duct. The common bile duct then connects with the duodenum. At the base of the bile
duct is a sphincter, which controls the flow of bile from the liver and gallbladder into the
small intestine. The sphincter, called the sphincter ampulla, can therefore remain
constricted and store bile until it is needed within the digestive tract.
The liver has three major blood vessels, two of which lead into the structure and
one departs from it. The former vessels are the hepatic portal vein and the hepatic
artery. The hepatic artery is a branch of the aorta that functions to bring oxygenated
blood to the liver. It branches to arterioles and eventually into sinusoids (capillaries)
within the liver. From the sinusoids, blood flows to the central vein to sublobular veins
and departs from the liver via the hepatic vein. The second large blood vessel entering
the liver is the hepatic portal vein (figure 27), which receives blood rich in nutrients
from the digestive tract. This vein enters the liver and divides into portal venules, which
subdivide to sinusoids. From the sinusoids, blood from the hepatic portal vein follows
similar channels as blood from the hepatic artery. That is, blood flows from a sinusoid
to a central vein, to a sublobular vein, and to the hepatic vein. The hepatic vein
therefore receives blood from the hepatic artery and portal veins and returns the blood
to the heart via the inferior vena cava. The enriched blood is oxygenated prior to being
distributed to vital organs and tissues of the body.
2-9. MICROSCOPIC ANATOMY
The microscopic anatomy of the liver ncludes the functional unit of the liver, the
iiver lobule (figure 28). A typical liver lobule consists of hepatic cellular plates,
usually two cells thick. Blood vessels found in the liver lobule include a portal venule,
a venous sinusoid, and a central vein. Lining the venous sinusoids are Kupffer's cells.
Kupffer's cells are very mobile and can enter and leave the bloodstream. Between the
parenchymal (functional) cells are tiny vessels called bile canaliculi. Many canaliculi
fuse forming larger and larger bile ducts. The contents of these ducts leave the
liver via the left and right hepatic ducts.
210. PROTECTIVE FUNCTIONS
a. Kupffer's Cell Activity. Blood entering the liver through the portal system
from the intestines, contains large numbers of colon bacilli. The Kupffer's cells in the
liver remove successfully over 99 percent of these bacteria. The Kupffer's cells act as a
very efficient filter for bacteria or any other particles in this size range from the blood.
Without the activity of the Kupffer's cells, bacteria would be allowed to enter the entire
systemic circulation and a generalized septicemia would result.
b. Ammonia Removal. Large amounts of ammonia are formed during
deamination in protein metabolism. The liver produces large amounts of urea from
ammonia to remove it from body fluids. If the liver did not function in the secretion of
urea, the plasma ammonia concentration would rise so high that very shortly the result
would be hepatic failure and death would occur.