lumen

LUMEN
In general, a lumen is a unit of measurement that describes the amount of light emitted by a source of illumination, such as a light bulb or flashlight. However, in biology and medicine, the term "lumen" has a different meaning.

In biology, a lumen refers to the space within a tubular structure, such as a blood vessel, intestine, or gland. The lumen is the cavity or channel through which substances such as blood, food, or secretions flow. The term is often used to describe the interior space of hollow organs or ducts in the body. For example, the lumen of a blood vessel refers to the space inside the vessel where blood flows. The lumen of the small intestine refers to the inner space of the intestine where food is digested and absorbed. The lumen of a gland, such as the pancreas or salivary gland, refers to the internal cavity where secretions are produced and transported.

The size and shape of a lumen can vary depending on the structure and function of the organ or vessel. In some cases, a blockage or narrowing of the lumen can lead to health problems, such as reduced blood flow or digestive issues.