R2 - Gas Exchange

Respiratory System Overview

  • The respiratory system is responsible for inhalation, exhalation, and gas exchange.

Breathing Mechanism

  • Inhalation:

    • External rib muscles and diaphragm contract.

    • Intercostal muscles pull ribs upward and outward.

    • Diaphragm moves downward, increasing thoracic cavity volume.

    • Decreased air pressure causes air to rush into the lungs.

  • Exhalation:

    • External rib muscles and diaphragm relax.

    • Intercostal muscles move ribs back down and inward.

    • Diaphragm moves upward, decreasing thoracic cavity volume.

    • Increased air pressure pushes air out of the lungs.

Structures Involved in Breathing

  • Diaphragm:

    • Dome-shaped muscle at the bottom of the thoracic cavity.

  • Intercostal Muscles:

    • Located between the ribs, assist in expanding and contracting the rib cage during inhalation and exhalation.

Gas Laws and Composition

  • Dalton’s Law of Partial Pressure:

    • Each gas in a mixture contributes its own pressure (partial pressure).

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

  • Atmospheric Gas Composition:

    • Nitrogen: 78%

    • Oxygen: 21%

    • Carbon Dioxide: 0.03%

Alveolar Structure and Function

  • Alveoli:

    • One cell thick, surrounded by capillaries.

    • Surface area approximately 70 m² (size of a tennis court) for efficient gas exchange.

Stages of Respiration

  • Four Stages:

    1. Breathing: Exchange between external environment and lungs.

    2. External Respiration: Exchange of gases between lungs and blood.

    3. Internal Respiration: Exchange of gases between blood and body cells.

    4. Cellular Respiration: Usage of oxygen and production of carbon dioxide for energy.

External Respiration Process

  • Occurs in lungs.

  • Gases exchanged between alveoli and blood in capillaries:

    • Oxygen moves from alveoli to capillaries.

    • Carbon dioxide moves from capillaries to alveoli.

Oxygen Transport in Blood

  • Transport Mechanism:

    • 99% of oxygen is carried by hemoglobin in red blood cells.

    • A small amount is dissolved in plasma.

Carbon Dioxide Transport

  • Transport Mechanism:

    • ~27% of carbon dioxide carried by hemoglobin.

    • ~9% carried in plasma.

    • ~64% combines with water in plasma to form carbonic acid (H2CO3).

    • H2CO3 dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+), aiding in blood buffering.

Internal Respiration Process

  • Occurs in tissues.

  • Exchange of gases between capillaries and cells:

    • Oxygen moves from capillaries to cells.

    • Carbon dioxide moves from cells to capillaries via diffusion.

Regulation of Breathing

  • High acidity (from excess CO2) detected by chemoreceptors in medulla oblongata, causing increased breathing.

  • A second mechanism involving carotid artery chemoreceptors detects low oxygen levels and sends impulses to increase breathing rate.