The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of
extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling.
The basement membrane sits between
epithelial tissues including
mesothelium
The mesothelium is a membrane composed of simple squamous epithelium, simple squamous epithelial cells of mesodermal origin, which forms the lining of several body cavities: the pleura (pleural cavity around the lungs), peritoneum (abdominopelvic ...
and
endothelium
The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the r ...
, and the underlying connective tissue.
Structure

As seen with the
electron microscope
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing it ...
, the basement membrane is composed of two layers, the
basal lamina and the
reticular lamina
Reticular fibers, reticular fibres or reticulin is a type of fiber in connective tissue composed of type III collagen secreted by reticular cells. They are mainly composed of reticulin protein and form a network or mesh. Reticular fibers cross ...
.
The underlying connective tissue attaches to the basal lamina with
collagen VII anchoring fibrils and
fibrillin microfibrils.
The basal lamina layer can further be subdivided into two layers based on their visual appearance in electron microscopy. The lighter-colored layer closer to the epithelium is called the
lamina lucida, while the denser-colored layer closer to the connective tissue is called the
lamina densa. The
electron-dense lamina densa layer is about 30–70
nanometers thick and consists of an underlying network of reticular
collagen IV fibrils which average 30 nanometers in diameter and 0.1–2
micrometers in thickness and are coated with the heparan sulfate-rich proteoglycan
perlecan. In addition to collagen, this supportive matrix contains intrinsic macromolecular components. The lamina lucida layer is made up of
laminin,
integrins,
entactins, and
dystroglycans. Integrins are a key component of
hemidesmosomes which serve to anchor the epithelium to the underlying basement membrane.
To represent the above in a visually organised manner, the basement membrane is organized as follows:
*
Epithelial/
mesothelial/
endothelial tissue (outer layer)
* Basement membrane
**
Basal lamina
***
Lamina lucida
****
laminin
****
integrins (
hemidesmosomes)
****
nidogens
****
dystroglycans
***
Lamina densa
****
collagen IV (coated with
perlecan, rich in
heparan sulfate
Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs in a proteoglycan (HSPG, i.e. Heparan Sulfate ProteoGlycan) in which two or three HS chains are attached in close proximity to cell surface or extracellular ma ...
)
** Attaching proteins (between the basal and reticular laminae)
***
collagen VII (anchoring fibrils)
***
fibrillin (
microfibrils)
**
Lamina reticularis
***
collagen III (as
reticular fibers)
*
Connective tissue
Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...
(
Lamina propria)
Function
The primary function of the basement membrane is to anchor down the
epithelium
Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
to its loose
connective tissue
Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...
(the
dermis
The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...
or
lamina propria) underneath. This is achieved by cell-
matrix
Matrix (: matrices or matrixes) or MATRIX may refer to:
Science and mathematics
* Matrix (mathematics), a rectangular array of numbers, symbols or expressions
* Matrix (logic), part of a formula in prenex normal form
* Matrix (biology), the m ...
adhesions through
substrate adhesion molecules (SAMs).
The basement membrane acts as a mechanical barrier, preventing
malignant
Malignancy () is the tendency of a medical condition to become progressively worse; the term is most familiar as a characterization of cancer.
A ''malignant'' tumor contrasts with a non-cancerous benign tumor, ''benign'' tumor in that a malig ...
cells from invading the deeper tissues. Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called
carcinoma in situ.
The basement membrane is also essential for
angiogenesis (development of new blood vessels). Basement membrane proteins have been found to accelerate
differentiation of
endothelial cells.
The most notable examples of basement membranes is the
glomerular basement membrane of the
kidney
In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...
, by the fusion of the
basal lamina from the
endothelium
The endothelium (: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the r ...
of glomerular capillaries and the
podocyte basal lamina, and between
lung
The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...
alveoli and pulmonary
capillaries, by the fusion of the basal lamina of the lung alveoli and of the basal lamina of the lung capillaries, which is where oxygen and diffusion occurs (
gas exchange).
As of 2017, other roles for basement membrane include blood filtration and muscle homeostasis.
Fractones may be a type of basement membrane, serving as a
niche for
stem cell
In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can change into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of cell ...
s.
Clinical significance
Some diseases result from a poorly functioning basement membrane. The cause can be genetic defects, injuries by the body's own immune system, or other mechanisms. Diseases involving basement membranes at multiple locations include:
* Genetic defects in the collagen fibers of the basement membrane, including
Alport syndrome and
Knobloch syndrome
*
Autoimmune diseases targeting basement membranes. Non-collagenous domain basement membrane collagen type IV is autoantigen (target antigen) of autoantibodies in the autoimmune disease
Goodpasture's syndrome.
* A group of diseases stemming from improper function of basement membrane zone are united under the name
epidermolysis bullosa.
In
histopathology
Histopathology (compound of three Greek words: 'tissue', 'suffering', and '' -logia'' 'study of') is the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopatholog ...
, thickened basement membranes are found in several inflammatory diseases, such as
lichen sclerosus,
systemic lupus erythematosus
Lupus, formally called systemic lupus erythematosus (SLE), is an autoimmune disease in which the body's immune system mistakenly attacks healthy tissue in many parts of the body. Symptoms vary among people and may be mild to severe. Common ...
or
dermatomyositis in the skin, or collagenous colitis in the colon.
Evolutionary origin
These are only found within
diploblast
Diploblasty is a condition of the blastula in which there are two primary germ layers: the ectoderm and endoderm.
Diploblastic organisms are organisms which develop from such a blastula, and include Cnidaria and Ctenophora, formerly grouped t ...
ic and
homoscleromorphic sponge animals. The homoscleromorph were found to be sister to diploblasts in some studies, making the membrane originate once in the history of life. But more recent studies have disregarded diploblast-homoscleromorph group, so other sponges may have lost it (most probable) or the origin in the two groups may be separate.
See also
*
References
Further reading
*
{{Authority control
Angiology
Tissues (biology)
Histology