylation and oxidative phosphorylation.
Substrate-level phosphorylation - occurs when high-energy phosphate groups are transferred directly from phosphorylated substrates (metabolic intermediates such as glyceraldehyde phosphate) to ADP
Oxidative phosphorylation - much more complicated, but it also releases most of the energy that is eventually captured in ATP bonds during cellular respiration.
Summarize the important events and products of glycolysis, the Krebs cycle, and electron transport.
glycolysis - anaerobic process occurs in the cytosol of cells. This pathway is a series of ten chemical steps by which glucose is converted to two pyruvic acid molecules.
•Phase 1 Sugar Activation Glucose is activated by phosphorylation and converted to fructose-1, 6-bisphosphate
•Phase 2 Sugar Cleavage Fructose-1, 6-bisphosphate is cleaved into two 3-carbon fragments
•Phase 3 Sugar oxidation and formation of ATP The 3-carbon fragments are oxidized (by removal of hydrogen) and 4 ATP molecules are formed
Krebs Cycle - In aerobic pathways, pyruvic acid is transported into the mitochondrion.
•Pyruvic acid is first converted to acetyl CoA by removing a carbon, oxidizing the acetic acid fragment, and adding coenzyme A.
•Acetyl CoA enters the Krebs cycle, where it proceeds through eight successive steps that produce a series of ketoacids, ultimately ending at the production of oxaloacetic acid.
•The net yield of the Krebs cycle is four molecules of CO2, six molecules of NADH, two molecules of FADH2, and two molecules of ATP per pair of acetyl CoA molecules that were produced from glucose.
Electron Transport Chain - is the oxygen-requiring process of aerobic respiration involving the pickup of hydrogens removed from food fuels during oxidation by O2, resulting in the formation of water, a process called oxidative phosphorylation.
•In the electron transport chain, hydrogens from NADH and FADH2 are shuttled through a series of coenzymes, which results in the transport of H+ from the mitochondrial matrix to the intermembrane space.
•H+ diffuses back to the mitochondrial membrane through an enzyme, ATP synthase, which phosphorylates ADP to ATP as the H+ diffuses.
Define glycogenesis, glycogenolysis, and gluconeogenesis.
Glycogenesis - a process that forms glycogen from glucose when high cellular ATP begins to inhibit glycolysis.
Glycogenolysis - a process that breaks down glycogen to glucose when blood glucose levels begin to fall.
Gluconeogenesis - a process that forms glucose from nonglucose molecules to maintain blood glucose when dietary sources and glucose reserves begin to be depleted.
Describe the process by which fatty acids are oxidized for energy.
•Lipids are the body’s most concentrated source of energy, producing approximately twice the energy of either carbohydrates or proteins.
•Catabolism of triglycerides involves the splitting of the molecule into glycerol and fatty acids: the glycerol portion is converted to glyceraldehyde phosphate, which enters into glycolysis, and the fatty acids are converted to acetyl CoA through beta oxidation.
•Lipogenesis is a process used to store excess glycerol and fatty acids in adipose tissue as triglycerides.
•Lipolysis is a process that breaks down stored triglycerides into glycerol and fatty acids, to be directed into lipid catabolism.
Define ketone bodies, and indicate the stimulus for their formation.
Ketone bodies are three water-soluble compounds that are produced as by-products when fatty acids are broken down for energy in the liver.
The stimulus for the formation of ketone bodies when carbohydrates are so scarce that energy must be obtained from breaking down fatty acids.
Describe how amino acids are metabolized for energy.
•Step 1: Transamination Transfer of an amine group from an amino acid to -ketoglutaric acid, thereby transforming -ketoglutaric acid to glutamic acid
•Step 2: Oxidative deamination Removal of an amine group from glutamic acid as ammonia and regeneration of -ketoglutaric acid (NH3 is converted to urea by the liver)
Describe the need for protein synthesis in body cells.
Amino acids are the most important anabolic nutrients. Not only do they form all protein structures, but they form the bulk of the body’s functional molecules as well.
Explain the concept of amino acid or carbohydrate–fat pools, and describe pathways by which substances in these pools can be interconverted.
Amino acid pool is the body’s total supply of free amino acids. Small amounts of amino acids and proteins are lost daily in urine and in sloughed hairs and skin cells. Typically, these lost molecules are replaced via the diet. Otherwise, amino acids arising from tissue breakdown return to the pool. This pool is the source of amino acids used for protein synthesis and in the formation of amino acid derivatives
Because carbohydrates are easily and frequently converted to fats, the carbohydrate and fat pools are usually considered together. There are two major differences between this pool and the amino acid pool:
•Fats and carbohydrates are oxidized directly to produce cellular energy, whereas amino acids can be used to supply energy only after being converted to a carbohydrate intermediate (a keto acid).
•Excess carbohydrate and fat can be stored as such, whereas excess amino acids are not stored as protein. Instead, they are oxidized for energy or converted to fat or glycogen for storage.
List important events of the absorptive and postabsorptive states, and explain how these events are regulated.
Absorptive State - the time during and shortly after eating, when nutrients are flushing into the blood from the gastrointestinal tract.
•During the absorptive state anabolism exceeds catabolism
•Glucose is the major energy fuel. Dietary amino acids and fats are used to remake degraded body protein or fat and small amounts are oxidized to provide ATP.
•Excess metabolites, regardless of source, are transformed to fat if not used for anabolism.
•Insulin directs essentially all events of the absorptive state Rising blood glucose levels after a carbohydratecontaining meal act as a humoral stimulus that prods the beta cells of the pancreatic islets to secrete more insulin.
Postabsorptive State - fasting state, is the period when the GI tract is empty and energy sources are supplied by the breakdown of body reserves.
•net synthesis of fat, glycogen, and proteins ends, and catabolism of these substances begins to occur.
•The primary goal during this state, between meals when blood glucose levels are dropping, is to maintain blood glucose levels within the homeostatic range (70–110 mg of glucose per 100 ml).
•Most events of the postabsorptive state either make glucose available to the blood or save glucose for the organs that need it most by using fats for energy
•The sympathetic nervous system and several hormones interact to control events of the postabsorptive state.
•Glucagon - insulin antagonist.
•Hyperglycemic Hormones - promotes a rise in blood glucose levels
Describe several metabolic functions of the liver.
•Cholesterol is transported in the blood bound to lipoprotein complexes, which solubilize lipids and regulate entry and exit at specific target cells.
•Lipoprotein complexes vary in the percentage of lipid they contain, but all contain triglycerides, phospholipids, and cholesterol, in addition to protein.
•Blood levels of cholesterol are partly regulated through negative feedback, and a high intake of cholesterol will somewhat inhibit cholesterol synthesis by the liver.
•Diets high in saturated fats stimulate liver synthesis of cholesterol and reduce its elimination from the body, while unsaturated fatty acids enhance excretion of cholesterol to bile for removal from the body.
Differentiate between LDLs and HDLs relative to their structures and major roles in the body.
•The greater the proportion of lipid in the lipoprotein, the lower its density, and there are very-low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs).
VLDLs transport triglycerides from the liver to peripheral tissues, LDLs transport cholesterol to peripheral tissues, and HDLs transport excess cholesterol from peripheral tissues to the liver and provide cholesterol to steroid-producing organs.
•High levels of HDL are considered beneficial, as the cholesterol they contain is bound for removal, but high levels of LDL are considered a risk, because the cholesterol they contain may be laid down on vessel walls, forming plaques.
Explain what is meant by body energy balance.
There is a balance between the body’s energy intake, defined as the energy produced during food oxidation, and energy output, which includes energy lost as heat, used to do work, or stored as fat or glycogen.
When energy intake and energy output are balanced, body weight remains stable, but when they are not, weight is gained or lost.
Describe some theories of food intake regulation.
The hypothalamus produces several peptides controlling feeding behavior, which ultimately reflect two sets of neurons: one set promoting hunger and the other set promoting satiety.
Short-term regulation of food intake involves neural signals from the digestive tract, blood levels of nutrients, and GI hormones.
Long-term regulation of food intake relies on the hormone leptin, secreted by adipose cells.
•Leptin is a hormone that is secreted in response to an increase in the body’s fat mass, and suppresses activity of the neurons that promote hunger while increasing activity of neurons that promote satiety.
Other factors that may affect food-seeking behaviors are changes in ambient temperature, stress, other psychological factors, infections, sleep deprivation, or composition of gut bacteria.
Define basal metabolic rate and total metabolic rate. Name factors that influence each.
The body’s rate of energy output is called the metabolic rate.
The basal metabolic rate reflects the amount of energy required for performance of only the essential activities of the body, and is expressed as kilocalories per square meter of body surface area.
•Factors that influence the basal metabolic rate include body surface area, age, gender, stress, and hormones.
The most important factor is surface area, because of its impact on heat loss from the body.
Basal metabolic rate is higher if the individual is younger, or male, and tends to rise and fall with body temperature.
The most important hormonal factor affecting basal metabolic rate is thyroxine, which increases O2 consumption and heat production.
Distinguish between core and shell body temperature.
•Body temperature averages 37°C, and is usually maintained between 35.8–38.2°C.
•Temperature homeostasis keeps body temperature at a value that is optimal for enzymatic activity within the body.
•The core of the body, which includes organs within the skull, thoracic, and abdominal cavities, has the highest body temperature, while the shell (mostly the skin) has the lowest temperature.
•Heat exchange between our skin and the external environment occurs through radiant flow of heat, conductive flow of warmth from warmer to cooler objects, convective movement of warm air away from the body, and heat loss due to evaporation of fluids from the lungs, oral mucosa, and the skin.
Describe how body temperature is regulated, and indicate the common mechanisms regulating heat production/retention and heat loss from the body.
•The hypothalamus contains the heat-loss and heat-promoting centers that aid in the regulation of behavioral and physiological mechanisms to maintain normal body temperature.
Heat-promoting mechanisms maintain or increase body core temperature, and include constriction of cutaneous blood vessels, shivering, increase in metabolic rate, and increased release of thyroxine.
Heat-loss mechanisms protect the body from excessively high temperatures, and include dilation of cutaneous blood vessels, enhanced sweating, and behaviors that promote heat loss or reduce heat gain.
Describe the effects of inadequate protein intake on the fetal nervous system.
Inadequate nutrition during pregnancy and in the first three years of life seriously compromises brain growth and development, as well as muscle and bone development.
Several genetic disorders affect metabolism, such as cystic fibrosis, phenylketonuria, and glycogen storage disease.
Describe the cause and consequences of the low metabolic rate typical of the elderly.
•With the exception of insulin-dependent diabetes mellitus, genetically normal children rarely exhibit metabolic disorders, but by middle and old age, non-insulin-dependent diabetes mellitus becomes a significant problem
•Metabolic rate declines throughout life, and this decline may affect the body’s ability to digest and absorb nutrients
List ways that medications commonly used by aged people may influence their nutrition and health.
•Some diuretics prescribed for congestive heart failure or hypertension (to flush fluids out of the body) can cause severe hypokalemia by promoting excessive loss of potassium
•Some antibiotics, for example, sulfa drugs, tetracycline, and penicillin, interfere with food digestion and absorption. They may also cause diarrhea, further decreasing nutrient absorption.
•Although its use is discouraged by physicians because it interferes with absorption of fat-soluble vitamins, mineral oil is still a popular laxative with the elderly.
•Alcohol is used by about half the elderly population in the U.S. When it is substituted for food, nutrient stores can be depleted. Excessive alcohol intake leads to absorption problems, certain vitamin and mineral deficiencies, deranged metabolism, and damage to the liver and pancreas.