NE

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