1.25. Components of Blood http://www.ck12.org
These bags of blood will be stored until they are needed for a transfusion. But what exactly is blood? What makes
up the blood? Most of your blood is water. However, there are also many other important components of your blood.
Components of Blood
Did you know that blood is a tissue? Blood is a fluid connective tissue that is made up of red blood cells, white blood
cells, platelets, and plasma. The cells that make up blood are pictured below (Figure1.44). The different parts of
blood have different roles.
FIGURE 1.44
A scanning electron microscope (SEM) image of human blood cells. Red
blood cells are the flat, bowl-shaped cells, the tiny disc-shaped pieces are
platelets, and white blood cells are the round cells shown in the center.Plasma
If you were to filter out all the cells in blood, a golden-yellow liquid would be left behind.Plasmais this fluid part
of the blood. Plasma is about 90% water and about 10% dissolved proteins, glucose, ions, hormones, and gases.
Blood is made up mostly of plasma.
Red Blood Cells
Red blood cells(RBCs) are flattened, disk-shaped cells that carry oxygen. They are the most common blood cell in
the blood. There are about 4 to 6 million RBCs per cubic millimeter of blood. Each RBC has 200 million molecules
of hemoglobin.Hemoglobinis the protein that carries oxygen. Hemoglobin also gives the red blood cells their red
color.
Red blood cells (Figure1.45) are made in the red marrow of long bones, rib bones, the skull, and vertebrae. Each
red blood cell lives for only 120 days (about four months). After this time, they are destroyed in the liver and spleen.
Mature red blood cells do not have a nucleus or other organelles. Lacking these components allows the cells to have
more hemoglobin and carry more oxygen.
White Blood Cells
White blood cells(WBCs) are usually larger than red blood cells. They do not have hemoglobin and do not carry
oxygen. White blood cells make up less than one percent of the blood’s volume. Most WBCs are made in the bone
marrow, and some mature in the lymphatic system. There are different WBCs with different jobs. WBCs defend the
body against infection by bacteria, viruses, and otherpathogens. WBCs do have a nucleus and other organelles.