Nutrition, Metabolism & Body Temperature: Structured Study Notes

Nutrition, Metabolism & Body Temperature

Introduction

This section covers the essential concepts of nutrition, metabolism, and body temperature regulation, focusing on the biochemical pathways that support cellular energy production and physiological homeostasis.

Nutrition

Definition and Importance

• Nutrition is the process of taking in food and using it to supply the body with nutrients required for energy, growth, and maintenance.

• Nutrient: Any substance needed by cells for function, growth, and repair.

• Essential nutrients must be obtained from food (e.g., water, vitamins, minerals, some amino acids).

• Non-essential nutrients can be synthesized by the body (e.g., most amino acids).

• Water is a major nutrient, making up about 2/3 of the human body and is vital for chemical reactions.

Macronutrients include carbohydrates, fats, and proteins, which provide energy and building blocks. Micronutrients include vitamins and minerals, which are required in smaller amounts for metabolic processes.

Metabolism

Overview

• Metabolism refers to all chemical reactions in the body that build (anabolism) or break down (catabolism) molecules.

• Anabolism: Building complex molecules from simpler ones; requires energy (ATP).

• Catabolism: Breaking down complex molecules into simpler ones; releases energy.

Key Terms

• Reactant: Substance you start with in a chemical reaction.

• Product: Substance produced by a chemical reaction.

Cellular Respiration

Major Pathways

• Glycolysis: Anaerobic breakdown of glucose in the cytosol to produce pyruvic acid and a net gain of 2 ATP.

• Citric Acid Cycle (Krebs Cycle): Aerobic process in mitochondria; breaks down pyruvic acid, producing high-energy electron carriers (NADH, FADH2), CO2, and 2 ATP.

• Electron Transport System (ETS): Aerobic process in mitochondria; uses electrons from NADH and FADH2 to generate a proton gradient, driving ATP synthesis (oxidative phosphorylation).

Summary of ATP Yield:

• Glycolysis: 2 ATP

• Citric Acid Cycle: 2 ATP

• Electron Transport System: 28 ATP

• Total: 32 ATP per glucose molecule

I Equation for Cellular Respiration:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 32\text{ATP}$

Carbohydrate Metabolism

Key Processes

• Glycolysis: Breakdown of glucose to pyruvic acid (catabolism).

• Glycogenesis: Conversion of glucose to glycogen for storage (anabolism).

• Glycogenolysis: Breakdown of glycogen to glucose (catabolism).

• Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources (anabolism).

Lipid Metabolism

Digestion and Absorption

• Dietary lipids are emulsified by bile salts in the small intestine, forming micelles for absorption.

• Inside intestinal cells, fats are rebuilt into triglycerides and packaged as chylomicrons for transport in blood.

Lipid Catabolism (Lipolysis)

• Triglycerides are hydrolyzed to glycerol and fatty acids.

• Fatty acids undergo beta-oxidation to generate acetyl-CoA, which enters the citric acid cycle.

• Lipids yield more energy per gram than carbohydrates.

Protein Metabolism

Digestion and Absorption

• Proteins are broken down into amino acids in the stomach and small intestine.

• Amino acids are absorbed and transported to the liver for metabolism.

Metabolic Fate

• Amino acids can be used for protein synthesis (anabolism) or converted to energy (catabolism) via deamination and entry into the citric acid cycle.

Metabolic States

Absorptive State

• Occurs after a meal (up to 4 hours).

• Main energy source: Glucose from food.

• Dominant process: Anabolism (building and storing molecules).

• Hormone in control: Insulin (promotes glucose uptake and storage).

Postabsorptive State

• Occurs when no nutrients are being absorbed (between meals).

• Main energy source: Stored nutrients (glycogen, fat).

• Dominant process: Catabolism (mobilizing stored energy).

• Hormone in control: Glucagon (promotes glucose release and production).

Vitamins and Minerals

Vitamins

• Organic compounds essential for metabolic pathways.

• Act as co-enzymes to assist enzyme function.

• Fat-soluble: A, D, E, K (absorbed with lipids).

• Water-soluble: B vitamins, C (components of enzymes).

Minerals

• Inorganic elements required in moderate amounts (e.g., calcium, phosphorus, potassium).

• Work with nutrients to ensure proper body function.

Energetics & Thermal Regulation

Basal Metabolic Rate (BMR)

• BMR: Minimum resting energy expenditure of an individual.

• Average BMR: 70 Cal/hour (1,680 Cal/day).

• Actual energy consumption depends on weight, activity, and age.

Appetite Regulation

• Leptin: Hormone produced by fat cells; inhibits hunger by acting on the hypothalamus.

• Neuropeptide Y (NPY): Brain molecule; stimulates appetite, especially for carbohydrates.

Thermal Regulation

• Body temperature is maintained by balancing heat gained and lost.

• Normal body temperature: 37°C (98.6°F).

• Heat is produced by metabolism and lost via radiation, convection, conduction, and evaporation.

Summary Table: Energy Yield from Cellular Respiration

Process	Location	ATP Yield	Aerobic/Anaerobic
Glycolysis	Cytosol	2 ATP	Anaerobic
Citric Acid Cycle	Mitochondria	2 ATP	Aerobic
Electron Transport System	Mitochondria	28 ATP	Aerobic
Total		32 ATP

Checkpoint Questions

• Define: metabolism, anabolism, catabolism.

• Describe the basic steps and main purpose of glycolysis, citric acid cycle, and electron transport system.

• Identify where each process takes place and whether it is aerobic or anaerobic.

• Summarize the net ATP yield from each process.

Additional info: Expanded explanations and context were added to clarify metabolic pathways, regulatory hormones, and physiological mechanisms based on standard Anatomy & Physiology curriculum.