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A. Trachea And Bronchi:

  1. The trachea is up to 25 cm in length and up to 2.5 cm in diameter. The right bronchus diverges at a lesser angle from the trachea than does the left, which is why foreign material is more frequently aspirated on the right side.  Q On entering the lung, the bronchi divide into lobar bronchi, then into segmental bronchi, which supply the 19 lung segments. Because the segments are individual units with their own bronchovascular supply, they can be resected individually. Q
  2. The tracheobronchial tree contains cartilage and submucosal mucous glands in the wall. The latter are compound tubular glands with mucous cells (pale) and serous cells (granular, more basophilic).
  3. The lining is pseudostratified epithelium, which appears as layers, although all cells reach the basement membrane. Most cells are ciliated, but there are also mucus-secreting (goblet) cells, and basal cells.  Q

B.  Bronchioles:

  1. Distal to the bronchi are bronchioles, which differ from bronchi in that they lack cartilage and mucus-secreting glands.
  2. The terminal bronchioles divide into respiratory bronchioles, which merge into alveolar ducts and alveoli.
  3. The acinus, which is the unit of gas exchange in the lung, consists of respiratory bronchioles, alveolar ducts, and alveoli.Q 

C.  Alveoli:

  1. The alveoli are lined by two types of epithelium –Q
    a.  Type I cells cover 95% of the alveolar surface, but comprise only 40% of alveolar epithelial cells. They are thin and have a large surface area, a combination that facilitates gas exchange.
    b.  Type II cells produce surfactant and are 60% of the alveolar lining cells. However, as they are more cuboidal, they constitute only 5% of the alveolar surface. Type I cells are particularly vulnerable to injury. When they are lost, type II pneumocytes multiply and differentiate to form new type I cells, reconstituting the alveolar surface.

D. Pulmonary Vasculature:

  1. The lung has a dual blood supply: the pulmonary circulation and the bronchial system. Pulmonary arteries accompany the airways in a sheath of connective tissue, the bronchovascular bundle. The more proximal arteries are elastic.

E.  Defense Mechanisms

  1. The respiratory system has effective defense mechanisms to cope with the numerous particulates and infectious agents inhaled on inspiration. Q
  2. The nose and trachea warm and humidify the air entering the lung. The nose traps almost all particles over 10 µm in diameter and about half of all particles of 3 µm aerodynamic diameter (Aerodynamic diameter refers to the way particles behave in air rather than to their actual size.)
  3. The mucociliary blanket of the airway epithelium disposes of particles 2 to 10 µm in diameter. The ciliary beat drives the mucous blanket toward the trachea.Q
  4. Particles that land on it are thus removed from the lungs and swallowed or coughed up.Q

The Lungs

  1. Congenital Anomalies
    1. Bronchial Atresia:
    2. Pulmonary Hypoplasia:
      1. Pulmonary hypoplasia, the most common congenital lesion of the lung, is found in 10% of neonatal autopsies.
      2. Pulmonary hypoplasia also is seen in trisomies 13, 18, and 21.
  1. Three major factors
  2. Congenital diaphragmatic hernia.
  3. Abnormalities of the chest wall, pleural effusions, and ascites, as in hydrops fetalis. Q
  4. Oligohydramnios (inadequate volume of amniotic fluid). Q
  1. Congenital Cystic Adenomatoid Malformation:
  • Seen in the first 2 years of life.  Q
  • The lesion usually affects one lobe of the lung and consists of multiple cystlike spaces.
  • Most common presenting symptom is respiratory distress and cyanosis.  Q
  1. Bronchogenic Cyst:
  • Discrete, extrapulmonary, fluid-filled mass lined by respiratory epithelium
  • Most commonly found in the middle mediastinum.  Q

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