Respiratory Physiology

• Respiration


  The exchange of gases between the atmosphere, blood, and cells
• Processes required for respiration

  • Ventilation (breathing)
  • External (pulmonary) respiration
  • Internal (tissue) respiration
• The cardiovascular system assists the respiratory system by transporting gases
• Normal human breathing at rest

  12 to 15 times a minute, 500 mls of air per breath, 6 to 8 litres per minute inspired and expired
• Gas exchange in the alveoli


  Air mixes with gas in the alveoli, oxygen enters the blood in the pulmonary capillaries, carbon dioxide enters the alveoli
• Components of the respiratory system

  • Upper respiratory system (nose, pharynx, and associated structures)
  • Lower respiratory system (larynx, trachea, bronchi, and lungs)
• Functional zones of the respiratory system

  • Conducting zone
  • Respiratory zone
• Anatomical dead space


  Part of the airway that is not involved in gas exchange (conducting zone), average 150ml
• Alveolar dead space


  Alveoli that are ventilated but not perfused, varies depending on circumstances in normal individuals and can be influenced in disease
• Functions of the conducting zone

  • Transports air to the lungs
  • Warms, humidifies, filters, and cleans the air
  • Voice production in the larynx
• The upper airway consists of all structures from the nose to the vocal cords, the lower airway consists of the trachea and the bronchial structures to the alveolus
• The tracheobronchial tree is an arrangement of branching tubes that begins at the larynx and ends in the alveoli
• The right main-stem bronchus is larger than the left, and the angle of the takeoff is less acute
• Lung Function


  Outline various lung volumes and capacities and demonstrate their significance in defining normal or abnormal lung function
• Nasal breathing


  Preferential as the nose filters particulate matter, plays a major role in lung defense, and humidifies inspired air
• Nose offers higher resistance than mouth, switch to mouth breathing during exercise
• Surface tension


  The attraction between molecules at a gas/liquid interface that tends to pull those molecules together
• Flow-volume loops


  In obstructive and restrictive conditions
• Smaller alveoli


  Have greater pressure within due to surface tension
• Surfactant


  Reduces the surface tension, essential to enable the expansion of alveoli
• Principle of ventilation


  Air moves down its pressure gradient, from an area of high pressure to an area of lower pressure
• Boyle's Law


  The volume of a gas varies inversely with its pressure
• Pulmonary disorders


  • chronic obstructive pulmonary disease (COPD)
  • asthma
  • pneumothorax
  • pulmonary embolism
• Decreased thoracic volume


  Increases air pressure in the lungs, resulting in exhalation
• Increased thoracic volume


  Decreases air pressure in the lungs, resulting in inhalation
• Inspiration and expiration


  • Inspiration is active, expiration is passive at rest
  • During exercise, expiration is active and the abdominal muscles contract
• Diaphragm


  The most important muscle of inspiration, supplied by phrenic nerves originating at C3, 4, 5
• Transpleural pressure


  The pressure difference across the lungs, the difference between the pressure at the airway opening and the pressure on the visceral pleural surface
• Pulmonary Ventilation


  Respiratory passages
• Lung compliance


  The ease with which the lungs and thoracic wall can be expanded, defined as the change in lung volume per change in transpulmonary pressure
• Elasticity


  The lungs contain elastic tissue that stretches on inhalation and recoils during exhalation, aiding the flow of air out of the lungs
• Disorders that cause loss of elasticity (e.g. Emphysema) can affect ventilation
• Ficks Law


  The blood gas barrier is extremely thin (0.2-0.3 μm) and has a large surface area (50-100 m2)
• Increased fluid or mucus in the lungs

  Increases the distance of diffusion
• Normally the distance of diffusion is very short in healthy lungs (0.2 – 0.4 μm)
• The lung has two separate circulations: the pulmonary circulation brings deoxygenated blood from the right ventricle to the gas-exchanging units, and the bronchial circulation arises from the aorta and nourishes the lung parenchyma
• The circulation to the lung is unique in its dual circulation and in its ability to accommodate large volumes of blood at low pressure
• Type I cells


  Line most of the alveolar surface, with long thin cytoplasmic processes
• Type II cells


  More numerous, occupy only about 7% of the alveolar surface, source of surfactant
• Control of Respiration


  The three major elements of the respiratory control system. Sensors, including central and peripheral chemoreceptors and pulmonary mechanoreceptors, feed information to the respiratory control center. In turn, the respiratory control center sends signals to the respiratory muscles.