Breathing/Ventilation

• Ventilation in large organisms helps achieve the highest rate of diffusion in gas exchange as possible.
• Ventilation in humans helps achieve a high concentration of oxygen in the alveoli and a low concentration of carbon dioxide in the alveoli which maintains a very steep concentration gradient.
• In humans, ventilation involves the action of two sets of muscles, the intercostal muscles which lie between the ribs, and the diaphragm which separates the thoratic cavity and the abdomen.
• In ventilation the two sets of muscles work together to change the volume of the thorax which in turn changes the air pressure of the lungs; drawing air in or out.
• the external intercostal muscles are involved in regular breathing ut internal intercostal muscles are involved in heavier breathing.
• During inhalation, the external intercostal muscles contract, pushing the ribs upwards and upwards. The diaphragm also contracts, pushing the abdominal wall downwards. Both of these increase the volume of the thorax: decreasing air pressure in the lungs causing it to be less than atmospheric pressure and air to rush in.
• Because inhalation involves muscle contraction, it is an active process as it requires energy.
• Exhalation is mostly a passive process however when the internal intercostal muscles are involved and contract, energy is required.
• In exhalation, external intercostal muscles relax, returning the ribs to their original position. The diaphragm also relaxes, returning to its domed shape. These both decrease the volume of the thorax which increases air pressure in the lungs higher than atmospheric pressure, causing air to be pushed out.
• During exhalation, elastic fibres between alveoli also recoil in a process called elastic recoil which helps push air out of the airways.
• The lungs are surrounded by pleural membranes with pleural fluid between them which acts as a lubricant during changes in air volume within the lungs.
• The internal and external intercostal muscles are antagonistic because when one contracts, the other relaxes.
• Pulmonary ventilation = tidal volume x ventilation rate
• Pulmonary ventilation is a measure of lung function - it is the volume of air taken into the lungs in one minute.
• The tidal volume is the volume of air that moves in and out of the lungs with each resting breath.
• Ventilation rate is the number of breaths per minute.
•  Tidal volume of a male is 500cm3, his ventilation rate is 6dm3 per minute. How many breaths does he take per minute?

  6dm^3 = 6,000cm^3

  6000/500 = 12 breaths per minute.
• A males breathing rate is 20 breaths per minute, his pulmonary ventilation rate is 15dm3 per minute. What is his tidal volume?

  15dm3 = 15000 cm3

  15000/20 = 750cm3 per breath
• In one breathing cycle, the lungs only lose some of it's oxygen content. This allows mouth to mouth to be effective. 21% of inhaled air is oxygen but 15% of exhaled air is oxygen.
• The vital capacity is the largest volume of air which can be breathed in.
• The inspiratory reserve volume is the maximum volume of air which can be breathed in over and above normal inhalation.
• The expiratory reserve volume is the maximum volume of air you can force out of your lungs over and above the normal tidal volume of air you breath out.
• The residual volume is the volume of air which is left in your lungs when you have exhaled as hard as possible, this stops lungs from collapsing.
• The total lung capacity is the sum of your residual volume and your vital capacity.
• The residual volume cannot be measured.
• Peak flow meters measure the rate at which air is expelled from the lungs.
• A vitalograph is a more complex version of the peak flow meter and produced a graph about the amount of air breathed out and how quickly it is expelled.
• How the spirometers works:

  • static lower half of tank is full of water, mobile upper half is full of oxygen
  • Breath out into tank and the upper half will rise
  • Breath in from tank and upper half will wall
  • Trace marker is attached to the upper half and this movement produces a graph.
• The spirometers trace slants down with successive cycles because oxygen is removed from the spirometer for respiration and carbon dioxide that is expelled is absorbed by soda lime. This means the chamber doesn't rise as high.