C3.3 - Mechanisms of Breathing

Breathing

• breathing / ventilation: the process of moving air into and out of your lungs
• Air will flow from high pressure to low pressure
• Associated muscles:
  • intercoastal muscles (between ribs)
  • diaphragm
• Statistics
  • Humans breathe 15 times/min. on avg.
    • >21,000 breaths / day
  • Lungs about size of football
  • Total capacity of lungs: 6 L avg.
  • 0.6 L of volume used on normal breath
  • Humans can use 20x more oxygen when exercising compared to rest

Breathing Mechanism and Diaphragm

• diaphragm: large dome-shaped sheet of muscle that forms bottom wall of chest cavity
• Inhalation
  • Intercoastal muscles contract lifting rib cage up and out
  • Diaphragm contracts and pulls downwards
  • Increases volume of lungs → reduces air pressure in alveoli
  • Air moves in from high pressure to low pressure
• Exhalation
  • Intercoastal muscles relax, rib cage returns to resting position
  • Diaphragm relaxes and moves upward to normal position
  • Decreases volume of lungs → increases air pressure in alveoli
  • Air moves out from high pressure to low pressure

Gas Exchange Composition

• Inhaled air
  • 20.94% oxygen
  • 0.04% carbon dioxide
  • 79.02% nitrogen and other gases
• Exhaled air
  • 16.49% oxygen
  • 4.49% carbon dioxide
  • 79.02% nitrogen and other gases

Lung Capacity

Spirometer: Device used to measure lung capacity

• tidal volume (TV): air inhaled and exhaled in a normal breath.
• inspiratory reserve volume (IRV): the additional volume of air that can be taken in
• expiratory reserve volume (ERV): the additional volume of air that can be forced out of the lungs
• vital capacity (VR): total volume of air that can be moved in or out of the lungs
• residual volume: amount of gas that remains in the lungs no matter what
• respiratory efficiency: rate at which oxygen can be transferred to the blood

$$\begin{array}{c}\mathrm{VR}=\mathrm{TV}+\mathrm{IRV}+\mathrm{ERV}\end{array}$$

Counter-Current Flow: Fish Gills

• Blood vessels of lining gills flow in opposite direction to movement of water
• Increases fish gill efficiency by using dissolved gas concentration gradient
• Most oxygen depleted blood meets most oxygen depleted water
• Oxygen diffuses in by simple concentration gradient
• Blood continues to pick up oxygen as concentration increases

Counter-Current Flow: Birds

• No alveoli or diaphragm
• Anterior and posterior air sacs branch out from lungs like bellows
• No gas exchange occurs in air sacs
• parabronchi: tubes acting as respiratory surfaces in birds
• Expansion and contraction of air sacs ventilate lungs
• Air circulates through lungs and air sacs
• Fresh air in contact w/ lungs at all times
• More efficient than humans