Gas Exchange and Transport - 2.20.25

The Respiratory System Overview

• Focus on gas exchange and transport

• Anatomy & Physiology 2 course, Spring 2025

• Date: Thursday, February 20

Anatomy of the Respiratory System

• Trachea

  • Main airway leading from the larynx to the bronchi

  • Carina of trachea - point where trachea bifurcates into left and right bronchi

• Bronchi

  • Right main (primary) bronchus - wider, shorter, and more vertical than the left

  • Left main (primary) bronchus

• Lungs

  • Right lung has three lobes, Left lung has two lobes

  • Diaphragm - major muscle for respiration

Alveolar Gas Exchange

• Alveoli are lined with a thin layer of water

• Oxygen Dissolution

  • Oxygen must dissolve in the water to facilitate gas exchange

  • Dissolved gases pass through the respiratory membrane

• Surfactant

  • Disrupts water surface tension to prevent alveolar walls from collapsing

Factors Impacting Gas Exchange

• Concentration Gradient

  • Gas diffusion continues until equilibrium is reached

• Surface Area

  • Respiratory membrane surface area is crucial; reduced in degenerative lung diseases

• Membrane Thickness

  • Typically ~0.5 mm; increased fluid builds-up can hinder diffusion

Ventilation-Perfusion Coupling

• Ensures airflow matches blood flow

• Physiological Responses

  • Pulmonary hypoxia induces vasoconstriction

  • Increased ventilation leads to vasodilation

Gas Transport: Oxygen

• ~98% of oxygen is bound to hemoglobin

• Oxygen Saturation

  • Represents the percentage of hemoglobin occupied by oxygen

• ~2% of oxygen is dissolved in plasma

Gas Transport: Carbon Dioxide

• 90% of CO2 is converted to bicarbonate (HCO3-) via enzyme action

• 5% is transported dissolved in plasma

• 5% binds to hemoglobin; Hemoglobin can transport both O2 and CO2 simultaneously

Carbon Monoxide

• Colorless and odorless gas from burning organic materials

• Displaces O2 on hemoglobin sites

• Common symptoms include headache, nausea, and drowsiness; can lead to fatal outcomes

• Treatment includes oxygen therapy

Systemic Gas Exchange: CO2 Loading

• Most CO2 is transported as bicarbonate

  • Chemical equation: CO2 + H2O ↔ H2CO3 ↔ HCO3− + H+

• In RBCs, CO2 is converted to HCO3− via carbonic anhydrase

• Chloride Shift

  • HCO3− exchanged for Cl− in plasma

Systemic Gas Exchange: O2 Unloading

• Utilization Coefficient - Typically ~22% of blood oxygen delivered to tissues

• Venous Reserve - The remaining oxygen in blood post-exchange

• Arterial blood saturation is ~97%, venous blood saturation is ~75%

Adjustment to Individual Tissue Metabolic Needs

• Factors influencing oxygen unloading:

  • O2 concentration, Bohr Effect: release of O2 increases when blood pH is lower (higher H+ concentration)

  • Increased CO2 production lowers pH and promotes O2 unloading

  • Temperature also influences unloading, with higher temperatures promoting greater O2 release

Mechanisms of Gas Exchange

• Oxygen release and carbon dioxide pick-up occurs across interstitial fluid

• Utilizes carbonic anhydrase for rapid conversion of CO2 to bicarbonate

• Chloride Shift enhances gas transport efficiency between blood plasma and red blood cells

Blood Gases and Respiratory Rhythm

• Breathing rate and depth adjusted based on blood chemistry to maintain homeostasis

• Chemoreceptors primarily monitor H+ ions

  • Normal pH range: 7.45-7.55

• Bicarbonate buffer system is crucial for maintaining pH levels

• Acidosis: pH < 7.45; Hyperventilation is a corrective response

Emphysema

• Condition characterized by the degradation of lung tissue

• Leads to less elastic lungs and alveolar breakdown

• Breathing requires significantly more energy, leading to exhaustion

Visual Comparisons

• Normal lung vs lung with emphysema (images included)

Conclusion

• In-depth understanding of respiratory physiology and associated pathologies is essential for clinical knowledge and applications.