It can refer to:
- The interior of a vessel, such as the central space in an artery, vein or capillary through which blood flows.
- The interior of the gastrointestinal tract
- The pathways of the bronchi in the lungs
- The interior of renal tubules and urinary collecting ducts
- The pathways of the female genital tract, starting with a single pathway of the vagina, splitting up in two lumina in the uterus, both of which continue through the fallopian tubes
- Stedman's Medical Dictionary, 24th ed.
- Adds, John; Erica Larkcom; Ruth Miller. Exchange and transport, energy and ecosystems. Nelson Advanced science (Nelson Thornes). p. 16. ISBN 0-7487-7487-4.
- Makar, A. B.; McMartin, K. E.; Palese, M.; Tephly, T. R. (June 1975). "Formate assay in body fluids: application in methanol poisoning". Biochemical Medicine. 13 (2): 117–126. doi:10.1016/0006-2944(75)90147-7. ISSN 0006-2944. PMID 1.