TOPIC 9 Nutrition, Metabolism & Body Temperature Regulation

Biology 221 Anatomy & Physiology II TOPIC 9 Nutrition, Metabolism & Body Temperature Regulation Chapter 25 pp. 949-997 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 • Majornutrients • 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 Vitamins Vit. 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) • Enzymecofactors – 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: Phosphorylation Substrate-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. 25.4 p. 964

Metabolism: Phosphorylation Oxidative 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. 25.4 p. 964

Glucose Oxidation: Overview Three main stages • Glycolysis • Krebs cycle • Electron transport chain with oxidative phosphorylation See also animations of aerobic and anaerobic metabolism - Metabolism Review Fig. 25.5 p. 965

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 space Fig. 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 Metabolism Fat 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 Metabolism Protein 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 Metabolism Carbohydrate 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 Metabolism Miscellaneous • 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) • Increasedmetabolic 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 children Decreased 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 Thermoregulation Hyperthermia – 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 Thermoregulation Hypothermia – 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)

TOPIC 9 Nutrition, Metabolism & Body Temperature Regulation