A normal functioning liver will secrete 600-1200 ml of bile to the gall bladder on a daily basis. Bile is made up of bile salts, lecithin, conjugated bilirubin, phospholipids, cholesterol, electrolytes, and water. Bile salts, which are the predominant component of bile, are synthesized from cholesterol in the hepa-tocyte. The primary function of bile salts lies in their interaction with lipid digestion. Bile salts bind with large fat particles, which alone are insoluble in water, and act on them as an emulsifier, breaking down into smaller particles called micelles. Micelles, the product of the fat particle and bile salt structure, aid in the transport of fat to the mucosal membrane for absorption. Fat-soluble vitamins and cholesterol are also incorporated into mixed micelles for proper absorption.
Micellar solubilization is only required for long-chain fatty acids. Short-chain fatty acids (10 carbons or less) do not require micelle formation for absorption; instead, they enter the portal circulation directly, bound to albumin, and are transferred to the liver for oxidation. Approximately 94% of the micelle forming bile acids are reabsorbed in the ileum and shuttled via the portal hepatic vein bound to albumin back to the liver. Only 6% of bile acids are lost in excretion.
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