8.1 Respiratory structures and gas exchange mechanisms

Breathing is essential for life, and animals have evolved diverse structures to exchange gases. From gills in fish to lungs in mammals, these organs maximize surface area for efficient oxygen uptake and carbon dioxide removal.

Gas exchange relies on diffusion and specialized mechanisms like countercurrent flow. Respiratory pigments like hemoglobin boost oxygen-carrying capacity, while adaptations like surfactant in alveoli optimize lung function. These systems keep organisms alive and thriving.

Respiratory Structures

Aquatic Respiratory Structures

Top images from around the web for Aquatic Respiratory Structures

• 

  2.2 – Respiratory Structures and Their Function – Introductory Animal Physiology 2nd Edition View original

  Is this image relevant?

• 

  2.3 – Gaseous Exchange Mechanisms – Introductory Animal Physiology View original

  Is this image relevant?

• 

  Fish gill - Wikipedia View original

  Is this image relevant?

• 

  2.2 – Respiratory Structures and Their Function – Introductory Animal Physiology 2nd Edition View original

  Is this image relevant?

• 

  2.3 – Gaseous Exchange Mechanisms – Introductory Animal Physiology View original

  Is this image relevant?

1 of 3

Top images from around the web for Aquatic Respiratory Structures

• 

  2.2 – Respiratory Structures and Their Function – Introductory Animal Physiology 2nd Edition View original

  Is this image relevant?

• 

  2.3 – Gaseous Exchange Mechanisms – Introductory Animal Physiology View original

  Is this image relevant?

• 

  Fish gill - Wikipedia View original

  Is this image relevant?

• 

  2.2 – Respiratory Structures and Their Function – Introductory Animal Physiology 2nd Edition View original

  Is this image relevant?

• 

  2.3 – Gaseous Exchange Mechanisms – Introductory Animal Physiology View original

  Is this image relevant?

1 of 3

• Gills are specialized organs for gas exchange in aquatic animals
  • Consist of thin, highly vascularized filaments that maximize surface area for efficient gas exchange
  • Countercurrent flow of water and blood enhances oxygen uptake and carbon dioxide removal (fish)
  • Gills can be external (sea stars) or internal (fish) depending on the species

Terrestrial Respiratory Structures

• Lungs are the primary respiratory organs in terrestrial vertebrates
  • Consist of highly branched airways that terminate in alveoli, the site of gas exchange
  • Ventilation mechanisms vary among species (negative pressure breathing in mammals, positive pressure breathing in birds)
  • Lungs are internalized to prevent desiccation and allow for efficient gas exchange
• Tracheal system is a network of air-filled tubes that directly delivers oxygen to tissues in insects
  • Consists of spiracles (openings) and tracheae that branch throughout the body
  • Allows for efficient gas exchange without the need for a circulatory system
• Cutaneous respiration involves gas exchange across the skin surface
  • Occurs in amphibians and some reptiles with thin, moist skin
  • Relies on a dense network of blood vessels near the skin surface to facilitate gas exchange

Alveoli: The Site of Gas Exchange

• Alveoli are the functional units of the lungs where gas exchange takes place
  • Consist of thin, single-cell layered sacs surrounded by capillaries
  • Provide an enormous surface area for efficient gas exchange between the air and blood
  • Surfactant reduces surface tension, preventing alveolar collapse during exhalation

Gas Exchange Mechanisms

Countercurrent Exchange and Diffusion

• Countercurrent exchange maximizes the diffusion gradient for efficient gas exchange
  • Blood flows in the opposite direction to the flow of water (gills) or air (lungs)
  • Maintains a constant concentration gradient, promoting continuous gas exchange
• Gas diffusion is the passive movement of gases from high to low concentration
  • Oxygen diffuses from the air/water into the blood, while carbon dioxide diffuses out
  • Rate of diffusion depends on the concentration gradient, surface area, and diffusion distance

Surface Area to Volume Ratio

• Surface area to volume ratio is a key factor in determining gas exchange efficiency
  • Larger surface area relative to volume allows for more efficient gas exchange
  • Smaller organisms have a higher surface area to volume ratio, facilitating gas exchange
  • Respiratory structures (gills, alveoli) are designed to maximize surface area for optimal gas exchange

Respiratory Pigments

• Respiratory pigments are molecules that bind and transport gases in the blood
  • Hemoglobin is the primary respiratory pigment in vertebrates
    • Consists of four subunits, each containing an iron-based heme group that binds oxygen
    • Exhibits cooperative binding, allowing for efficient oxygen loading and unloading
  • Other respiratory pigments include hemocyanin (mollusks, arthropods) and chlorocruorin (some annelids)
  • Respiratory pigments increase the oxygen-carrying capacity of the blood, enhancing oxygen delivery to tissues