F orm ation and d estru ctio n o f red b lo o d cells • Figure 10.6
Red blood cells are destroyed by many organs. Their hemoglobin is broken
down, and some parts are recycled. The remainder of the hemoglobin is
excreted in a process that involves the liver, intestines, and kidney.
Macrophages in the spleen, liver,
and red bone marrow phagocytize
worn-out RBCs and break down
hemoglobin into heme and globin.
RBCs circulate for about
Iron binds to a
complex travels i
the blood to red
bone marrow, where
the iron is taken up
Globin is broken down
to amino acids and
released into the blood.
The non-iron part of heme breaks
down into biliverdin (green pigment),
which is broken down in turn into
bilirubin (yellow pigment). Bilirubin
travels through the blood to the liver,
which secretes bile that goes to
the small intestine.
In the large intestine, bacteria
convert bilirubin to urobilinogen.
Some ot the urobilinogen gets
absorbed back into the blood
and is converted to urobilin
(yellow pigment), which is
excreted by the kidneys. Most
urobilinogen is eliminated in
the teces as stercobilin, which
gives teces its brown color.
fUnder stimulation by the hormone erythropoietin, erythropoiesis
occurs in red bone marrow. Iron combines with globin protein to
make hemoglobin in reticulocytes, which differentiate into RBCs
that are released into the blood.
Sometimes too much bilirubin and its by-products
can build up in the body, causing a yellowing of
the tissues—a condition known as
of the following would
be a likely cause of
a. Reduced production of red blood cells.
b. Liver disease that is reducing liver function.
c. Excess destruction of RBCs.
d. Kidney disease that is reducing kidney function.
e. Blockage of the tubing that connects the liver to
Blood Cells Are Created in the Red Bone Marrow 293