The capillaries consist of a tube lined by endothelial cells with a central lumen. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. It is outside the capillary lumen, but surrounded by capillaries. This pain is caused by a narrowing and stiffening of the urethral lumen. The capsule and tubule are connected and are composed of epithelial cells with a lumen. The mucosa surrounds the lumen, or open space within the tube. These all are secreted into the lumen of renal tubule. All posterior midgut activity is restricted to the posterior midgut lumen. The SI unit of luminous flux is the lumen (lm). This does not spread but remains confined to the lumen of the small intestine. These sensory receptors are located on the medial concave surface of the crescent lumen. The tonsils are a compact mass which point away from the lumen of the pharynx. Inflammatory processes result in an influx of neutrophils into the bowel lumen. Thyroglobulin contains 123 units of tyrosine, which reacts with iodine within the follicular lumen. The lumen or surface of the lamella has a complex structure.