Transcript Nutrition and Metabolism

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
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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
• In the mitochondrial matrix
CYCLE SEEN OCCURS TWICE
• Starts with:
– 2 Acetyl CoA
• Ends with:
6 C’s
4 C’s
– 4 CO2
• Important products of this
process:
– 2 ATP  substrate level
phosphorylation
– 6 NADH
– 2 FADH2
4 C’s
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
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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