lung structure and gas exchange

• lung diagram:

  A) nasal cavity

  B) trachea

  C) lung

  D) bronchus

  E) brochiole

  F) alveoli

  G) blood capillaries

  H) intercostal muscles

  I) ribs

  J) diaphragm

  
• cartilage - provides strength to trachea and bronchus, holds the airway open to prevent the collapse of airway when air pressure falls
• surfactant - phospholipid layer which maintains moisture but reduces surface tension to stop alveoli collapsing when air pressure falls
• smooth muscle - can contract to constrict the airways
• goblet cells - secrete mucus which traps particles of dust and bacteria which are breathed into the lungs
• ciliated epithelial cells - beats regularly to move mucus up the airways towards the mouth to be removed. Helps keep the airways clear and prevent infections. contain lots of mitochondria to provide energy required to move cilia
• elastin - allows lung tissue to stretch when breathing in, recoil when breathing out to help force air out of the lungs. Allows alveoli to return to original shape after exhaling
• squamous epithelium - gives a short diffusion distance pathway for oxygen and carbon dioxide in the alveoli
• thin alveolar epithelium and capillary endothelium are thin to shorten diffusion distance
• a large number of alveoli increase surface are for gas exchange
• capillaries that surround the alveoli are narrow to increase time for diffusion
• large number of capillaries around alveoli to maintain a steep concentration gradient
• constant ventilation of air in and out the lungs to maintain a steep concentration gradient