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.