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Module 1: Anatomical Bases

Lesson 5: Respiratory System

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RESPIRATORY FUNCTION AND RESPIRATORY SYSTEM

  • The respiratory system provides the body with oxygen and eliminates carbon dioxide produced in the cells.
  • This process is involuntary and automatic: air containing oxygen is drawn in (inspiration), and waste gases including CO₂ are expelled (expiration)

ANATOMY OF THE RESPIRATORY SYSTEM

Divisions of the Respiratory System:

  • Airways
  • Lungs

AIRWAYS

Upper Airways:

  • Mouth and Nostrils:
    • Air enters through the nostrils
    • Nostrils are lined with highly vascularized mucosa and nasal turbinates
    • Functions: warm, moisten air and prevent coarse particles from entering the respiratory system
  • Pharynx:
    • Tube-shaped structure connecting mouth and nostrils to the larynx
  • Larynx:
    • Entrance to the respiratory tract
    • Contains vocal cords (organ of phonation)
    • The epiglottis, a cartilage, protects the larynx during swallowing

Transition Pathway:

  • Trachea:
    • Flattened tube running from the neck to the thorax
    • Composed of ~20 incomplete cartilaginous rings joined by a fibro-elastic membrane
    • Divides into two branches: the bronchi

Lower Airways:

  • Bronchi and Bronchioles:
    • Two main bronchi: right bronchus descends vertically to the right lung, left bronchus goes transversely to the left lung
    • Bronchi subdivide up to 25 times, forming the bronchial or respiratory tree
    • Bronchioles (diameter <1 mm) end in alveolar clusters
  • Alveoli:
    • Tiny hollow sacs with thin walls
    • Site of gas exchange in the lungs
    • Over 300 million alveoli in adult lungs
    • Surface area: 70–100 m²

THE LUNGS

  • Two spongy reddish masses for gaseous exchange between blood and air
  • Shape: Conical with apex at the base of the neck and base resting on diaphragm
  • Mediastinum: Space between lungs containing heart, great vessels, and esophagus
  • Structure: Each lung contains bronchial branches ending in pulmonary alveoli

THE BREATHING

Definition: Physiological act of oxygen intake and CO₂ release

Phases of Breathing:

  1. Exchange in the lungs
  2. Transport of gases
  3. Respiration in cells and tissues

Exchange in the Lungs:

  • Inspiration:
    • Rib cage volume increases
    • Lungs swell
    • Diaphragm and external intercostal muscles raise the ribs
  • Expiration:
    • Rib cage volume decreases
    • Lungs compress
  • Upper airways act as air conditioning system
  • Breathing rate: 14–16 times/minute
  • Air intake per breath: ½ liter
  • Lung capacity: ~5 liters

THE TRANSPORT OF GASES

  • Oxygen:
    • Taken up in alveoli
    • Carried by red blood cells to heart
    • Distributed via arteries to body cells
  • Carbon Dioxide:
    • Carried by red blood cells and plasma
    • Transported to heart via venae cavae
    • Expelled by lungs

RESPIRATION IN CELLS AND TISSUES

  • Cells take oxygen from blood to burn absorbed food
  • Produces:
    • Energy
    • Heat (maintains body temperature at ~37°C)

RESPIRATORY ADAPTATIONS DURING EXERCISE

  • Increased muscle metabolism requires enhanced:
    • Ventilation
    • Circulation
    • Gas diffusion

Phases of Ventilation During Exercise:

  1. Rapid rise at exercise start
  2. Slower sustained ascent
  3. Post-exercise decrease (repayment of oxygen debt)
  • Increased pulmonary blood flow enhances gas exchange and oxygen availability to muscles
  • Diffusing capacity:
    • Resting: 23 ml/min
    • Max exercise: 64 ml/min

LONG-TERM RESPIRATORY SYSTEM ADAPTATIONS

  • Enhanced respiratory efficiency and economy
  • Increased alveolar respiratory surface
  • Improved alveolar-capillary diffusing capacity
  • Enlarged pulmonary capillary network

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