Quick Facts
The cell membrane is the structure enveloping a cell, enclosing the cytoplasm and forming a selective permeability barrier; it consists of a lipid bilayer with integral and peripheral proteins and contains channels and pumps to transport substances across the membrane, as well as receptors to receive stimuli from the external environment and transduce them into intracellular signals (Dorland, 2011).
Related parts of the anatomy
Structure and/or Key Feature(s)
The cell membrane (or plasmalemma) is a bi-layered membrane, containing primarily phospholipids, cholesterol, and protein molecules. About 7.5-10 nm in width, it can have integral proteins attached to either the internal or the external surface of the bilayer.
The external surface of the cell membrane contains a carbohydrate-rich region termed the glycocalyx which links to cell membrane proteins and lipids (Ross and Pawlina, 2006; Ovalle, Nahirney and Netter, 2013; McKinley, O'Loughlin and Pennefather-O'Brien, 2016).
Anatomical Relations
The cell membrane is the external boundary of the cell.
Function
The cell membrane is the barrier between the very stable internal environment of the cell and the external environment. It allows transfer of materials across the cell membrane. Oxygen, nutrients, waste products, and other materials, pass in and out of the cell through the cell membrane using a very detailed set of transport processes. Bulk transfer of material occurs through the cell membrane. The bulk intake of materials is called endocytosis and the release of bulk materials is exocytosis. Both of these processes involve different proteins and other molecules that associate with the cell membrane.
The integral proteins perform very important functions:
- form intercellular junctions;
- create pumps or channels to allow ions and molecules to go in and out of the cell;
- serve as receptors;
- act as enzymes on the surface of the cell;
- act in cell recognition.
The glycocalyx plays a role in cell recognition and attachments to other cells and extracellular molecules (Ross and Pawlina, 2006; Ovalle, Nahirney and Netter, 2013; McKinley, O'Loughlin and Pennefather-O'Brien, 2016).
Clinical Correlates
Cystic fibrosis is an inherited disease and is partly due to a defect in the proteins that affect chloride ion (Cl-) channels within the cell membrane.
Many glycoproteins and glycolipids in the cell membrane act as receptors that mediate various cell activities, cell adhesions, and responses to chemical messengers. A number of diseases are a result of defective receptors e.g., target cells of some hormones do not respond because they lack the relevant, competent receptors (McKinley, O'Loughlin and Pennefather-O'Brien, 2016).
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
McKinley, M. P., O'Loughlin, V. D. and Pennefather-O'Brien, E. E. (2016) Human Anatomy. 5th edn.: McGraw-Hill Education.
Ovalle, W. K., Nahirney, P. C. and Netter, F. H. (2013) Netter's Essential Histology. ClinicalKey 2012: Elsevier Saunders.
Ross, M. H. and Pawlina, W. (2006) Histology: A text and atlas. Lippincott Williams & Wilkins.
