Venous system in the context of "Arachnoid granulation"

Lymph (from Latin lympha 'water') is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to be recirculated. At the origin of the fluid-return process, interstitial fluid—the fluid between the cells in all body tissues—enters the lymph capillaries. This lymphatic fluid is then transported via progressively larger lymphatic vessels through lymph nodes, where substances are removed by tissue lymphocytes and circulating lymphocytes are added to the fluid, before emptying ultimately into the right or the left subclavian vein, where it mixes with central venous blood.

Because it is derived from interstitial fluid, with which blood and surrounding cells continually exchange substances, lymph undergoes continual change in composition. It is generally similar to blood plasma, which is the fluid component of blood. Lymph returns proteins and excess interstitial fluid to the bloodstream. Lymph also transports fats from the digestive system (beginning in the lacteals) to the blood via chylomicrons.

A venule is a very small vein in the microcirculation that allows blood to return from the capillary beds to drain into the venous system via increasingly larger veins. Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50 μm they can incorporate smooth muscle and are known as muscular venules. Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. Many venules unite to form a vein.

A varix (pl.: varices) is an abnormally dilated blood vessel with a tortuous course. Varices usually occur in the venous system, but may also occur in arterial or lymphatic vessels.

Examples of varices include: