Gas Exchange

• Why do we need a respiratory system
  • Need O2
  • Aerobic cellular respiration
  • Make ATP
  • Need CO2 out
  • Waste products from the Krebs cycle
• Gas Exchange
  • O2 and CO2 exchange between environment and cells
  • Need moist membrane
  • Need high surface area
• Optimizing Gas Exchange
  • High surface area
  • Maximizing rate of gas exchange
  • CO2 and O2 move across cell membrane by diffusion
    • Rate of diffusion is proportional to surface area
  • Moist Membranes
  • Moisture maintains cell membrane structure
  • Gases diffuse only dissolved in water
• Evolution of Gas Exchange Structures
  • Aquatic organisms
  • External system with lots of surface area exposed to aquatic environment
  • Terrestrial
  • Moist internal respiratory tissues with lots of surface area
• Counter Current Exchange System
  • Water carrying gas flows in one direction, blood flows in the opposite direction
• Gas Exchange on Land
  • Advantages
  • Air has many advantages over water
    • Higher concentration of O2
    • O2 and CO2 diffuse much faster through air
    • Respiratory surfaces exposed to air do not have to be ventilates as thoroughly as gills
    • Air is much lighter than water and therefore much easier to pump
    • Expend less energy moving air in and out
  • Disadvantages
  • Keeping large respiratory surface moist causes high water loss
    • Reduce water loss by keeping lungs internal
• Terrestrial Adaptations
  • Tracheae
  • Air tubes branching throughout the body
  • Gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system
• Alveoli
  • Gas exchange across thin epithelium of millions of alveoli
• Negative Pressure Breathing
  • Breathing due to changing pressures in lungs
  • Air flows from higher pressure to lower pressure
  • Pulling air instead of pushing it
• Mechanics of Breathing
  • Air enters nostrils
  • Filtered by hairs, warmed, and humidified
  • Sampled for odors
  • Pharynx → glottis → larynx (vocal cords) → tracheae (windpipe) → bronchi → bronchioles → air sacs (alveoli)
  • Epithelial lining covered by cilia and thin film of mucus
  • Mucus traps dust, pollen, and particulates
  • Beating cilia moves mucus upward to pharynx, where it is swallowed
• Autonomic Breathing Control
  • Medulla sets rhythm and pons moderates it
  • Coordinate respiratory, cardiovascular systems and metabolic demands
  • Nerve sensors in walls of aorta and carotid arteries in the neck detect O2 and CO2 in blood
• Medulla Monitors Blood
  • Monitors CO2 level of blood
  • Measures pH of blood and cerebrospinal fluid bathing the brain
  • If pH decreases then increase depth and rate of breathing and excess CO2 is eliminated in exhaled air
• Breathing and Homeostasis
  • Homeostasis
  • Keeping the internal environment of the body balance
  • Need to balance O2 in and CO2 out
  • Need to balance energy production
  • Exercise
  • Breathe faster
    • Need more ATP
    • Bring in more O2 and remove more CO2
  • Disease
  • Poor lung and heart function
    • Breathe faster
    • Need to work harder to bring in O2 and remove CO2
• Hemoglobin
  • Why use a carrier molecule
  • O2 is not soluble enough in water for animal needs
    • Blood alone could not provide enough O2 to animal cells
    • Hemocyanin in incest
    • Copper
    • Hemoglobin in vertebrates
    • Iron
  • Reversibly binds O2
  • Loading O2 at lungs or gills and unloading cells
• Cooperatively in Hemoglobin
  • Binding O2
  • Binding O2 to first subunit causes shape change to other subunits
    • Conformational change
  • Increasing attraction to O2
  • Releasing O2
  • When first subunit release O2, causes shape change to other subunits
    • Conformational change
  • Lowers attraction to O2
• O2 dissociation curve for hemoglobin
  • Drop in pH lowers affinity of Hb for O2
  • Active tissue lowers blood pH and induces Hb to release for O2
  • Increase in temperature lowers affinity of Hb for O2
  • Active muscle produces heat
• Transporting CO2
  • Dissolved in blood plasma as bicarbonate ion
• Releasing CO2 from blood and lungs
  • Lower CO2 pressure at lungs allow CO2 to diffuse out of blood into lungs
• Adaptation for pregnancy
  • Mother and fetus exchange O2 and CO2 across placenta tissue
• Fetal Hemoglobin
  • Fetal hemoglobin had greater attraction to O2 than hemoglobin
  • Low % O2 by time blood reaches placenta
  • Fetal hemoglobin must be able to bind O2 with greater attraction than maternal Hemoglobin

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