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Red arrows indicate secreted lamellar bodies, and green arrows indicate lamellar bodies in the cytoplasm. Scale bar = 200 nm. In cell biology, lamellar bodies (otherwise known as lamellar granules, membrane-coating granules (MCGs), keratinosomes or Odland bodies) are secretory organelles found in type II alveolar cells in the lungs, and in keratinocytes in the skin.
Confocal image of the stratum spinosum already showing some clusters of basal cells Keratinocytes become connected through desmosomes and produce lamellar bodies, from within the Golgi, enriched in polar lipids, glycosphingolipids, free sterols, phospholipids and catabolic enzymes. [3]
Lamella, in cell biology, is also used to describe the leading edge of a motile cell, of which the lamellipodia is the most forward portion. [5] The lipid bilayer core of biological membranes is also called lamellar phase. [6] Thus, each bilayer of multilamellar liposomes and wall of a unilamellar liposome is also referred to as a lamella.
At the transition between this layer and the stratum corneum, cells secrete lamellar bodies (containing lipids and proteins) into the extracellular space. This results in the formation of the hydrophobic lipid envelope responsible for the skin's barrier properties. Concomitantly, cells lose their nuclei and organelles.
The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.
Club cells also produce a component of lung surfactant. [20] Alveolar surfactant has a half-life of 5 to 10 hours once secreted. It can be both broken down by macrophages and/or reabsorbed into the lamellar structures of type II pneumocytes.
The natural moisturizing factor is a collection of water-soluble compounds produced from the degradation of histidine-rich proteins called filaggrin, which are responsible for aggregating keratin filaments to form keratin bundles that maintain the rigid structure of the cells in stratum corneum. [11]
The fibrils of each lamella are parallel with one another, but at different angles to those of adjacent lamellae. The lamellae are produced by keratocytes (corneal connective tissue cells), which occupy about 10% of the substantia propria. Apart from the cells, the major non-aqueous constituents of the stroma are collagen fibrils and proteoglycans.