Lamellar bodies
Encyclopedia
Lamellar granules are secretory organelles found in type II pneumocytes and keratinocyte
s. They are oblong structures, appearing about 300-400 nm in width and 100-150 nm in length in transmission electron microscopy
images. Lamellar granules fuse with the cell membrane and release their contents into the extracellular space.
-based phospholipids that are stored in the lamellar bodies serve as pulmonary surfactant
after being released from the cell.
layer of the epidermis, lamellar bodies are secreted from keratinocytes, resulting in the formation of an impermeable, lipid-containing membrane that serves as a water barrier and is required for correct skin barrier function. These granules release components that are required for skin shedding (desquamation
) in the uppermost epidermal layer, the stratum corneum
. These components include lipids (eg. glucosylceramides), hydrolytic enzymes (eg. proteases, acid phosphatases, glucosidases
, lipases) and proteins (eg. corneodesmosin). Lamellar granules have been observed to contain distinct aggregates of the secreted components glucosylceramide, cathepsin D, KLK7
, KLK8
and corneodesmosin. Transportation of molecules via lamellar granules is thought to prevent enzymes from interacting with their relevant substrates or inhibitors prior to secretion.
Recent work suggests that lamellar granules form a continuous membranous structure with the trans-Golgi network
Lamellar body secretion and lipid structure is abnormal in the epidermis of patients with Netherton syndrome
, a skin disorder characterised by chronic inflammation and universal pruritis (itch).
Keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
s. They are oblong structures, appearing about 300-400 nm in width and 100-150 nm in length in transmission electron microscopy
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
images. Lamellar granules fuse with the cell membrane and release their contents into the extracellular space.
Role in Lungs
In pneumocytes, the cholineCholine
Choline is a water-soluble essential nutrient. It is usually grouped within the B-complex vitamins. Choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation....
-based phospholipids that are stored in the lamellar bodies serve as pulmonary surfactant
Pulmonary surfactant
Pulmonary surfactant is a surface-active lipoprotein complex formed by type II alveolar cells. The proteins and lipids that surfactant comprises have both a hydrophilic region and a hydrophobic region...
after being released from the cell.
Role in Epidermis
In the stratum granulosumStratum granulosum
The stratum granulosum is a thin layer of cells in the epidermis. Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in this layer...
layer of the epidermis, lamellar bodies are secreted from keratinocytes, resulting in the formation of an impermeable, lipid-containing membrane that serves as a water barrier and is required for correct skin barrier function. These granules release components that are required for skin shedding (desquamation
Desquamation
Desquamation , also called skin peeling, is the shedding of the outermost membrane or layer of a tissue, such as the skin.-Skin:Normal, nonpathologic desquamation of the skin occurs when keratinocytes, after moving apically over about 14 days, are individually shed unnoticeably...
) in the uppermost epidermal layer, the stratum corneum
Stratum corneum
The stratum corneum is the outermost layer of the epidermis, consisting of dead cells that lack nuclei and organelles. The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress...
. These components include lipids (eg. glucosylceramides), hydrolytic enzymes (eg. proteases, acid phosphatases, glucosidases
Glucosidases
Glucosidases are glycoside hydrolase enzymes categorized under the EC number 3.2.1.-Function:α-glucosidases are enzymes involved in breaking down complex carbohydrates such as starch and glycogen...
, lipases) and proteins (eg. corneodesmosin). Lamellar granules have been observed to contain distinct aggregates of the secreted components glucosylceramide, cathepsin D, KLK7
KLK7
Kallikrein-related peptidase 7 is a serine protease that in humans is encoded by the KLK7 gene. KLK7 was initially purified from the epidermis and characterised as stratum corneum chymotryptic enzyme...
, KLK8
KLK8
Kallikrein-8 is a protein that in humans is encoded by the KLK8 gene.-External Links:* The MEROPS online database for peptidases and their inhibitors:...
and corneodesmosin. Transportation of molecules via lamellar granules is thought to prevent enzymes from interacting with their relevant substrates or inhibitors prior to secretion.
Recent work suggests that lamellar granules form a continuous membranous structure with the trans-Golgi network
Lamellar body secretion and lipid structure is abnormal in the epidermis of patients with Netherton syndrome
Netherton syndrome
Netherton syndrome is a severe, autosomal recessive form of ichthyosis associated with mutations in the SPINK5 gene. It is named after E.W. Netherton.- Characteristics :...
, a skin disorder characterised by chronic inflammation and universal pruritis (itch).