Chapter 26Lecture Outline

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Nutrition & Metabolism

• Nutrients– Six classes are required

• carbohydrates - 125-175 g 4calories/gram• proteins - 50 g 4calories/gram• lipids - 80 - 100 g 9calories/gram• vitamins• electrolytes / minerals

• Water Importance of water– solvent chemical reactions & body temp.

• metabolism– BMR : amount of energy in kilocalories ; weight in

kilograms x 1 male x .9 female– anabolism : make larger molecule, amino acids -->

proteins– catabolism : break down digestion (hydrolysis)

• carbohydrate metabolism– carbohydrate --> monosaccharide– starches enzyme amylase– Disaccharides sucrose, lactose and maltose

• Enzymes : sucrase, lactase, and maltase

– phases of cellular respiration

• lipid metabolism– lipids --> fatty acids enzyme: lipase

• protein metabolism– proteins --> amino acids enzymes: proteases pepsin, trypsins

• General metabolic functions– glycogenesis : making of glycogen– glycogenolysis : breaking down of glycogen to

glucose– glucogenesis : fats or proteins made into

glucose

• cholesterol metabolism– 15 % from diet & 85 % made by liver

• LDL’s - low density lipoproteins transport cholesterol to body cells

• HDL’s - high density lipoproteins transport cholesterol to liver and out of body.

Body Energy Balance• regulation of food intake

• nutrient levels• hormones, body temp.• glucose in blood & psychological

• body temperature regulation• heat promoting

– vasoconstricting» shivering, pyrogens

• heat loss– radiation --> blood vessels skin dilating– evaporation --> sweat

Metabolism – all chemical reactions in the body

A. Energy conservation – food energy ATP

• Anaerobic – without O2, glycolysis, fermentation• Aerobic – with O2, Kreb’s, electron transport

Glycolysis – anaerobicGlycogen – (stored glucose) ATP lactic acid- formed with no or little O2• Glycogen stored in muscles and liverGlycogen + (2ATP) (4ATP) + pyruvicacid(citric acid) -formed from

breakdownof glycogen under normal conditions• Net gain of 2 ATP (s)

Krebs Cycle A. Citric acid cycle (gain 2 ATP)

• By products of glycolysis citric or pyruvic acid ATP

• Net gain of 1 ATP per cycle 2 cycles Electron Transport – aerobic

• Glucose net gain of 32 ATP’s

Cellular Respiration – net gain of 36 ATP’s • C6H12O6 + O2 + 2ATP + 38 ADP + 38( – P) CO2 + H2O + 38 ATP

Fermentation – anaerobic “yeasts” and bacteria

A. Alcohol – sugar or starch alcohol + carbon dioxide

B. Lactate – lactose lactic acid + CO2

Pyruvic acid is turned into lactic acid Energy sources in the human

“Cellular Respiration” total of 36 ATP’s• Glycolysis – 2 ATP’s anaerobic• Krebs – 2 ATP’s aerobic • Electron transport – 32 ATP’s aerobic

Nutrition and Metabolism

• Nutrition• Carbohydrate Metabolism• Lipid and Protein Metabolism• Metabolic States and Metabolic Rate• Body Heat and Thermoregulation

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Body Weight

• Stable with equal energy intake and output– around a homeostatic set point

• Determined by combination of environmental and hereditary factors– 30-50% of variation between individuals due to

heredity – rest due to eating and exercise habits

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Gut-Brain Peptides

• Appetite regulators– short term

• effects last minutes to hours

– long term• effects last weeks to years

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Short-term Appetite Regulators• Ghrelin – produces hunger

– from parietal cells of empty stomach– also stimulates hypothalamus release of

human growth hormone releasing hormone

• Peptide YY – satiety– secreted in proportion to calories consumed– acts as ileal break

• slows stomach emptying

• Cholecystokinin – satiety – from enteroendocrine cells of duodenum and jejunum– appetite-suppressing effect on brain

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Long-term Appetite Regulators

• Leptin – secreted by adipocytes in proportion to body fat stores

• Insulin – pancreatic beta cells– effect similar to leptin (but weaker)

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Appetite Regulation

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Other Factors in Appetite Regulation

• Appetite is briefly satisfied by– chewing– swallowing– stomach filling

• Neurotransmitters stimulate desire for different foods– norepinephrine – carbohydrates– galanin – fats – endorphins – protein

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Calories• One calorie - amount of heat required to raise

temperature of 1 g of water 1 °C– 1000 calories is a kilocalorie or Calorie

• Fats contain about 9 kcal/g• Carbohydrates and proteins, about 4 kcal/g

– sugar and alcohol are “empty” calories -- few nutrients

• Substance used for fuel is oxidized primarily to make ATP

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Nutrients• Ingested chemical used for growth, repair or

maintenance• Macronutrients consumed in large amounts

– proteins, fats and carbohydrates

• Micronutrients needed in small amounts• Recommended daily allowances (RDA)

– safe estimate of daily intake for standard needs

• Essential nutrients can not be synthesized– minerals, vitamins, 8 amino acids and 1-3 fatty acids

must be consumed in the diet 26-20

Carbohydrates

• Carbohydrates found in 3 places in body– muscle and liver glycogen; blood glucose

• Most carbohydrate serves as fuel– neurons and RBCs depend on glucose

• Sugars do serve as structural components– nucleic acids, glycoproteins and glycolipids, ATP

• Blood glucose carefully regulated by insulin and glucagon

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RDA and Dietary Sources of Carbs

• Carbohydrates are rapidly oxidized, RDA greater than any other nutrient (175 g/day)

• Dietary sources:– monosaccharides = glucose, galactose and fructose

• liver converts galactose and fructose to glucose– outside hepatic portal system, only blood sugar is glucose– normal blood sugar concentration ranges 70 to 110 mg/dL

– disaccharides = table sugar (sucrose), maltose, lactose– polysaccharides = starch, glycogen and cellulose

• Nearly all dietary carbohydrates come from plants

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Dietary Fiber• Fibrous material that resists digestion• Fiber is important to diet (RDA is 30 g/day)

– excess interferes with mineral absorption - iron

• Water-soluble fiber (pectin)– blood cholesterol and LDL levels

• Water-insoluble fiber (cellulose, lignin)– absorbs water in intestines, softens stool, gives it bulk,

speeds transit time

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Lipids• Average adult male 15% fat; female 25% fat

– body’s stored energy• hydrophobic, contains 2X energy/g, compact storage• glucose and protein sparing (no protein utilized for energy)

– fat-soluble vitamins (A,D,E,K) absorbed with dietary fat• ingest less than 20 g/day risks deficiency

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Functions of Lipids• Diverse functions

– structural • phospholipids and cholesterol are components of plasma

membranes and myelin

– chemical precursors • cholesterol - a precursor of steroids, bile salts and vitamin D• fatty acids - precursors of prostaglandins and other

eicosanoids

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Fat Requirements and Sources• Should be less than 30% of daily calorie intake

– typical American gets 40-50%

• Most fatty acids synthesized by body– essential fatty acids must be consumed

• Saturated fats – animal origin -- meat, egg yolks and dairy products

• Unsaturated fats – found in nuts, seeds and most vegetable oils

• Cholesterol – found in egg yolks, cream, shellfish, organ meats and other

meats26-26

Serum Lipoproteins

• Lipids transported in blood as lipoproteins– protein and phospholipid coat around a

hydrophobic cholesterol and triglyceride core– soluble in plasma; bind to cells for absorption

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Serum Lipoproteins

• Categorized into 4 groups by density: more protein = higher density– chylomicrons– very low-density (VLDLs)– low-density (LDLs)– high-density (HDLs)

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VLDL and LDL• VLDL

– produced by liver to transport lipids to adipose tissue for storage

– when triglycerides removed become LDLs (mostly cholesterol)

• LDL – absorbed by cells in need of cholesterol for membrane

repair or steroid synthesis

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HDL• Production and function

– liver produces an empty protein shell– travels through blood, picks up cholesterol– delivers cholesterol to liver, for elimination in bile

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Total Cholesterol• Desirable to maintain total cholesterol concentration of <

200 mg/dL– most cholesterol is endogenous– dietary restrictions lower blood cholesterol levels

• by 5% with restriction of dietary cholesterol• by 15 to 20% with restriction of certain saturated fats

– vigorous exercise lowers blood cholesterol

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Desirable Lipoprotein Levels• High levels of HDL

– indicate cholesterol is being removed from arteries

• Low levels LDL– high LDL correlates with cholesterol deposition in arteries

• Recommendations– exercise regularly– avoid smoking, saturated fats, coffee and stress

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Lipoprotein Processing

• Three pathways26-33

Proteins• 12-15% of body mass

– mostly in skeletal muscles

• Functions– muscle contraction

• movement of body, cells, cell structures

– cell membranes (receptors, cell identity, pumps)

– fibrous proteins (collagen, keratin) • structural

– globular proteins (antibodies, myoglobin, enzymes)• functional

– plasma proteins: blood osmolarity and viscosity 26-34

Requirements for Protein• RDA - 44-60 g/day• Nutritional value depends on proportions of

amino acids– 8 essential amino acids can not be synthesized

• isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine

• Cells do not store surplus protein• Complete proteins (dietary)

– supply all amino acids in right amount needed to synthesize protein

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Dietary Sources• Animal proteins (meat, eggs and dairy) are

complete proteins – closely match human proteins in amino acid

composition

• Plant sources must be combined in the right proportions– beans and rice are a complementary choice

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Functions of Minerals• Calcium and phosphorus

– bones and teeth

• Phosphorus– phospholipids, ATP, CP, buffers, nucleic acids

• Calcium, iron, magnesium and manganese – cofactors for enzymes

• Iron - essential for hemoglobin and myoglobin

• Chlorine - component of stomach acid (HCl)

• Mineral salts – electrolytes; govern function of nerve and muscle cells;

regulate distribution of body water26-37

Dietary Sources of Minerals• Vegetables, legumes, milk, eggs, fish and shellfish• Animal tissues contain large amounts of salt

– carnivores rarely lack salt in their diets– herbivores often supplement by ingesting soils

• Recommended sodium intake is 1.1 g/day• Typical American diet contains 4.5 g/day

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Vitamins• Body synthesizes some vitamins from precursors

– niacin, vitamin A and D– vitamin K, pantothenic acid, biotin, folic acid

• produced by intestinal bacteria

• Water-soluble vitamins (C, B) – absorbed with water in small intestine; not stored

• Fat-soluble vitamins (A, D, E, K)– absorbed with dietary lipids; stored

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Carbohydrate Metabolism

• Dietary carbohydrate burned as fuel within hours of absorption (glucose catabolism)

C6H12O6 + 6O2 6CO2 + 6H2O

• Transfers energy from sugar to ATP

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Glucose Catabolism• Series of small steps to efficiently transfer energy

to ATP (reduces energy lost as heat)

• Three major pathways– Anaerobicglycolysis (yields 2 ATP)

– aerobic respiration (yields 34-36 ATP) Krebs cycle(2ATP) and electron transport(32 ATP)

– anaerobic fermentation (if no O2 available)• pyruvic acid reduced to lactic acid

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Overview of ATP Production

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Anaerobic Fermentation• Fate of pyruvic acid depends on oxygen availability• In an exercising muscle, demand for ATP > oxygen supply;

ATP produced by glycolysis+

• Lactic acid travels to liver to be oxidized back to pyruvic when O2 is available (oxygen debt)– then stored as glycogen or released as glucose

• Fermentation is inefficient, not favored by brain or heart

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Aerobic Respiration

• Most ATP generated in mitochondria, require oxygen as final electron acceptor

• Principle steps– matrix reactions occur in fluids of mitochondria– membrane reactions whose enzymes are bound

to the mitochondrial membrane

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Overview of ATP Production

• Complete aerobic oxidation of glucose to CO2 and H2O produces 36-38 ATP– efficiency rating of 40% -- rest is body heat

– ADP bonds with recharged Phosphates to make ATP

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ATP Generated by Oxidation of Glucose

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Glycogen Metabolism• ATP is quickly used after it is formed -- it is not a storage

molecule– extra glucose will not be oxidized, it will be stored

• Glycogenesis -- synthesis of glycogen– stimulated by insulin (average adult contains 450 g)

• Glycogenolysis -- glycogen glucose– stimulated by glucagon and epinephrine– only liver cells can release glucose back into blood

• Gluconeogenesis -- synthesis of glucose from noncarbohydrates, such as fats and amino acids

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Lipids• Triglycerides are stored in adipocytes

– constant turnover of molecules every 3 weeks • released into blood, transported and either oxidized or redeposited in

other fat cells

• Lipogenesis = synthesizing fat from other sources– amino acids and sugars used to make fatty acids and glycerol

• Lipolysis = breaking down fat for fuel– glycerol is converted to PGAL and enters glycolysis– fatty acids are broken down 2 carbons at a time to produce

acetyl-CoA (beta oxidation)

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Lipogenesis and Lipolysis Pathways

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Ketogenesis• Fatty acids catabolized into acetyl groups (by beta-

oxidation in mitochondrial matrix) may – enter citric acid cycle as acetyl-CoA– undergo ketogenesis

• metabolized by liver to produce ketone bodies• rapid or incomplete oxidization of fats raises blood ketone

levels (ketosis) and may lead to a pH imbalance (ketoacidosis)

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Proteins• Amino acid pool - dietary amino acids plus 100 g of tissue

protein broken down each day into free amino acids• May be used to synthesize new proteins• As fuel -- first must be deaminated (removal of NH2)--

what remains is converted to pyruvic acid, acetyl-CoA or part of citric acid cycle– during shortage of amino acids, the reverse occurs for protein

synthesis– the NH2 become ammonia (NH3) which is toxic and which the

liver converts to urea (excreted in urine)

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Urea Synthesis

• Liver converts ammonia (NH3) to urea which is removed from blood by kidneys

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Absorptive State• Lasts about 4 hours during and after a meal

– time of nutrient absorption and use for energy needs• Carbohydrates

– blood glucose is available to all cells for ATP synthesis– excess is converted by liver to glycogen or fat

• Fats– taken up by fat cells from chylomicrons in the blood– primary energy substrate for liver, fat and muscle cells

• Amino acids– most pass through the liver and go onto other cells– in liver cells, may be used for protein synthesis, used for fuel for

ATP synthesis or used for fatty acid synthesis

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Regulation of Absorptive State• Regulated by insulin secreted in response to elevated

blood glucose and amino acid levels and the hormones gastrin, secretin and cholecystokinin

• Insulin– increases the cellular uptake of glucose by 20-fold– stimulates glucose oxidation, glycogenesis and lipogenesis but

inhibits gluconeogenesis– stimulates active transport of amino acids into cells and

promotes protein synthesis• high protein, low carbohydrate meals stimulate release of both insulin

and glucagon preventing hypoglycemia

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Postabsorptive State• Homeostasis of blood glucose critical to brain

– when stomach and small intestine are empty- stored fuels are used

• Carbohydrates– glucose is drawn from glycogen reserves for up to 4 hours and

then synthesized from other compounds• Fat

– adipocytes and liver cells convert glycerol to glucose– free fatty acids are oxidized by liver to ketone bodies

• other cells use for energy-- leaving glucose for brain

• Protein metabolism– used as fuel when glycogen and fat reserves depleted– wasting away occurs with cancer and other diseases from loss of

appetite and altered metabolism 26-55

Regulation of Postabsorptive State

• By sympathetic nervous system and glucagon• Blood glucose drops, glucagon secreted

– glycogenolysis and gluconeogenesis raise glucose levels

– lipolysis raises free fatty acid levels

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Regulation of Postabsorptive State

• Sympathoadrenal effects– promotes glycogenolysis and lipolysis under

conditions of injury, fear, anger and stress– adipose, liver cells and muscle cells are richly

innervated and also respond to epinephrine from adrenal medulla

– Cortisol from adrenal cortex promotes blood glucose• fat and protein catabolism and gluconeogenesis

– Growth hormone – opposes rapid in blood glucose

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Metabolic Rate

• Amount of energy used in the body in a given period of time (kcal/hr or kcal/day)– measured directly in calorimeter (water bath)– measured indirectly by oxygen consumption

• Basal metabolic rate (BMR) – relaxed, awake, fasting, room comfortable temperature– adult male BMR is 2000 kcal/day(slightly less female)

• Factors affecting total MR– pregnancy, anxiety, fever, eating, thyroid hormones, and

depression

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Body Heat and Thermoregulation

• Homeostasis requires heat loss to match heat gain

• Hypothermia - excessively low body temperature– can slow metabolic activity and cause death

• Hyperthermia - excessively high body temperature– can disrupt enzymatic activity and metabolic activity

and cause death• Thermoregulation - ability to balance heat

production and heat loss

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Body Temperature

• “Normal” body temperature varies about 1.8 degrees F. in a 24-hour cycle– low in morning and high in late afternoon

• Core body temperature is temperature of organs in cranial, thoracic and abdominal cavities– rectal temperature is an estimate– adult varies normally from 99.0 - 99.7 degrees F.

• Shell temperature is temperature closer to the surface (oral cavity and skin)– adult varies normally from 97.9 - 98.6 degrees F.

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Heat Production

• Comes from energy-releasing chemical reactions such as nutrient oxidation and ATP use

• From brain, heart, liver, endocrine and muscles– exercise greatly heat production in muscle

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Modes of Heat Loss

• Radiation - loss of body heat to objects around us– caused by molecular motion producing infrared radiation

• Conduction - loss of body heat to the air which when warmed rises to be replaced by cooler air

• Evaporation - heat loss as sweat evaporates – extreme conditions as much as 2L of sweat lost per hour,

dissipating heat by as much as 600 kcal/hour

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Thermoregulation• Hypothalamic thermostat monitors

temperature of blood and skin, signals– heat-losing center to stimulate

• cutaneous vasodilation• sweating

– signals heat-promoting center to stimulate• cutaneous vasoconstriction• arrector pili muscle contraction• shivering thermogenesis (if needed)• nonshivering thermogenesis - thyroid hormone

and BMR (seasonal adjustment)

• Behavioral thermoregulation– get out of sun, remove heavy clothing

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Disturbances of Thermoregulation• Fever

– normal protective mechanism that elevates BMR which produces more heat elevating the BMR, etc.

• Hyperthermia - exposure to excessive heat– heat cramps are muscle spasms due to electrolyte imbalance

from excessive sweating– heat exhaustion -- severe electrolyte imbalance producing

fainting, dizziness, hypotension– heat stroke -- body temperature > 104 °F, may cause delirium,

convulsions, coma, and death• Hypothermia - exposure to excess cold

– as core body temperature , BMR causing a further body temperature decrease, etc. (fatal if body temperature 75 °F)

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