Page 628 - Atlas of Histology with Functional Correlations

addition, the liver performs vital functions early in life, functioning as the site

of hematopoiesis or blood cell production in the fetus.

EXOCRINE FUNCTIONS

One major exocrine function of hepatocytes is to synthesize and release
about 500 to 1,200 mL of bile per day. The bile enters the bile canaliculi and
flows through the liver via a system of small ductules and larger ducts that
carry the bile from the liver to the gallbladder where it is stored and

concentrated by removal of water. Release of bile from the liver and
gallbladder is regulated by regulatory hormones. Bile flow is increased when
a hormone cholecystokinin is released by the mucosal enteroendocrine cells

(DNES) of the duodenum by the presence of fats or fatty meal in the
duodenum. Cholecystokinin causes intermittent contraction of smooth
muscles in the gallbladder wall and relaxation of the sphincter (of Oddi),
expelling the bile into the duodenum.

Bile salts in the bile emulsify partially digested fats into smaller

molecules for more efficient completion of digestion by pancreatic lipases
produced by the pancreas. The digested fats are absorbed in the small
intestine, and the long fatty acid chains enter the blind-ending lymphatic
lacteals in the lamina propria of individual villi. From the lacteals, fats are

carried into larger lymphatic ducts that eventually drain into the major veins
and systemic circulation.

Hepatocytes also excrete bilirubin, a toxic chemical formed after
degradation of worn-out erythrocytes by liver macrophages Kupffer cells.
Bilirubin is taken up by hepatocytes from the blood and added to and

excreted into bile.

ENDOCRINE FUNCTIONS

Hepatocytes are also endocrine cells, releasing substances directly into the
bloodstream. The arrangement of hepatocytes in a liver lobule allows
hepatocytes direct contact with the contents of the blood to take up and

metabolize carbohydrates, proteins, and fats and store them in their
cytoplasm. Hepatocytes then release many of the metabolized products back
into the bloodstream, as the blood flows through the sinusoids and contacts
hepatocytes. The hepatocytes also synthesize most of the circulating plasma

proteins, including albumins, lipoproteins, glycoproteins, and the blood-

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