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Basement Membrane

What Is It, How It’s Formed, and More

Author: Maria Emfietzoglou, MD

Editors: Alyssa Haag, Ian Mannarino, MD, MBA, Kelsey LaFayette, DNP, RN

Illustrator: Jessica Reynolds, MS

Copyeditor: David G. Walker

What is a basement membrane?

The basement membrane, also known as basal lamina, is a thin, dense layer of extracellular matrix that lines most human tissues forming the supporting structure and scaffolding for epithelial tissue and separates different types of cells, such as nerve cells and muscle cells. The basement membrane plays an important role in maintenance of tissue structure and function. 

How is the basement membrane formed?

The basement membrane is formed by a mixture of molecules, including type IV collagen (i.e., the structural protein found in the basement membrane, the lens of the eye, and the cochlea of the ear) primarily and laminin (i.e., a glycoprotein, or protein that contains oligosaccharide chains). Several other proteins, like nidogen and perlecan, can also be present in the basement membrane. Each tissue (e.g., epithelial, connective, muscular, and nervous tissue) has an extracellular matrix and a basement membrane with a unique composition adapted for each tissue’s unique needs. Additionally, the basement membrane is a dynamic structure, meaning that it can change over time in response to triggers, such as mechanical stress, aging, or disease. 

Where is the basement membrane located?

The basement membrane is located in almost every tissue of the body. It can lie beneath endothelial and epithelial cells; separate cells from the underlying connective tissue; or surround cells, like muscle (myofibrils), fat, and nerve cells (neurofibrils). In  the kidney glomerulus (i.e., a network of small blood vessels), the basement membrane is located between the endothelial and epithelial layer to form the glomerular filtration barrier. On the other hand, in the lungs, the basement membrane is found between the alveoli (i.e., the smallest air sacs that serve as the basic respiratory units) and the pulmonary capillaries. In the neuromuscular junction (i.e., the place where a neuron synapses, or meets, a skeletal muscle fiber causing it to contract), the basement membrane is found within the synaptic cleft (the gap between the neuron and the muscle fiber). 

What is the function of the basement membrane?

The basement membrane predominantly provides structural support as it helps cells to attach and anchor to the underlying tissues. It also acts as a barrier, preventing cancer cells from invading the deeper tissue layers, and is essential in regulating cell behavior, such as proliferation, differentiation, adhesion, or migration. Angiogenesis, which is formation of new blood vessels, is also mediated by the basement membrane as key components of basement membrane, like collagen type IV, are thought to play an important role in this process. 

The basement membrane also has tissue-specific functions. In the kidney glomerulus, the basement membrane acts as a filter by allowing only water and small molecules to pass into the urine, whereas in the lungs, the basement membrane allows rapid gas (i.e., oxygen and carbon dioxide) exchange. At the neuromuscular junction, the basement membrane separates nerve cells from muscle cells; directs the formation of presynaptic and postsynaptic membranes; and in case of an injury, helps to regenerate the synapse. 

What are the most important facts to know about the basement membrane?

The basement membrane is a thin, dense layer of extracellular matrix that consists of collagen type IV, laminin, and a variety of other molecules. The exact composition is dynamic and differs depending on the tissue. The basement membrane can be found in almost every tissue and can either lie underneath endothelial and epithelial cells, separate cells from the underlying connective tissue, or surround cells (like muscle, fat, and nerve cells). It serves a variety of functions, including structural support, prevention of tumor invasion, regulation of cell behavior, angiogenesis, as well as other tissue-specific functions.  

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