resp

• Respiration

  Physiological process of breathing in oxygen and breathing out carbon dioxide for the liberation of energy that is required for the sustenance of living cells

  
• Phases of respiration

  • Inspiration (inhalation)
  • Expiration (exhalation)
• Types of respiration

  • Internal respiration
  • External respiration
• Functions of respiration


  • Ventilation (breathing)
  • Gaseous exchange between air and blood, and between blood and other body tissues
  • Oxygen utilization by the tissues for energy liberation

  
• Conducting zone


  Anatomical structures through which air passes before reaching the respiratory zone. Gaseous exchange does not occur in this zone.

  
• Respiratory zone


  Where gaseous exchange occurs
• Alveolus (plural = alveoli) is a sac-like structure that confers on the respiratory zone the ability to allow for gaseous exchange

  
• Structures of the anatomical (conducting) zone


  • Mouth
  • Nose
  • Pharynx
  • Larynx
  • Trachea
  • Primary bronchi
  • Successive branchings of the bronchioles up to (and including) the terminal bronchioles

  
• Structures of the respiratory zone

  • Respiratory bronchioles
  • Alveoli

  
• The exchange of gases in the lungs occur across an estimated 300 million tiny air sacs known as alveoli
• The enormous number of alveoli provides a large surface area (60 to 80 square meters) for diffusion of gases

  
• The diffusion rate across the alveoli is further increased by the fact that each alveolus is only one cell-layer thick
• Air-blood barrier


  Structural barrier of about 2 μm thick, between air and blood, made up of the alveolar cell membrane and the pulmonary capillary endothelial cell membrane
• The basement membranes of type 1 alveolar cells and capillary endothelial cells fuse in such a way that the diffusion distance between them is only about 0.3 μm thick
• The alveolar wall isn't fragile but is strong enough to withstand high stress during heavy exercise and high lung inflation due to the fused membranes of the air-blood barrier which are composed of type IV collagen proteins
• Types of alveolar cells

  • Type I alveolar cells (95 - 97% of total lung alveolar population), primarily dedicated to gaseous exchange
  • Type II alveolar cells (remaining percentage), dedicated for the secretion or production of pulmonary surfactant

  
• Functions of the anatomical (conducting) zone

  • Warming and humidification of inspired air
  • Filtering and cleaning
• The mucus lining of the conducting zones are moved at a rate of 1 to 2cm per minute by cilia projections from the top of the epithelial cells that lines the conducting zone
• There are about 300 cilia per cell that beat in a coordinated fashion to move mucus toward the pharynx, where it can either be swallowed or expectorated
• Particles larger than 6 μm do not normally enter the respiratory zone of the lungs

  
• The alveoli are normally kept clean by the action of resident macrophages
• Respiratory protective reflexes

  • Sneezing reflex
  • Coughing reflex
  • Swallowing or deglutition reflex
• Pleural membranes


  Two layers of wet epithelial membranes that envelop the structures in the central region of the thoracic cavity
• Parietal pleural

  Superficial layer that lines the inside of the thoracic wall

  
• Visceral pleural

  Deep layer that covers the surface of the lungs
• Normally, the lungs fill the thoracic cavity so that the visceral pleural constantly pushes against the parietal pleural, with little or no air between these pleural membranes under physiological conditions

  
• The intra-pleural space can become a real space if the visceral and parietal plurae separate when a lung collapses

  
• Lung compliance


  Change in lung volume per change in trans-pulmonary pressure (∆V/∆P)

  
• Lung elasticity

  Tendency of the lungs to return to its initial size after being distended
• Surface tension

  Phenomenon at the surface of liquid that is caused by intermolecular forces
• Elastic resistance and the surface tension exerted by the alveolar fluid are forces that act to resist lung distension
• Pneumothorax

  Presence of gas in the intra-pleural space with a resultant collapse of the lungs (one or both lungs, depending on the degree of chest injury that allows for air leak into the intra-pleural space)

  
• Atelectasis


  Deflation or collapse of the alveoli or lungs

  
• Types of atelectasis


  • Compressive atelectasis
  • Resorptive/obstructive atelectasis
  • Contraction atelectasis

  
• Pulmonary surfactants


  Substances secreted by type II alveolar cells that act on the surface of alveolar fluids to prevent alveolar and lung collapse following an elastic recoil

  
• Pulmonary surfactants consist of phospholipids, primarily phosphatidylcholine and phosphatidylglycerol, together with hydrophobic surfactant proteins
• Pulmonary surfactants reduce the hydrogen bonds between water molecules at the surface to bring about a drastic reduction of surface tension, making the surface tension of the alveoli negligible

  
• The ability of surfactant to lower surface tension improves as the alveoli get smaller during expiration, as the surfactant molecules become more concentrated
• Surfactant prevents the alveoli from collapsing during expiration, allowing a residual volume of air to remain in the lungs

  
• Surfactants

  Consist of phospholipids, primarily phosphatidylcholine and phosphatidylglycerol, together with hydrophobic surfactant proteins. They are interspersed between water molecules and water-air interface thereby reducing the hydrogen bonds between water molecules at the surface to bring about a drastic reduction of surface tension.