FIGURE 19.19 • Electron micrograph of the alveolar septum. This high-magnification micrograph shows the thin portion of the air–blood barrier where it consists of type I alveolar cells, capillary endothelium, and the fused basal lamina shared by both cells. In the thick portion, the type I alveolar cell (arrows) rests on a basal lamina, and on the opposite side is connective tissue in which collagen fibrils and elastic fibers are evident. 33,000.
FIGURE 19.20 • Photomicrograph of alveolar macrophages.
This high-magnification photomicrograph shows the structure of the alveolar septum and the lumen of an alveolus containing alveolar macrophages and red blood cells. The cytoplasm of the alveolar macrophages, when they are present in significant numbers, often contains the brown pigment hemosiderin from phagocytosed red blood cells. These hemosiderin-laden macrophages (often called “heart failure cells”) are typically found in heart disease, mostly left ventricular failures that cause pulmonary congestion and edema. This results in enlargement of the alveolar capillaries and small hemorrhages into the alveoli. 560.
trachea main bronchus lobar bronchus segmental bronchus terminal bronchiole respiratory bronchioles alveolar duct alveolar sacs alveoli RESPIRATORY CONDUCTING FIGURE 19.21 • Divisions of the bronchial tree and summary of its histological features. 684  FOLDER 19.2 Clinical Correlation: Cystic Fibrosis
Cystic fibrosis (CF, mucoviscidosis) is a chronic obstructive pulmonary disease of children and young adults. It is an autosomal recessive disorder caused by a mutation in a gene called the cystic fibrosis transmembrane conductance regulator (CFTR) located on chromosome 7. The product of this gene the Cl channel protein is involved in final alteration of mucus and digestive secretions, sweat, and tears. All mutations of CFTR gene results in abnormal epithelial transport of Cl that affects the viscosity of the secretion of the exocrine glands. Almost all exocrine glands secrete abnormally viscid mucus that obstructs the glands and their excretory ducts.
The course of the disease is largely determined by the the CFTR gene could lead to the use of gene therapy in degree of pulmonary involvement. At birth, the lungs are the near future.
FIGURE F19.2.1 • Schematic diagram of pathology in cystic fibrosis. In cystic fibrosis, secretion of Cl anions into the lumen of the bronchial tree is markedly decreased because of a defective or nonexistent chloride channel protein. Na resorption from the lumen of the bronchial tree is then increased, causing movement of water into the cell. As a result, the mucous layer within the bronchial tree becomes dehydrated and viscous. This thick mucus is difficult to move by the mucociliary escalator mechanism, and it clogs the lumen of the bronchial tree, obstructing airflow.
normal. However, the defective Cl channel protein in the bronchial epithelium causes decreased Cl secretion and increased Na and water reabsorption from the lumen (Fig. F19.2.1). As a result, the “mucociliary escalator” malfunctions, with consequent accumulation of an unusually thick, viscous mucous secretion. The pulmonary lesion is probably initiated by obstruction of the bronchioles. Bronchiolar obstruction blocks the airways and leads to thickening of the bronchiole walls and to other degenerative changes in the alveoli. Because fluids remain trapped in the lungs, individuals with cystic fibrosis have frequent respiratory tract infections. The cloning of