Human respi

• Functions of the respiratory system

  • Oxygenation of blood and removal of carbon dioxide
  • Exchange of heat with the environment by evaporation of water and forced convection
  • Production of sounds, such as talking and singing

  
• Lungs


  The center of the respiratory system, composed of two upside-down cones in the chest

  
• Parts of the respiratory system

  • Upper respiratory tract: mouth and nose, nasal cavity, pharynx, larynx
  • Lower respiratory tract: lungs, trachea, bronchi

  
• Trachea and bronchi


  • Combine to form the bronchial tree
  • Bronchi branch off into smaller bronchioles, with almost 30,000 bronchioles in each lung
• Ribs and diaphragm muscle


  • Help the lungs expand and contract as a person breathes

  
• Breathing


  1. Air enters through mouth and nose, travels through lungs to alveoli

  2. Oxygen and carbon dioxide exchange happens in the alveoli

  
• Breathing


  • Stretches the lung-chest system, causing airflow
  • Requires about 1% of basal energy requirements, can be increased during exercise or illness
  • Normal resting capacity is about 6 liters per minute, can be increased to 150 liters per minute

  
• Inhalation


  Chest expands, diaphragm moves downward, pressure drops

  
• Exhalation


  Chest contracts, diaphragm rises, pressure rises
• Cohesive and adhesive forces in lung liquids

  • Adhesive force pulls lungs open during inhalation
  • Surface tension in alveoli makes lungs elastic, allowing expansion and contraction

  
• Boyle's Law


  Relationship between volume and pressure in a gas at constant temperature: P = k/V

  
• Boyle's Law: P1V1 = P2V2
• Pressure gradient


  Air flows from higher pressure to lower pressure, driving pulmonary ventilation
• Exhalation is a passive action, with no energy required to push air out of the lung</b>
• Coughing


  Rapid expulsion of air from the lungs accompanied by a sharp sound, intended to clear airways of obstructions
• Alveoli


  • About 200 μm in diameter, with walls about 0.4 μm thick
• Gas transfer in respiratory system

  Blood passing through capillaries adjacent to alveoli exchanges gases with air in the alveoli by diffusion through capillary and alveolar walls

  
• Dalton's Law of Partial Pressures

  Total pressure due to gases is equal to the sum of the partial pressures due to each gas

  
• If air in lungs has oxygen partial pressure of 105 mm Hg and blood has 40 mm Hg, then oxygen will be transferred from air to blood

  
• The figure shows estimated partial pressures of oxygen and carbon dioxide in the cardio-pulmonary system