TOPIC 9 Nutrition, Metabolism &

Body Temperature Regulation

Chapter 25pp. 949-997

Biology 221Anatomy & Physiology II

E. Lathrop-Davis / E. Gorski / S. Kabrhel

Definitions• “Calorie” (kilocalorie) – “amount of heat energy

needed to raise the temperature of 1 kilogram of water 1 oC”

• Nutrient – substance that is used to promote normal growth, body maintenance and tissue repair– major nutrients – needed in large amounts – minor nutrients – needed in small amounts

Nutrients• Major nutrients

– include protein [amino acids], carbohydrate, lipid

– water is also a major nutrient° ingested water comes in food and drink° metabolic water is made during respiration

• Minor nutrients– vitamins are organic (Vit. B, Vit. C, Vit. D,

etc.)– minerals are inorganic (e.g, iron, calcium,

iodine)

Major Food Groups• Grains• Fruits• Vegetables• Protein• Dairy• Fats, oils, sweets

Fig. 25.1, p. 949

Carbohydrates: Sources & Uses• Dietary sources – mostly from plants (lactose

comes from milk)• Uses in the body

– energy source ° glucose (six-carbon sugar or hexose) is the

primary sugar used to make ATP° fructose and galactose (also hexose sugars)

can be converted to glucose– structure – backbone of nucleic acids (ribose

and deoxribose) – cell recognition – joined to proteins to form

glycoproteins

Carbohydrates: Miscellaneous• Stored as

– glycogen in liver, and skeletal and cardiac muscle (medium-term storage)

– excess is converted to fat in adipose cells (long-term storage)

• Cellulose (a polymer of glucose) – is not digested but provides bulk to feces

Hormonal Control of Blood Glucose

• see A&P I “Unit 11 – Endocrine System”• hypoglycemic hormones decrease blood sugar –

insulin• hyperglycemic hormones increase blood sugar

– glucagon– glucocorticoids (cortisol)– epinephrine– growth hormones

Lipids: Sources• most are neutral fats (triglycerides - fats & oils)• saturated fats – fatty acid chains contain no double

bonds– found in animal products and a few plant products

(e.g., coconut)– generally solid at room temperature

Lipids: Sources• unsaturated fats come mainly from plants; liquid at

room temp.– monounsaturated fats (fatty acid chains have one

double bond)– polyunsaturated fats (fatty acid chains have more

than one double bond)• cholesterol – comes from animal products

Lipids: Sources: Essential Fatty Acids

• must be in diet because liver lacks enzymes to synthesize them – found in plants

• linoleic acid – fatty acid component of lecithen, a membrane lipid

• linolenic acid – may be “essential”, research not clear

Lipids: Uses in the Body• Component of adipose

– long-term energy storage– cushions organs– insulates (keeps body heat in)

• Components of plasma membranes (phospholipids; cholesterol)– unsaturated fats and cholesterol help prevent

cell membrane from crystallizing at low temperatures

Lipids: Uses in the Body• Regulatory molecules

– steroid hormones – gonads & adrenal cortex– prostaglandins – paracrines (locally acting)

° Pain, sensitize blood vessels to inflammatory compounds (See Topic 6)

Proteins: Dietary Sources• All-or-none rule – all amino acids needed must be

present for a protein to be synthesized (if any are lacking, the protein will not be made)

• Complete proteins – contain all essential amino acids– from animal products (eggs, milk, meat)– Soybeans – only plants with complete protein

Proteins: Dietary Sources• Incomplete proteins

– low amounts or lacking certain amino acids– plant proteins

° need to be mixed to get all essential amino acids at the same time

° mix grains (like rice or corn) with legumes (peas or beans)

Proteins: Essential Amino Acids• Cannot be made by the body (liver lacks the proper

enzymes); therefore, must be in diet

• Vegetarians can get all by combining grains (e.g., corn, rice) with legumes (beans, peas)– tryptophan– Methionine (cysteine)– valine– threonine– phenylalanine (tyrosine)– leucine– histadine (needed by infants)

Fig. 25.2, p. 952

Proteins: Uses in the Body• Structure

– important components of plasma membranes– collagen and elastin fibers of CTs– cytoskeleton– cell junctions

• Catalysts - enzymes (increase reaction rates)

Proteins: Uses in the Body• Transport & storage

– intracellular transport– membrane transport proteins (channels, pumps,

facilitated transport carriers)– hemoglobin (O2 transport), transferrin (Fe

transport)– storage proteins: hemosiderin (Fe), ferritin

(Fe), myoglobin (O2 in red-twitch skeletal and cardiac muscle), thyroglobulin (thyroxine)

Proteins: Uses in the Body• Contraction – myosin, actin, tropomyosin, troponin• Regulation

– hormones ° control body functions° e.g., insulin, ADH, glucagon, and other

hormones except from adrenal cortex and gonads

– calmodulin – intracellular regulation• Defense – immunoglobulins (antibodies) provide

specific resistance to disease by attacking antigens

Proteins: Miscellaneous• Adequacy of caloric intake – diet must include

sufficient carbohydrates or fat for ATP production so that amino acids are used for protein synthesis

• Nitrogen balance of the body – balance occurs when intake (through diet)

equals loss through urine and feces– transamination – adds amino (NH3) group from

one molecule to another to make nonessential amino acid

– deamination – removes amino group from amino acid so that carbon skeleton can be used for energy (amino is converted to urea)

Proteins: Hormonal Control of Protein Synthesis

• Anabolic hormones (e.g., testosterone, GH) promote protein synthesis

• Catabolic hormones (e.g., glucocorticoids) promote degradation

Water-soluble Vitamins

• Vit. C, B-complex vit. – absorbed along with water in the small intestine

• Absorption of Vit. B12 requires presence of intrinsic factor produced by stomach– pernicious anemia – anemia caused by

inadequate intake of vit. B12 due to lack of intrinsic factor

• Some B vitamins produced by gut bacteria• Excesses usually eliminated in urine

Fat-soluble VitaminsVit. A, D, E and K• Vit. K produced by gut bacteria• Vit. D made by body• Absorption aided by micelles in small intestine• Excesses of Vit. A, D, and E stored in fat

(megadoses may cause problems)

Functions of Vitamins• Coenzymes – molecules that help enzymes

perform their functions– riboflavin and niacin form part of electron

carriers (FAD and NAD+, respectively) that carry electrons during catabolism of glucose

• Antioxidants (Vit. A, C and E) – interact with free radicals in cell to prevent damage to cell

• Vit. A is precursor to visual pigments in retina

Minerals: Miscellaneous & Sources• Dietary sources – vegetables, legumes, milk, some

meats• Some minerals required in large amounts

– calcium, potassium, phosphorus, sulfur, sodium, chloride, magnesium

• Others required in small amounts = trace minerals– include iron, zinc and iodine

Minerals: Uses in Body• Structure (especially Ca2+ and Mg2+ / PO4

= salts in bones and teeth)

• Enzyme cofactors – form part of active sites of enzymes (Mg2+)

• Oxygen transport by hemoglobin and storage by myoglobin (Fe)

• Ionic and osmotic balances (especially Na+, Cl-, and K+) – affect blood pressure as a result of water

retention (especially Na+)

Minerals: Uses in Body• Essential to action potentials and impulses (Na+,

K+, Ca2+)• Essential to contraction (Na+, K+, Ca2+)• Thyroid hormones (I-)• Essential to clotting (Ca2+ = clotting factor IV)• Energy transfers (PO4

=)

Metabolism: Definitions• Metabolism – sum of all the chemical processes

occurring in the body• Anabolism – reactions in which larger molecules

manufactured from smaller ones– require energy (ATP) input– e.g., amino acids --> peptides (proteins)

Metabolism: Definitions• Catabolism – reactions in which larger molecules

are broken into smaller ones– includes breakdown of food in GI tract– cellular respiration releases energy, some of

which is used to make ATP– e.g., glucose oxidation

Metabolism: PhosphorylationSubstrate-level phosphorylation • phosphate group passed from phosphorylated

(energized) molecule to ADP to make ATP• occurs during glycolysis and Kreb’s cycle• also transfer from phosphocreatine to ADP (in

skeletal muscle)

Fig. 25.4p. 964

Metabolism: PhosphorylationOxidative phosphorlyation • under aerobic conditions• occurs in mitochondria• ATP synthesized by addition of phosphate to ADP

using energy of H+ gradient• used to make most of cell’s ATP

Fig. 25.4p. 964

Glucose Oxidation: OverviewThree main stages• Glycolysis• Krebs cycle• Electron transport chain with oxidative

phosphorylation

Fig. 25.5p. 965

See also animations of aerobic and anaerobic metabolism - Metabolism Review

Glucose Oxidation: Glycolysis

• Produces pyruvate (3-carbon) as glucose (6-carbon) is cleaved

• Net of 2 ATP are made by substrate-level phosphorylation

• Occurs in cytoplasm• Anaerobic (does not require oxygen)

Fig. 25.6, p. 966

Glucose Oxidation: Krebs cycle• Produces 2 ATP• Occurs in mitochondria• Aerobic (requires oxygen)• Requires intermediate step involving acetyl-CoA• Produces:

– reduced energy carriers (NADH+H; FADH2)– CO2

Fig. 25.7, p. 968

Glucose Oxidation: Electron Transport and Oxidative Phosphorlyation

• Most ATP is made by oxidative phosphorylation• Occurs in mitochondria• Reduced electron carriers (FADH2 and NADH +

H+) pass electrons to membrane proteins• Energy associated with transfer of electrons used to

pump H+ into intermembrane spaceFig. 25.8, p. 969

Glucose Oxidation: Electron Transport and Oxidative Phosphorlyation

• Energy of H+ gradient used by ATP synthase to make ATP

• Aerobic (requires oxygen as final electron acceptor produces metabolic water)

Fig. 25.8, p. 969

Fig. 25.9, p. 971

Summary of ATP Production• Glycolysis produces a net of 2 ATP• Krebs cycle produces a net of 2 ATP• Oxidative phosphorylation produces 32 (most

cells) or 34 (liver) ATP• Total net ATP produced = 36 or 38 ATP

Fig. 25.10, p. 965

Role of the Liver in MetabolismFat metabolism• Packages fatty acids into forms that can be stored

or transported• Stores fat• Synthesizes cholesterol (from which it can

synthesize bile salts)• Forms lipoproteins for transport of fats, fatty

acids and cholesterol to and from other tissues

Role of the Liver: Lipoproteins• VLDLs – carry triglycerides from liver to

peripheral tissues (mostly adipose)• LDLs – cholesterol-rich lipoproteins transporting

cholesterol from adipose to peripheral tissues for incorporation into plasma membrane

• HDLs – transport cholesterol from peripheral tissues to

liver for removal– pick up cholesterol from tissues and from

arterial walls– transport cholesterol to gonads and adrenal

cortex

Role of the Liver in MetabolismProtein metabolism• Synthesizes plasma proteins

– including clotting proteins– albumins (osmotic balance)

• Synthesizes nonessential amino acids by transamination (transferring amino group (NH2) from one molecule to another)

• Converts ammonia formed by deamination of amino acids into urea– urea is less toxic than ammonia– carbon skeleton “burned” as fuel

See Fig. 25.14, p. 976

Role of the Liver in MetabolismCarbohydrate metabolism• Stores glucose as glycogen

– Glycogenesis– stimulated by insulin

• Releases glucose when blood sugar is low– stimulated by hyperglycemic hormones

(glucagon) or under stress (GH, epinephrine, cortisol)

– gluconeogenesis – formation of glucose from noncarbohydrate sources (e.g., fats or amino acids)

– glycogenolysis – break down of glycogen

Role of the Liver in MetabolismMiscellaneous• Stores vitamins A, D, B12

• Stores iron from worn-out red blood cells• Degrades hormones• Detoxifies toxic substances (e.g., drugs, alcohol)

– prolonged substance abuse or exposure to toxins/toxics damages liver

Body Temperature• Normal body temperature = 96-100 oF (35.6-37.8 oC)

– varies with activity and time of day– averages around 98.2 oF (36.6 oC)– represents a balance between heat production and

heat loss• Core temperature

– temperature of organs within skull, thoracic and abdominal cavities (ventral body cavity)

– more critical than shell temp.• Shell temperature = temperature of skin and

appendages• Increased temperature chemical reaction rates

Heat Exchange Mechanisms• Radiation – loss or gain of heat in the form of

infrared radiation• Conduction – transfer of heat from one object to

another (e.g., touching a warm radiator or a cold cement bench)

• Convection – loss to air moving over body surface• Evaporation – loss of body heat to water as it

evaporates from body surface

See Fig. 25.25

Heat Producing Mechanisms• Basal metabolism (amount of energy needed to

maintain body at rest without activity from digestion)– most heat is generated by activity in the brain,

liver, endocrine organs, and heart– inactive skeletal muscle accounts for 20-30%

• Muscular activity– uses more ATP so increases metabolism– includes shivering

• Thyroxine and epinephrine stimulate metabolic rates in cells

Role of the Hypothalamus• Thermoreceptors respond to changes in temperature• Thermoregulatory centers

– heat-loss center° activated when core temperature rises above

normal range° promotes heat loss

– heat-promoting center° activated when core temperature falls below

normal range° promotes production of heat

Keeping the Body Warm Fast-acting Mechanisms

• Vasocontriction of cutaneous blood vessels– keeps warm blood closer to core (away from

surface where heat is lost)• Increased metabolic rate

– non-shivering thermogenesis = increased metabolic rate in response to norepinephrine secreted by sympathetic nervous system

– shivering (brain alternately stimulates small contractions in antagonistic muscles)

• Behavioral modifications

Keeping the Body WarmSlow-acting mechanism

Not very important in adult, but does work in childrenDecreased body temperature in response to seasonal

cooling:Hypothalamus releases more thyrotropin releasing

hormone (TRH) Adenohypophysis responds by releaseing more

thyroid-stimulating hormone (TSH)Thyroid responds with enhanced thyroxine release increases basal metabolic rate increases heat production

Cooling the Body When Core Becomes Too Hot

• Vasodilation of cutaneous blood vessels• Enhanced sweating --> evaporative cooling• Behavioral changes

– decreased activity– removing insulating layers of clothing

Imbalances of ThermoregulationHyperthermia – excessive body heat• Heat exhaustion – elevated body temperature and

mental confusion or fainting due to dehydration• Heat stroke – loss of ability to regulate body heat

due to increased body temperature (a rather nasty form of positive feedback)

• Fever – controlled hyperthermia in response to infection and release of pyrogens (see Topic 6)– may also be caused by cancer, allergic

reactions, CNS injuries– promotes function of white blood cells

Imbalances of ThermoregulationHypothermia – decreased body temperature due to

excessive loss of body heat• Core temperature may drop so low that CNS

function stops (chemical reaction rates decrease to level that does not support life)

• Lowers oxygen requirement (improves chances of survival during drowning)