Respiratory system

• Respiratory system


  The system responsible for the exchange of gases (oxygen and carbon dioxide) between the body and the environment
• Major functions of the respiratory system

  • To supply oxygen to the body and remove carbon dioxide
• Major organs of the respiratory system

  • Nose
  • Pharynx
  • Larynx
  • Trachea
  • Main (primary) bronchi
  • Lobar bronchi
  • Terminal bronchioles
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveolar sacs
  • Lungs
• Exchange of gases during external and internal respiration

  1. External respiration: Exchange of gases between the alveoli and the blood

  2. Internal respiration: Exchange of gases between the blood and the body tissues
• Volumes of air exchanged during pulmonary ventilation

  • Tidal volume
  • Vital capacity
• Mechanisms that regulate respiration

  • Respiratory center in the brain stem
  • Carotid and aortic bodies that monitor blood oxygen and carbon dioxide levels
• Structures of the upper respiratory tract

  • Nose
  • Pharynx
  • Larynx
• Structures of the lower respiratory tract

  • Trachea
  • Main (primary) bronchi
  • Lobar bronchi
  • Terminal bronchioles
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveolar sacs
  • Lungs
• Conducting zone


  The part of the respiratory system that brings air into and out of the lungs
• Respiratory zone


  The part of the respiratory system where gas exchange occurs, starting with the respiratory bronchioles
• Functions of the respiratory system

  • Filtration of inspired air
  • Warming of inspired air
  • Humidification of inspired air
  • Acid-base balance
  • Conversion of Angiotensin I to Angiotensin II
• Goblet cells


  • Secrete mucus to trap dust and other particles in the air
• Ciliated columnar cells


  • Move the trapped material toward the pharynx where it can be swallowed or spit out
• Alveolar type I pneumocytes


  • Line the alveoli
• Alveolar type II pneumocytes


  • Secrete pulmonary surfactant
• Pulmonary surfactant


  A mixture of phospholipids and proteins that reduces surface tension and allows expansion of the alveoli during respiration and prevents their collapse during expiration
• Each alveolus has an abundance of pulmonary capillaries, allowing efficient gas exchange between the air and the blood
• Extensive branching of alveoli produces a large surface area for gas exchange between air and blood
• Alveolar and capillary walls are thin, permitting rapid diffusion of gases
• Pulmonary ventilation


  The process of moving air into and out of the lungs
• Gas exchange


  The exchange of oxygen and carbon dioxide between the air in the alveoli and the blood in the pulmonary capillaries
• Gas transport


  The transport of oxygen and carbon dioxide in the blood
• Cellular respiration


  The metabolic process by which an organism obtains energy through the reaction of oxygen with glucose
• Mechanism of pulmonary ventilation

  1. Air moves through the conducting zone by flow

  2. Diffusion of gases occurs in the respiratory zone where air flow velocity is reduced

  3. A pressure gradient between the atmosphere and the alveoli is generated to allow inflow and outflow of air
• Pleura


  The sac/membrane that lines the inner surface of the thoracic cavity and covers the outer surface of the lung, playing a central role in generating the pressure gradient for pulmonary ventilation
• Intrapleural pressure


  The pressure inside the pleural sac, which is negative (sub-atmospheric) due to the inward elastic forces of the lung and the outward elastic recoil of the chest wall
• Mechanism of inspiration


  Contraction of the diaphragm and intercostal muscles increases the volume of the thoracic cavity, decreasing the intrapleural pressure and causing air to flow into the lungs
• Mechanism of expiration


  Relaxation of the diaphragm and intercostal muscles decreases the volume of the thoracic cavity, increasing the intrapleural pressure and causing air to flow out of the lungs
• Dalton's law


  The total pressure of a gas mixture is equal to the sum of the partial pressures of each individual gas
• Partial pressure


  The pressure that a particular gas in a mixture would exert independently
• Dry air at sea level contains 20.93% oxygen, 0.04% carbon dioxide, and 79.03% nitrogen
• In the lungs, the concentration gradients favor the inward diffusion of oxygen and the outward diffusion of carbon dioxide, but these gradients are reversed at the interface of the blood and active cells due to metabolic activities
• Oxygen transport in the blood

  Oxygen is transported both dissolved in the plasma and bound to hemoglobin
• Carbon dioxide transport in the blood

  Carbon dioxide is transported dissolved in the plasma, as bicarbonate, and as carbamino compounds bound to proteins
• Respiratory center in the brain stem

  • Generates the rhythmical nerve impulses that control breathing movements
• Carotid and aortic bodies


  • Sensory organs that monitor arterial blood oxygen and carbon dioxide levels and modulate the basic breathing pattern
• A severe reduction in arterial oxygen concentration can stimulate hyperventilation
• Small changes in blood carbon dioxide content quickly trigger changes in ventilation rate