b. Formation of Clotting Factors. The liver produces a large proportion of the
blood clotting factors, including fibrinogen, prothrombin, and several others.
c. Erythrocyte Destruction. When red blood cells become old and worn out in
the circulatory system, most of them are phagocytized in the bone marrow, the spleen,
and the liver. The bilirubin that is formed by all of these organs is excreted by the
parenchymal cells of the liver into the bile canaliculi and on through the bile ducts into
the intestines. Bilirubin from the spleen and bone marrow is carried by the bloodstream
to the liver sinusoids. The bilirubin diffuses through the walls of the liver sinusoids to
enter the parenchymal cells.
214. BILE PIGMENT METABOLISM
a. Hemoglobin Breakdown. When red blood cells break down, hemoglobin is
immediately released into the plasma.
b. Jaundice. Any failure of the liver to excrete bile causes an increased
quantity of bilirubin to be excreted into the body fluids. These fluids containing an
increased amount of bilirubin produce a yellow color in the skin, which is known as
jaundice. Jaundice can also occur if, due to disease, an abnormally large amount of
bile pigment is produced. The excessive amount of pigment causes the body fluids to
become pigmented as well as the bile itself.
(1) Hemolytic. A type of jaundice known as hemolytic jaundice occurs when
the reticuloendothelial cells of the body phagocytize and destroy the red blood cells so
rapidly that the parenchymal cells of the liver cannot excrete all of the bile in an effective
manner. This occurs most frequently when the red blood cells are imperfect due to the
existence of a pathological condition in the body.
(2) Obstructive. Jaundice may occur if the bile ducts become obstructed so
that the pigment excreted by the parenchymal cells cannot reach the intestine. In this
type of case, bile is absorbed into the lymph and blood capillaries.
Section III. THE GASTROINTESTINAL SYSTEM (Figure 29)
215. DIGESTION IN THE MOUTH
Digestion is the splitting of large chemical compounds into simpler substances
that can be used by the body.
a. Ptyalin (Salivary Amylase). Ptyalin is an enzyme found in the saliva that
has the same properties as amylase. Ptyalin converts cooked starch into maltose.
Most starches that man ingests must be cooked, because plant cells are surrounded by
an envelope of cellulose that is indigestible for man. Since food normally stays in the