Gas exchange

• ventilation is the exchange of air between the atmosphere and the lungs
• ventilation maintains oxygen and carbon dioxide concentration gradients between the alveoli and the blood flow in adjacent capillaries
• oxygen is consumed by cells during cellular respiration, leaving carbon dioxide as the waste product
• within the alveoli, oxygen levels stay at high concentrations, whereas carbon dioxide concentrations are low
• the lungs function as the ventilation system is to cycle fresh air into the alveoli
• oxygen is constantly being removed from the alveoli into the bloodstream
• air is carried to the lungs in the trachea and bronchi and then to the alveoli and the bronchioles
• alveolus are the site of gas exchange, for this they have many features:

  • thin epithelial
  • rich capillary network
  • spherical shape to maximise surface area
  • internal fluid as dissolved carbon dioxide is easier to diffuse
• the respiratory system:

  • air enters the respiratory system via nose or mouth and passes through the pharynx to the trachea
  • air travels down the trachea which divides into two bronchi, which connect to the lungs
  • Within the right lung, there are three lobes whereas in the left there are two due to the heart
  • within each lung the bronchi divide into smaller bronchioles to increase surface area
  • each bronchiole terminates with an air sac called alveoli
• as exercise intensity increases, the demand for gas exchange increases and therefore ventilation increases
• A spirometer measures the amount and/or flow at which air can be inhaled or exhaled
• an increase in the ventilation rate increases the number of breaths so that more gas exchange takes place
• an increase in tidal volume increases the volume of air in and out per breath
• ventilation can be measured using observations, chest belts and mostly spirometers
• pnuemocytes are alveolar cells that line the inside of the alveoli and comprise of the majority of inner space of the lung
• type 1 pneumocytes are involved in gas exchange between alveoli and the capillaries. They are extremely thin to carry out gas exchange
• type 2 pneumocytes are responsible for the secretion of pulmonary surfactant which reduces the surface tension in alveoli
• pulmonary surfactant creates a moist surface inside the alveoli to prevent adhering by reducing surface tension
• type 1 pneumocytes are amitotic and cant replicate but type 2 are able to differentiate into type 1
• inspiration: when muscles increase the volume of the chest
• expiration: when muscles decrease the volume of the chest
• when volume in the thoracic cavity increases, the pressure in the thorax decreases. When the pressure is less than the pressure of the atmosphere then air will move into the lung
• the principle of Boyles law states that pressure is inversely proportionate to volume
• inspiration is caused by the diaphragm muscles contracting to flatten and increase the volume in the thoracic cavity. The external intercostal muscles contract to pull the ribs up and outwards
• expiration is caused by the diaphragm relaxing, decreasing the volume in the thoracic cavity. The intercostal muscles contract to bring the ribs inward and down. The abdominal muscles contract to push the diaphragm up during forced exhalation
• gas exchange is the exchange of oxygen and carbon dioxide between the alveoli and blood stream
• cell respiration is the release of energy from organic molecules
• the main two lung disorders are lung cancer and emphysema
• causes of lung cancer:

  • pollution
  • radiation
  • age
  • genes
  • occupation
  • asbestos
  • smoking
• symptoms of lung cancer:

  • coughing blood
  • wheezing
  • chest pain
  • respiratory distress
• Emphysema is when the walls of the alveoli lose their elasticity due to damage
• causes of emphysema:

  • smoking- causes damage to tissue which leads to the promotion of phagocytes which produce enzymes called elastase. This enzyme can be inhibited by alpha 1-antitrypsin but not at high concntrations of elastase
• symptoms of emphysema:

  • shortness of breath
  • phlegm
  • expanding of the ribcage
  • increases susceptibility to infection