Electron microscopic studies of the lung of the frog. II. Topography of the inner surface by scanning and transmission electron microscopy

Atrial natriuretic peptide (ANP) system in the lung ofRana esculenta

The atrial natriuretic peptide (ANP)-system was examined in Rana esculenta lung with cytochemical and immunocytochemical methods. The results showed a cellular type that synthesizes the hormone and the presence of receptors in various components of the lung. The lung, therefore, produces ANP and at the same time is a target organ for the hormone. ANP may play an important physiological role in pulmonary function and in protecting against pulmonary edema.

Neuroepithelial bodies and solitary neuroendocrine cells in the lungs of amphibia

In the lungs of 12 species of Amphibia investigated so far, solitary neuroendocrine (NE) cells, as well as groups of these cells called "neuroepithelial bodies" (NEB), are observed. They occur in the position strategic to monitoring gas composition, mainly in the ciliated epithelium of the apical part of the septa. A great diversity in the structure of NEB is observed. The NE cells and NEB in Amphibia are predominantly of the "closed type," separated from the air space by a thin cytoplasmic layer of ciliated cells, goblet cells or pneumocytes. In two species, Bufo marinus and Ambystoma tigrinum, the "open type" of NEB occur, where NEB communicate with the air space, by apical cells in Bufo and type II NE cells in Ambystoma. Both types of cells possess single atypical cilia with an 8+1 microtubule arrangement and microvilli on the free surface. Single and grouped NE cells are characterized by small dense core vesicles (DCV) dispersed in the cytoplasm. In Salamandra and Ambystoma the second type of NE cells with large DCV are observed. The DCV represent sites of storage of serotonin and several neuropeptides. The basal parts of NEB and of some solitary cells are invested by the intraepithelial sensory nerve terminals, both afferent and efferent morphologically. In the lungs of Amphibia, similarly to other vertebrates, NE cells, which act as endocrine/paracrine receptors, form epithelial endocrine systems.

Lung of the tree frog, Hyla arborea L. A scanning and transmission electron microscopic study

Lungs of Hyla arborea L. were examined by scanning and transmission electron microscopy and morphometric methods. The lungs contain several interconnected folds in a netlike reticular arrangement of first, second and third order, mainly covered with pneumocytes. On the septa of first and second order, irregularly distributed small patches of ciliated epithelium devoid of goblet cells are located. Dome-shaped neuroepithelial bodies can be seen in the vicinity of ciliated epithelium. The pulmonary epithelium consists of one type of pneumocyte, which contain in their cytoplasm three kinds of bodies: lamellar, dense and multivesicular. The dense bodies are precursors of lamellar bodies (LBs), while the multivesicular bodies are incorporated into the LBs, being later secreted to the air space. The lining layer covering the internal lung surface contains numerous transformed LBs but tubular myelin figures are scarce. The surface of the lining layer is coated by a thin film. The air-blood barrier, consisting of three layers: epithelium, interstitial space and endothelium, is 0.6 micron thick.

Neuroepithelial bodies in the lung of the tree frog, Hyla arborea L. A scanning and transmission electron microscopic study

The endocrine-like cells (ELC), which together with nerve endings form the neuroepithelial bodies, are located on primary and secondary septa in the non-ciliated epithelium of the lung of Hyla arborea. ELC protrude markedly toward the lumen of the lung and are surrounded by pneumocytes, which separate ELC from the lumen by thin cytoplasmic processes. ELC possess a light cytoplasm containing two types of granules: (i) numerous small granules, 50-110 nm in diameter, and (ii) single large granules, 290-860 nm in diameter. Numerous nerve fibers, often forming synaptic junctions, can be observed in contact with ELC.

Methods of heavy metal electron microscopic histochemistry applied to frog lung surfactant

Four heavy metal staining methods have been applied to frog lung surfactant. Among them, the iodoplatinate method is the only one that almost exclusively visualizes the phospholipid moiety being produced in the lamellated bodies of the pulmonary epithelial cells and forming the backbone of organized structures within the extracellular lining layer. The other three techniques-ruthenium red-osmium tetroxide, osmium tetroxide-ferrocyanide, acidic phosphotungstic acid in chromatic (Rambourg technique)--more or less give electron contrast to glycoproteins and to a lesser extent to the hydrophilic parts of phospholipids. They all show the extracellular lining layer to be a two component system: the content of the lamellar bodies form--when released--membranous configurations, similar to those observed in mammalian lungs; they unfold in an amorphous hypophase, which is apparently secreted by goblet cells of the pulmonary epithelium.

Ultrastructural and morphometric study of the lung of the European salamander, Salamandra salamandra L

Ultrastructural and morphometric investigations were performed on the lung of the European salamander, Salamandra salamandra L. Folds of first and second order are covered with a ciliated epithelium containing goblet cells. The respiratory surface of the lung is lined by a single type of cell which, in amphibians, combines features of type I and type II alveolar cells of the mammalian lung. In the salamander the respiratory and ciliated epithelial cells as well as goblet cells possess electron dense and lucent vesicles in their cytoplasm as well as lamellar bodies. A small amount of surfactant, composed most probably of phospholipids and mucopolysaccharides, was observed covering the entire inner surface of the lung. Morphometric methods were used to determine the dimensions of the perinuclear region of pneumocytes, the thickness of the air-blood barrier and lung wall, and also the diameter of capillaries. The thickness of the respiratory air-blood barrier was found to be considerably higher than that of the corresponding barrier in mammals.