List of abbreviations
of micros-
specialist terms
explained in
English +

Every attempt was made to provide correct information and labelling, however any liability for eventual errors or incompleteness is rejected!

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Dr. med.
H. Jastrow

of use
Overview basement membrane (Membrana basalis) & basal lamina (Lamina basalis):
Pages with explanations are linked to the text below the images if available! (Labelling is in German)
hemidesmosome anchored to the
 basement membrane (monkey)
overview of the
previous image
basement membrane in tran-
sitorial epithelium (monkey)
basement membrane of
human skin
Detail thereof with 2
hemidesmosomes (human)
basal lamina continues
into junctional folds (rat)
basal membrane kid-
ney glomerulus (rat)
anchoring of keratin
filaments, skin (rat)
basement membrane in a striated
duct of a slivary gland (rat)
basolateral foldings with pro-
trusions of L. densa (rat)
basement membrane
striated duct (Ratte)
basement membrane
smooth muscle cell (rat)
basement membrane as filtra-
tion barrier in kidney (monkey)
podocytes attached to a
basallamina, kidney (monkey)
basement membrane of a non-
myelinated nerve (rat)
basement membranes of
smooth muscle cells (monkey)
basement membrane
palatine tonsil (human)
reduced basal lamina
blood-air barrier (rat)
The basement membrane (Terminologia histologica: Membrana basalis) is a homogenous layer of the extracellular space located closely beneath basal epithelial cells or membranes of some special types of cells (see below). The name basement membrane derives from light microscopic appearance. Using the electron microscope the following layers of the basement membrane can be distinguished:
1. a Lamina rara externa (or lucida since it is not electron-dense) directly bordering the adjacent cell forms the upper portion of the basal lamina (Terminologia histologica: Lamina basalis) and is 10 to 50 nanometers (nm) thick;
2. die next layer is the electron-dense Lamina densa comprising the intermediate part of the basal lamina. It has a thickness of 20 to 300, mostly 50 nm.
3. The following hardly electron-dense Lamina rara interna is only about 10 nm thick and the basal portion of the basal lamina.
4. The consequent Lamina fibroreticularis has a thickness of 200 - 500 nm.
In short the basement membrane is comprised of the 3-layered basal lamina and the lamina fibroreticularis.
The electron-lucent Lamina rara externa and interna show hardly any substructures whereas the other layers are more electron-dense. Larger collagen fibrils (type 1 + 3) are present as components of the lamina fibroreticularis.
major components of the different layers (molecular composition) & further information:
1. The extracellular endings of a.) alpha6-beta4-Integrins of hemidesosomes, b.) cell surface receptor proteins (CD 44 - receptor and lamininreceptors) and c.) integrins of adhesion plaques (Areae densae of smooth muscle cells) to which anchoring filaments are bound reach into the Lamina rara externa. Relevant molecules in this context are: Kalinin, Nicein, K-Laminin (Laminin 5), Epiligin and 19DEJ1 antigen (a), hyaluronic acids bound to the CD 44 rezeptor (b), Perlecan which is switched to different laminin receptors, thrombospondin and Laminins (b) or Fibronectin which is bound to the alpha subunit of integrins (c). Further molecules reach from the cell membrane into the lamina densa: syndecan and high-density basement membrane proteoglycan, collagen-4, heparin/heparansulfate.
2. The most important components of the Lamina densa are (pro-)collagen type 4, heparansulfate proteoglycane and chondroitin-6-sulfate proteoglycan. Collagen-4 terminal peptide chains are preserved in the lamina densa and thus may connect to each other instead of  binding to collagen1 or 3.
3. Major molecules of the Lamina rara interna are collagen-7, fibronectin, thrombospondin and hyaluronic acid. The first 3 of them, especially fibronectin are resonsible for connection to the following layer.
4. A Lamina fibroreticularis is missing at these locations: a.) basement membrane of glomeruli in kidney located between podocyte processes and endothelial cells of the glomerular capillaries; b.) in the capsule of the lens of the eye and c.) beneath transverse tululi (T-Tubuli) of heart muscle cells. This is causedby the fact that no connective tissue is present beyond the basal lamina at these locations. Besides Collagen-1 and -3 fibrils which can be seen in the electron microscope due to their thickness of about 50 nm, further important substances are encountered here: fibrillin-microfibrils, collagen-7, anchoring fibrils, collagen-4 anchoring plaques, decorin, fibromodulin, biglykan, versican, during growth tenascin and fibronectin for fixation of fibres and fibrils to fibronectin receptors of fibroblasts/fibrocytes.Since already the basal lamina has over 50 different glycoproteins and  proteoglcans only some of its major components are mentioned here. Some of these components are synthetised by connective tissue cells (mainly fibroblasts), others by adjacent epithelial cells and few from other cells located further distant.
presence of basement membranes:
As mentioned above, basement membrane is present between epithelial cells or endothelial cells and adjacent connective tissue. It surrounds smooth and striated muscle cells, fat cells, Schwann's cells (= cells ensheating peripherical nerves), cells of adrenal medulla, reticular epithelial cells of the thymus and the surface of brain and spinal cord. All tissues that derive from ektoderm show a basal lamina not only the epithelium.
A specially thick basallamina is seen as Descement's membrane under corneal endothelium and the lense capsule in the eye as well as in the filtration barrier of renal glomeruli.
The thick basement membrane between the epithelium and connective tissue at the base of hair follicles which appears hyalinic is called glassy membrane (Terminologia histologica: Membrana vitrea) a similar glassy membrane is located between the follicle epithelium and the ovum in the ovary. In some cases the lamina densa protrudes a little in basolateral infoldings of the cell membrane of epithelial cells as can be seen above. In neuromuscular junctions the basal lamina continues into subjunctional folds.
In the area of the blood air barrier between alveolar epithelial cells type 1 and endothelial cells of the capillaries in lung alveols the basal laminae of both cells join to a common relatively thin lamina to facilitate diffusion of gases.
electron microscopic techniques:
Application of different fixation techniques is able to visualize different components of the basement membrane:
- Glutaraldehyd alone: lamina densa appears as fine meshwork of thin filaments;
- Glutaraldehyd/Alcianblue: proteoglycans are visible as comma-like structures in outer lamina densa;
- Glutaraldehyd/Rutheniumred: proteoglycans appear as fine granules;
- Glutaraldehyd/Tannin: glycoproteins are visible as very electron-dense granules.

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Six images were kindly provided by Prof. H. Wartenberg; other images, page & copyright H. Jastrow