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Functional Anatomy

A. Weibel’s classification of airway generations: From trachea to alveolar sacs, the airways divide 23 times. (Trachea is generation ‘0’). The first 16 generations form the conducting zone (consisting of bronchi, bronchioles and terminal bronchioles); the remaining 7 generations are the transitional and respiratory zones (consisting of the respiratory bronchioles, alveolar ducts and alveoli)

B. Presence of cilia, smooth muscle, glands, cartilage in the air passages

Cilia Present upto respiratory bronchioles
Cartilage Only in trachea and bronchi
Glands     Only in trachea & bronchi
Smooth muscle Maximum in terminal bronchiole

Generation 1 to 10 →Bronchi
Generation 11th to 10th →Terminal Bronchioles
Generation 17th to 18th 19th →Respiratory Bronchioles
Generation 20, 21,22 →Alveolar duet
Generation 23 →Alveole

  1. Types of cells
  1. Alveolar epithelial cells

These are of 2 types:

  1.  Type I (There form the main living)
  2.  Type II (also called granular pneumocytes), These secrete surfactant
  1. Other cells in lungs
  • Pulmonary alveolar macrophages, lymphocyte,
  • plasma cells, APUD cells, mast cells
  1. Bronchoconstriction and dilation
    1. Bronchoconstriction : Reflexly (by irritants; this is cholinergically mediated), cool air, exercise, expiration, leukotrienes, substance P , cholinergic stimulation, early morning (around 6 A.M.)
    2. Bronchodilation : Adrenergic stimulation, by non adrenergic – non cholinergic nerve stimulation (NANC) where the neurotransmitter is VIP, inspiration, in the evening (around 6 P.M.)
  2. Gas Laws
    1. Dalton’s law of partial pressure: The partial pressure of a gas in a mixture of gases is equal to the total pressure times its percentage
    2. Boyle’s Law: P X 1 / V, if T is constant
    3. Charle’s law: P X T (if V is constant) and V X TC if P is constant
    4. Henry’s law: The dissolved gas is already proptional to its partial pressure
    5. Graham’s law: The rate of effusion is reversely proportional to the square

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