Basement membrane

Your body has tiny sheets.

These sheets are very thin. They are strong and bendy. They act like a floor for cells.

This floor holds cells in place. It also helps cells move. The sheet helps move food to cells. It can even help make new blood vessels. Some cells live right on top of it. This sheet is found in all animals. It helps keep your body working well.

Your body is made of many cell layers.

A basement membrane is a thin, strong sheet. It acts like a floor for cells. This floor is called the extracellular matrix. It holds cells in place. It also separates different layers of cells.

This sheet helps cells grow and move. It even helps make new blood vessels. It also helps move food and waste. The sheet sits on top of connective tissue. This tissue is full of blood vessels. These vessels give nutrients to the cells.

The basement membrane has two main layers. One layer faces the top cells. We call this the basal lamina. The other layer faces the tissue below. We call this the reticular lamina. In the kidney, this sheet is very thick.

It works like a filter. It stops big things in the blood from entering urine. In the skin, the sheet is more complex. It is part of a basement membrane zone. This zone helps hold the skin together. Some diseases happen when these sheets do not work well.

The basement membrane is a very thin and strong sheet. It is a special kind of extracellular matrix. This matrix is common to all multicellular animals.

The membrane acts as a base for epithelial tissue. It separates these cells from other layers like the endothelium. It also anchors the cells to the connective tissue below. This connective tissue is called the stroma. Some individual cells also have their own membrane. This includes muscle cells, fat cells, and Schwann cells.

This sheet works in a very organized way. It has two main layers called laminae. The external layer is the basal lamina. This layer faces the epithelium. The internal layer is the reticular lamina. This layer faces the connective tissue.

Cells on both sides help make the membrane. One set of parts comes from the epithelial cells. The other set comes from the connective tissue. They mix together to form the sheet. This sheet contains proteins like laminins and collagen. It also contains things called proteoglycans. These parts include perlecan, agrin, and heparan sulfate proteoglycan.

Scientists first saw this membrane in the 1800s. They found it in skeletal muscle tissue.

It took much longer to understand it. We did not learn about its tiny parts until the 1970s and 1980s. This was when molecular understanding began to grow. We now know how these parts work together. This knowledge helps us understand how cells grow and move. It also shows how cells know which way is up. This is called cell polarity.

Different parts of the body use the membrane in different ways. The kidney has a very thick basement membrane. This is called the glomerular basement membrane.

It has three layers instead of two. These are the lamina rara interna, the central lamina densa, and the lamina rara externa. This thick layer acts like a filter. It stops large molecules in the blood from entering urine. In the skin, the membrane is part of the basement membrane zone. This zone has four distinct layers. These layers include the basal cell layer and the lamina lucida. It also includes the lamina densa and the sublaminal densa.

This membrane is vital for staying healthy. It acts as a barrier to stop bad cells from spreading. It also helps make new blood vessels.

Sometimes, the membrane does not work correctly. Genetic defects can cause diseases like Alport syndrome. There are also autoimmune diseases like Goodpasture's syndrome. Some skin problems, called epidermolysis bullosa, come from the membrane zone. The membrane also helps cells replace themselves. This is important in the skin and the digestive tract. It helps replace cells damaged by acid or scrapes.

The basement membrane is a specialized form of extracellular matrix, or ECM. This term refers to the material that surrounds cells in animals. The basement membrane is a very thin, flexible, and strong sheet. It serves as a vital supporting base for all epithelial tissues. These tissues are the layers of cells that line our organs and skin. The membrane also separates epithelium from other layers, such as the endothelium. It anchors the epithelium to the underlying connective tissue, which is called the stroma.

This structure works through a specific biological mechanism. The membrane is synthesized by cells located on both sides of it. One set of components is made by the basal epithelial cells. The other set is produced by the underlying connective tissue. These components blend together to form the finished sheet. The membrane contains glycoproteins, which are proteins with sugar chains. These include laminins, type IV collagen, and nidogen. It also contains proteoglycans, such as perlecan, agrin, and heparan sulfate proteoglycan.

The basement membrane is often described as having two distinct layers, or laminae. The external layer is the basal lamina, which faces the epithelium. The internal layer is the reticular lamina, which faces the connective tissue. This organization helps with cell polarity. Polarity means the cells know which side is the top and which is the bottom. The surface facing the open space is the apical surface. The surface facing the membrane is the basal surface. This structure also acts as a platform for cell signaling and migration.

Scientists have been studying this structure for a long time. It was first described in skeletal muscle tissue during the 1800s. However, we did not truly understand its molecular makeup for much longer. A deep molecular understanding only began to develop in the 1970s and 1980s. This era allowed researchers to identify the specific proteins involved. We now know how these proteins allow cells to differentiate, or become specialized.

Different organs use the membrane in unique ways. In the kidney, the glomerular basement membrane is unusually thick. It has three layers instead of two. These layers are the lamina rara interna, the lamina densa, and the lamina rara externa. This thick structure acts as a molecular filter. It prevents large macromolecules from moving from the blood into the urine. In the lungs, the membranes of the alveoli and capillaries are fused. This fusion allows for the easy exchange of gases.

The skin uses a more complex version called the basement membrane zone, or BMZ. The BMZ contains four distinct layers. These are the basal cell layer, the lamina lucida, the lamina densa, and the sublaminal densa. The lamina densa is mostly a scaffold made of type IV collagen. In the skin, the membrane is vital for cell replacement. Cells near the internal membrane show high rates of mitosis, or cell division. This helps replace skin cells lost to abrasions.

The basement membrane is essential for maintaining health and stability. It acts as a mechanical barrier against certain diseases. It can prevent malignant cells from invading deeper tissues. When these cells are limited to the epithelial layer, it is called carcinoma in situ. The membrane is also essential for angiogenesis, which is the development of new blood vessels. However, if the membrane fails, it can lead to serious medical conditions. Genetic defects can cause Alport syndrome or Knobloch syndrome. Autoimmune diseases, like Goodpasture's syndrome, can also target these membranes.