A key characteristic of life is the ability to separate the external environment from the internal space. To do this, cells have evolved semi-permeable membranes that regulate the passage of biological molecules. Additionally, the cell membrane defines a cell’s shape and interactions with the external environment. Eukaryotic cell membranes also serve to compartmentalize the internal space into organelles, including the endomembrane structures of the nucleus, endoplasmic reticulum and...

A cell's plasma membrane demarcates the cell's borders and determines the nature of its interaction with the environment. Cells exclude certain substances, take in others, and excrete some others in controlled quantities. The plasma membrane must be flexible to allow certain cells, such as red and white blood cells, to change their shape while passing through narrow capillaries. These are the more obvious plasma membrane functions. In addition, the plasma membrane's surface carries...

A tissue membrane is a thin layer of cells that covers the outside of the body, the organs, internal passageways that lead to the exterior of the body, and the lining of the moveable joint cavities. There are two basic types of tissue membranes— connective tissue and epithelial membranes.
Connective Tissue Membranes
The connective tissue membrane is formed solely from connective tissue. These membranes encapsulate organs, such as the kidneys, and line our movable joints. A synovial...

The protrusion of the cell surface is an initial step for several cellular processes, including cell migration, phagocytosis, and neurite outgrowth. These membrane protrusions are a result of cytoskeletal rearrangement. The most  widely observed cell protrusions include lamellipodia, pseudopodia, filopodia, microvilli, invadopodia, and podosomes. These protrusions can be of two types — static or dynamic.
The microvilli, an example of stable protrusions, are finger-like projections...