Pallor

Pallor is undue paleness of the skin.

Presentation

Along with paleness of skin it is "observable also in certain mucous membranes, such as the conjunctiva and the lining of the mouth. Transient pallor may result from constriction of the blood vessels near the surface. Longer-term pallor may be due to anaemia or lack of exposure to sunlight. Permanent pallor may be caused by Albimism."

Symptom recognition

• In the London criteria, facial pallor is mentioned under the criteria of periods of impaired circulation compatible with autonomic dysfunction.

membrane The word "membrane" can have different meanings in different fields of biology. In cell biology, a membrane is a layer of molecules that surround its contents. Examples of cell-biology membranes include the "cell membrane" that surrounds a cell, the "mitochondrial membranes" that form the outer layers of mitochondria, and the "viral envelope" that surrounds enveloped viruses. In anatomy or tissue biology, a membrane is a barrier formed by a layer of cells. Examples of anatomical membranes include the pleural membranes that surrounds the lungs, the pericardium which surrounds the heart, and some of the layers within the blood-brain barrier.