631 TABLE Composition of Bile18.1 Component Function Water Serves as solute in which other components are carried Phospholipids (i.e., lecithin) and cholesterol Are metabolic substrates for other cells in the body; act as precursors of membrane components and steroids; largely reabsorbed in the gut and recycled Bile salts (also called bile acids): primary (secreted by liver): cholic acid, chenodeoxycholic acid;  secondary (converted by bacterial flora in the intestine): deoxycholic acid, lithocholic acid Act as emulsifying agents that aid in the digestion and absorption of lipids from the gut and help to keep the cholesterol and phospholipids of the bile in solution, largely recycled, going back and forth between the liver and gut Bile pigments, principally the glucuronide of the bilirubin produced in the spleen, bone marrow, and liver by the breakdown of hemoglobin Detoxify bilirubin, the end product of hemoglobin  degradation, and carry it to the gut for disposal Electrolytes: Na, K, Ca2, Mg2, Cl, and HCO3 Establish and maintain bile as an isotonic fluid; also largely reabsorbed in the gut
Digestive System III: Liver, Gallbladder, and Pancreas  LIVER
The blood delivered to the liver by the hepatic portal vein comes from the digestive tract and the major abdominal organs, such as the pancreas and spleen. The portal blood carried to the liver contains  nutrients and toxic materials absorbed in the intestine.  blood cells and breakdown products of blood cells from the spleen. endocrine secretions of the pancreas and enteroendocrine cells of the gastrointestinal tract.
Thus, the liver stands directly in the pathway of blood vessels that convey substances absorbed from the digestive tract. Although the liver is the first organ to receive metabolic substrates and nutrients, it is also the first exposed to toxic substances that have been absorbed.
The hepatic artery, a branch of the celiac trunk, carries oxygenated blood to the liver, providing the remaining 25% of its blood supply. Because blood from the two sources mixes just before it perfuses the hepatocytes of the liver parenchyma, the liver cells are never exposed to fully oxygenated blood.
Within the liver, the distributing branches of the portal vein and hepatic artery, which supply the sinusoidal capillaries (sinusoids) that bathe the hepatocytes, and the draining branches of the bile duct system, which lead to the common hepatic duct, course together in a relationship termed the portal triad. Although a convenient term, it is a misnomer because one or more vessels of the lymphatic drainage system of the liver always travel with the vein, artery, and bile duct (Fig. 18.2).
The sinusoids are in intimate contact with the hepatocytes and provide for the exchange of substances between the blood and liver cells. The sinusoids lead to a terminal hepatic venule (central vein) that in turn empties into the sublobular veins. Blood leaves the liver through the hepatic veins, which empty into the inferior vena cava.
Structural Organization of the Liver
As introduced previously, the structural components of the liver include  parenchyma, consisting of organized plates of hepatocytes, which in the adult are normally one cell thick and are separated by sinusoidal capillaries. In young individuals up to 6 years of age, the liver cells are arranged in plates two cells thick.
 connective tissue stroma that is continuous with the fibrous capsule of Glisson. Blood vessels, nerves, lymphatic vessels, and bile ducts travel within the connective tissue stroma.