Chapter 22 - Gross Metabolism-1

Chapter Overview

• Chapter Title: Metabolism and Energy Balance

• Focuses on various aspects of metabolism, energy regulation, appetite, and homeostasis.

• Structure of the chapter includes:

  • Appetite and Satiety

  • Energy Balance

  • Metabolism

  • Fed-State and Fasted-State Metabolism

  • Homeostatic Control of Metabolism

  • Regulation of Body Temperature

22.1 Appetite and Satiety

• Control of food intake is a complex process influenced by both physiological and psychological factors.

• Competing behavioral states:

  • Appetite (Hunger): Desire to eat.

  • Satiety: Feeling of fullness.

• Hypothalamus contains two control centers:

  • Feeding Center: Initiates hunger.

  • Satiety Center: Signals fullness, stopping intake.

• Theories of regulation:

  • Glucostatic Theory: Suggests blood glucose levels determine appetite.

  • Lipostatic Theory: Focuses on fat stores influencing hunger.

• Neural inputs are vital:

  • Inputs from the hypothalamus, cerebral cortex, and limbic system.

  • Key hormones include adipokines, neuropeptide Y (NPY), ghrelin, and sensory inputs.

22.2 Energy Balance

• Energy balance is maintained when energy input equals energy output.

• Total body energy consists of:

  • Energy stored in fats and glycogen.

  • Energy intake from foods.

  • Energy output from bodily processes.

• Energy output equates to work done + heat produced.

• Types of cellular work include:

  1. Transport Work: Movement of ions and molecules.

  2. Mechanical Work: Muscle contractions, movement.

  3. Chemical Work: Synthesis of molecules (proteins, nucleic acids).

• Energy storage forms:

  • Short-term: ATP.

  • Long-term: Glycogen and fats.

• Conscious control over energy output and intake exists but is often unconscious regarding regular metabolism.

22.3 Metabolism

• Metabolism includes both anabolic and catabolic pathways:

  • Anabolism: Synthesis of larger molecules (fed state).

  • Catabolism: Breakdown of molecules to extract energy (fasted state).

• Three fates of ingested biomolecules:

  1. Energy for mechanical work.

  2. Synthesis for growth and maintenance.

  3. Storage as glycogen or fat.

• Nutrient pools in plasma:

  • Free fatty acids pool.

  • Glucose pool (regulated tightly).

  • Amino acids pool available for protein synthesis and energy.

• Enzymes regulate the direction of metabolism via push-pull mechanisms.

22.4 Fed-State Metabolism

• Carbohydrates are utilized for ATP production, primarily via glycolysis and citric acid cycle.

• Amino acids are converted into proteins and can be utilized for energy if in excess.

• Fats are stored and mobilize energy when required.

• Chylomicrons transport dietary fats from the intestines; lipases break down triglycerides into usable forms.

22.5 Fasted-State Metabolism

• During fasting, glycogen is converted to glucose through glycogenolysis.

• Proteins can be deaminated to produce ATP, with ammonia being converted to urea.

• Lipids, being a dense energy source, are broken down into glycerol and fatty acids, which enter metabolic pathways:

  • Beta-oxidation leads to acetyl CoA production, which can form ketone bodies.

  • Excess ketone bodies can lead to ketoacidosis.

22.6 Homeostatic Control of Metabolism

• Pancreas plays a crucial role by secreting hormones:

  • Insulin (from beta cells): Dominates in the fed state, facilitating glucose uptake and storage.

  • Glucagon (from alpha cells): Dominates during fasting, promoting glucose production and release.

• Hormone balance (insulin-to-glucagon ratio) is vital for metabolism regulation.

Key Figures in the Chapter

• Figure 22.1: Illustrates complex chemical signaling for food intake control.

• Figure 22.3: Displays nutrient pools and metabolic pathways.

• Figures 22.5: Summarizes biochemical pathways for energy production in fed vs. fasted states.

Conclusion

• This chapter emphasizes the importance of understanding the physiological mechanisms governing metabolism, energy balance, appetite, and their regulation in maintaining overall health and homeostasis. The interplay between different biochemical pathways and hormonal responses plays a critical role in managing energy supply and demand within the body.