RESPIRATORY PHYSIOLOGY

• Respiration


  The process by which oxygen from the atmosphere is delivered to the tissue and carbon dioxide from the tissue is removed into the atmosphere
• Stages of respiration


  • Ventilation stage
  • Transport stage
  • Exchange stage
  • Tissue stage
• Ventilation stage


  Exchange of gases between the atmosphere and pulmonary capillary blood occurs due to pulmonary ventilation
• Transport stage


  Gases are transported between the lungs and the tissue
• Exchange stage


  Gases are exchanged between the systemic blood and the tissue
• Tissue stage


  Oxygen delivered to the tissue is utilized by the mitochondrial enzymes of the cells for the metabolism of foodstuffs for the production of energy during which carbon dioxide is produced
• Components of the respiratory system

  • Upper respiratory tract
  • Lower respiratory tract
• Upper respiratory tract


  Structures from nose to the vocal cords that include sinuses, glottis, pharynx and larynx
• Function of upper respiratory tract


  • Processes the inspired air so that it gets humidified and it attains body temperature by the time it reaches trachea
• Nose


  Contains olfactory epithelium that receives smell sensation, filters particles greater than 10 μm, secretions contain immunoglobulins and interferons that kill organisms, offers about 50% of resistance to airflow in the respiratory system
• Paranasal sinuses


  Offer resonance to the voice, lighten the skull for easier upright posture, provide protection to brain during facial trauma
• Divisions of the pharynx

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
• Larynx and epiglottis


  Epiglottis and arytenoids cover the vocal cord during deglutition to prevent aspiration, arytenoids enlarge during infections increasing resistance to airflow, abductor muscles contract in early inspiration to open the glottis, adductor muscles contract during swallowing to close the glottis and prevent entry of food
• Lower respiratory tract


  Consists of trachea, airways and alveoli
• Components of the airway tree

  • Trachea
  • Bronchi
  • Bronchioles
  • Terminal bronchioles
• Changes in the airway tree with increasing generation

  • Airways become smaller, narrower and shorter
  • Amount of cilia decreases
  • Number of mucus secreting cells decreases
  • Quantity of submucosal glands becomes less
  • Amount of cartilage in the airway wall decreases
  • Quantity of smooth muscle increases
• Bronchial tone


  Tone of smooth muscles of bronchi, contributes to patency of bronchi and aids in respiration, influenced by neural, chemical and hormonal factors
• Categories of airways


  • Conducting airways
  • Respiratory airways
• Conducting airways


  Move air by convection into the gas exchange areas of lungs, include trachea and first 16 generations of airway
• Respiratory airways


  Participate in gas exchange, include respiratory bronchioles, alveolar ducts and alveoli
• Alveolus


  Functional unit of gas exchange, surrounded by capillaries forming the alveolar-capillary membrane, lined by type I and type II epithelial cells
• Pleura


  Covering of the lungs, consists of parietal pleura and visceral pleura, pleural fluid facilitates changes in size and shape of lungs during respiration and protects lungs from external damage
• Lobes of the lungs

  • Right lung has 3 lobes, left lung has 2 lobes
• Bronchopulmonary segments


  Parts of the lungs supplied by a segmental bronchus, 10 in the right lung and 9 in the left lung, each is a single functional unit
• Functions of the respiratory system

  • Respiratory functions
  • Non-respiratory functions
• Respiratory functions


  Gas exchange, regulation of blood pH
• Non-respiratory functions


  Left ventricular reservoir, filtering small emboli from blood, biochemical functions
• Lungs


  Central structures in respiration
• Respiration


  1. Inhalation of oxygen into the body

  2. Removal of carbon dioxide from the body
• Regulation of blood pH

  Lungs control plasma bicarbonate concentration by controlling carbon dioxide output from the body
• Lungs


  • Play an important role in acid-base balance
• Left ventricular reservoir


  Pulmonary vessels normally accommodate about 0.5 liter of blood at any given time, serving as a reservoir for left ventricular filling
• Filtering small emboli from blood

  Pulmonary vasculature traps and removes emboli before they get the chance to enter into systemic circulation
• Substances removed by lungs

  • PGE1
  • PGE2
  • PGF2α
  • Leukotrienes
  • Serotonin
  • Bradykinin
• Olfactory function


  Breathing is essential for delivering odorants from the environment to the olfactory epithelium
• Processing of inhaled air

  Filtration, warming, and moisturizing of inhaled air by the conducting airways
• Angiotensin converting enzyme


  Mainly secreted by endothelium of pulmonary blood vessels, converts angiotensin I to angiotensin II
• Respiratory system


  • Involved in defence functions through phagocytosis by alveolar macrophages, IgA in bronchial secretions, and protease activated receptors
• Metabolic functions of lungs

  • Synthesis of surfactant
  • Lysis of clot (local fibrinolytic system)
  • Synthesis and release of histamine, kallikrein, prostaglandins
• Removal from blood


  Lungs partially remove prostaglandins, bradykinin, adenosine, serotonin, acetylcholine and norepinephrine