17A

Overview of the Respiratory System

  • Chapter Content: Focuses on the gas exchange and regulation of breathing.

Learning Outcomes

  • Understand circulatory pathway for oxygenated/deoxygenated blood.

  • Explain gas exchange in lungs and tissues.

  • Recognize partial pressures of oxygen and carbon dioxide in blood.

Pulmonary Circulation

General Principles

  • O2 and CO2 levels in systemic arterial blood are stable.

  • O2 moves from alveoli to blood, CO2 moves from blood to alveoli at equal rates to cellular consumption/production.

Circulation Patterns

  • Heart Perspective: Systemic vs. Pulmonary circulation.

  • Lungs Perspective: Oxygenated vs. Deoxygenated blood.

  • Respiratory Quotient: CO2 produced : O2 consumed approximately 0.8 at rest, varies by diet.

Respiratory Membrane

  • Components: Type 1 epithelial cell, fused basement membranes, endothelial cell.

  • Characteristics: Very thin with large surface area.

Diffusion of Gases

Key Concepts

  • Partial Pressure: Governed by the ideal gas law and Dalton’s Law.

  • Gas mixtures have total pressure equal to the sum of individual gas pressures.

  • Partial pressure formula for a gas: Pgas = %gas × Ptotal.

Atmospheric Composition

  • 79% Nitrogen, 21% Oxygen, 0.03% Carbon Dioxide.

  • Calculations of partial pressures in atmospheric conditions and in lungs under 100% humidity at body temperature.

Solubility of Gases

  • Equilibrium: Partial pressures of vaporized and dissolved gases equalize.

  • [O2] in 100 mm Hg pressure = 0.15 mmole/L; [CO2] = 3.0 mmole/L.

Gas Exchange

Lungs vs. Respiring Tissue

  • Gases diffuse from areas of high partial pressure to low.

  • In lungs: PO2 alveoli = 100 mm Hg; PCO2 = 40 mm Hg.

  • In tissues: PO2 cells <40 mm Hg; PCO2 cells ≥46 mm Hg.

Factors Affecting Gas Exchange

  • In Lungs: Diffusion efficiency is high due to thin barrier and large surface area.

  • In Tissues: Mixed venous blood reflects metabolic activity; higher metabolic rates lead to greater gas exchange.

Alveolar Partial Pressures

Determinants

  • Factors: Inspired air composition, minute ventilation, tissue utilization rates of O2 and CO2.

  • Alveolar ventilation must match metabolic demands for normal function (Eupnea).

Conditions Affecting Ventilation

  • Hyperpnea: Increased ventilation during exercise.

  • Hypoventilation: Inadequate ventilation leads to decreased PO2 and increased PCO2.

  • Hyperventilation: Excessive ventilation raises PO2 and lowers PCO2.

Terminology in Respiratory Physiology

  • Hyperpnea: Increased ventilation for metabolic needs.

  • Dyspnea: Difficulty breathing.

  • Apnea: Temporary cessation of breathing.

  • Tachypnea: Rapid, shallow breathing.

  • Hypoxia: Oxygen deficiency in tissues.

  • Hypoxemia: Oxygen deficiency in blood.

  • Hypercapnia: Excess carbon dioxide in blood.

  • Hypocapnia: Deficiency of carbon dioxide in blood.