The Liver

The liver is a compound tubular gland that secretes bile that aids in digestion of dietary fat. Bile is a solution containing bile salts, bilirubin, cholesterol, the phospholipid lecithin, and electrolytes that include sodium, potassium, chloride and bicarbonate. Bile is synthesized by hepatic cells of the liver which are arranged in lobules. Bile is stored in the gallbladder until released. Horses do not have gallbladders. They secrete bile directly into the duodenum. The common bile duct empties bile into the duodenum. Bile salts in the bile cause emulsification of fat and aid in digestion by pancreatic lipase. After absorption, nutrients are transported to the liver by the portal vein. The portal vein carries blood from the stomach, pancreas, spleen, and intestines. The passage of blood from these organs into liver sinusoids help the liver cleanse the blood and process the nutrients it carries.

Liver sinusoids are lined with Kupfer's cell (macrophages) that engulf (phagocytize) foreign materials, tissue debris, including aging red blood cells destroyed by the liver. The liver also receives nutrients (Oxygen) from the hepatic artery. Blood from both the hepatic artery and portal vein, after passage through the liver sinusoids, collects in the central vein of the liver lobule. Blood leaves the liver through the hepatic vein.

In addition to bile, the liver synthesizes glucose, many proteins and clotting factors. It contributes to fat and glucose metabolism, stores iron and vitamin A, detoxifies and modifies many substances, and performs other functions. It is a vital organ to the body.