Figure 1818

Diagram of the interalveolar septum. This diagram shows the thick and thin portions of the interalveolar septum. The thin portion forms the air-blood barrier and is responsible for most of the gas exchange that occurs in the lung. Arrows indicate the direction of C02 and 02 exchange between the alveolar air space and the blood. The thick portion of the interalveolar septum plays an important role in fluid distribution and its dynamics. It contains connective tissue cells. Note the macrophage in the thick portion that extends its processes into the lumen of the alveolus.

type II

alveolar cell surfactant type I alveolar cell alveolar lumen (

fibroblast erythrocyte macrophage capillary lumen endothelial

capillary lumen alveolar space ^

type I cell basal lamina endothelium

collagen \

¬°elastic fiber

Emphysema is a condition of the lung characterized by permanent dust, textile fibers, and construction dust. The most common cause, enlargement of the air spaces distal to the terminal bronchiole. This however, is cigarette smoking.

enlargement is caused by chronic obstruction of airflow, most of- The destruction of the alveolar wall may be associated with ex-

ten because of narrowing of the bronchioles, and is accompanied cess lysis of elastin and other structural proteins in the alveolar by destruction of the alveolar wall (Fig. 18.20). Thus, significant septa. Elastase and other proteases are derived from lung neu-

area for gas exchange is lost in this disease. Emphysema is rela- trophils, macrophages, and monocytes. A specific genetic disease, tively common; it is seen in about half of all autopsies and is eas- a,-antitrypsin deficiency, causes a particularly severe form of em-

ily recognized. Pathologists identify several types of emphysema, physema in both heterozygous and homozygous individuals. It is

The severity of the disease is clinically more important, however, usually fatal in homozygotes if untreated, but its severity can be re-

than recognition of the specific type. Emphysema is often caused duced by supplying the enzyme inhibitor exogenously. by chronic inhalations of foreign particulate material such as coal

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