AM

Topic 7 Ch 39

Metabolism Overview

  • Types of Metabolism

    • Anaerobic Metabolism: Occurs without oxygen, primarily involves glycolysis.

    • Aerobic Metabolism: Involves oxygen, includes the citric acid cycle and oxidative phosphorylation.

  • Metabolic Rate

    • Definition: Rate of energy consumption, measured through oxygen consumption.

    • Factors influencing metabolic rate: Activity level and body mass.

    • Basal Metabolic Rate (BMR): Energy used at rest, varies with body temperature, and is higher in endotherms (warm-blooded animals).

Nutrition Basics

  • Energy Balance: The relationship between energy intake and usage; essential for maintaining weight.

  • Essential Nutrients: Includes essential amino acids, vitamins, and minerals critical for health.

    • minerals or organic substances that humans cannot synthesize

Digestion Process

  • Digestion Anatomy

    • Foregut:

      • Mouth & Esophagus: Mechanical breakdown, swallowing process.

      • Stomach: Secretes gastrin and pepsin; initial protein digestion occurs.

    • Midgut:

      • Small Intestine: Three sections (duodenum, jejunum, ileum), where most digestion and absorption takes place. Accessory organs (liver, pancreas) supply enzymes.

    • Hindgut:

      • Large Intestine: Reabsorption of water; compacts waste.

    • Accessory organs:

      • salivary glands, liver, gall bladder, pancreas. Secrete enzymes or other substances to aid digestion

Cellular Metabolism

  • Glycolysis:

    • Occurs in the cytosol; breaks down glucose into pyruvate.

    • In anaerobic conditions, converts pyruvate to lactic acid.

    • In aerobic conditions, yields Acetyl CoA for the citric acid cycle.

  • Citric Acid Cycle: Generates NADH and FADH2, driving ATP production via the electron transport chain.

  • ATP Production:

    • Aerobic metabolism produces up to 32 ATP from one glucose molecule.

Nutrient Metabolism

Carbohydrate Metabolism

  • Glucose transport into cells; lactic acid produced under low oxygen.

  • Excess stored as glycogen or converted to fat.

Lipid Metabolism

  • Triglycerides processed by the liver; free fatty acids broken down into Acetyl CoA.

  • Efficient energy storage (9.4 kcal/g for lipids vs. 4.2 kcal/g for carbs & proteins).

Protein Metabolism

  • Proteins digested into amino acids, used for tissue synthesis or ATP as a last resort.

  • Amino acids can be converted into ammonia for excretion.

Metabolic Rate Insights

  • Measured in O2 consumption (ml/hr), BMR indicates energy use while at rest.

  • Metabolic rate increases with mass (mass^(3/4)).

Energy Homeostasis

  • Endotherms produce heat through metabolism, maintaining constant body temperature; are active over broad temperatures.

  • Ectotherms rely on environmental heat; lower metabolic rates, cannot sustain prolonged activity in cold.

Behavioral Adaptations for Thermoregulation

  • Physiological: Shivering, vasodilation/constriction, etc.

  • Behavioral: Seeking shade, huddling for warmth, or burrowing mechanisms.

Nutritional Needs

  • Recommended Daily Allowances (RDAs) outline essential nutrient requirements.

  • Essential nutrients must be obtained from food as the body cannot synthesize them.

Digestion Phases

  • Stages of Digestion:

    • Mouth: Chewing (mechanical), salivary amylase (chemical).

    • Stomach: Secretes HCl, pepsin for protein digestion.

    • Small Intestine: Primary site for digestion/absorption; completion of carbohydrate, fat, and protein breakdown.

Accessory Organ Functions

  • Liver: Produces bile for lipid emulsification.

  • Pancreas: Secretes digestive enzymes; reacts based on pH of stomach contents using bicarbonate for neutralization.

Nutrient Absorption in the Small Intestine

  • The jejunum and ileum assist in nutrient absorption; features like villi and microvilli enhance surface area for absorption.

Glucose Absorption

  • Glucose is transported via Na+ co-transport into epithelial cells of the intestine, then enters the bloodstream via specific transport proteins.

Large Intestine Functions

  • Primarily absorbs water and compacts waste, essential for hydration and excretion.

  • Houses beneficial gut flora for further digestion and vitamin production.