BASAL LAMINA: CHARACTERISTICS, HISTOLOGY AND FUNCTIONS - BIOLOGY - 2024

The basal lamina is a thin layer of extracellular matrix proteins secreted by epithelial cells. It is found by separating the cells from the epithelial tissue and the underlying connective tissue. It also separates a large number of other cells belonging to other tissues, such as muscle and adipose.

The basal lamina is very difficult or impossible to observe with conventional microscopes, but it is visible in detail with electron microscopy equipment, since it manifests as an electrodense layer of approximately 40 to 120 nanometers (nm) thick, being composed at its once for three sheets.

Electron micrograph of the neuromuscular junction (cross section). T is the terminal of the axon, M is the muscle fiber. The arrow shows junctional folds with the basal lamina. Taken and edited from: National Institute of Mental Health; originally uploaded by Nrets at en.wikipedia..

It is usually called the external lamina when it is observed surrounding or covering muscle tissue or adipose cells (adiposites). The basal lamina fulfills a wide variety of functions in the body. The best known are cell adhesion, epithelial support, and hormone filtering, among others.

characteristics

The basal lamina is characterized by being a highly cross-linked extracellular matrix, composed of type IV collagen, laminin (glycoproteins), perlecan, and entactin (proteoglycans). It can also contain proteases and growth factors such as beta transformant, fibroplasts, among others.

It is a fairly thin and flexible layer about 40-120 nm thick (sometimes more). Some authors describe it as a gelatinous liquid. It is present in all epithelial tissue between cells, in the underlying connective tissue, and in all tissues derived from the ectoderm. It is known to be produced or secreted by epithelial cells.

Histology

The basal lamina is part of the basement membrane. This membrane is a homogeneous layer that is located below the basal epithelial cells. It is composed of 4 layers or sheets of which three make up the basal lamina.

External or lucid rare lamina

It does not present electronic density. It is the upper layer of the basal lamina and, therefore, is the first to come into contact with the plasma membrane of the underlying epithelial tissue. It has a thickness of between 10 and 50 nm.

They can contain laminin, epiligin, fibronectin (glycoproteins), hyaluronic acid and also perlecan, among other compounds.

Dense sheet

It is the intermediate lamina, it is located in the electrodense zone below the lucid lamina. It is seen as a dense layer of electrons composed of type IV collagen, collagen VII fibrils, and dermal microfibrils. It has a thickness that varies between 20 to 300 nm, however it is very common to have a thickness of 50 nm.

Internal rare lamina

It is a sheet with low electron density. It is found below the lamina densa, in the basal portion of the lamina basalis. It is generally 10 nm thick. It is composed mainly of collagen VII, fibronectin, thrombospondin, and hyaluronic acid.

Various authors do not recognize this layer as different from those mentioned above, however, others do recognize it and even describe it in detail.

Features

Cell attachment or adhesion

The basal lamina serves as an anchoring element for epithelial cells, acting as a point of attachment. They do this using electrostatic forces or nonspecific interactions such as the use of adhesion molecules.

Support and support

It is known that its functions include providing support and support to the underlying epithelium.

Cell polarity

Eukaryotic organisms have polarized cells. This characteristic is fundamental for a great variety of cellular physiological processes such as the transmission of chemical signals or the transport of waste and nutrients, among others.

Studies have revealed that the basal lamina is involved in the determination of polarity in cells.

Cell differentiation

The basal lamina induces the process of cell differentiation, which is a phenomenon whereby a non-specialized cell undergoes changes in its structure, becoming more complex and acquiring specific functions.

Synaptic adhesion

The basal lamina has been found to surround muscle cells and separate nerve cells from muscle cells at the synapse. It also intervenes in the reactivation and regeneration of the synapse after injury.

Selective filtration

One of the most studied functions of the basal lamina is that of selective permeability, also called filtration. Multiple studies reveal that these basement membranes are capable of creating filtration barriers in the glomerulus of the kidneys.

It is also known to act on the skin, the blood-brain barrier, and the vascular system as a molecular filter, creating barriers that selectively allow water and small molecules to pass through.

Structural diagram of the renal corpuscle. In the image the number 1 indicates the location of the basal lamina. Taken and edited from: M • Komorniczak -talk- (Polish Wikipedist) Illustration by: Michał Komorniczak This file has been released into the Creative Commons 3.0. Attribution-ShareAlike (CC BY-SA 3.0) If you use on your website or in your publication my images (either original or modified), you are requested to give me details: Michał Komorniczak (Poland) or Michal Komorniczak (Poland).For more information, write to my e-mail address:.

Diseases

The conditions in which the basal lamina is involved are related to those of the basement membrane, of which it is a part.

Muscular dystrophy

This condition is known as a group of diseases that cause progressive weakness and loss of muscle mass whose causes and symptoms are numerous. However, one of these causes is directly associated with the basal lamina.

The presence of a defective form (or the total absence) of a protein called dystrophin that naturally binds to laminin in the extracellular matrix, is the cause of a type of muscular dystrophy. This is because it reduces the union between the muscle cells and the basal lamina.

Alport syndrome

It is a genetic disorder that affects 1 in 5,000-10,000 children. It is caused by mutations in the COL4A3, COL4A4 and COL4A5 genes, which are responsible for the production or biosynthesis of type IV collagen and which participate in the formation of the basement membranes of the kidneys, ears and eyes.

These mutations prevent a folding of the collagen molecule from occurring and breaking the basement membranes that form the blood filtration barriers. This would cause in the case of the kidneys progressive renal failure, in the eyes various ocular anomalies or progressive loss of hearing.

Applications

There is a wide variety of investigations related to the basal laminae that seek to decipher the biochemical composition and physicochemical processes (such as viscosity and permeability) of these structures. The goal is to understand not only aspects of cell biology, but also possible applications.

To date, basal lamina studies are known to have provided insights in pharmacology (drug delivery) and medicine (tumor treatment), as well as innovative tattoo removal techniques and tissue engineering.

References

1. Overview basement membrane (Membrana basalis) & basal lamina (Lamina basalis). Recovered from: drjastrow.de.
2. Basal Lamina. Recovered from: leeds.ac.uk.
3. Basal Lamina. Recovered from: wikipedia.org.
4. Alport syndrome. Recovered from: wikipedia.org.
5. TD Pollard, WC Earnshaw, J. Lippincott-Schwartz & GT Johnson (2017). Cell Biology. 3rd Edition. Elsevier.
6. Epithelial tissue. Basal lamina. Recovered from: uc.cl.
7. F. Arends & O. Lieleg (2016). Biophysical Properties of the Basal Lamina: A Highly Selective Extracellular Matrix. Recovered from: intechopen.com.