Detailed Notes on Ventilation and Gas Exchange

Respiratory Components

• VENTILATION: The mechanism for breathing, supplying air or water to respiratory surfaces (lungs or gills).
• DIFFUSION: Movement of O2 and CO2 across respiratory surfaces or skin.
• CIRCULATION: Transport of O2 and CO2 throughout the body via the circulatory system.
• CELLULAR RESPIRATION: Utilization of O2 by cells and production of CO2.

Gas Exchange Mechanism

• O2 flows from areas of higher concentration (environment) to lower concentration (tissues).
• Conversely, CO2 flows from tissues to the environment.

Composition of Air

• Major Components:
  • 76% Nitrogen
  • 21% Oxygen
  • 0.98% Argon
  • 0.04% Carbon Dioxide
• Partial Pressure: The pressure exerted by a specific gas in a mixture of gases.

Dalton’s Law of Partial Pressure

• Total atmospheric pressure at sea level: 760 ext{ mm Hg}.
  • Nitrogen Partial Pressure: 76 imes 760 ext{ mm Hg} = 578 ext{ mm Hg}
  • Oxygen Partial Pressure: 21 imes 760 ext{ mm Hg} = 159 ext{ mm Hg}
  • Argon Partial Pressure: 0.0098 imes 760 ext{ mm Hg} = 7.45 ext{ mm Hg}
  • Carbon Dioxide Partial Pressure: 0.0004 imes 760 ext{ mm Hg} = 0.30 ext{ mm Hg}

Factors Affecting Gas Solubility in Water

• Solubility of Gas: O2 has low solubility in water; fish use hemoglobin to transport O2.
• Temperature: Higher water temperatures decrease gas solubility.
• Presence of Other Solutes: More solutes in seawater reduce dissolved O2.
• Partial Pressure: O2 moves from high to low partial pressure.

Conditions Affecting Oxygen Levels

• Habitats with photosynthetic organisms are oxygen-rich.
• Surface water in ponds and streams contains more O2 than deeper waters.
• Rapids and waterfalls increase oxygenation due to agitation and splashing water.

Fick’s Law of Diffusion Parameters

• Key parameters for efficient gas exchange:
  • Solubility of gases in fluid
  • Temperature (in Kelvin)
  • Surface area of gas exchange
  • Partial pressure difference across the exchange surface (P2 - P1)
  • Thickness of the gas-exchange surface (D)

Optimal Conditions for Gas Diffusion

• Maximize gas exchange by:
  • Large surface area (A)
  • Thin exchange surface (D)
  • Large partial pressure difference (P2 - P1)

Gas Exchange Mechanisms

Gills

• Gills have a high surface area and are thin to facilitate gas exchange.
• Counter-Current Exchange: Water and blood flow in opposite directions to optimize O2 uptake.
  • As blood moves through filaments, it absorbs O2 efficiently.

Insect Respiration

• Insects use a tracheal system of air-filled tubes, minimizing water loss.
• Spiracles control air intake and minimize evaporation.

Lungs

• Frogs use positive pressure breathing, pushing air into lungs.
• Mammals use negative pressure breathing, pulling air into lungs via diaphragm contraction.

Surfactant in the Lungs

• Surfactant reduces surface tension in alveoli, enhancing lung compliance.
• Insufficient surfactant in premature infants leads to respiratory distress syndrome.

Avian Respiratory System

• Birds have a unidirectional airflow for efficient gas exchange.
• Air sacs facilitate continuous airflow through lungs during both inhalation and exhalation.

Blood Physiology

• Blood is approximately 45% red blood cells.
• Hemoglobin (Hb) bound to O2 enhances oxygen transport capacity compared to plasma alone.
• CO2 is primarily transported in plasma as bicarbonate ions (HCO3-).

Hemoglobin Functionality

• Each hemoglobin can carry up to 4 O2 molecules, constituting 98.5% of O2 in blood.
• Cooperative binding allows for efficient unloading of O2 under varying tissue conditions.
• The Bohr effect indicates that increased CO2 and decreased pH reduce hemoglobin's affinity for O2, facilitating delivery to tissues.

Carbon Dioxide Transport

• CO2 is converted to bicarbonate via carbonic anhydrase in RBCs, enabling efficient transport.
• Blood acts as a buffer system to minimize pH changes during gas exchange.