Three‐dimensional reconstruction and quantitative analysis of rat lung type II cells: A computer‐based study

Abstract

The three-dimensional structure of alveolar epithelial type II cells was imaged using a computer-based system designed for reconstruction and quantitative analysis of serially sectioned specimens. Six type II cells were reconstructed from serial ultrathin sections of lungs from two Sprague Dawley male rats and the results were compared to standard morphometric estimates of type II cell composition from five other Sprague Dawley male rats. A minor portion of the type II cell surface was in contact with the alveolar airspace while most of the cell surface was embedded in the alveolar septal interstitium. The type II cells contained multiple Golgi regions located close to the nucleus. Mitochondria formed a few branching filamentous networks extending throughout the cell. The reconstructed cells appeared to represent a homogeneous population having fractional volumes of intracellular organelles very similar to those found by morphometric techniques. The spatial distribution of secretory organelle volume suggests that the organization of this cell type reflects an ordered progression of secretory particle maturation which is consistent with earlier hypotheses of lamellar body assembly.

Improved preservation of phospholipid‐rich multilamellar bodies in conventionally embedded mammalian lung tissue—an electron spectroscopic study

“…Thus, it seems that not only are phospholipids concentrated in special organelles as has been shown biochemically and autoradiographically (e.g. Askin & Kuhn, 1971;Chevalier & Collet, 1972;King, 1984;Young et al, 1985) but neutral lipids as well. The electron spectroscopic data presented are indicative of a separation of different lipid components of the pulmonary surfactant material on the subcellular level.…”

“…Amorpheus, granular or vesicular regions which have been reported to be a component of multilamellar bodies (e.g. Stratton, 1975;Gil, 1985;Young et al, 1985;Ishii et al, 1989) were shown cytochemically to be the site of different enzymatic activities (e.g. Meban, 1972;Kalina, 1988).…”

Architecture and Cellular Composition of the Air–Blood Tissue Barrier

“…Alveolar type II cells also serve as the stem cells for the generation of daughter type II cells and can undergo changes in cell shape and organelle content to form alveolar type I cells (Evans et al, 1972). Although the generation and secretion of lamellar bodies in type II cells can occur over a short period of time (see the review of Wright and Clements, 1987), lamellar body volume fraction in type II cells is remarkably constant under normal conditions (Young et al, 1985). Lamellar body volume fraction is similar for a wide variety of mammalian species, with ferrets, rabbits, and humans having the highest values, and baboons and neonatal rats the lowest.…”

Alveolar epithelial type II cell: defender of the alveolus revisited

“…4), which gives rise to the surface-active lining layer from which, in turn, small vesicular forms derive that are thought to represent spent surfactant (for review, see [71]). These categories of surfactant subtypes were defined by early ultrastructural studies and were consistently seen in both chemically and cryofixed surfactant [72,73]. By differential centrifugation of BAL material, surfactant is separated into large and small aggregates, while equilibrium buoyant density gradient centrifugation separates light, heavy and ultraheavy fractions.…”