Smooth muscle

Bronchial vein, artery,and nerve

Branch of pulmonary artery

Deep lymphatic vessel

Terminal

Alveolus

Respiratory

Alveolar

Alveoli

Alveolar

Connectivetissue

Superficial lymphatic vessel

Lymph nodes

Pulmonary capillaries

Visceral

Branch of pulmonary vein

Pleural

Parietal

Elastic fibers

(a)

Terminalbronchus

Respiratorybronchiole

Alveolarduct

Alveolarsacs

Alveoli

(b)

exchange between alveolar air and the blood takes place throughthese cells. Type II pneumocytes are round or cube-shaped secre-tory cells that produce surfactant, which makes it easier for thealveoli to expand during inspiration (see “Lung Recoil” insection 23.3).

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12. Explain the branching of the tracheobronchial tree.

13. Describe the arrangement of cartilage, smooth muscle,and epithelium in the tracheobronchial tree. Explain whybreathing becomes more difficult during an asthma attack.