Skip to Main Content

++

The Air Passages

++

The air passages—nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles—transmit air from the atmosphere to the alveoli (ventilation).

++

The bronchi divide dichotomously, becoming gradually smaller and more thin-walled as they progress away from the hilum toward the periphery. When the walls lose their cartilage, they are called bronchioles. Bronchioles are less than 2 mm in diameter, have smooth muscle walls, and terminate in the alveoli. The lining epithelium is ciliated columnar in the larger air passages and ciliated cuboidal in the distal bronchioles. Mucus-producing goblet cells are present, mainly in the larger bronchi. Scattered “small granule cells” are present in the bronchi on the basement membrane between epithelial cells; these are neuroendocrine cells that contain serotonin, bombesin, and other polypeptides. Small dome-shaped Clara cells in the terminal bronchioles secrete a protein that lines the small air passages.

++

The Lung Parenchyma

++

Two units of lung parenchyma are recognized. The pulmonary lobule is represented by the structures derived from a small bronchiole, composed of 5–7 terminal bronchioles and the structures distal to them. The lobule is separated from other lobules by connective tissue.

++

The pulmonary acinus is represented by the structures arising from a single terminal bronchiole and consists of respiratory bronchioles and alveoli. Respiratory bronchioles are lined by simple cuboidal epithelium and participate in gas exchange. They lead into alveolar ducts. Alveolar sacs arise as saccular outpouchings from the alveolar ducts and respiratory bronchioles. The alveolar wall is 5–10 μm thick and covered by flat type I pneumocytes over 90% of the surface and by type II pneumocytes over the remainder. Type II pneumocytes are cuboidal cells with abundant cytoplasm that contains distinctive granules on electron microscopy. They produce surfactant and proliferate rapidly when there is alveolar injury.

++

The Pleura

++

The lung is encased by a layer of mesothelial cells, the visceral pleura, which becomes continuous with the internal lining of the chest wall (parietal pleura) at the lung hilum. The pleural cavity is lubricated by a small film of pleural fluid that permits movement of the lung in relation to the chest wall.

++

The Blood Supply

++

The lung has a dual blood supply. The bronchial arteriolar branches follow the bronchial tree and have a nutritive function. The pulmonary artery divides to produce a network of capillaries, the primary function of which is gas exchange.

++

Evaluation of the Integrity of Lung Structure

++

Lung structure may be assessed by several methods:

++

  1.  Physical examination of the chest.

  2.  Examination of sputum (coughed-up tracheal secretion) for the presence of specific microorganisms by culture and malignant cells by cytologic examination. Microbiologic interpretation requires care because sputum is almost invariably contaminated by saliva, which normally has a rich commensal flora. Less contaminated samples of sputum may be obtained by transtracheal ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessPhysiotherapy Full Site: One-Year Subscription

Connect to the full suite of AccessPhysiotherapy content and resources including interactive NPTE review, more than 500 videos, Anatomy & Physiology Revealed, 20+ leading textbooks, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPhysiotherapy

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.