Respiratory

• Respiration


  All processes of gas movement and metabolism
• Internal / Cellular Respiration

  Intracellular metabolic processes in mitochondria which use O2 and produce CO2 to derive energy from nutrient molecules
• External Respiration


  Sequence of events involved in exchange of O2 and CO2 between external environment and cellular mitochondria
• Mitochondria


  • Cell "powerhouse"
  • Site of internal/cellular respiration
• External Respiration


  1. Breathing movements to ensure supply

  2. Diffusion of O2 and CO2 across respiratory surfaces

  3. Bulk transport of gases in blood: O2 on proteins, CO2 as bicarbonate

  4. Diffusion of O2 and CO2 across capillaries between blood and mitochondria
• Fick's Law


  Gas diffusion follows Fick's Law for partial pressure, not concentration
• Partial pressure


  • In mixture of gases, individual gas independently exerts pressure known as partial pressure (e.g. PO2)
• Factors affecting diffusion


  • Diffusion changes linearly with surface area, coefficient D, inversely with distance
• External respiration


  • Must meet animal's O2 demands
  • Depends on (i) size, (ii) metabolism and (iii) habitat
• Simple exchange animals


  • Small
  • Thin
  • Sluggish
• Animals with enhanced transport and exchange


  • Large
  • More active
  • Low O2 environments
• Respiratory Organs


  • Skin
  • Gills
  • Lungs
  • Gas Bladders
• Gills


  • Vg/Q = 10-20 (ventilation : perfusion ratio)
  • External: larvae of lungfishes, some teleosts
  • Internal: amphibians
• Lungs


  • Va/Q = 1
• Cutaneous gas exchange


  Cutaneous = "of the skin"
• Tracheal System


  • Air tubes throughout the body
• Water Breathers


  • Problems: Less O2 in water than air, water viscosity, lower diffusion rates, decreased solubility with temperature, wide habitat variation
  • Solutions: Gills highly branched + very efficient (90% O2 extraction), Increased ventilation, Countercurrent flow enhances gas gradients in fish: gill lamellae blood always encounters water with higher O2
• Air Breathers


  • Problems: Do not need to be as efficient exchange surfaces BUT need to prevent drying out
  • Solutions: Snails/slugs – moist habitats, Insects use tracheae, actively ventilated by air sacs and body movements, Vertebrates – skin + lungs
• Tracheae in a Grasshopper


  • Tracheae lined with moist, thin epithelium forming respiratory surface for gas exchange
• Mammals use less air than fish do water
• Ventilation / Perfusion


  Mammals = 1, Fish = 10
• Mammalian Lungs


  • Airways terminate in alveoli
  • Involved in both ventilation and gas exchange (c.f. reptiles and birds)
  • Lungs inflated and deflated by changes in pressures produced by respiratory muscles (e.g. diaphragm, ribs)
• Human Respiratory Tract


  • Trachea
  • Primary Bronchi
  • Secondary Bronchi
  • Tertiary Bronchi
  • Bronchioles
  • Lungs
• Rat Dissection


  • Trachea
  • Lungs
  • Lungs
  • Heart
• Mammalian Lung Alveoli


  • Surfactants required to keep from sticking shut
• Respiratory surface vs body weight


  Non-smoker vs Smoker
• Negative Pressure Breathing


  1. Inhalation

  2. Exhalation
• Breathing movements


  1. Front View: Inhalation, Exhalation

  2. Side View: Inhalation, Exhalation
• Lungs


  • Stretched to fill thorax: air pressures important in respiratory mechanics
• Regulation of Ventilation


  • Ventilation of airways regulated to match perfusion
  • Breathing in mammals by negative feedback system
  • Peripheral chemosensors in arteries/brainstem
  • Multiple regulatory centres in brainstem
  • Effector breathing muscles
• PO2


  Important in homeostasis in water breathers
• PCO2 and H+


  Important in homeostasis in air breathers
• Haemoglobin


  • 4 globin subunits, each with 1 haem group
  • Fe in haem binds oxygen: Reversible
  • ~250 million molecules of haemoglobin per rbc
• Haemoglobin Binding


  • Affected by Temperature, pH, phosphate, CO2
• O2-Haemoglobin Curve


  Sigmoidal curve arises from Hb subunit "co-operativity"
• The Bohr Effect


  Haemoglobin loses affinity for oxygen with decreasing pH
• P50


  Partial pressure of oxygen when 50% of respiratory protein is saturated
• High Altitude Adaptation


  • Llama, Andes, S.America: Haemoglobin adapted to lower O2 levels
• O2 stores of diving organisms


  • Generally, majority of O2 stored in blood
• Icefish


  • Only vertebrates lacking red blood cells and haemoglobin
  • Survives with large heart, low metabolic rate and high O2 solubility at low temp.
  • Less than 10% of normal O2 carrying capacity (dissolved in plasma)