Red blood cells (also called erythrocytes) perform the most important blood duty. A single drop of blood contains millions of red blood cells which are constantly traveling through the body delivering oxygen and removing waste.
Red blood cells are red only because they contain protein chemical called hemoglobin which is bright red in color. Hemoglobin contains the element Iron, making it an excellent vehicle for transporting oxygen and carbon dioxide. When the blood is passing through the lungs, oxygen molecules attach to the hemoglobin. When the blood is passing through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bond with the tissue's carbon dioxide or other waste gases, transporting it away.
The average life cycle of a red blood cell is 120 days. Since the human body is continually making more blood, it is safe for healthy adults to donate blood. The blood is then stored for using in emergency situations. Initially after giving blood, the donor may feel some momentary lightheadedness due to the loss of oxygen-rich red blood cells and blood sugar. The body quickly stabilizes itself.
When an infection enters the body, the white blood cells (also called leukocytes) are passing toward the scene of the crime. When a germ appears, the white blood cells have a variety of ways by which they can attack. Some will produce protective antibodies that will overpower the germ. Others will surround and destroy the bacteria.
The white blood cells, living from a few days to a few weeks have a rather short life cycle. A drop of blood can contain from 7,000 to 25,000 white blood cells. If an invading infection persists, their number will significantly increase.
The human body does not handle excessive blood loss well. Therefore, the body has ways of protecting itself. When, for some unexpected reason, sudden blood loss occurs, the blood platelets (also called thrombocytes) kick into action.
Platelets are irregularly-shaped, colorless bodies that are present in blood. Their sticky surface lets them, along with other substances, form clots and stops bleeding.
When bleeding from a wound suddenly occurs, the platelets gather at the wound and attempt to block the blood flow. The mineral calcium, vitamin K, and a protein called fibrinogen help the platelets form a clot. A clot begins foreign when the blood is exposed to air. Important proteins called clotting factors are critical to the clotting process. Although platelets alone can plug small blood vessel leaks and temporarily stop or slow bleeding, the action of clotting factors is needed to produce a strong, stable clot.
Ex. 13. Read the passages below and answer the question: What blood cells is each passage about?
1. They are shaped like slightly indented, flattened disks. They contain the iron-rich protein hemoglobin. Blood gets its bright red color when hemoglobin picks up oxygen in the lungs. As the blood travels through the body, the hemoglobin releases oxygen to the tissues. The body contains more them than any other type of cell, and each has a life span of about 4 months. Each day, the body produces these new blood cells to replace those that die or are lost from the body.
2. These blood cells are a key part of the body's system for defending itself against infection. They can move in and out of the bloodstream to reach affected tissues. Blood contains far fewer them than red blood cells, although the body can increase their production to fight infection. New cells are constantly being formed in the bone marrow.
3. They are tiny oval-shaped cells made in the bone marrow. They help in the clotting process. When a blood vessel breaks, they gather in the area and help seal off the leak. Platelets survive only about 9 days in the bloodstream and are constantly being replaced by new cells. The process of clotting is like a puzzle with interlocking parts. When the last part is in place, the clot happens — but if even one piece is missing, the final pieces can't come together. When large blood vessels are severed (or cut), the body may not be able to repair itself through clotting alone. In these cases, dressings or stitches are used to help control bleeding
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| Class work. | | | Ex. 15. Read, translate and memorize the word combinations. |