Respiratory System Concepts

Respiratory Volumes and Capacities

  • Tidal Volume (TV):

    • Definition: The amount of air that moves in and out of the lungs during normal breathing.
    • Note: This is a regular volume of air.

  • Inspiratory Volume (IV):

    • Definition: The maximum amount of air that can be forcibly inhaled after a normal tidal inhalation.
    • Context: This volume is greater than that of tidal volume.

  • Expiratory Volume (EV):

    • Definition: The maximum amount of air that can be forcibly exhaled after a normal tidal exhalation.

  • Residual Volume (RV):

    • Definition: The amount of air that remains in the lungs after maximal exhalation to keep the alveoli open and prevent lung collapse.
    • Approximate Value: Usually around 1-1.5 L (4 to 6 pints).

  • Inspiratory Capacity (IC):

    • Calculation: TV + Inspiratory Volume (IV).
    • Meaning: Total air that can be inhaled after normal tidal inhalation.

  • Functional Residual Capacity (FRC):

    • Calculation: Residual Volume (RV) + Expiratory Reserve Volume (ERV).
    • Meaning: Air remaining in lungs after a normal tidal exhalation.

  • Vital Capacity (VC):

    • Calculation: Tidal Volume (TV) + Inspiratory Reserve Volume (IV) + Expiratory Reserve Volume (EV).
    • Meaning: The amount of exchangeable air.

  • Total Lung Capacity (TLC):

    • Calculation: Tidal Volume (TV) + Inspiratory Reserve Volume (IV) + Expiratory Reserve Volume (EV) + Residual Volume (RV).
    • Meaning: Sum of all lung volumes.

Gas Exchange and Respiratory Mechanisms

  • External Respiration:

    • Definition: Gas exchange between blood and lungs.

  • Internal Respiration:

    • Definition: Gas exchange between blood and body tissues.

Properties of Gases

  • Dalton's Law:

    • Definition: The total atmospheric pressure of a gas mixture equals the sum of the partial pressures of the individual gases.
    • Example: Total pressure at sea level = 760 mmHg = P(N2) + P(O2) + P(CO2) + P(H2O).

  • Henry's Law:

    • Definition: The amount of gas that dissolves in a liquid is proportional to the partial pressure of that gas above the liquid.
    • Example: Partial pressure of O2 in air = 159 mmHg.

  • Partial Pressure (PP):

    • Concept: The pressure exerted by a gas in a mixture is known as its partial pressure.
    • Relation: Higher pressure results in more gas dissolving into a liquid.

  • Concentration:

    • Definition: The amount of a substance in a given volume.
    • Example: Higher concentration means more O2 can be transported.

Partial Pressure Gradients

  • Gas Pressure Difference:

    • Importance: Steep partial pressure gradients facilitate efficient gas exchange.

  • Example in O2 Exchange:

    • Venous blood PO2 = 40 mmHg, Alveolar PO2 = 104 mmHg.
    • This gradient drives O2 from the alveoli into the blood.

Hemoglobin Affinity for Oxygen

  • Oxyhemoglobin Dissociation Curve:

    • Meaning: Relates the saturation of hemoglobin with oxygen to the partial pressure of O2.
    • As hemoglobin saturation increases, its affinity for O2 also increases.
    • Example: At high altitudes, lower P_O2 decreases hemoglobin saturation.

  • O2 Release:

    • Hemoglobin releases O2 more readily when PCO2 is high and pH is low (right shift of the curve).

Hypoxia

  • Definition: Condition in which body tissues do not receive enough oxygen.

  • Classification:

    • Anemic Hypoxia: Due to reduced hemoglobin.
    • Ischemic Hypoxia: Due to reduced blood flow.
    • Histotoxic Hypoxia: Due to poisons like cyanide.
    • Hypoxemic Hypoxia: Low arterial oxygen pressure.
    • Carbon Monoxide Poisoning: CO binds with hemoglobin more effectively than O2, leading to tissue hypoxia.

  • Symptoms: Headaches, flushed skin, dizziness, and potential cyanosis.