Gas exchange in humans

• ventilation


  process which moves air into and out of the lungs
• Inspiration - it’s an active process so requires energy
• Normal expiration is passive
• Forces expiration - occurs due to expel of extra air - external intercostal muscles contract, pulling rib cage further down and in - two sets of intercostal muscles opposing
• Goblet cells - secrete mucus in the airway linings to trap particles
• Ciliated epithelium - cilia waft dust and bacteria caught in mucus up to the throat to be swallowed
• Smooth muscle — controls diameter of of trachea, bronchi and bronchioles and allows expansion and increased airflow during exercise
• Elastic fibres — when breathing in lungs inflate as airways widened due to elastic fibres stretching - recoil to push air out during exhalation
• Cartilage — rings of cartilage in trachea and bronchi support airways and prevent collapse when breathing in and pressure falls, strong flexible tissue provides support
• Large surface area due to millions of tiny air sacs called alveoli and large car pillars network where exchange occurs
• Very thin walls (alveoli epithelium and blood capillary endothelium each one cell thick) so short diffusion path
• Good blood supply - fine network of capillaries and blood flow - look constantly arrives at alveolus oxygen poor and carbon dioxide rich - maintains diffusion gradient
• Ventilation - maintains diffusion gradient - fresh oxygen rich and carbon dioxide poor - air constantly brought into lungs
• Moist lining in alveoli to dissolve gases
• Pulmonary ventilation rate = tidal volume x breathing rate