Bile is formed by the hepatocytes and is released into bile canaliculi,
which are located between the lateral surfaces of adjacent hepatocytes. The
direction of flow is from the hepatocytes toward the bile duct, which drains
bile from the liver on its path to the gallbladder, where the bile is stored
and concentrated. The hepatic artery and hepatic portal vein (shown in the
photomicrograph) plus the bile duct comprise the portal triad. Blood flows
from the triad (hepatic artery, portal vein, and bile duct) toward the central
vein, whereas bile flows in the opposite direction toward the triad.
Bile is synthesized by hepatocytes using the smooth endoplasmic retic-
ulum (SER) and consists of bile acids and bilirubin. Bile acids are 90%
recycled from the distal small and large intestinal lumen and 10% newly
synthesized by conjugation of cholic acid, glycine, and taurine in the SER.
Bilirubin is the breakdown product of hemoglobin derived from the action
of Kupffer cells in hepatic sinusoids and other macrophages, particularly
those lining the sinusoids of the spleen where degradation of RBCs is
prominent.
217.The answer is a.(Junqueira, pp 334–335. Kasper, pp 1817–1820.
Kumar, pp 885–888.) Commonly, initial low levels of glucuronyl (glu-
curonysl) transferase in the underdeveloped smooth endoplasmic reticulum
of hepatocytes in the newborn, result in jaundice (neonatal unconjugated
hyperbilirubinemia); less commonly, this enzyme is genetically lacking. The
neonatal small intestinal epithelium also has an increased capacity for
absorption of unconjugated bilirubin, which contributes to the elevated
serum levels.
Bilirubin, a product of iron-free heme, is liberated during the destruc-
tion of old erythrocytes by the mononuclear macrophages of the spleen
and, to a lesser extent, of the liver and bone marrow. The hepatic portal sys-
tem brings splenic bilirubin to the liver, where it is made soluble for excre-
tion by conjugation with glucuronic acid. Increased plasma levels of
bilirubin (hyperbilirubinemia) result from increased bilirubin turnover,
impaired uptake of bilirubin, or decreased conjugation of bilirubin.
Increased bilirubin turnover occurs in Dubin-Johnson and Rotor’s syn-
dromes, in which there is impairment of the transfer and excretion of
bilirubin glucuronide into the bile canaliculi. In Gilbert’s syndrome, there
is impaired uptake of bilirubin into the hepatocyte and a defect in glu-
curonyl transferase. In Crigler-Najjar syndrome, a defect in glucuronyl
transferase occurs in the neonate.
336 Anatomy, Histology, and Cell Biology