Chapter 24: Nutrition, Metabolism, and Body Temperature Regulation – Study Notes

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Understanding the basic definitions of nutrients and energy units is foundational for studying metabolism and nutrition.

Nutrient: A substance in food required for growth, maintenance, and repair.
Essential nutrients: Nutrients that must be obtained from the diet because the body cannot synthesize them in sufficient quantities (e.g., certain amino acids, fatty acids, vitamins, minerals).
Calorie: The amount of heat needed to raise the temperature of 1 g of H2O by 1°C. In nutrition, energy is measured in kilocalories (kcal).
1 dietary "Calorie" (capital C) = 1 kilocalorie (kcal).

Carbohydrates are a primary energy source and are classified based on their complexity.

Simple carbohydrates: Sugars such as glucose, fructose, and sucrose.
Complex carbohydrates: Starches and fibers found in grains, vegetables, and legumes.

Fats are classified based on their chemical structure and health effects.

Saturated fats: Found in meat, dairy foods, tropical oils, and hydrogenated oils (trans fats). They have no double bonds between carbon atoms.
Unsaturated fats: Found in seeds, nuts, olive oil, and most vegetable oils. They have one or more double bonds between carbon atoms.
Trans fats: Modified unsaturated oils that have been hydrogenated, associated with negative health effects.

Proteins are classified based on their amino acid composition.

Complete proteins: Contain all essential amino acids in sufficient amounts (e.g., animal proteins such as meat, eggs, dairy).
Incomplete proteins: Lack one or more essential amino acids (e.g., most plant proteins).

All-or-none rule: All amino acids needed must be present for protein synthesis; otherwise, excess amino acids are used for energy.

Each macronutrient serves specific roles in metabolism and physiology.

Carbohydrates (Glucose):
- Main fuel for ATP production, especially in neurons and red blood cells.
- Excess glucose is stored as glycogen or fat.
- Recommended daily intake: 45–65% of total calories.
Lipids:
- Adipose tissue for protection, insulation, and energy storage.
- Phospholipids are essential for cell membranes.
- Cholesterol is a precursor for bile salts, steroid hormones, and vitamin D.
- Fatty acids are important for smooth muscle contraction, blood pressure control, and inflammation.
- Recommended intake: < 30% of total caloric intake; saturated fats < 10% of total caloric intake; cholesterol < 300 mg/day.
Proteins:
- Structural material (e.g., keratin, collagen, elastin).
- Functional molecules (e.g., enzymes, hormones, hemoglobin).
- Protein is used for energy only when carbohydrate and fat intake is inadequate.
- Daily intake: 0.8 g per kg body weight.

Vitamins are classified based on their solubility, which affects their absorption and storage.

Fat-soluble vitamins: Vitamins A, D, E, K (stored in body fat; excess can be toxic).
Water-soluble vitamins: B-complex vitamins and vitamin C (not stored; excess excreted in urine).

Minerals are inorganic elements required for various physiological functions.

Major minerals: Calcium, phosphorus, potassium, sulfur, sodium, chloride, magnesium.
Trace elements: Iron, zinc, copper, manganese, iodine, selenium, chromium, fluoride, molybdenum.

Metabolism encompasses all chemical reactions in the body, divided into two main types:

Anabolism: Synthesis of large molecules from smaller ones (e.g., protein synthesis from amino acids).
Catabolism: Breakdown of complex molecules into simpler ones (e.g., hydrolysis of proteins into amino acids).

Metabolism equation:

Oxidation-reduction (redox) reactions are essential for energy transfer in cells.

Coenzymes assist enzymes in catalyzing oxidation-reduction reactions.

ATP is generated by two main mechanisms during cellular respiration:

Substrate-level phosphorylation:
- Direct transfer of a phosphate group to ADP from a phosphorylated substrate.
- Occurs in glycolysis and the Krebs cycle.
Oxidative phosphorylation:
- Indirect process; energy from electron transport is used to create a proton gradient, driving ATP synthesis via ATP synthase.
- Occurs in mitochondria during the electron transport chain.

These pathways are central to cellular energy production.

Glycolysis:
- Occurs in the cytosol.
- Final products: 2 pyruvic acids, 2 NADH, net gain of 2 ATP.
Transitional phase:
- Pyruvic acid is converted to acetyl coenzyme A (acetyl CoA).
- Decarboxylation: 1 carbon removed as CO2.
- Oxidation: Remaining fragment is oxidized to acetate, forming NADH.
- Acetyl group combines with coenzyme A to form acetyl CoA.
Krebs cycle:
- Acetyl CoA enters the cycle, producing NADH, FADH2, ATP, and CO2.
Electron transport chain and oxidative phosphorylation:
- NADH and FADH2 donate electrons to the chain, generating a proton gradient for ATP synthesis.
- Each NADH yields about 2.5 ATP; each FADH2 yields about 1.5 ATP.
- Oxygen is the final electron acceptor, forming water.

Summary equation for aerobic respiration:

The following table summarizes the major dietary sources, functions, and deficiency symptoms of key vitamins and minerals.

Vitamin/Mineral	Major Dietary Sources	Major Functions in the Body	Symptoms of Deficiency
Vitamin A	Liver, fish, dairy, leafy greens	Vision, epithelial health, immune function	Night blindness, dry skin
Vitamin D	Sunlight, fortified milk, fish oils	Calcium absorption, bone health	Rickets, osteomalacia
Vitamin E	Vegetable oils, nuts, seeds	Antioxidant, protects cell membranes	Hemolytic anemia (rare)
Vitamin K	Leafy greens, gut bacteria	Blood clotting	Bleeding disorders
Vitamin C	Citrus fruits, peppers, broccoli	Collagen synthesis, antioxidant	Scurvy
Calcium	Dairy, leafy greens	Bone and teeth formation, muscle contraction	Osteoporosis, muscle spasms
Iron	Red meat, legumes, spinach	Hemoglobin synthesis, oxygen transport	Anemia
Iodine	Iodized salt, seafood	Thyroid hormone synthesis	Goiter, hypothyroidism
Zinc	Meat, seafood, whole grains	Enzyme function, immune health	Growth retardation, impaired immunity

Additional info: Table entries inferred and summarized from standard A&P sources for completeness.