Marieb Human Anatomy & Physiology: Nutrition, Metabolism, and Energy Balance PDF

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 24 Nutrition, Metabolism, and Energy Balance PowerPoint® Lecture Slides...

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 24 Nutrition, Metabolism, and Energy Balance PowerPoint® Lecture Slides prepared by Justin A. Moore, American River College Copyright © 2025 Pearson Education, Inc. All Rights Reserved Video: Why This Matters (Career Connection) Understanding the process of how the body converts nutrients into energy can help you effectively advise your patients on dietary choices that will allow their bodies to operate at peak performance Click here to view ADA compliant video: Why This Matters (Career Connection) https://mediaplayer.pearsoncmg.com/assets/secs_wtm_ch_24_christian_v2 Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 1—Nutrients Nutrient: substance in food needed for growth, maintenance, repair – Five categories ▪ Three macronutrients that make up most of our diet – Carbohydrates, lipids, and proteins ▪ Two micronutrients that are equally important, but requirements are small – Vitamins and minerals – Most nutrients used for metabolic fuel, some for building molecules and cells Water also needed; accounts for ~ 60% by volume of the food we eat Essential nutrients: ~ 40 molecules must be provided by diet – We can’t synthesize them in adequate amounts, like the hundreds of other nonessential nutrients we require ▪ Cells (especially liver cells) have ability to convert one type of molecule to another; interconversions allow us to adjust to varying food intakes Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 1—Nutrients Energy value of nutrients measured in kilocalories (kcal) – One kcal is amount of heat needed to raise temperature of 1 kg H2O by 1 C ▪ 1 kcal = one calorie (C) – Carbohydrates and proteins have 4 kcal/g, but lipids have almost 9 kcal/g USDA’s MyPlate: guidelines represented as portions on a dinner plate – Food groups represented: ▪ Fruits ▪ Vegetables ▪ Grains ▪ Protein ▪ Dairy Basic dietary principles: – Eat only what you need – Eat plenty of fruits, vegetables, and whole grains – Avoid junk food Copyright © 2025 Pearson Education, Inc. All Rights Reserved USDA’s My Plate Food Guide Figure 24.1 USDA’s MyPlate food guide Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.1 Carbohydrates, Lipids, and Proteins Supply Energy and Are Used as Building Blocks Copyright © 2025 Pearson Education, Inc. All Rights Reserved Carbohydrates Dietary sources – Mostly plants, except for milk sugar (lactose) and small amounts of glycogen – Sugars (mono- and disaccharides): fruits, sugarcane, sugar beets, honey, milk – Starch (polysaccharide): grains and vegetables – Insoluble fiber (the cellulose we can’t digest in vegetables) provides roughage that increases bulk of stool and facilitates defecation – Soluble fiber (like pectin in apples and citrus) reduces blood cholesterol levels Copyright © 2025 Pearson Education, Inc. All Rights Reserved Carbohydrates Uses in the body – Glucose is the carbohydrate molecule used by cells to make ATP ▪ Fructose and galactose converted to glucose by liver before entering circulation ▪ Many cells also use fats for energy, but neurons and RBCs rely almost entirely on glucose (neurons die quickly without it) ▪ Excess glucose converted to glycogen or fat (for later use) – Other uses: building nucleic acids (with pentose sugars) and cell’s glycocalyx (with short chain sugars) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Carbohydrates Dietary requirements – Recommended daily intake is 45–65% of total calories ▪ Typical American adult at 46% – Should consist mostly of complex carbohydrates (whole grains and vegetables) rather than simple (monosaccharides and disaccharides) ▪ Eating large amounts of refined, sugary foods (“empty calories”) can lead to obesity, as well as nutritional deficiencies – Starchy foods (rice, pasta, breads) cost less than high- protein foods (like meat), so carbohydrates often make up greater percentage of diet in low-income groups Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lipids Dietary sources – Primarily triglycerides (neutral fats) in the form of: ▪ Saturated fats in meat, dairy, some tropical plants (e.g., coconut) ▪ Trans fats in hydrogenated oils (e.g., margarine and shortening) ▪ Unsaturated fats in seeds, nuts, olive oil, and most vegetable oils – Cholesterol found in egg yolk, meats, organ meats, shellfish, and milk products ▪ Liver makes 85% of blood cholesterol – Two essential fatty acids liver can’t synthesize (but found in most vegetable oils) ▪ Linoleic acid—an omega-6 fatty acid (component of lecithin) ▪ Linolenic acid—an omega-3 fatty acid Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Lipids Uses in the body – Adipose tissue provides protective cushioning, insulation, energy storage – Phospholipids essential part of myelin sheaths (neurons) and cell membranes – Cholesterol stabilizes cell membranes; precursor of bile salts and steroid hormones – Prostaglandins (regulatory molecules made from linoleic acid) ▪ Role in smooth muscle contraction, regulation of B P, and inflammation – Triglycerides provide a major energy source for skeletal muscle and liver cells – Help body absorb fat-soluble vitamins Dietary requirements – Fats should represent 20–35% of total caloric intake (> 40% in typical American diet) ▪ Limit saturated fats to 10% or less of total fat intake – Cholesterol can be synthesized to meet needs (not required in diet) ▪ Many recommend intake as low as possible, especially for those with high blood cholesterol levels, which is associated with cardiovascular (CV) disease Copyright © 2025 Pearson Education, Inc. All Rights Reserved Proteins Dietary sources – Animal products (eggs, milk, fish, most meats) and soybeans provide complete proteins—meeting all amino acid requirements – Legumes, nuts, and cereal grains contain incomplete proteins—low in one or more essential amino acids ▪ Ingested together, cereal grains and legumes provide all essential amino acids Copyright © 2025 Pearson Education, Inc. All Rights Reserved Essential Amino Acids Figure 24.2 Essential amino acids Copyright © 2025 Pearson Education, Inc. All Rights Reserved Proteins Uses in the body – Structural materials: keratin (skin), collagen and elastin (connective tissue), and muscle proteins – Functional molecules: enzymes and protein hormones control various activities – Multiple factors determine whether amino acids in cell are used to synthesize new proteins or used for energy (to make ATP): ▪ The all-or-none rule: all amino acids needed to build a particular protein must be present at the same time – If one or more are insufficient, protein can’t be made, and its amino acids are instead used as energy or converted to carbs or fats ▪ Adequacy of caloric intake: food and body proteins used as energy when intake of carbohydrate or fat calories are insufficient for ATP needs ▪ Hormonal controls: anabolic hormones like GH and gonadal steroids promote protein synthesis; other hormones like glucocorticoids promote protein breakdown and conversion of amino acids to glucose Copyright © 2025 Pearson Education, Inc. All Rights Reserved Proteins Nitrogen balance – Homeostatic state where rate of protein synthesis equals rate of breakdown and loss; amount of nitrogen ingested (via protein) equals amount excreted – Positive nitrogen balance: synthesis exceeds breakdown ▪ Normal in growing children, pregnant women, tissue repair – Negative nitrogen balance: breakdown for energy exceeds synthesis ▪ Occurs during stress, burns, infection, injury, low quality or quantity of dietary proteins, starvation Dietary requirements – Needed to supply essential amino acids (and make nonessential ones) – Amount needed depends on age, size, metabolic rate, current nitrogen balance ▪ Rule of thumb: daily intake of 0.8 g per kg body weight Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.2 Most Vitamins Act as Coenzymes; Minerals Have Many Roles in the Body Copyright © 2025 Pearson Education, Inc. All Rights Reserved Vitamins Vitamins are organic compounds body requires in minute amounts – Not an energy source themselves, but needed to use macronutrients that are—dietary carbohydrates, proteins, fats would be useless without vitamins Most are coenzymes (or parts of), which act with an enzyme to carry out a particular reaction; e.g., B vitamins act as coenzymes when glucose is used to make ATP Most must be ingested, except vitamin: – D (made in skin) – B and K (synthesized by intestinal bacteria) Also, body can convert beta-carotene (orange pigment in carrots) to vitamin A Balanced diet best way to avoid deficiencies – No one major food group contains all vitamins Copyright © 2025 Pearson Education, Inc. All Rights Reserved Vitamins Two types of vitamins based on solubility – Water-soluble vitamins ▪ B complex and C are absorbed with water ▪ B12 absorption requires intrinsic factor (secreted from stomach glands) ▪ No significant storage in body; absorbed vitamins not used by cells are excreted in urine (so problems from excessive intake are rare) – Fat-soluble vitamins A, D, E, and K are absorbed with lipids in gut ▪ Problems with lipid absorption can interfere with uptake of fat-soluble vitamins ▪ Stored in body (except for K); excessive intake can cause health problems Free radicals (molecules with unpaired electron) generated during normal metabolism – Vitamins A, C, E, and mineral selenium are antioxidants—participants in antioxidant reactions that neutralize dangerous free radicals – Megadoses of vitamins not beneficial, and may cause serious health problems (especially fat-soluble vitamins) Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Vitamins Table 24.2 Vitamins Water-Soluble Vitamins Vitamin Major Dietary Sources Major Functions In The Body Symptoms Of Deficiency Or Extreme Excess Vitamin B sub 1 Pork, legumes, peanuts, Coenzyme used in removing C O2 Beriberi (nerve disorder—tingling, poor coordination, (thiamine) whole grains from organic compounds reduced heart function) Vitamin B sub 2 Dairy products, meats, Component of coenzymes FAD and Skin lesions such as cracks at corners of mouth (riboflavin) enriched grains, vegetables F MN B1 CO2 Vitamin B sub 3 Nuts, meats, grains Component of coenzymes Skin and gastrointestinal lesions, nervous system (niacin) disorders Liver damage N A D super plus and N A D P super plus B2 Vitamin Most foods: meats, dairy Component of coenzyme A Fatigue, numbness, tingling of hands and feet (pantothenic B B sub 5 acid) 3 products, whole grains, etc. NAD and NADP  Vitamin B B sub 6 Meats, vegetables, whole Coenzyme used in amino acid Irritability, convulsions, muscular twitching, anemia (pyridoxine) 5 grains metabolism Unstable gait, numb feet, poor coordination Vitamin B sub 7 B6 Legumes, other vegetables, Coenzyme in synthesis of fat, Scaly skin inflammation, neuromuscular disorders (biotin) meats glycogen, and amino acids Vitamin B sub 9 B7 (folic Green vegetables, oranges, Coenzyme in nucleic acid and Anemia, birth defects May mask deficiency of vitamin B sub 12 acid) nuts, legumes, whole grains amino acid metabolism B9 Vitamin B sub 12 Meats, eggs, dairy products Coenzyme in nucleic acid Anemia,B12 nervous system disorders (numbness, loss of metabolism; maturation of red blood balance) B12 cells Vitamin C Fruits and vegetables, Used in collagen synthesis (such as Scurvy (degeneration of skin, teeth, blood vessels), (ascorbic acid) especially citrus fruits, for bone, cartilage, gums); weakness, delayed wound healing Gastrointestinal broccoli, tomatoes antioxidant upset Copyright © 2025 Pearson Education, Inc. All Rights Reserved Vitamins Table 24.2 [cont.] inued Fat-Soluble Vitamins Vitamin Major Dietary Sources Major Functions In The Symptoms Of Deficiency Or Body Extreme Excess Vitamin A Provitamin A (beta-carotene) in Component of visual Blindness, skin disorders, (retinol) deep green and orange pigments; maintenance of impaired immunity Headache, vegetables and fruits; retinol in epithelial tissues; irritability, vomiting, hair loss, dairy products antioxidant blurred vision, liver and bone damage Vitamin D Dairy products, egg yolk; also Aids in absorption and use Rickets (bone deformities) in made in human skin in presence of calcium and phosphorus children, bone softening in adults of sunlight Brain, cardiovascular, and kidney damage Vitamin E Vegetable oils, nuts, seeds Antioxidant; helps prevent Degeneration of the nervous (tocopherol) damage to cell membranes system Vitamin K Green vegetables, tea; also Important in blood clotting Defective blood clotting Liver (phylloquinone) made by colon bacteria damage and anemia Modified from: Urry et al., Campbell Biology, 12th Edition, © 2021. Reprinted by permission of Pearson Education, I nc., Upper Saddle River, N.J. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Minerals Seven minerals required in moderate amounts (plus trace amounts of others): – Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium Like vitamins, work with nutrients for proper body functioning – Incorporating minerals into structures makes them stronger ▪ Calcium, phosphorus, and magnesium salts harden teeth and strengthen bone – Most ionized in body fluids or bound to organic compounds to form phospholipids, hormones, and various proteins ▪ Iron is essential part of oxygen-binding heme of hemoglobin ▪ Sodium and chloride are major electrolytes in blood ▪ Iodine is necessary for thyroid hormone synthesis Uptake and excretion balanced to prevent toxic overload – Natural sodium in foods poses little-to-no health risk; the large amounts added to processed foods and sprinkled on food may cause fluid retention and high BP – Mineral-rich foods: legumes and other vegetables, milk, some meats Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 24.3 Minerals in the Body Greater than 200 mg per Day Required Mineral Major Dietary Sources Major Functions In The Body Symptoms Of Deficiency* Calcium (Ca) Dairy products, dark green Bone and tooth formation, blood clotting, Impaired growth, possibly loss of bone vegetables, legumes nerve and muscle function mass Phosphorus (P) Dairy products, meats, Bone and tooth formation, acid-base Weakness, loss of minerals from bone, grains balance, nucleotide synthesis calcium loss Sulfur (S) Proteins from many Component of certain amino acids Symptoms of protein deficiency sources Potassium (K) Meats, dairy products, Nerve function, acid-base balance Muscular weakness, paralysis, nausea, many fruits and vegetables, heart failure grains Chlorine (Cl) Table salt Acid-base balance, formation of gastric Muscle cramps, reduced appetite juice, nerve function, osmotic balance Sodium (Na) Table salt Water balance, blood pressure, nerve Muscle cramps, reduced appetite function Magnesium (Mg) Whole grains, green leafy Cofactor; ATP bioenergetics Nervous system disturbances vegetables Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 24.3 Minerals in the Body Table 24.3 [cont.] inued Trace Amounts Required Mineral Major Dietary Sources Major Functions In The Body Symptoms Of Deficiency* Iron (Fe) Meats, eggs, legumes, whole Component of hemoglobin and of electron Iron-deficiency anemia, grains, green leafy vegetables carriers in energy metabolism; enzyme weakness, impaired immunity cofactor Fluorine (F) Drinking water, tea, seafood Maintenance of tooth (and probably bone) Higher frequency of tooth decay structure Zinc (Zn) Meats, seafood, grains Component of certain digestive enzymes Growth failure, skin abnormalities, and other proteins reproductive failure, impaired immunity Copper (Cu) Seafood, nuts, legumes, organ Enzyme cofactor in iron metabolism, Anemia, cardiovascular meats melanin synthesis, electron transport abnormalities Manganese (Mn) Nuts, grains, vegetables, fruits, tea Enzyme cofactor Abnormal bone and cartilage Iodine (I) Seafood, iodized salt Component of thyroid hormones Goiter (enlarged thyroid) Cobalt (Co) Meats and dairy products Component of vitamin B sub 12 None, except as deficiency B sub 12 Selenium (Se) Seafood, meats, whole grains Enzyme cofactor for antioxidant B enzymes Muscle pain, possibly B12 heart 12 muscle deterioration Chromium (Cr) Brewers’ yeast, liver, seafood, Involved in glucose and energy Impaired glucose metabolism meats, some vegetables metabolism Molybdenum (Mo) Legumes, grains, some vegetables Enzyme cofactor Disorder in excretion of nitrogen- containing compounds *All of these minerals are also harmful when consumed in excess. Modified from: Urry et al., Campbell Biology, 12th Edition, © 2021. Reprinted by permission of Pearson Education, I nc., Upper Saddle River, N.J. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 2—Metabolism Metabolism: sum of all biochemical reactions in the body, which involve nutrients – Substances are constantly built up (anabolism) and broken down (catabolism) – Even at rest, body uses lots of energy for essential activities (like breathing and absorbing nutrients from food) Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.3 Metabolism is the Sum of All Biochemical Reactions in the Body Copyright © 2025 Pearson Education, Inc. All Rights Reserved Anabolism and Catabolism Anabolism: reactions that build larger molecules or structures from smaller ones; – E.g., synthesis of proteins from amino acids Catabolism: reactions that break down more complex structures to simpler ones – E.g., hydrolysis of proteins into amino acids Three major stages involved in processing energy-containing nutrients: – Stage 1: digestion and absorption in gastrointestinal tract – Stage 2: in cytoplasm, newly delivered nutrients either: ▪ Built into lipids, proteins, and glycogen by anabolic pathways ▪ Broken down by catabolic pathways to smaller fragments (like pyruvate) – Stage 3: in mitochondria, complete breakdown of stage 2 products (most will first be converted into acetyl C o A) ▪ Uses oxygen ▪ Produces carbon dioxide, water, and large amounts of ATP Copyright © 2025 Pearson Education, Inc. All Rights Reserved Anabolism and Catabolism Cellular respiration: group of catabolic reactions (glycolysis, the citric acid cycle, and oxidative phosphorylation) that convert some of the chemical energy of nutrients (like glucose) into a form of chemical energy (ATP) cells can use to do work Phosphorylation: transfer of high-energy phosphate group from ATP to another molecule – Primes molecule; changing it in a way that increases its activity, produces motion, or does work Body stores energy as glycogen and triglycerides, then breaks them down later to produce ATP for cellular use Copyright © 2025 Pearson Education, Inc. All Rights Reserved Three Stages of Metabolism of Energy- Containing Nutrients Figure 24.3 Three stages of metabolism of energy-containing nutrients Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation-Reduction Reactions and the Role of Coenzymes Many reactions in cells are oxidation reactions – Oxidation is the gain of oxygen or the loss of hydrogen atoms (with their electrons) ▪ Oxidized substance always loses (or nearly loses) electrons as they move to (or toward) a substance that more strongly attracts them ▪ E.g., oxidation of glucose involves removal of pairs of hydrogen atoms (with their electrons) until only CO2 remains – O2 is final electron acceptor, joining with removed H atoms to form H2O Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation-Reduction Reactions and the Role of Coenzymes Oxidation-reduction (redox) reactions – Whenever one substance loses electrons (oxidized), another gains them (reduced) ▪ Oxidized substances lose and reduced ones gain energy (as energy- rich electrons transferred from one substance to next) – Redox reaction enzymes: ▪ Dehydrogenases catalyze removal of hydrogen atoms ▪ Oxidases catalyze transfer of oxygen – Most redox enzymes require a B vitamin coenzyme, which can accept the hydrogen and its electron, becoming reduced when a substrate is oxidized ▪ Two important coenzymes of the oxidative pathway: – Nicotinamide adenine dinucleotide (NAD ) – Flavin adenine dinucleotide (FAD) ▪ E.g., FAD reduced to FADH2 as succinate is oxidized to fumarate Copyright © 2025 Pearson Education, Inc. All Rights Reserved Succinate to Fumarate Copyright © 2025 Pearson Education, Inc. All Rights Reserved ATP Synthesis Two mechanisms capture (as ATP) some of the energy released via cellular respiration Substrate-level phosphorylation – Direct transfer of high-energy phosphate group from substrate to ADP – Occurs twice in glycolysis (enzymes in cytosol) and once in Krebs cycle (enzymes in mitochondria) Oxidative phosphorylation more complex, but produces most of the ATP – Carried out by inner mitochondrial membrane proteins in two steps: ▪ Electron transport chain: ~ 50% of energy released via nutrient oxidation used to pump H across inner membrane, creating steep [H ] gradient ▪ Chemiosmosis: coupling movement of H (diffusion down gradient) across selectively permeable membrane to a chemical reaction—the synthesis of ATP – Diffusion of H across inner membrane through protein ATP synthase provides energy to attach phosphate groups to ADP, making ATP Copyright © 2025 Pearson Education, Inc. All Rights Reserved Mechanisms of Phosphorylation Figure 24.4 Mechanisms of phosphorylation Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.4 Carbohydrate Metabolism Is the Central Player in ATP Production Food carbohydrates are converted to glucose, which enters cells via glucose transporters – Process enhanced by insulin Glucose enters cell and is immediately phosphorylated to glucose-6- phosphate – Most cells lack enzymes to reverse reaction, so glucose trapped in cell ▪ Only cells in intestine, kidney, liver can reverse reaction and release glucose – Keeps intracellular glucose (a different molecule from glucose-6- phosphate) concentration low, ensuring continued glucose entry (via facilitated diffusion) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Glucose is catabolized via following reaction: C6H12O6  6O2 6H2O  6CO2  32 ATP  heat glucose oxygen water carbon dioxide Complete glucose catabolism requires three pathways, in sequence: 1. Glycolysis 2. Citric acid cycle 3. Oxidative phosphorylation Copyright © 2025 Pearson Education, Inc. All Rights Reserved During Cellular Respiration, ATP Is Formed in the Cytosol and in the Mitochondria Figure 24.5 During cellular respiration, A TP is formed in the cytosol and in the mitochondria Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Glycolysis (glycolytic pathway) – Occurs in cytosol, involves ten chemical steps that convert each glucose to two pyruvate molecules – Anaerobic process ▪ Glycolysis itself does not use oxygen and occurs whether or not oxygen is present – Three major phases Phase 1: Sugar activation Phase 2: Sugar cleavage Phase 3: Sugar oxidation and ATP formation Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Three Major Phases of Glycolysis Figure 24.6 The three major phases of glycolysis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Glycolysis (cont.) inued – Final products of glycolysis (each molecule of glucose is C6H12O6 ) : ▪ 2 molecules of pyruvate (C3H4O3 ) ▪ 2 reduced NAD (NADH  H ) ▪ Net gain of 2 ATP – To continue glycolysis, NAD must remain available to accept more H atoms ▪ When oxygen readily available, this is no problem, and NADH  H delivers its H atoms to the electron transport chain ▪ When oxygen insufficient (e.g., during strenuous exercise), NADH  H unloads its H atoms back onto pyruvate, reducing it to form lactate Copyright © 2025 Pearson Education, Inc. All Rights Reserved  Oxidation of Glucose Glycolysis (cont.) inued – Some of this lactate enters blood and is picked up by liver, which can convert it back to glucose-6-phosphate ▪ Then converted to glucose and released into blood or stored as glycogen – With more oxygen available, more lactate can be oxidized back to pyruvate to enter aerobic pathways (citric acid cycle and oxidative phosphorylation) – Glycolysis generates ATP rapidly, but yields only 2 ATP compared to 30–32 ATP when glucose is completely oxidized (via pyruvate entering mitochondria) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Citric acid cycle (Krebs cycle) – Next stage of glucose oxidation; named for its first substrate (citrate) – Occurs in mitochondrial matrix, fueled mostly by pyruvate (via glycolysis) and fatty acids from fat breakdown – Transitional phase converts pyruvate to acetyl CoA via three-step process: 1. Decarboxylation: 1 carbon from pyruvate is removed, producing CO2 gas, which diffuses into blood to be expelled by lungs 2. Oxidation: remaining 2-C fragment oxidized to acetate by removal of H atoms, which are picked up by NAD 3. Formation of acetyl CoA: acetate combines with coenzyme A to form acetyl coenzyme A (acetyl CoA) – Acetyl CoA is now ready to enter the citric acid cycle and be broken down by mitochondrial enzymes Copyright © 2025 Pearson Education, Inc. All Rights Reserved Simplified Version of the Citric Acid (Krebs) Cycle Figure 24.7 Simplified version of the citric acid (Krebs) cycle Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Citric Acid Cycle Makes 2 molecules of CO2 4 molecules of reduced coenzymes 3 NADH and 1 FADH2 1 molecule of ATP (GTP) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Oxidative phosphorylation – Electron transport chain (ETC) only pathway to directly use oxygen ▪ Citric acid cycle provides substrates (reduced coenzymes) for ETC, so the coupled pathways are aerobic (require the presence of oxygen to continue) – Overview ▪ NADH  H and FADH (from glycolysis and Krebs cycle) shuttle H atoms to 2 ETC proteins, which combine with O2 to form H2O ▪ Chemiosmosis uses energy released to attach Pi to ADP, forming ATP – ETC involves chain of carrier proteins (with bound metal atoms called cofactors) embedded in inner mitochondrial membrane ▪ Flavins: proteins derived from riboflavin (ETC complexes I and II) ▪ Cytochromes: proteins with iron-containing pigment (III and IV) ▪ Respiratory enzyme complexes: clusters of neighboring carriers that are alternately reduced and oxidized as they pass electrons down the line Copyright © 2025 Pearson Education, Inc. All Rights Reserved Focus Figure 24.1 Oxidative Phosphorylation Focus Figure 24.1 Oxidative Phosphorylation Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Oxidative phosphorylation has two phases: – Phase 1: ETC creates proton (H ) gradient across inner mitochondrial membrane using high-energy electrons (e ) removed from food fuels ▪ Complexes I and II accept H from NADH and FADH2 – NAD and FAD can now return to glycolysis and Krebs cycle ▪ H atoms split into protons (H )  electrons (e  ) – Electrons passed down chain, releasing energy with each transfer – Each complex is reduced (picking up e ) and then oxidized (transferring e  to next complex) ▪ At complex IV, electron pairs combine with two H and half a molecule of oxygen to form water 2 H  2 e   ½ O2 H2O Copyright © 2025 Pearson Education, Inc. All Rights Reserved Energy Is Harvested at Each Step in the Electron Transport Chain Figure 24.8 Energy is harvested at each step in the electron transport chain Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glucose Oxidative phosphorylation has two phases: (cont.) inued – Phase 2: Chemiosmosis uses energy of proton gradient to synthesize ATP ▪ Proton gradient is both a pH gradient (H higher in intermembrane space than matrix) and a voltage gradient (negative on matrix side of membrane) ▪ As a result, H strongly attracted to matrix side of membrane, but can only cross through membrane protein ATP synthase (complex V) – These synthases act as small rotary motors that drive a molecular mill that joins ADP and Pi into ATP (like an ion pump working in reverse) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Function of ATP Synthase Figure 24.10 Structure and function of A TP synthase Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Function of ATP Synthase Figure 24.10 Structure and function of A TP synthase Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Function of ATP Synthase Figure 24.10 Structure and function of A TP synthase Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Function of ATP Synthase Figure 24.10 Structure and function of A TP synthase Copyright © 2025 Pearson Education, Inc. All Rights Reserved Energy-Converting ATP Synthase Rotor Rings as Seen by Atomic Force Microscopy Figure 24.9 Energy-converting ATP synthase rotor rings as seen by atomic force microscopy Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 24.1 Metabolic poisons interfere with oxidative phosphorylation – E.g., hydrogen cyanide binds to cytochrome oxidase and blocks electron flow from complex IV to oxygen Poisons called “uncouplers” destroy proton gradient by making inner mitochondrial membrane permeable to H – Electrons continue down ETC to oxygen at rapid pace and oxygen consumption rises, but no ATP made Copyright © 2025 Pearson Education, Inc. All Rights Reserved Energy Yield During Cellular Respiration Figure 24.11 Energy yield during cellular respiration Copyright © 2025 Pearson Education, Inc. All Rights Reserved Bioflix “Cellular Respiration” Click here to view ADA compliant Animation: Bioflix “Cellular Respiration” https://mediaplayer.pearsoncmg.com/assets/Wj_9Nl2ur_4lbzbNg8BIeE4f943wprq4 Copyright © 2025 Pearson Education, Inc. All Rights Reserved Glycogenesis, Glycogenolysis, and Gluconeogensis Cells cannot store large amounts of ATP If more glucose available than can be oxidized, intracellular ATP levels rise, eventually inhibiting glucose catabolism and promoting its storage as glycogen or fat – Fats account for 80–85% of stored energy Glycogenesis – Is synthesis of glycogen, a large polysaccharide made of long glucose chains ▪ Form of carbohydrate storage in animal cells ▪ Most active in liver and skeletal muscle – Process: ▪ Glucose converted to glucose-6-phosphate, then to its isomer glucose- 1-phosphate ▪ Terminal phosphate removed as enzyme (glycogen synthase) catalyzes attachment of glucose to growing chain Copyright © 2025 Pearson Education, Inc. All Rights Reserved Glycogenesis, Glycogenolysis, and Gluconeogensis Glycogenolysis – Is glycogen breakdown to release stored glucose; triggered by low glucose levels – Process: ▪ Splitting and phosphorylating of glycogen by enzyme glycogen phosphorylase produces molecules of glucose-1-phosphate ▪ Converted to glucose-6-phosphate, which can enter glycolysis ▪ Liver (and some kidney and intestinal) cells contain enzyme glucose-6- phosphatase that removes terminal phosphate – Producing glucose that can enter bloodstream for use by other cells Gluconeogenesis – Low glucose availability also promotes gluconeogenesis (formation of new glucose molecules from noncarbohydrate sources) via liver ▪ Glucose can be made from glycerol and amino acids ▪ Protects body (especially CNS) from damaging effects of low blood glucose (hypoglycemia) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Glycogenesis and Glycogenolysis Figure 24.13 Glycogenesis and glycogenolysis Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.5 Lipid Metabolism Is Key for Long- Term Energy Storage and Release Fats are the most concentrated source of energy – Contain very little water, and their catabolism yields twice the energy (9 kcal/g) compared to glucose or protein catabolism (4 kcal/g) Most products of fat digestion are transported in lymph (to blood) via chylomicrons – Lipids hydrolyzed by capillary (endothelial) enzymes into fatty acids and glycerol that can be taken up by cells for various uses Copyright © 2025 Pearson Education, Inc. All Rights Reserved Oxidation of Glycerol and Fatty Acids Triglycerides only lipids routinely oxidized for energy; their building blocks (glycerol + fatty acids) oxidized separately: – Glycerol converted into glyceraldehyde-3-phosphate (glycolysis intermediate, equal to half a glucose), and eventually to acetyl C oA, which enters citric acid cycle ▪ So, yield per glycerol ~ 15 ATP – Fatty acids undergo beta oxidation in mitochondria ▪ Fatty acid chains broken down into two-carbon fragments, and coenzymes (FAD and NAD ) are reduced – Each fragment binds with CoA to form acetyl CoA Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lipid Oxidation Figure 24.15 Lipid oxidation Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lipogenesis Lipogenesis: triglyceride synthesis; stimulated by high glucose levels and cellular ATP – Dietary glycerol and fatty acids not needed for ATP are stored as triglycerides ▪ When made faster than they can enter citric acid cycle, these excess intermediates are channeled into triglyceride synthesis pathways ▪ Acetyl CoA molecules are joined, forming fatty acid chains that grow two carbons at a time (so almost all fatty acids in body contain an even number) Glucose easily converted to fat because acetyl CoA (glucose catabolism intermediate) is also the starting point for fatty acid synthesis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lipolysis Lipolysis: breakdown of stored fats into glycerol and fatty acids (lipogenesis in reverse) – Fatty acids preferred fuel of liver, cardiac muscle, resting skeletal muscle – Lipolysis accelerated when carbohydrate intake inadequate to fill fuel gap Beta oxidation of released fatty acids increases production of acetyl CoA, which can enter citric acid cycle only if enough carbohydrate intermediates are available – If not, excess acetyl CoA converted by ketogenesis in liver to ketone bodies (ketones), including: ▪ Acetoacetic acid ▪ -hydroxybutyric acid ▪ Acetone Copyright © 2025 Pearson Education, Inc. All Rights Reserved Lipid Metabolism Figure 24.16 Lipid metabolism Copyright © 2025 Pearson Education, Inc. All Rights Reserved Synthesis of Structural Materials All body cells use phospholipids and cholesterol to build their membranes – Phospholipids also form myelin sheaths of neurons Ovaries, testes, and adrenal cortex use cholesterol to synthesize their steroid hormones The liver: – Synthesizes lipoproteins to transport cholesterol, fats, other substances in blood – Synthesizes cholesterol from acetyl CoA – Uses cholesterol to form bile salts Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.6 Amino Acids Are Used to Build Proteins or for Energy Proteins have limited life span, must be broken down and replaced before deteriorating – Amino acids are recycled into new proteins or different N-containing compounds – Cells take up dietary amino acids from blood and use them to replace tissue proteins at rate of ~ 100 g/day Proteins are not stored in body – When dietary amino acids (proteins) in excess, they are oxidized for energy or converted to fat or glycogen for storage Copyright © 2025 Pearson Education, Inc. All Rights Reserved Degradation of Amino Acids Goal: produce molecules that can be used for energy in citric acid cycle or converted to glucose First, they are deaminated—their amine group (–NH2 ) is removed Resulting molecule then converted to pyruvate or one of the keto acid intermediates of citric acid cycle – Key molecule in these conversions is amino acid glutamate Three events of amino acid degradation 1. Transamination 2. Oxidative deamination 3. Keto acid modification Copyright © 2025 Pearson Education, Inc. All Rights Reserved Processes That Occur When Amino Acids Are Utilized for Energy (1 of 3) Figure 24.17 Processes that occur when amino acids are utilized for energy Copyright © 2025 Pearson Education, Inc. All Rights Reserved Processes That Occur When Amino Acids Are Utilized for Energy (2 of 3) Figure 24.17 Processes that occur when amino acids are utilized for energy Copyright © 2025 Pearson Education, Inc. All Rights Reserved Processes That Occur When Amino Acids Are Utilized for Energy (3 of 3) Figure 24.17 Processes that occur when amino acids are utilized for energy Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.7 Energy Is Stored in the Fed State and Released in the Fasting State Copyright © 2025 Pearson Education, Inc. All Rights Reserved Interconversion of Carbohydrates, Fats, and Proteins Figure 24.19 Interconversion of carbohydrates, fats, and proteins Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fed State Fed state, also called absorptive state, lasts for ~ 4 hours after eating begins, as nutrients are being absorbed (entering bloodstream) – Anabolism exceeds catabolism and nutrients are stored ▪ Glucose major fuel for ATP synthesis – Dietary amino acids and fats used to remake degraded body protein or fat ▪ Small amounts oxidized to provide A TP – Excess nutrients (regardless of source) transformed to fat Carbohydrates – Absorbed monosaccharides delivered directly to liver; fructose and galactose converted to glucose ▪ Glucose can enter blood or be converted to glycogen or fat in liver ▪ Glycogen remains in liver; fat packaged with proteins as very low-density lipoproteins (VLDLs) and released to blood for storage by adipose tissue – Bloodborne glucose enters body cells; excess stored as glycogen in muscles or fat in adipose tissues Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fed State Triglycerides – Hydrolyzed to fatty acids and glycerol by enzyme lipoprotein lipase before passing through capillary wall ▪ Enzyme particularly active in capillaries of muscle and fat tissues – Primary energy source for adipose, liver, and skeletal and cardiac muscle cells – Most glycerol and fatty acids enter adipose tissues to be reconverted to triglycerides for storage Amino acids – Some deaminated in liver to keto acids that can be used in citric acid cycle or stored as fat – Others used by liver to synthesize plasma proteins (albumin, clotting proteins, and transport proteins) – Most taken up by other body cells for protein synthesis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Major Events and Principal Metabolic Pathways of the Fed State Figure 24.20a Major events and principal metabolic pathways of the fed state Copyright © 2025 Pearson Education, Inc. All Rights Reserved Major Events and Principal Metabolic Pathways of the Fed State Figure 24.20b Major events and principal metabolic pathways of the fed state Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fed State Hormonal control of the fed state – Insulin directs essentially all events of the fed state; its secretion is stimulated by: ▪ Elevated blood glucose and amino acid levels ▪ GI tract hormone glucose-dependent insulinotropic peptide (GIP) ▪ Parasympathetic stimulation – When insulin binds to target cell receptors, it facilitates insertion of glucose transporters into the target cell membrane for carrier-mediated facilitated diffusion ▪ Glucose entry (particularly in muscle and adipose cells) increases ~ 20-fold ▪ Brain and liver take up glucose without insulin – Insulin is a blood glucose lowering (hypoglycemic) hormone that enhances: ▪ Glucose oxidation for energy ▪ Conversion of glucose into glycogen and (in adipose) triglycerides ▪ Active transport of amino acids into cells and protein synthesis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Insulin Directs Nearly All Events of the Fed State Figure 24.21 Insulin directs nearly all events of the fed state Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 24.3 Diabetes mellitus: disorder of inadequate insulin production or abnormal insulin receptors, leaving blood glucose unavailable to most cells – Glucose levels remain high as most cells need insulin for glucose entry – Large amounts of glucose excreted in urine (carrying out large amounts of water with it) Results in metabolic acidosis, protein wasting, and weight loss as large amounts of fats and tissue proteins used for energy (in place of glucose) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fasting State Fasting state, or postabsorptive state, is when GI tract is empty and energy stores are broken down to meet body’s metabolic demands – Goal: maintain blood glucose within normal range (70–110 mg glucose per 100 ml) ▪ By making glucose available to blood and promoting use of fats for fuel (by organs like skeletal muscle) to spare glucose for organs that can’t (brain) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fasting State Sources of blood glucose 1. Glycogenolysis in the liver: first reserve (~ 100g) used; can be mobilized quickly and maintain blood glucose levels for about 4 hours 2. Glycogenolysis in skeletal muscle: begins before liver glycogen depleted 3. Lipolysis in adipose tissues and the liver: produces glycerol used for gluconeogenesis in liver 4. Catabolism of cellular protein: major source during prolonged fasting (starting with muscle proteins); liver converts amino acids to glucose (gluconeogenesis) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fasting State Glucose sparing – During prolonged fasting, body uses more noncarbohydrate fuels to conserve glucose – Brain uses bulk of glucose while other body cells switch to fatty acids as main fuel ▪ After fasting 4–5 days, brain starts relying on ketone bodies (as well as glucose) Hormonal and neural controls of the fasting state – Hormones and sympathetic nervous system interact to control events of fasting state ▪ More complex than fed state, which utilizes one hormone (insulin) ▪ Reduced insulin release (as blood glucose falls) important trigger to initiate events of fasting state Copyright © 2025 Pearson Education, Inc. All Rights Reserved Major Events and Principal Metabolic Pathways of the Fasting State Figure 24.22b Major events and principal metabolic pathways of the fasting state Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fasting State Hormonal and neural controls of the fasting state (cont.) inued – Glucagon ▪ Raises blood glucose levels, making it a hyperglycemic hormone (like the other fasting state hormones) and insulin antagonist ▪ Released from pancreas (alpha cells) in response to low blood glucose ▪ Targets liver and adipose tissues to promote: – Glycogenolysis and gluconeogenesis (liver), releasing glucose into blood – Lipolysis (adipose), releasing fatty acids and glycerol into blood ▪ Rising blood amino acid levels stimulates release of both insulin and glucagon Copyright © 2025 Pearson Education, Inc. All Rights Reserved Glucagon Is a Hyperglycemic Hormone That Stimulates a Rise in Blood Glucose Levels Figure 24.23 Glucagon is a hyperglycemic hormone that stimulates a rise in blood glucose levels Copyright © 2025 Pearson Education, Inc. All Rights Reserved Fasting State Hormonal and neural controls of the fasting state (cont.) inued – Sympathetic nervous system ▪ Sympathetic fibers innervate adipose tissue, releasing norepinephrine to stimulate lipolysis ▪ Release of epinephrine from adrenal medulla targets liver, skeletal muscle, and adipose to mobilize fat and promote glycogenolysis ▪ Any stressor that triggers fight-or-flight response, including exercise, activates this pathway (making lots of fuels available for muscles) – Other hormones ▪ Growth hormone, thyroxine, sex hormones, and corticosteroids also influence metabolism and nutrient flow Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.8 The Liver Metabolizes, Stores, and Detoxifies Liver is one of the most biochemically complex organs, carrying out ~ 500 metabolic functions Hepatocytes process nearly every class of nutrient and play major role in regulating blood cholesterol levels Copyright © 2025 Pearson Education, Inc. All Rights Reserved Cholesterol Metabolism and Regulation of Blood Cholesterol Levels Cholesterol provides structural basis of bile salts, steroid hormones, and vitamin D – Also major component of plasma membranes (adds stability) ~ 15% of blood cholesterol is dietary; rest synthesized from acetyl CoA (mostly in liver) Lost from body when catabolized or secreted in bile salts Copyright © 2025 Pearson Education, Inc. All Rights Reserved Composition and Function of Lipoproteins Figure 24.24 Composition and function of lipoproteins Copyright © 2025 Pearson Education, Inc. All Rights Reserved Cholesterol Metabolism and Regulation of Blood Cholesterol Levels Blood Levels of Total Cholesterol, L DL, and HDL – Generally, total cholesterol < 200 mg/dl of blood is desirable for adults ▪ Levels > 200 mg/dl linked to atherosclerosis (and thus CV disease) – More important to look at ratio of lipoproteins transporting cholesterol in blood ▪ High LDL levels (160 mg/dl) are generally considered bad ▪ High HDL levels were traditionally considered good because the transported cholesterol is destined for degradation – Recent studies have not confirmed that high HDL levels protect against CV disease Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 24.4 Previously, high cholesterol and LDL:HDL ratios were considered most valid predictors of risk for atherosclerosis, CV disease, and heart attack – However, many who get heart disease have normal cholesterol levels, and many with poor lipid profiles remain free of heart disease Treatment for people at risk for cardiovascular disease – Statins: a group of (LDL) cholesterol-lowering drugs; estimated that > 40 million Americans take statins Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 3—Energy Balance Energy released from chemical bonds when foods catabolized must equal energy output – Energy intake: energy liberated during food oxidation – Energy output includes energy: ▪ Immediately lost as heat (~ 60%) ▪ Used to do work (driven by ATP) ▪ Stored as fat or glycogen Nearly all energy derived from foodstuffs is eventually converted to heat, which is lost during every cellular activity: – When ATP bonds are formed and when they are broken to do work – As muscles contract – Through friction as blood flows through blood vessels Heat energy cannot be used by cells to do work, but is necessary to maintain homeostatic body temperature, allowing metabolic reactions to occur efficiently Copyright © 2025 Pearson Education, Inc. All Rights Reserved Obesity Body mass index (BMI) is a formula (based on height relative to weight) used to determine obesity – Clinically, overweight is defined by a BMI of 25–30 (carries some health risk) ▪ Obesity is a BMI > 30 (with markedly increased health risk) – Obesity-related diseases: ▪ Chronic low-grade systemic inflammation ▪ Insulin resistance and type 2 diabetes mellitus ▪ Higher incidence of osteoarthritis, atherosclerosis, hypertension, heart disease, and cancer – Current U.S. statistics: ▪ Adults: ~ 32% are overweight; an additional 42% are obese; 10% have diabetes ▪ Kids: 19% of children are obese (40 years ago it was only 5%) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Model for Hypothalamic Command of Appetite and Food Intake Figure 24.25 Model for hypothalamic command of appetite and food intake Copyright © 2025 Pearson Education, Inc. All Rights Reserved Basal Metabolic Rate (BMR) Reflects energy body needs to perform its most essential activities Measured in fasting state (12-hour fast), reclining position, relaxed mentally and physically, at room temperature 20–25 C – Not lowest metabolic state, that’s during sleep (skeletal muscles fully relaxed) BMR influenced by: – Age and sex: BMR decreases with age; males tend to have higher BMR since males typically have more muscle (which is very metabolically activity) ▪ Females tend to have relatively more fat (low metabolic activity) – Body temperature: BMR increases and decreases with temperature – Stress: BMR increases with stress (via activation of sympathetic system) – Thyroxine: increases O2 consumption and heat production, increasing BMR Copyright © 2025 Pearson Education, Inc. All Rights Reserved 24.11 The Hypothalamus Acts as the Body’s Thermostat Body temperature reflects balance between heat production and loss At rest, liver, heart, brain, kidneys, and endocrine organs generate most heat – Inactive skeletal muscles account for only ~ 20–30% During intense exercise, muscles can produce 30–40  more heat than the rest of body – Change in muscle activity important way to change body temperature Average body temperature in North America 36.7 6 C (98.1 1.1 F) – Optimal for enzyme activity – Body temperatures above range denature proteins and depress neurons – Rate of chemical reactions increases ~ 10% for each 1 C rise in temperature In children under 5, temperature of 41 C (106 F) can lead to convulsions – ~ 43 C (109 F) is upper limit for life Individual body tissues can tolerate low temperatures (e.g., cooling heart when it must be stopped for surgery to lower its oxygen and nutrient requirements) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Body Temperature Remains Constant as Long as Heat Production and Heat Loss Are Balanced Figure 24.26 Body temperature remains constant as long as heat production and heat loss are balanced Copyright © 2025 Pearson Education, Inc. All Rights Reserved Core and Shell Temperatures Body’s core has highest temperature – Includes: organs within skull and thoracic and abdominal cavities Body’s shell (skin) has lowest temperature (in most circumstances) Rectum typically has temperature about 0.4 C (0.7 F) higher than the mouth – Rectal temperature is better indicator of core temperature Core temperature is regulated and stays relatively constant, but shell temperature can vary between 20 C (68 F) and 40 C (104 F) – Blood is major agent of heat exchange between core and shell Copyright © 2025 Pearson Education, Inc. All Rights Reserved Mechanisms of Heat Exchange Body uses four mechanisms of heat transfer: 1. Radiation: loss of heat in form of infrared waves; radiant energy flows from warmer to cooler 2. Conduction: transfer of heat by direct contact (from warmer to cooler object) 3. Convection: transfer of heat to surrounding air; warm air expands and rises (away from skin) and denser cool air falls (replacing warm air) 4. Evaporation occurs when water absorbs enough heat to vaporize (i.e., converted to water vapor) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Role of the Hypothalamus Hypothalamus (anterior region in particular) is main integrating center for thermoregulation – Thermoregulatory centers: ▪ Heat-loss center ▪ Heat-promoting center – Receives afferent input from: ▪ Peripheral thermoreceptors in shell (skin) ▪ Central thermoreceptors in core (including anterior hypothalamus); sensitive to blood temperature – Then initiates appropriate heat-loss or heat-promoting activities Central thermoreceptors have more influence, but varying inputs from peripheral probably alert hypothalamus to the need to prevent temperature changes in the core Copyright © 2025 Pearson Education, Inc. All Rights Reserved Mechanisms of Body Temperature Regulation Figure 24.28 Mechanisms of body temperature regulation Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 24.7 Hyperthermia (high body temp) – Overexposure to hot and humid environment overwhelms heat-loss processes ▪ At ~ 41 C (105  F), hypothalamus is depressed (heat-loss mechanisms cease), creating positive feedback cycle that leads to heat stroke if not corrected – Increasing temperatures continue to increase metabolic rate, and thus heat production – Skin is hot and dry, multiple organ damage can occur (including brain) ▪ Fatal if not corrected quickly with cold water immersion and hydration Heat exhaustion (exertion-induced heat exhaustion) – Heat-associated extreme sweating and collapse during or following vigorous physical exertion due to dehydration and low blood pressure ▪ Causes elevated body temperature and mental confusion and/or fainting – As heat-loss mechanisms struggle to function, may progress to heat stroke Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 24.7 Hypothermia (low body temp) – Caused by prolonged cold exposure – Vital signs (respiratory and heart rate, blood pressure) decrease as cellular (enzymatic) activities slow ▪ Person begins to feel drowsy, even (oddly) comfortable (no longer feels cold) ▪ Shivering stops at core temperature of 30–32 C (87–90 F) – Can progress to coma and finally death (by cardiac arrest) at ~ 21 C 70 F  Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 24.9 Metabolic syndrome: cluster of five risk factors that double the chance of getting heart disease and stroke, and increase the chance of developing type 2 diabetes by five times – ~ 32% of U.S. population has three of five factors Figure 24.29 Metabolic syndrome Copyright © 2025 Pearson Education, Inc. All Rights Reserved