Anatomy of the respiratory system

• Upper respiratory system includes

  the nose, nasal cavity, pharynx and associated structures
• Lower respiratory system includes

  larynx, trachea, bronchi and lungs
• Functions of the respiratory system

  1.      Provides for gas exchange: intake of O2 for delivery to body cells and removal of CO2 produced by cells

  2.      Helps regulate blood pH

  3.      Contains receptors for sense of smell, filters inspired air, produces vocal sounds (phonation), and excretes small amounts of water and heat
• Functions of the external nose

  -          Warms, moistens and filters incoming air

  -          Detects  olfactory stimuli

  -          Modifies speech vibrations (by prolonging and amplifying sound
• Pharynx (throat)

  -          Funnel shaped tube -13cm long

  -          Posterior to the nasal/ oral cavities and superior to the larynx

  -          Extends down to the inferior cartilage of the larynx

  -          Composed of skeletal muscle

  -          Contraction of these muscles help with deglutition (swallowing)

  -          Outer circular and inner longitudinal layer

  -          Lined with mucous membrane
• Functions of pharynx

  -          Acts as a passageway for air and food

  -          Resonating chamber for speech sounds

  -          Houses tonsils for immune protection
• Larynx

  -          Voicebox

  -          Short passageway that connects the laryngopharynx with the trachea

  -          Lies anterior to the oesophagus and the fourth through sixth cervical vertebrae (C4-C6)

  -          Contains vocal chords important for speech- vestibular (false) vocal cords and true vocal cords

  -          Composed of 9 pieces of cartilage

  -          3 single pieces (thyroid cartilage, epiglottis, & cricoid cartilage)

  -          3 paired pieces (arytenoid, cuneiform, & corniculate cartilages)
• Trachea

  -          The windpipe

  -          Tubular passageway for air

  -          Located anterior to the oesophagus

  -          16–20 incomplete, horizontal rings of hyaline cartilage resemble the letter C

  -           semirigid support to maintain patency of airway

  -          Extends from the larynx and divides into right and left bronchi
• 4 layers of the trachea

  1.       Mucosa- consists of pseudostratified ciliated columnar

  2.       Submucosa

  3.       Hyaline cartilage

  4.       Adventitia
• Bronchial tree


  The branching system of airways in the lungs
• Trachea divides into


  1. Right main (primary) bronchus

  2. Left main (primary) bronchus
• Right main bronchus


  • More vertical
  • Shorter
  • Wider than the left
• Main bronchi


  • Contain incomplete rings of cartilage
• Pseudostratified ciliated columnar epithelium


  The type of epithelium lining the main bronchi
• The extensive branching from the trachea resembles an inverted tree (hence bronchial tree)
• As the branching becomes more extensive in the bronchial tree

  1. Change of epithelium

  2. Plates of cartilage gradually replace incomplete rings & eventually disappear

  3. More smooth muscle as cartilage decreases
• Lungs

  -          Mediastinal surface of each lung contains the hilum

  • Bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit

  -          Medically, the left lung contains cardiac notch, where the apex of the heart lies

  •   The left lung is about 10% smaller than the right lung

  -          Right lung is thicker and broader but shorter

  • The diaphragm is higher on the right side, accommodating the liver

  -          Covered by serous membrane containing pleural fluid – parietal and visceral
• Pleural membrane

  Parietal pleura lines the thoracic cavity, and the  visceral pleura covers the lungs
• Bronchioles

  ·       Terminal bronchioles subdivide into microscopic branches called respiratory bronchioles

  • epithelial lining changes from simple cuboidal to simple squamous

  • Alveolar ducts connect respiratory bronchioles and alveoli which bud off in clusters

  Terminal bronchioles subdivide into microscopic branches called respiratory bronchioles • epithelial lining changes from simple cuboidal to simple squamous • Alveolar ducts connect respiratory bronchioles and alveoli which bud off in clusters
• Alveoli

  • Cup-shaped outpouching

  • Surrounded by fine elastic fibres

  • Contain open pores that connect adjacent alveoli

  • Allow air pressure throughout the lung to be equalised

  • Contain alveolar fluid known as surfactant

  •   mixture of phospholipids and lipoproteins
  • reduces the tendency of alveoli to collapse
• Respiratory Membrane

  Alveolus lined by simple squamous epithelium and supported by a thin elastic basement membrane

  • An alveolar sac consists of two or more alveoli that share a common opening

   • Consist of two types of alveolar epithelial cells

  • Type I alveolar (squamous pulmonary epithelial)

  -  Most numerous cell type (70%)

  -  Main site of gas exchange

  •   Type II alveolar

  -  Cuboidal epithelial cellsSecrete surfactant
• Conducting zone

  • Respiratory passages that carries air to the site of gas exchange

  • Helps filter, humidify and warm air
• Respiratory zone


  site of gas exchange

  Composed of respiratory bronchioles, alveolar ducts, alveoli (alveolar sacs)