They pass from the interstitial space into lymphatic vessels and are eventually dumped to the venous circulation via the thoracic duct. Thus, flow through lymphatic vessels greatly increases during absorption of a meal. Primary causes of maldigestion are enzyme insufficiency, and bile salt defects including defects in enterohepatic circulation. The absorption of Cl- is passive in the proximal intestine where tight junctions between cells are leaky. However, as the epithelia become less leaky through the distal intestine and colon, electroneutral transport of Cl- across the lumenal membrane becomes important for its absorption to the blood.
Magnesium interacts competitively with calcium transport.
Water permeability in the colon is low, so it is at this level that regulation of stool water content takes place under normal conditions. A normal colon can reabsorb a maximum of about 4.5 liters of H2O per day. Rapid equilibration of H2O between lumen and blood occurs in the proximal intestinal tract following the rules of osmosis. In the duodenum chyme is quickly brought to isotonicity. Ingestion of a hypotonic meal leads to rapid loss of water to blood with isotonicity reached prior to the jejunum.