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C HAPTER
Chapter 1. Blood
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Blood
Lesson Objectives
• Describe blood components, and list functions of the blood.
• Define blood type, and explain its medical significance.
• Identify some diseases of the blood.
Lesson Vocabulary
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anemia
antigen
blood
blood clot
blood type
hemoglobin
hemophilia
leukemia
plasma
platelet
red blood cell
sickle-cell disease
white blood cell
Introduction
The young man in Figure 1.1 is donating blood. By donating blood, he may well be saving lives. Blood transfusions,
in which patients receive blood from a donor, save countless lives each year. That’s because blood is such a vital
body fluid.
Structure and Functions of Blood
Blood is a liquid connective tissue. It circulates throughout the body via blood vessels due to the pumping action of
the heart. You couldn’t survive without the approximately 4.5 to 5 liters of blood that are constantly being pumped
through your blood vessels.
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FIGURE 1.1
Blood donation
Blood Components
Blood consists of both liquid and cells. The liquid part of blood is called plasma. Plasma is a watery, golden-yellow
fluid that contains many dissolved substances. Substances dissolved in plasma include glucose, proteins, and gases.
Plasma also contains blood cells. There are three types of blood cells: red blood cells, white blood cells, and
platelets. You can see all three types in Figure 1.2.
1. Red blood cells are shaped like flattened disks. There are trillions of red blood cells in your blood. Each red
blood cell has millions of molecules of hemoglobin. Hemoglobin is a protein that contains iron. The iron in
hemoglobin gives red blood cells their red color. It also explains how hemoglobin carries oxygen. The iron in
hemoglobin binds with oxygen molecules so they can be carried by red blood cells.
2. White blood cells are larger than red blood cells, but there are far fewer of them. Their role is to defend the
body in various ways. For example, white blood cells called phagocytes engulf and destroy microorganisms
and debris in the blood.
3. Platelets are small, sticky cell fragments that help blood clot. A blood clot is a solid mass of cell fragments
and other substances that plugs a leak in a damaged blood vessel. Platelets stick to tears in blood vessels and
to each other, helping to form a clot at the site of injury. Platelets also release chemicals that are needed for
clotting to occur.
Functions of Blood
The main function of blood is transport. Blood in arteries carries oxygen and nutrients to all the body’s cells. Blood
in veins carries carbon dioxide and other wastes away from cells to be excreted. Blood also transports the chemical
messengers called hormones to cells throughout the body where they are needed to regulate body functions. Blood
has several other functions as well. For example, blood:
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defends the body against infections.
repairs body tissues.
controls the body’s pH.
helps regulate body temperature.
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Chapter 1. Blood
FIGURE 1.2
Blood cells include disk-shaped red blood
cells (left), spherical white blood cells
(right), and small cell fragments called
platelets (center).
Blood Type
Red blood cells carry proteins called antigens on their surface. People may vary in the exact antigens their red blood
cells carry. The specific proteins are controlled by the genes they inherit from their parents. The particular antigens
you inherit determine your blood type.
Why does your blood type matter? Blood type is important for medical reasons. A patient can’t safely receive a
transfusion of blood containing antigens not found in the patient’s own blood. With “foreign” antigens, the transfused
blood will be rejected by the person’s immune system. This causes a reaction in the patient’s bloodstream, called
agglutination. The transfused red blood cells clump together, as shown in Figure 1.3. The clumped cells block blood
vessels and cause other life-threatening problems.
FIGURE 1.3
Normal and agglutinated blood: normal
blood smear (left) and agglutinated blood
smear (right).
There are many sets of antigens that determine different blood types. Two of the best known are the ABO and Rhesus
antigens. Both are described below. You can also learn more about them by watching this video: http://www.youtu
be.com/watch?v=L06TJTMVkBo .
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MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/137144
ABO Blood Type
ABO blood type is determined by two common antigens, often called antigen A and antigen B.
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If your red blood cells carry only antigen A, you have blood type A.
If your red blood cells carry only antigen B, you have blood type B.
If your red blood cells carry both antigen A and antigen B, you have blood type AB.
If your red blood cells carry neither antigen A nor antigen B, you have blood type O.
Rhesus Blood Type
Another red blood cell antigen determines a person’s Rhesus blood type. This blood type depends on a single
common antigen, typically referred to as the Rhesus (Rh) antigen.
• If your red blood cells carry the Rhesus antigen, you have Rhesus-positive blood, or blood type Rh+.
• If your red blood cells lack the Rhesus antigen, you have Rhesus-negative blood, or blood type Rh-.
Diseases of the Blood
Some diseases affect mainly the blood or its components. They include anemia, leukemia, hemophilia, and sicklecell disease.
Anemia
Anemia is a disease that occurs when there is not enough hemoglobin (or iron) in the blood so it can’t carry adequate
oxygen to the cells. There are many possible causes of anemia. One possible cause is excessive blood loss due to an
injury or surgery. Not getting enough iron in the diet is another possible cause.
Leukemia
Leukemia is a type of cancer in which bone marrow produces abnormal white blood cells. The abnormal cells can’t
do their job of fighting infections. Like most cancers, leukemia is thought to be caused by a combination of genetic
and environmental factors. It is the most common cancer in children.
Hemophilia
Hemophilia is a genetic disorder in which blood fails to clot properly because a normal clotting factor in the blood
is lacking. In people with hemophilia, even a minor injury can cause a life-threatening loss of blood. Most cases of
hemophilia are caused by a recessive gene on the X chromosome. The disorder is expressed much more commonly
in males because they have just one X chromosome.
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Chapter 1. Blood
Sickle-Cell Disease
Sickle-Cell Disease is another genetic disorder of the blood. It is more common in people with African origins
because it helps protect against malaria. Sickle-cell disease occurs in people who inherit two copies of the recessive
mutant gene for hemoglobin. The abnormal hemoglobin that results causes red blood cells to take on a characteristic
sickle shape under certain conditions. You can compare sickle-shaped and normal red blood cells in Figure 1.4. The
sickle-shaped cells get stuck in tiny capillaries and block blood flow. This causes serious, painful symptoms. Watch
this video animation to learn more about the genetic basis of sickle-cell disease: http://www.dnalc.org/resources/3
d/17-sickle-cell.html
FIGURE 1.4
Comparison of sickle-shaped and normal
red blood cells
Lesson Summary
• Blood consists of liquid plasma, which contains dissolved substances, and three types of cells: red blood cells,
white blood cells, and platelets. The main function of blood is transport. Blood also fights infections, repairs
tissues, controls pH, and helps regulate body temperature.
• Specific antigens on the surface of red blood cells determine blood type. The best-known blood types are ABO
and Rhesus (Rh) blood types. Blood type is important in cases of blood transfusion. A patient must receive
blood of his or her own blood type to avoid clumping of red blood cells.
• Many diseases affect the blood or its components. They include anemia, leukemia, hemophilia, and sickle-cell
disease.
Lesson Review Questions
Recall
1. What is blood?
2. Identify the main function of blood.
3. Describe two diseases of the blood and their causes.
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Apply Concepts
4. Why might it be necessary to determine your ABO blood type?
5. If you have type O blood, which type(s) of blood can you safely receive?
Think Critically
6. Compare and contrast red blood cells and white blood cells.
7. Relate antigens to blood types.
Points to Consider
The blood picks up oxygen in the lungs and carries it to cells throughout the body.
1. How does oxygen enter the lungs?
2. How does oxygen get from the lungs into the blood?
References
1. Michael Buslovich, US Navy. http://commons.wikimedia.org/wiki/Blood#mediaviewer/File:Blood_donation_at_Fleet_Week_USA.jpg . public domain
2. Courtesy of the Electron Microscopy Facility at The National Cancer Institute at Frederick. http://commons.w
ikimedia.org/wiki/File:Red_White_Blood_cells.jpg . Public Domain
3. Apers0n. http://commons.wikimedia.org/wiki/File:Bedside_card.jpg . CC BY 2.0
4. Courtesy of Drs. Noguchi, Rodgers, and Schechter, NIDDK. http://commons.wikimedia.org/wiki/File:Sickl
ecells.jpg; http://commons.wikimedia.org/wiki/File:Redbloodcells.jpg . Public Domain
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