Respiratory System

• The respiratory system is a network of organs and tissues responsible for supplying the body with oxygen and removal of carbon dioxide

  
• Components of the respiratory system

  • Airways
  • Lungs
  • Blood vessels
  • Respiratory muscles
• Zones of the respiratory system

  • Conducting zone: passageways to reach the site of gas exchange
  • Respiratory zone: site of gas exchange
• Function of the respiratory system


  • Supplying the body with oxygen
  • Removal of carbon dioxide
• Respirationprocesses


  1. Ventilation (breathing: inspiration, expiration)

  2. External respiration: gas exchange between lungs and blood

  3. Transport of gases

  4. Internal respiration: gas exchange between blood and tissue

  
• Additional functions of ventilation

  • Air warming
  • Air moisturizing
  • Air cleansing
  • Smelling
  • Phonation
• Components of the upper respiratory system

  • Nasal cavity
  • Oral cavity
  • Pharynx
  • Larynx

  
• Nasal cavity

  • Contains olfactory mucosa with smell receptors
  • Contains respiratory mucosa with ciliated epithelium and mucus producing cells
  • Contains nasal conchae that humidify, warm and clean the air
• Paranasal sinuses


  • Hollow, air-filled cavities lined by mucous secreting epithelial cells
  • Humidify, warm and clean the air
  • Voice amplification

  
• Epiglottis


  • Cartilage tissue flap that closes the airways to avoid food going into the trachea
• Larynx


  • Houses the vocal folds for phonation
• Components of the lower respiratory system

  • Bronchioles
  • Respiratory bronchioles
  • Alveolar ducts
  • Alveoli

  
• Bronchioles


  • No cartilage
  • Diameter < 1 mm
• Respiratory mucosa


  • Contains goblet cells that secrete mucus
  • Contains ciliated cells that move mucus to the pharynx

  
• Alveoli


  • 500,000,000 in number
  • Diameter 200-500 μm
  • Surface area 75 m2
  • No mucus, no cilia but macrophages
  • Contain type I and type II pneumocytes

  
• Type II pneumocytes


  • Secrete surfactants to decrease surface tension and keep alveoli open
  • Regenerate type I pneumocytes

  
• Pleura


  • Airtight
  • Fluid film creates capillary forces
  • Negative pressure of -4 mmHg
• Breathing mechanics


  1. Abdominal breathing: diaphragm muscle lowers dome, increases thoracic volume

  2. Thoracic breathing: intercostal muscles elevate ribs, increase thoracic volume
• Minute ventilation


  Amount of air breathed per minute 7,5L/min
• Anatomical dead space


  Volume in the conductive passageways that does not contribute to gas exchange
• Work of breathing


  • Affected by airway resistance
  • Affected by lung compliance (distensibility of lung tissue and alveolar surface tension)
• External respiration (gas exchange air-blood)

  1. Diffusion of O2 and CO2 along concentration gradients

  2. Requires ventilation, perfusion, large exchange surface, short diffusion distance

  
• Partial pressure gradients and gas solubilities

  • Steep O2 gradient (40/104 mmHg)
  • Gentle CO2 gradient (40/45 mmHg)
  • CO2 20x more soluble in plasma than O2
• Ventilation-perfusion coupling


  • V/Q = 1 is good ventilation and perfusion
  • V/Q > 1 is good ventilation, poor perfusion
  • V/Q < 1 is poor ventilation, good perfusion
  • Normal lung has up to 15% mismatch
• Homeostatic responses to ventilation-perfusion mismatch

  • Hypoxic pulmonary vasoconstriction: capillaries in low PO2 alveolar areas constrict to reduce perfusion
  • Hypocapnic bronchoconstriction: bronchioles in low PCO2 capillary areas constrict to reduce ventilation
• Oxygen transport in blood

  1.5% dissolved in plasma, 98.5% bound to hemoglobin
• Carbon dioxide transport in blood

  1. 10% dissolved in plasma, over 20% bound to hemoglobin, about 70% as bicarbonate ions
• Bicarbonate buffer system


  Regulates blood pH to enable enzymatic reactions (lungs:fast, kidneys:slow)
• Pathologies of the respiratory system

  • Ventilation defect
  • Diffusion defect
  • Perfusion defect
• Emphysema


  • Alveolar walls weaken and rupture, creating larger air spaces
  • Reduces surface area for gas exchange
  • Causes air trapping
• Chronic bronchitis


  • Inflammation of bronchi lining
  • Chronic excessive mucus production
  • Persistent cough
• COPD


  • Combination of emphysema and chronic bronchitis
  • Leading cause is smoking
• Diffusion defect


  Disturbed gas diffusion capacity between alveoli and capillaries
• Perfusion defect


  Disturbance in arterial blood supply or pulmonary venous drainage
• Emphysema (=inflate, swell): the walls of the alveoli weaken and rupture, creating larger air spaces (instead of many small ones). This reduces the surface area for gas exchange. Air becomes trapped, leaving no room for fresh, oxygen-rich air to enter. Most people with emphysema also have chronic bronchitis.
• Chronic bronchitis


  Inflammation of the lining of the bronchi (COPD), chronic production of excessive mucus, persistent cough
• Emphysema and chronic bronchitis


  Two conditions that make up chronic obstructive pulmonary disease (COPD)
• Smoking is the leading cause of COPD. Treatment may slow the progression of COPD, but it can't reverse the damage.
• Ventilation - obstructive disease

  Increased resistance to airflow due to partial or complete obstruction. Shortness of breath is a symptom.
• Asthma


  Inflammation that causes tightening of the muscles around the airways, swelling and narrowing of the airways with excess mucus