Nutrition, Metabolism, and Body Temperature Regulation (Chapter 24, Part I) – Study Notes

Nutrition, Metabolism, Body Temperature Regulation

Topics Overview

• Energy production and measurement

• Nutrition and nutrients (carbohydrates, lipids, proteins)

• Vitamins and minerals

• Metabolism overview

Food Energy Production and Measurement

Energy in Nutrients

Most nutrients are oxidized by cells to produce ATP, the primary metabolic fuel for cellular work. The energy content of nutrients is measured in calories, a standard unit of energy.

• Calorie (small calorie, gram calorie): The amount of energy required to raise the temperature of 1 gram of water by 1°C at 1 ATM pressure.

• Food chemists use a calorimeter to measure the heat generated when food is burned, which is transferred to a measured volume of water. The temperature increase indicates the energy released.

• Standard International Units: 1 small calorie = 4.2 joules.

Nutrition

Nutrients and Their Classification

Nutrients are substances in food that promote normal growth, maintenance, and repair. Essential nutrients must be obtained from the diet because the body cannot synthesize them fast enough to meet changing demands.

• Nutrient utilization order: Carbohydrates > Lipids > Proteins

• Major nutrients: Carbohydrates, lipids, proteins (bulk of intake)

• Minor nutrients: Vitamins, minerals (required in small amounts)

• Technical nutrient: Water (no energy value)

Carbohydrates

Types and Functions

Carbohydrates are recommended as 45–65% of daily caloric intake in the US, mostly derived from plants and providing dietary fiber.

• Simple carbohydrates: Monosaccharides and disaccharides (e.g., refined sugars in soft drinks, candy, fruit, ice cream). These are considered "empty calories" due to low nutritional value.

• Complex carbohydrates: Polysaccharides (e.g., whole grains, bread, cereal, flour, pasta, nuts, potatoes). These provide energy, vitamins, minerals, fiber, antioxidants, and amino acids.

Glucose and Storage

• Glucose (C6H12O6): The most abundant monosaccharide metabolized by body cells to produce ATP.

• Red blood cells (RBCs) rely almost entirely on glucose for energy, using anaerobic glycolysis to generate ATP.

• Excess glucose is converted to glycogen (C6H10O5) for storage (mainly in liver and skeletal muscles) or to triglyceride (stored in adipose tissue).

Equation for Glycogen Formation:

$\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow \text{C}_6\text{H}_{10}\text{O}_5$

Lipids

Types and Functions

Lipids are recommended as 20–35% of daily caloric intake. Major sources include dairy, meats, and oils. Lipids are the primary energy storage form for skeletal muscle and liver.

• Triglycerides (neutral fats): Most abundant dietary fat, composed of a glycerol molecule bonded to three fatty acids via ester bonds. Per gram, fat provides more than twice the calories of carbohydrates or proteins.

• Cholesterol: Stabilizes cell membranes, precursor for bile salts and steroid hormones, but not an energy source.

• Phospholipids: Found in all cell membranes; lecithin is a major dietary source.

• Essential fatty acids: Required for absorption of fat-soluble vitamins; liver cannot synthesize linoleic and linolenic acids (vegetable sources).

Dietary lipid requirements are higher in infants and children for proper brain/neural development and myelin sheath production.

Proteins

Types and Functions

Protein requirements vary by body weight and physiological state. Proteins must supply all 8 essential amino acids for synthesis and enough nitrogen for non-protein nitrogen substances.

• Complete proteins: Contain all essential amino acids in correct ratios (animal sources: eggs, milk, meat, fish).

• Incomplete proteins: Low in one or more essential amino acids (plant sources: legumes, nuts, seeds, grains, vegetables).

Protein Principles

• All-or-none rule: All required amino acids must be present in a cell at the same time and in correct quantities for protein synthesis. If one is absent, the others are oxidized for energy.

• Nitrogen (N) balance: Difference between dietary nitrogen intake and nitrogen excretion as urea and other waste products.

  • Protein synthesis > protein catabolism = positive N balance

  • Protein synthesis < protein catabolism = negative N balance

• Hormonal control: Anabolic hormones (e.g., growth hormone) accelerate protein synthesis and growth.

Vitamins & Minerals

Vitamins

Vitamins are organic compounds needed in small amounts, mostly functioning as coenzymes to speed up reaction rates.

• Water-soluble vitamins: Readily absorbed (B-complex, C)

• Fat-soluble vitamins: Must bind to lipids to be co-absorbed (A, D, E, K)

• Vitamin B12: Requires intrinsic factor (IF) for absorption in the small intestine

Minerals

Minerals are inorganic elements needed in moderate amounts. Some function as cofactors for enzyme activation, while others work with nutrients to ensure proper body functioning.

• Moderate amounts: Calcium, sodium, phosphorus

• Trace amounts: Iron, zinc, copper, iodine

Vitamins/Minerals Deficiencies

Deficiencies in vitamins and minerals can lead to specific diseases and affect major body systems.

Substance	Disease (targets)
Vit. B1 (thiamine)	BeriBeri (cardiovascular/nervous system)
Vit. B2 (riboflavin)	Chelosis (cracked lips & mouth corners)
Vit. B3 (niacin)	Pellagra (dermatitis)
Vit. B9 (folate)	Anemia (bone marrow)
Vit. B12 (cyanocobalamin)	Pernicious anemia (bone marrow)
Vit. C (ascorbate)	Scurvy (multiple systems)
Vit. K	Bruising/hemorrhage (blood clotting)
Iodine	Goiter (thyroid)
Iron	Iron deficiency anemia (bone marrow)
Phosphorus	Weakness (bone)

Metabolism: Overview

Metabolic Processes

Metabolism is the sum of all chemical reactions necessary to maintain life, including both catabolism and anabolism.

• Catabolism: Breakdown of complex molecules into simpler ones, often releasing energy (e.g., digestion).

• Anabolism: Synthesis of complex molecules from simpler ones.

• Cellular respiration: Catabolic process where food fuels are broken down within cells; some energy is captured to produce ATP from ADP.

ATP must be continually replaced as it is consumed.

ATP Hydrolysis and Phosphorylation

• ATP hydrolysis: Breaking high-energy bonds in ATP releases stored chemical energy for cellular work.

ATP Hydrolysis Equation:

$\text{ATP} \xrightarrow{\text{hydrolysis}} \text{ADP} + \text{inorganic phosphate (P}_i) + \text{E}$

• Phosphorylation: Shifting a high-energy phosphate group (PO43-) to another molecule, often activating protein enzymes and driving coupled reactions.

Phosphorylation Equation:

$\text{ATP} + \text{inactive enzyme} \rightarrow \text{ADP} + \text{active enzyme-P}$

Additional info: These notes provide foundational knowledge for understanding nutrition, metabolism, and their roles in maintaining homeostasis and supporting physiological functions in the human body.