Final_ Oxygen Consumption

Hemoglobin and Oxygen Transport

  • Hemoglobin

    • Respiratory pigment that enhances the oxygen-loading capacity of blood in vertebrates.

  • Oxygen Equilibrium Curve

    • Represents the percentage of heme that is bound to oxygen.

    • Exhibits a sigmoidal shape due to positive cooperativity; as one heme group binds oxygen, it facilitates additional oxygen binding.

    • Can be manipulated via changes in:

      • CO2 concentration

      • pH

      • Temperature

      • 2,3-Bisphosphoglycerate (2,3-BDG)

CO2 Transport in Blood

  • Carbon Dioxide (CO2) Solubility

    • CO2 is more soluble in plasma than O2, but overall solubility is still low.

    • Approximately 5% of CO2 is transported dissolved in plasma.

  • Carbaminohemoglobin

    • About 20% of CO2 is bound to hemoglobin, forming carbaminohemoglobin.

    • CO2 binds not to the heme group but to the amino-terminal groups of protein chains of hemoglobin.

  • Bicarbonate Conversion

    • Around 75% of transported CO2 is converted to bicarbonate (HCO3−) by red blood cells, then transported in plasma.

Carbonic Anhydrase

  • Function

    • Enzyme that converts carbon dioxide and water into carbonic acid (H2CO3).

    • Law of Mass Action: An increase in CO2 leads to an increase in bicarbonate and hydrogen ions (H+).

Gas Exchange in Systemic and Pulmonary Capillaries

  • Systemic Capillaries:

    • Blood flow has a PCO2 of approximately 46 mm Hg.

  • Pulmonary Capillaries:

    • Blood flow has a PCO2 of approximately 40 mm Hg.

  • Gas Exchange Dynamics:

    • CO2 and oxygen exchange occurs across capillary walls, with concentration gradients driving diffusion.

Haldane Effect

  • Oxygen Binding and CO2 Unloading:

    • Physiological response in which hemoglobin's affinity for oxygen decreases as CO2 concentration increases, favoring the unloading of O2 in tissues and the loading of CO2.

Lecture Goals: Applications of Oxygen Consumption

  • Explain the 2nd Law of Thermodynamics.

  • Discuss factors affecting metabolic rate:

    • Levels of activity

    • Temperature

    • Size

  • Describe allometric scaling and its relation to metabolic rate.

The Battle Against Entropy

  • Energy Metabolism

    • Process by which organisms utilize anabolic and catabolic reactions to:

      • Acquire energy

      • Use energy for biological functions

      • Lose energy to the environment

The 2nd Law of Thermodynamics

  • Key Principle

    • States that in an isolated system, internal changes result in increased disorder.

    • External energy input is required to maintain or increase order in systems (e.g., organisms need energy sources).

Forms of Energy and Work

  • Chemical Energy

    • Stored in the covalent bonds of macromolecules.

  • Electrical Energy

    • Voltage potentials across cellular membranes.

  • Mechanical Energy

    • Related to body position or motion.

  • Energy Expenditure

    • Animals expend energy across various functions such as metabolism, homeostasis, and mechanical motion.

Biological Functions for Energy Use

  1. Biosynthesis

    • Manufacturing of molecular and cellular components.

  2. Maintenance

    • Metabolic maintenance of body integrity, irreversibly lost as heat.

  3. External Work

    • Application of forces to external objects; potential energy conversion; heat loss.

Defining Metabolic Rate

  • Metabolic Rate

    • The rate at which an animal converts chemical energy to heat and external work.

    • Heat is the dominant component of metabolic rate, influencing food consumption and ecosystem impact.

Types of Metabolic Rate

  • Basal Metabolic Rate (BMR)

    • Measured in homeothermic animals at rest, inactive, and well-fed.

  • Standard Metabolic Rate (SMR)

    • Measured in poikilothermic animals under similar non-stressed conditions.

  • Maximum Metabolic Rate (MMR)

    • The peak rate of oxygen consumption achievable by an organism.

Measuring Metabolic Rate

  • Direct Calorimetry

    • Captures the rate of heat loss from a body, can be used at rest or during activity.

  • Indirect Calorimetry (Respirometry)

    • Infers metabolic rate from O2 consumption and CO2 generation.

    • Based on the combustion equation of glucose:

      • C6H12O6 + 6O2 → 6CO2 + 6H2O + 2820 kJ/mol

Factors Affecting Metabolic Rate

  • Major Factors:

    • Intensity of physical activity, temperature.

  • Additional Factors:

    • Ingestion of food, age, gender, time of day.

Specific Dynamic Action (SDA)

  • After fasting, ingestion of food leads to a rise in metabolic rate due to the energy needed for digestion and nutrient absorption.

  • SDA is the energy expenditure above BMR or SMR from processing food.

Thanksgiving Meal Example

  • Average Thanksgiving meal ranges from 4500 - 6000 calories.

    • SDA for humans is approximately 10% of caloric intake; thus, ~450-600 calories are spent on digestion, leading to post-meal drowsiness due to serotonin metabolism and carbohydrate absorption.

Allometric Equation

  • Dynamics of Size Variation

    • Expressed as:

      • Y = aM^b

    • Where Y = biological variable, M = body size (g), a = constant, b = scaling exponent.

Example of Allometric Scaling of Food Consumption

  • A 30g vole consumes 175g of food weekly (~600% of its body weight).

  • A 1900kg rhino consumes 650kg of food weekly (~34% of its body weight).

Metabolic Scaling and Size

  • Metabolic relationship with size exhibits negative allometric patterns in homeothermic animals (e.g., humans), meaning energy needs do not scale proportionately with body size.