Basal lamina

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Basal lamina
Basal lamina.jpg
Transmission electron micrograph displaying basal lamina that is lining the external surface of cell membrane.
Details
Identifiers
Latin lamina basalis
TA98 A15.2.03.007
A15.2.03.019
A15.3.03.102
TA2 7032
TH H2.00.00.0.00006
FMA 62918
Anatomical terms of microanatomy

The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often incorrectly referred to as the basement membrane, though it does constitute a portion of the basement membrane. The basal lamina is visible only with the electron microscope, where it appears as an electron-dense layer that is 20–100 nm thick (with some exceptions that are thicker, such as basal lamina in lung alveoli and renal glomeruli).

Contents

Structure

The layers of the basal lamina ("BL") and those of the basement membrane ("BM") are described below:

NamePart of BL?Part of BM?Notes
lamina lucida / lamina rara [1] yesyeselectron-lucid layer [2] containing the glycoprotein laminin
lamina densa yesyeselectron-dense layer [3] composed of type IV collagen
lamina reticularis [4] noyesThe three above layers of the basal lamina typically sit on top of the reticular lamina, which is synthesized by cells from the underlying connective tissue and contains fibronectin. The exception is when two epithelial layers abut one another as in the alveoli of the lungs and glomeruli of the kidneys, in which the basal lamina of one epithelial layer fuses with that of the other.

Anchoring fibrils composed of type VII collagen extend from the basal lamina into the underlying reticular lamina and loop around collagen bundles. Although found beneath all basal laminae, they are especially numerous in stratified squamous cells of the skin.

These layers should not be confused with the lamina propria, which is found outside the basal lamina. [5]

Basement membrane

The basement membrane is visible under light microscopy. Electron microscopy shows that the basement membrane consists of three layers: the lamina lucida (electron-lucent), lamina densa (electron-dense), and lamina fibro-reticularis (electron-lucent).

The lamina densa was formerly called the “basal lamina”. The terms “basal lamina” and “basement membrane” were often used interchangeably, until it was realised that all three layers seen with the electron microscope constituted the single layer seen with the light microscope. This has led to considerable terminological confusion; if used, the term “basal lamina” should be confined to its meaning as lamina densa. [6]

Some theorize that the lamina lucida is an artifact created when preparing the tissue, and that the lamina lucida is therefore equal to the lamina densa in vivo. [7]

The term "basal lamina" is usually used with electron microscopy, while the term "basement membrane" is usually used with light microscopy.

Examples of basement membranes include:

The glomerular basement membrane is a special case, consisting of a fusion of the podocyte and endothelial basal laminas, and lacking a lamina reticularis. Thus, it consists of an especially thick lamina densa, sandwiched on its inside and outside by layers of lamina lucida / rara (one from each cell type). These two enveloping layers are often referred to as lamina rara externa and lamina rara interna.

Function

The basal lamina is made and maintained by the cells that sit on it. It acts as a point of attachment for cells. However, it can also have other function such as a permeability barrier in the glomerulus (urine production). Some of the matrix molecules (of the basal lamina) mediate synaptic adhesion in neuromuscular synapses. [8]

Alport syndrome is a genetic disorder resulting from mutations in the COL4A3/4/5 genes. These genes are important in collagen IV synthesis and basement membrane formation. In individuals with this syndrome the basement membrane in structures such as the glomerulus, ears, and eyes does not function properly, causing symptoms such as blood in the urine, loss of hearing, and vision problems.

See also

Related Research Articles

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<span class="mw-page-title-main">Renal corpuscle</span> Blood-filtering component of the nephron of the kidney

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<span class="mw-page-title-main">Glomerulus (kidney)</span> Functional unit of nephron

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<span class="mw-page-title-main">Basement membrane</span> Thin fibrous layer between the cells and the adjacent connective tissue in animals

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<span class="mw-page-title-main">Brush border</span> Microvilli-covered surface of epithelium found throughout the body

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<span class="mw-page-title-main">Intraglomerular mesangial cell</span>

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<span class="mw-page-title-main">Extraglomerular mesangial cell</span>

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<span class="mw-page-title-main">Glomerular basement membrane</span> Part of the filtration apparatus of the kidney

The glomerular basement membrane of the kidney is the basal lamina layer of the glomerulus. The glomerular endothelial cells, the glomerular basement membrane, and the filtration slits between the podocytes perform the filtration function of the glomerulus, separating the blood in the capillaries from the filtrate that forms in Bowman's capsule. The glomerular basement membrane is a fusion of the endothelial cell and podocyte basal laminas, and is the main site of restriction of water flow. Glomerular basement membrane is secreted and maintained by podocyte cells.

The lamina lucida is a component of the basement membrane which is found between the epithelium and underlying connective tissue. It is a roughly 40 nanometre wide electron-lucent zone between the plasma membrane of the basal cells and the (electron-dense) lamina densa of the basement membrane.

The lamina densa is a component of the basement membrane zone between the epidermis and dermis of the skin, and is an electron-dense zone between the lamina lucida and dermis, synthesized by the basal cells of the epidermis, and composed of 1) type IV collagen, 2) anchoring fibrils made of type VII collagen, and 3) dermal microfibrils.

Anchoring fibrils extend from the basal lamina of epithelial cells and attach to the lamina reticularis by wrapping around the reticular fiber bundles. The basal lamina and lamina reticularis together make up the basement membrane. Anchoring fibrils are essential to the functional integrity of the dermoepidermal junction.

Histology is the study of the minute structure, composition, and function of tissues. Mature human vocal cords are composed of layered structures which are quite different at the histological level.

Tissue engineering of oral mucosa combines cells, materials and engineering to produce a three-dimensional reconstruction of oral mucosa. It is meant to simulate the real anatomical structure and function of oral mucosa. Tissue engineered oral mucosa shows promise for clinical use, such as the replacement of soft tissue defects in the oral cavity. These defects can be divided into two major categories: the gingival recessions which are tooth-related defects, and the non tooth-related defects. Non tooth-related defects can be the result of trauma, chronic infection or defects caused by tumor resection or ablation. Common approaches for replacing damaged oral mucosa are the use of autologous grafts and cultured epithelial sheets.

References

  1. ↑ Histology image:22403loa from Vaughan, Deborah (2002). A Learning System in Histology: CD-ROM and Guide. Oxford University Press. ISBN   978-0195151732.
  2. ↑ UIUC Histology Subject 500
  3. ↑ UIUC Histology Subject 499
  4. ↑ Histology image:20904loa from Vaughan, Deborah (2002). A Learning System in Histology: CD-ROM and Guide. Oxford University Press. ISBN   978-0195151732.
  5. ↑ Histology image:22203loa from Vaughan, Deborah (2002). A Learning System in Histology: CD-ROM and Guide. Oxford University Press. ISBN   978-0195151732.
  6. ↑ Wheater (2000). Functional Histology (4th ed.).
  7. ↑ Chan, F.; Inoue, S. (1994). "Lamina lucida of basement membrane: An artefact". Microsc Res Tech. 28 (1): 48–59. doi:10.1002/jemt.1070280106. PMID   8061357. S2CID   36363808.
  8. ↑ Klein, Bradley G., ed. (2013). Cunningham's Textbook of Veterinary Physiology (5th ed.). St. Louis, Mo.: Elsevier/Saunders. p. 61. ISBN   9781437723618.
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