breathing and exchange of gases

Respiration

  • Definition:

    • Process of exchange of oxygen (O₂) and carbon dioxide (CO₂) between the body and the environment.

    • Cellular utilization of O₂ to produce energy (ATP).

Respiratory Organs

  1. Humans:

    • Primary organ: Lungs

    • Other parts include: Nasal passage, pharynx, larynx, trachea, bronchi, bronchioles, alveoli.

  2. Other Animals:

    • Earthworms: Use skin for cutaneous respiration.

    • Insects: Have a tracheal system.

    • Fishes: Utilize gills for respiration.

    • Amphibians: Use lungs, skin, and buccal cavity.

Mechanism of Breathing

  1. Inspiration (Inhalation):

    • Diaphragm contracts and flattens.

    • External intercostal muscles contract, ribs move upward and outward.

    • Volume of thoracic cavity increases → Pressure decreases → Air enters lungs.

  2. Expiration (Exhalation):

    • Diaphragm relaxes and returns to dome-shaped position.

    • External intercostal muscles relax, ribs move downward and inward.

    • Volume of thoracic cavity decreases → Pressure increases → Air exits lungs.

  3. Breathing Rate:

    • Normal rate: 12-16 breaths per minute.

Respiratory Volumes and Capacities

  1. Tidal Volume (TV):

    • Air inhaled or exhaled during normal breathing (~500 mL).

  2. Inspiratory Reserve Volume (IRV):

    • Additional air inhaled beyond tidal volume (~2500-3000 mL).

  3. Expiratory Reserve Volume (ERV):

    • Additional air exhaled beyond tidal volume (~1000-1100 mL).

  4. Residual Volume (RV):

    • Air remaining in lungs after maximum exhalation (~1100-1200 mL).

  5. Vital Capacity (VC):

    • Sum of TV + IRV + ERV.

  6. Total Lung Capacity (TLC):

    • Sum of VC + RV.

Exchange of Gases

  • Occurs at:

    1. Alveoli:

      • O₂ diffuses from alveoli to blood; CO₂ diffuses from blood to alveoli.

    2. Tissues:

      • O₂ diffuses from blood to cells; CO₂ diffuses from cells to blood.

  • Based on partial pressure (pO₂ and pCO₂):

    • O₂ moves from high to low pO₂.

    • CO₂ moves from high to low pCO₂.

Transport of Gases

  1. Oxygen Transport:

    • 97% transported by hemoglobin in red blood cells (as oxyhemoglobin).

    • 3% dissolved in plasma.

    • Factors affecting oxygen binding: High pO₂, low pCO₂, low temperature, high pH favor binding; opposite conditions favor release.

  2. Carbon Dioxide Transport:

    • 70% transported as bicarbonate ions (HCO₃⁻).

    • 20-25% bound to hemoglobin (as carbaminohemoglobin).

    • 7% dissolved in plasma.

Regulation of Breathing

  • Controlled by the respiratory center located in the medulla oblongata and pons.

  • Chemoreceptors react to CO₂ and H⁺ levels to adjust breathing rate.

Respiratory Disorders

  1. Asthma:

    • Inflammation and narrowing of bronchioles, causing difficulty in breathing.

  2. Emphysema:

    • Damage to alveoli, reducing the surface area for gas exchange (common in smokers).

  3. Bronchitis:

    • Inflammation of bronchi due to infection or pollutants.

  4. Pneumonia:

    • Infection causing fluid accumulation in alveoli.

  5. Occupational Lung Diseases:

    • Result from inhalation of harmful substances (e.g., silica, asbestos).