Body Functioning

Chapter 24

NUTRITION

Nutrients

• Substances to promote/enable life

• Categories– Major nutrients (carbs,

lipids, and proteins)– Vitamins and minerals– Water

• Essential nutrients can’t be made ourselves

Carbohydrates

• Primarily from plants– Complex carbohydrates (e.g polysaccharides or

starches)• Bread, cereal, pasta, vegetables, potatoes

– Simple carbohydrates (e.g monosaccharides or sugars)• Pop, candy, fruit, ice cream, fruits

• Glucose is basic form and fuel source (4kcal/g)– Excess stored as glycogen and fat

• 45 – 60% daily calories recommended– Protein and fat used when less

Lipids• Triglycerides (fats)

– Unsaturated (vegetable fats/oils) and saturated (animal fats/solids)

– Protect, cushion, insulate, and fuel source (9kcal/g)• Cholesterol

– Egg yolk, meat, shellfish, milk products– Stabilizes PM and precursor for steroid hormones and bile salts

• Essential fatty acids (linoleic and linolenic acids)– Found in most vegetable oils– Prostaglandin production

• 20 – 35% daily calories

Proteins• Complete (animal products)

– Eggs, milk, fish, meats– Have all essential AA’s for maintenance and growth

• Incomplete (plant products)– Legumes, seeds, vegetables, grains– Lack 1 or more AA’s

• Vegetarian diets and rice w/bean diets

• Structural materials– Keratin, collagen, elastin, muscle fibers

• Functional uses– Enzymes, hormones, hemoglobin

• 12 – 20 % daily calories

Protein Use Determination• All-or-none rule

– AA’s not stored– Protein synthesis requires all AA’s needed present

• Caloric intake– Fuel (4kcal/g) w/ insufficient carbs or fats

• Nitrogen balance– Ingestion = excretion– Positive w/ synthesis > breakdown (growth & repair)– Negative w/ breakdown > synthesis (starvation & injury)

• Hormones– Anabolic hormones (GH & sex hormones) accelerate synthesis– Stress (glucocorticoids) accelerate breakdown

Vitamins• Organic molecules needed in small amounts

– Water soluble,• B-complex and C absorbed in GI tract w/water• B12 needs intrinsic factor from stomach

– Fat soluble• Vitamins A, D, E, and K absorbed in GI tract w/ source

• Obtained in most foods• Coenzymes in the body

– Most are essential– Vitamin D (skin) and K (intestines) are exceptions

• Table 24.2

Minerals• Inorganic molecules needed by the body

– Major needed in moderate amounts• Ca2+, phosphorus, K+, sulfur, Na+, Cl-, Mg2+

– Minor needed in trace amounts• Iron, iodine, fluorine, zinc

• Vegetables, legumes, milk, and meats = good• Refined cereals, fats, sugars, and grains = poor• Ca2+, phosphate, and Mg2 harden bone• Na+ and Cl- for nerve and muscle fxn and H2O balance• Table 24.3

METABOLISM

Metabolism (review)• All chemical reactions necessary for life• Reaction types

– Anabolic: build up/synthesis • AA + AA + … polypeptide

– Catabolic: break down/hydrolyze• Starch glucose + glucose + …• Cellular respiration (glucose catabolism)

– Redox reactions• Oxidation: lose electron/energy* (LEO) by dehydrogenase• Reduction: gain electron/energy* (GER) by oxidases

– Phosphorylation• Addition of a phosphate group (PO3-) to activate• ADP + P ATP• Substrate-level or oxidative

Metabolizing Nutrients (overview)

• Stage 1– Digestion and absorption in GI tract

• Stage 2– Anabolic and/or catabolic processing in tissues– Glycoysis

• Stage 3– Stage 2 products catabolized in mitochondria– Kreb’s cycle and oxidative phosphorylation

• Fig 24.3

Glucose Catabolism (overview)• Aerobic use of primary fuel source• Overall reaction

C6H12O6 + 6O2 6H2O + 6CO2 + 36-38 ATP + heat

• Overall process– Glycolysis (cytoplasm)

• Glucose pyruvate + NADH + 2 (net) ATP– Kreb’s Cycle (mitochondria)

• Pyruvate CO2 + NADH + FADH2 + 2 ATP

– Oxidative phosphorylation (mitochondria)• ETC and chemiosmosis• NADH + FADH2 + O2 H2O + 36 -38 ATP

• Fig 24.5

Glycolysis

• Aerobic or anaerobic conditions• In the cytoplasm• Starts with:

– Glucose (6C’s)– 2 ATP

• Ends with:– 2 pyruvate (3C’s) or– Lactic acid or CO2 and EtOH

• Important products of this process:– Net 2 ATP

• 4 ATP substrate-level phosphorylation– 2 NADH

Transition

• Cytoplasm to mitochondria• Starts with:

– 2 Pyruvate (3C’s)• Ends with:

– 2 Acetyl-CoA (2C’s)• Important products of this process:

– 2 CO2 Decarboxylation– 2 NADH

Kreb’sCycle

6 C’s4 C’s

4 C’s

• In the mitochondrial matrixCYCLE SEEN OCCURS TWICE

• Starts with:– 2 Acetyl CoA

• Ends with:– 4 CO2

• Important products of this process:– 2 ATP substrate level

phosphorylation– 6 NADH – 2 FADH2

Oxidative Phosphorylation: Electron Transport Chain (ETC)

• In the inner mitochondrial membrane (cristae)• Starts with:

– 10 NADH (2 glycolysis, 2 transition, and 4 Kreb’s cycle)– 2 FADH2 (citric acid cycle)– 6 O2 (final e- acceptor)

• Ends with:– H2O

• Important products of this process:– H + gradient

Oxidative Phosphorylation: Chemiosmosis

• In the inner mitochondrial membrane (cristae)• Starts with:

– H + gradient• Ends with:

– 32 – 34 ATP• ATP synthase facilitates

A Review of Glucose Catabolism

Substrate level phosphorylation

Regulating Glucose Levels

• High glucose and/or lots of ATP inhibits glucose catabolism– Body unable to store ATP– Glucose converted to glycogen for storage

• In liver and skeletal muscle storage = glycogenesis

• Drop in glucose signals glycogenolysis– Glycogen (liver) catabolized to glucose

• Low glucose levels signal gluconeogenesis– New glucose from non-carbs (fat and protein) in liver

Lipid Catabolism

• Triglycerides from GI tract, as chylomicrons (soluble lipids) – Glycerol pathway

• Glycerol glycolysis intermediate glucose catabolism (glycolysis start)

• ½ glucose molecule ~ 16 ATP– Fatty acid pathway

• FA’s acetic acid glucose catabolism (Kreb’s start)• FA’s NADH and FADH2

• More compact energy source w/ 2X’s more PE

Lipids and Adipose Tissue

• High ATP and glucose stimulates lipogenesis– Synthesis of triglycerides for liver & adipose storage

• High ATP = excess glycolysis intermediates• Converted into lipogenesis pathway• Excess carbs, but low fat diet = fat storage

• Glucose deficiency stimulates lipolysis (liver, cardiac & skeletal muscle) – Breakdown of stored fat– Severe depletion causes ketogenesis

• Incomplete breakdown of fats produce ketones• Lowers blood pH causing ketosis

Protein Metabolism

• Protein catabolism oxidizes AA’s for energy– Transamination: NH2 (amine) to Kreb’s intermediate

• Liver uses for non-essential AA synthesis

– Oxidative deamination: NH2 removed as NH3 (ammonia)• Combine w/ CO2 (liver) to detoxify = urea and H2O

– Keto acid modification: alters intermediate for Kreb’s entry

• Protein anabolism or fat storage– All-or-none rule (earlier)– Otherwise become energy fuels

ENERGY REGULATION

Heat Exchange• From variations between skin and external environment• Types

– Radiation• Heat transfer b/w 2 objects not in contact w/ each other• Body heat in rooms or sunbathing

– Conduction• Heat transfer b/w 2 objects in contact w/each other• Entering a hot tub or sitting in a seat

– Convection• Heat transfer b/c density (heat rises = less dense)• Fan direction in summer (air up) vs winter (air down)

– Evaporation • Heat transfer b/c H2O molecules evaporate• Sweating

Heat Production

• From low temps. in external environment or blood• Mechanisms

– Vasoconstriction: reduces superficial blood flow to reduce shell loss

• Frostbite when extended from decreased O2 and nutrients

– Shivering: involuntary relax/contract of muscles– Metabolic increase: Epi and NE release increased – Increased thyroxine release: increases metabolic rate– Behavioral changes: add layers/blankets, drinkhot beverages,

increase activity levels• Hypothermia when sluggish enzymes decreasing

mechanisms

Heat Loss

• From high internal temps• Mechanisms

– Types of heat exchange (previous)– Vasodilation: inhances superficial blood flow to increase shell

loss– Sweating: perspiration to enhance evaporation

• Ineffective w/ high humidity (the South)– Behavioral: finding shady spots/fans, reduce activity,

looser/lighter/less clothing• Hyperthermia depresses hypothalamus (control)

– Positive feedback mechanisms can cause heat stroke when mechanisms fail otherwise = heat exhaustion