lumen

(noun)

The inside space of a tubular structure, such as an artery or intestine.

Related Terms

Examples of lumen in the following topics:

  • Mucosa

    • Since the mucosa is the innermost layer within the GI tract, it surrounds an open space known as the lumen.
    • Food, mucus, and digestive juices pass through the lumen, and the mucosa comes in direct contact with digested food (chyme).
    • This cross section shows the mucosa in relation to the interior space, or lumen.

  • Transcytosis

    • Listeria monocytogenes has been shown to enter the intestinal lumen via transcytosis across goblet cells.
    • Shiga toxin secreted by entero-hemorrhagic E. coli has been shown to be transcytosed into the intestinal lumen.

  • Lymphatic Vessel Structure

    • The endothelium is designed with junctions between cells that allow interstitial fluid to flow into the lumen when pressure becomes high enough (such as from blood capillary hydrostatic pressure), but does not normally allow lymph fluid to leak back out into the interstitial space.
    • The next layer is smooth muscles arranged in a circular fashion around the endothelium that alters the pressure inside the lumen (space) inside the vessel by contracting and relaxing.
    • Smooth muscle contractions only cause small changes in pressure and volume within the lumen of the lymph vessels, so the fluid would just move backwards when the pressure dropped.

  • Histology of the Small Intestine

    • Because the lumen of the gastrointestinal tract is exposed to the external environment, much of it is populated with potentially pathogenic microorganisms.
    • Peyer's patches function as the immune surveillance system of the intestinal lumen and facilitate the generation of the immune response within the mucosa.
    • In other words, the increased surface area (in contact with the fluid in the lumen) decreases the average distance traveled by the nutrient molecules, so the effectiveness of diffusion increases.

  • Tubular Secretion

    • Tubular secretion is the transfer of materials from peritubular capillaries to the renal tubular lumen; it is the opposite process of reabsorption.
    • Active transport—the movement of molecules via ATPase pumps that transport the substance through the renal epithelial cell into the lumen of the nephron.

  • Absorption in the Small Intestine

    • The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids).

  • The Role of the Kidneys in Acid-Base Balance

    • Bicarbonate (HCO3-) does not have a transporter, so its reabsorption involves a series of reactions in the tubule lumen and tubular epithelium.

  • Glandular Epithelia

    • The exocrine glands secrete their products into a duct that then delivers the product to the lumen of an organ or onto the free surface of the epithelium.

  • Formation, Storage, and Release of Thyroid Hormones

    • Thyroglobulin, the pre-cursor of T4 and T3, is produced by the thyroid follicular cells before being secreted and stored in the follicular lumen.

  • Yolk Sac Development

    • Sometimes, a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct.