RGI 5

Overview of Gas Exchange and Transport

  • Objective: Understand how gases are exchanged in the lungs, carried in the blood, and the control of respiration.

Gas Exchange Process

  • Gaseous Exchange Basics

    • Oxygen (O2) is delivered to body tissues.

    • Carbon Dioxide (CO2) is removed from body tissues.

Control of Respiration

  • Respiratory Control Center

    • Part of the central nervous system regulating breathing rate.

    • Works synchronously with the cardiovascular system.

  • Herring-Breuer Reflex

    • Protects against over-inflation of lungs through stretch receptors in lung tissue.

Gas Partial Pressures

  • Understanding Partial Pressures

    • Key in the movement of gases during respiration.

    • Differences in partial pressures drive diffusion.

Oxygen Transport in Blood

  • Oxygen Carriage Mechanisms

    • Approximately 1.5-2% of oxygen is dissolved in blood plasma.

    • About 98-98.5% is transported by hemoglobin (heme protein in red blood cells).

  • Bohr Effect

    • Describes how CO2 concentration and pH affect oxygen release from hemoglobin.

    • Increase in CO2 or decrease in pH enhances oxygen unloading in tissues.

Carbon Dioxide Transport

  • Transport Mechanisms

    • Dissolved CO2: About 5% of CO2 is dissolved in plasma.

    • Carbamino Compounds: CO2 can bind with hemoglobin to form carbaminohemoglobin.

    • Bicarbonate Formation: Most CO2 is converted to bicarbonate (HCO3-) in plasma for transport.

Respiratory Control Centers in the Brain

  • Medullary Centers

    • Dorsal Respiratory Group: Controls inspiration (external intercostal muscles, diaphragm).

    • Ventral Respiratory Group: Associated with forced expiration.

  • Pons Centers

    • Pneumotaxic Center: Regulates the length of inspiration, affects breathing rate.

    • Apneustic Center: Works with the dorsal group to regulate inspiration.

Factors Affecting Breathing Rate

  • Conscious Control: Ability to override reflex breathing.

  • Irritant and Stretch Receptors: Trigger protective reflexes in response to harmful substances.

  • Emotional and Physiological Factors: Pain, excitement, and certain reflexes can change breathing patterns.

Diffusion of Gases in the Lungs

  • Alveolar Gas Exchange: Gases diffuse between alveoli and capillary blood based on partial pressures.

    • Oxygen: Comes from alveoli with high partial pressure to blood with lower pressure.

    • Carbon Dioxide: Diffuses from blood into alveoli for expiration.

Summary of Gas Partial Pressures in Blood and Tissues

  • Partial Pressures: Demonstrate the differences affecting diffusion.

    • Alveoli: O2 ~ 100 mmHg, CO2 ~ 40 mmHg.

    • Blood entering lungs: O2 ~ 40 mmHg, CO2 ~ 45 mmHg.

Hemoglobin and Respiratory Affinity

  • Oxygen Binding: Hemoglobin binds to oxygen in high partial pressures and releases it in low partial pressures.

  • Oxygen Dissociation Curve: Reflects how oxygen availability changes affinity.

    • Left shift: Increased affinity (low CO2, high pH).

    • Right shift: Decreased affinity (high CO2, low pH).

The Haldane Effect

  • As blood pH decreases, the affinity of hemoglobin for oxygen decreases, facilitating oxygen release under anaerobic conditions.

Conclusion

  • Understanding these mechanisms is crucial for comprehending how oxygen is utilized and carbon dioxide is removed in the body.