Gas Exchange and Oxygen Transport in Animals

Learning Objectives

  • Compare different strategies for water conservation in animals.

  • Compare gas exchange structures in different animal systems.

  • Explore different ways that animals breathe.

  • Describe how the structure of hemoglobin helps maximize distribution of oxygen in mammals.

  • Examine how CO2 is transported from tissues to the lungs to be removed in mammals.

Water Conservation on Land

  • Desert Mammals:

    • Produce highly hypertonic urine.

    • Possess long nephrons to maintain steep osmotic gradients for hydration.

  • Freshwater Mammals:

    • Have shorter nephron loops.

    • Produce urine with lower concentration of solutes to excrete excess water.

  • Birds:

    • Primarily produce uric acid instead of urea, which is highly water-efficient.

Gas Exchange

  • Definition:

    • Cellular respiration needs O2 and produces CO2.

    • Gas exchange is the uptake of O2 and discharge of CO2 to the environment.

    • Occurs via diffusion from high to low partial pressure

    • Must diffuse across a moist respiratory surface to be used

Mechanisms of Gas Exchange

  • Influencing Factors:

    • Organs and mechanisms vary with environmental conditions.

    • Surface area, concentration gradients, and liquid mediums affect efficiency.

Gas Exchange in Water

  • Challenges:

    • Water contains less O2 than air.

  • Aquatic Organisms:

    • Most rely on simple diffusion; gills enhance efficiency:

    • Gills provide a larger surface area for gas exchange.

    • Fish utilize countercurrent flow to maximize gas exchange efficiency.

Gas Exchange on Land: Insects

  • Tracheae System:

    • Consists of air tubes branching throughout the body.

    • Tracheae connect to the environment through spiracles.

    • O2 and CO2 exchange occurs directly at cells, independent of the circulatory system.

Gas Exchange on Land: Tetrapods

  • Lungs:

    • Serve as primary gas exchange organs in most tetrapods (except for certain salamanders).

Maximizing Gas Exchange: Breathing

  • Strategies to sustain high O2 and low CO2 concentration:

    • Variations in structure and efficiency across species.

Breathing in Amphibians

  • Mechanism:

    • Lower lung surface area compared to amniotes.

    • Use positive pressure breathing:

    • Floor of the throat lowers to push air from the mouth into lungs.

Breathing in Birds

  • Air Sac System:

    • Air sacs facilitate continuous air flow, preventing mixing of fresh and CO2-rich air.

    • Four phases of breathing: two inhalations and two exhalations required for air to move through the system.

Breathing in Mammals

  • Negative Pressure Breathing:

    • Muscular contractions expand the thoracic cavity, lowering lung pressure.

    • Results in inhalation of air, and relaxation of muscles reduces volume for exhalation, forcing air out.

Distributing Oxygen: Hemoglobin

  • Structure of Hemoglobin:

    • Composed of 4 subunits with heme groups; each iron atom can bind one O2 molecule.

    • Binding O2 increases hemoglobin's affinity for additional O2.

    • CO2 production promotes unloading of O2 from hemoglobin, influenced by changes in blood pH.

Removing Carbon Dioxide

  • Nature of CO2:

    • Byproduct of cellular respiration; primarily converted to bicarbonate (HCO3-) in red blood cells.

    • Travels to lungs, converting back to CO2 for exhalation.

Regulating Gas Exchange in Mammals

  • Control Mechanism:

    • Medulla oblongata regulates breathing.

    • Changes in cerebrospinal fluid pH relate to CO2 levels influenced by metabolic activity.

    • Increased activity leads to increased breathing rate due to lowered pH.