MID100

• Respiratory system


  • Facilitates gas exchange
  • Protects body from foreign matter such as particulates and pathogens
• Respiration


  1. Ventilation or breathing

  2. Alveolar-capillary gas exchange

  3. Transport of oxygen and carbon dioxide between tissues and lungs

  4. Movement of oxygen and carbon dioxide between systemic capillaries and tissues
• Upper respiratory system


  Mouth, nose, pharynx, larynx
• Lower respiratory system


  Trachea, lungs, bronchi, bronchioles, alveoli, pulmonary capillary network, pleural membranes
• Nose


  • Warms, humidifies, and filters air
  • Hairs trap large particles
  • Nasal turbinates and septum filter smaller particles
  • Sneeze reflex clears nasal passages
• Pharynx


  • Shared pathway for air and food
  • Nasopharynx and oropharynx have lymphoid tissue to trap and destroy pathogens
• Larynx


  • Maintains airway patency
  • Protects lower airways from swallowed food and fluids
  • Epiglottis closes during swallowing to route food to esophagus
• Cough reflex


  1. Nerve impulses sent through vagus nerve to medulla

  2. Large inspiration of approximately 2.5L

  3. Epiglottis and glottis close

  4. Abdominal and intercostal muscles contract to raise lung pressure

  5. Epiglottis and glottis open suddenly, air rushes out to dislodge mucus and foreign particles
• Respiratory bronchioles, alveolar ducts, alveoli


  Gas exchange occurs here
• Respiratory membrane


  Alveolar and capillary walls where gas exchange occurs
• Pleura


  Thin, double layer of tissue covering outer surface of lungs
• Intrapleural pressure


  Pressure in pleural cavity surrounding lungs, slightly negative relative to atmospheric pressure
• Intrapulmonary pressure


  Pressure within the lungs, equalizes with atmospheric pressure
• Inspiration


  Diaphragm and intercostal muscles contract, increasing thoracic cavity size, decreasing intrapulmonary pressure, air rushes in
• Expiration


  Diaphragm and intercostal muscles relax, thoracic cavity size decreases, intrapulmonary pressure rises, air is expelled
• Tidal volume


  Approximately 500mL of air inspired and expired with each normal breath
• Lung compliance


  Expansibility or stretchability of lung tissue, increases with each breath
• Lung recoil


  Continual tendency of lungs to collapse away from chest wall, necessary for normal expiration
• Surfactant


  Lipoprotein that reduces surface tension of alveolar fluid, enabling lung expansion
• Diffusion


  Movement of gases or particles from higher to lower pressure or concentration
• Partial pressure


  Pressure exerted by each individual gas in a mixture
• Surfactant


  A lipoprotein produced by specialized alveolar cells, acts like a detergent, reducing the surface tension of alveolar fluid
• Without surfactant, lung expansion is exceedingly difficult and the lungs collapse
• Premature infants whose lungs are not yet capable of producing adequate surfactant often develop respiratory distress syndrome
• Diffusion


  The movement of gases or other particles from an area of greater pressure or concentration to an area of lower pressure or concentration
• Partial pressure (PO2)


  The pressure exerted by each individual gas in a mixture according to its concentration in the mixture
• The partial pressure of oxygen (PO2) in the alveoli is about 100 mmHg, whereas the PO2 in the venous blood of the pulmonary arteries is about 60 mmHg
• The partial pressure of carbon dioxide (PCO2) in the venous blood entering the pulmonary capillaries is about 45 mmHg, whereas that in the alveoli has a partial pressure of about 40 mmHg
• PaO2


  Partial pressure of oxygen in arterial blood
• PVO2


  Partial pressure of oxygen in venous blood
• Blood for partial pressures (blood gases) are usually obtained from arterial blood, therefore the abbreviation "PO₂" is commonly used for arterial blood oxygen partial pressure
• Oxyhemoglobin


  The compound of oxygen and hemoglobin
• Factors influencing oxygen binding and release from hemoglobin


  • Decreasing partial pressure of oxygen stimulates hemoglobin to release oxygen
  • Changes in blood pH affect hemoglobin's ability to bind and release oxygen
• Factors affecting rate of oxygen transport from lungs to tissues


  • Cardiac output
  • Number of erythrocytes and blood hematocrit
  • Exercise
• Excessive increases in blood hematocrit raise the blood viscosity, reducing cardiac output and therefore reducing oxygen transport
• Excessive reductions in blood hematocrit, such as occur in anemia, reduce oxygen transport
• In well-trained athletes, oxygen transport can be increased up to 20 times the normal rate, due in part to an increased cardiac output and to increased use of oxygen by the cells
• Ways carbon dioxide is transported from cells to lungs


  • Inside RBCs as bicarbonate (65%)
  • Combines with hemoglobin as carbaminohemoglobin (30%)
  • In solution in plasma and as carbonic acid (5%)
• Systemic diffusion


  Diffusion of oxygen and carbon dioxide between the capillaries and the tissues and cells down to a concentration gradient
• In reduced blood flow states such as shock, capillary blood flow may decrease, interfering with tissue oxygen delivery