6.4 Gas Exchange ₊˚⊹♡

• Oxygenated blood is carried away from the lungs through pulmonary veins.
• The process of gas exchange happen by diffusion
• • In mammals the conditions for diffusion at the respiratory surface are improved by:

  1. A blood circulation system 
  2. A respiratory pigment, which increases the oxygen-carrying ability of the blood.
• during inspiration(inhalation) diaphragm contract
• during inspiration(inhalation) abdominal muscle relax
• during inspiration(inhalation) external intercostal muscle contract
• during inspiration(inhalation) internal intercostal muscle relax
• during inspiration(inhalation) volume of the thoracic cavity increases
• during inspiration(inhalation) air pressure of the thorax falls below atmospheric pressure
• during inspiration(inhalation) air flow is moving in
• during expiration(exhalation) diaphragm relax
• during expiration(exhalation) abdominal muscle contract
• during expiration(exhalation) external intercostal muscle relax
• during expiration(exhalation) internal intercostal muscle contract
• during expiration(exhalation) volume of the thoracic cavity decreases
• during expiration(exhalation) air pressure of the thorax rises above atmospheric pressure
• during expiration(exhalation) air flow is moving out
• label these

  A) trachea

  B) bronchus

  C) bronchiole

  D) alveoli

  E) diaphragm

  
• The alveoli is protected by two types of cells:

  1. Macrophages (dust cell), the main detritus-collecting cells of the body- these originate from bone marrow stem cells and are dispersed about the body in the blood circulation

  Surfactant cells (type II pneumocytes) - these produce a detergent-like mixture of lipoproteins and phospholipid-rich secretion that lines the inner surface of the alveoli.
• Surface area of alveoli:

  A huge surface area for gaseous exchange
• Wall of alveoli (of Type I pneumocytes):

  Very thin, flattened (squamous) epithelium means the diffusion pathway is short
• Capillary supply to alveoli:

  A network of capillaries around each alveolus (supplied with deoxygenated blood from the pulmonary artery and draining into pulmonary veins) maintains the concentration gradient of O2 and CO2
• Surface film of moisture:

  O2 dissolves in water lining the alveoli; O2 diffuses into the blood in solution