alveolar2

Pertaining to or arising from the lung alveolar epithelium.

• a. capillary — comprise the alveolar capillary bed, in immediate contact with the lung alveoli.
• a.–capillary membrane — the membranous partition between the alveolar space and the venous blood, consisting of an alveolar epithelium and capillary endothelium.
• a. cell — cover the alveolar surface. Type 1 cells are flattened and extended, offering maximum opportunity for oxygen diffusion, but vulnerable to damage and slow to repair. They cover the bulk of the healthy alveolar wall. Called also membranous pneumocytes. Type 2 cells are cuboidal and cover much less of the alveolar surface than do type 1 cells. Their function is to secrete surfactant in response to injury and the renewal and repair of the alveolar wall. Called also granular or secretory pneumocytes. See also alveolar epithelialization (below).
• a. collapse — the microscopic basis of acquired atelectasis.
• congenital a. dysplasia — a disease of the newborn in which the alveoli are uneven in distribution and shape and there is too much interstitial tissue. The lungs are poorly aerated and retain their fetal appearance.
• a. cyst — dilatations of pulmonary alveoli, which may fuse by breakdown of their septa to form large air cysts (pneumatoceles).
• a. dead space — that part of the dead space located in the alveoli. The space in the alveoli where gaseous exchange does not occur.
• a. duct — extensions from respiratory bronchioles that terminate in a number of alveoli-lined saccules through a common atrium.
• a. dysplasia — see congenital alveolar dysplasia (above).
• a. echinococcosis — see alveolar hydatid cyst (below).
• a. emphysema — abnormal enlargement of the alveoli, the air spaces at the end of the bronchioles, with some destruction of the alveolar walls. Alveolar emphysema is rarely a problem except in the horse. See also chronic obstructive pulmonary disease.
• a. epithelial cells — cover the alveolar surface. Type 1 cells are flattened and extended, offering maximum opportunity for oxygen diffusion, but vulnerable to damage and slow to repair. They cover the bulk of the healthy alveolar wall. Called also membranous pneumocytes. Type 2 cells are cuboidal and cover much less of the alveolar surface than do type 1 cells. Their function is the secretion of surfactant in response to injury and the renewal and repair of the alveolar wall. Called also granular or secretory pneumocytes. See also alveolar epithelialization (below).
• a. epithelialization — after severe damage to the alveolar lining there is a significant loss of type 1 membranous pneumocytes which are physiologically effective in gaseous transport but susceptible to injury. Their place may be taken by type 2 cells, the secretory pneumocytes, which are more cuboidal and active as producers of surfactant. The alveolar wall is thickened and is described as being in a stage of epithelialization.
• a. fibroblast — connective tissue cells in the lungs with contractile functions, cell and matrix interactions, and secrete substances important to the mechanical properties of lung.
• a. filling disorders — a group of incidental conditions characterized by the filling of alveoli by lipid-filled macrophages with minimal inflammation.
• a. gas exchange — the diffusion of CO₂ and O₂ across the alveolar–capillary membrane.
• a. histiocytosis — a pulmonary condition characterized by large, focal accumulations of foamy macrophages.
• a. hydatid cyst — multivesicular, infiltrative form of hydatid cyst found in rodents, e.g. ground squirrel, field mouse.
• a. lipoproteinosis — an accumulation of acidophilic, acellular material within pulmonary alveoli. The condition can be experimentally reproduced but has been associated with chronic interstitial pneumonia of goats. See also caprine arthritis–encephalitis.
• a. macrophage — derived from monocytes in the bone marrow, contains many lysosomes and phagosomes, and forms a major element in the pulmonary defense mechanism.
• a. metaplasia — a characteristic of pulmonary epithelial cells is their capacity to undergo metaplasia from one cell type to another. Called also transdifferentiation.
• a. microlithiasis — see microlithiasis.
• a. oxygen tension — the measure of oxygen level within the alveoli and a factor influencing diffusion of gases across the alveolar–capillary membrane; increased with oxygen administration to the patient.
• a. pattern — see alveologram.
• a. phospholipidosis — characterized by the accumulation of acidophilic, acellular material in pulmonary alveoli.
• a. pore — pore of Kohn.
• a. saccules — the intervening structures between pulmonary alveolar ducts and alveoli.
• a. transport system — refers to the clearance mechanisms within the lower respiratory system, including alveolar macrophages, mucociliary escalator and peribronchial lymphatics.
• a. ventilation — the volume of air entering and leaving the alveoli per unit of time.
• a. volume — the volume of the alveolar space. The dead space volume and the alveolar volume make up the total volume of the respiratory tract.