CK-12 Life Science

by CK-12 Foundation

  Coronary Circulation

  Just like every other organ in the body, the heart needs its own blood supply. It gets this blood in the coronary circulation. Although blood fills the chambers of the heart, the heart muscle tissue is so thick that it needs its own blood vessels to deliver oxygen and nutrients into the muscle. The coronary circulation is part of the systemic circulation. The vessels that deliver oxygen-rich blood to the heart muscle are called coronary arteries. The coronary arteries branch directly from the aorta, just above the heart, as shown in Figure below. The vessels that remove the deoxygenated blood from the heart muscle are known as cardiac veins. Problems with the coronary circulation are collectively referred to as heart disease.

  Figure 18.14

  In coronary circulation, the arteries that bring oxygen to the cardiac cells branch off the aorta; heart attacks are caused by blockages of the coronary arteries which prevent oxygen from getting to the heart muscle.

  The circulation of blood around the body has been studied by people for a long time. The functions of the organs of the circulatory system were a mystery for many hundreds of years. For example, it was once believed that the left ventricle and arteries were filled with air, and the liver made blood. The pulmonary circulation was first described by a Syrian physician, Ibn al-Nafis, in 1242. Ibn al-Nafis was also the first person to describe the coronary circulation. However, credit for the first description of blood circulation goes to the English physician William Harvey. In 1616, Harvey first described the pulmonary and systemic circulation designs in detail.

  Lesson Summary

  The heart is divided into four chambers, the left and right atria and the left and right ventricles. The right side of the heart collects deoxygenated blood from the body and pumps it into the lungs where it releases carbon dioxide and picks up oxygen. The left-side carries the oxygenated blood back from the lungs, into the left side of the heart which then pumps the oxygenated blood throughout the rest of the body.

  The valves in the heart prevent blood from flowing backward into the heart. The contraction rate of cardiac muscle is controlled by two small groups of cardiac muscle cells called the sinoatrial (SA) and atrioventricular (AV) nodes.

  The heart has its own blood supply, which is called the coronary circulation. The heart is fed oxygen-rich blood by coronary arteries. Oxygen-poor blood is collected by coronary veins.

  Further Reading / Supplemental Links

  http://en.wikipedia.org/wiki/William_Harvey

  http://thevirtualheart.org/anatomyindex.html

  http://en.wikipedia.org/wiki/Cardiac_cycle

  Review Questions

  Name the four chambers of the heart.

  Where does oxygen-poor blood first enter the heart?

  Do ventricles pump blood out of the heart or do they pump blood into the atria?

  What is the purpose of the valves in the heart?

  What do the AV valves do?

  Does the vena cava carry oxygen-poor or oxygen-rich blood?

  Why can the heart be considered to be two separate pumps?

  How might a hole in the heart wall between the two ventricles affect the circulation of blood?

  To what organ or organs does the coronary circulation bring blood?

  To what organ or organs does the pulmonary circulation bring blood?

  Vocabulary

  atrioventricular (AV) valves

  Valves that stop blood from moving from the ventricles back into the atria.

  atrium

  One of the two small, thin-walled chambers on the top of the heart that blood first enters.

  coronary circulation

  The blood supply that feeds the heart.

  semilunar (SL) valves

  Found in the arteries leaving the heart; prevents blood flowing back from the arteries into the ventricles.

  ventricle

  One of the two muscular V-shaped chambers that pump blood out of the heart.

  Points to Consider

  Identify how the different components of the blood have very different roles in the cardiovascular system.

  Consider how diet can affect the oxygen-carrying ability of blood.

  Lesson 18.3: Blood

  Lesson Objectives

  List the components of blood.

  Identify three functions of blood.

  Name the oxygen-carrying protein found in red blood cells.

  Identify the main function of white blood cells.

  Describe the importance of the ABO blood system.

  Identify three blood disorders or diseases.

  Check Your Understanding

  What is the main function of the blood?

  What is the role of oxygen in aerobic (cellular) respiration?

  Introduction

  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. It moves around the body through the blood vessels due to the pumping action of the heart. Oxygen rich blood carried in arteries brings oxygen and nutrients to all the body’s cells. Oxygen-poor blood carries carbon dioxide and other metabolic wastes away from the cells. In addition to the transport of gases, nutrients, and wastes, blood has many other functions that are important to homeostasis. You will learn more about those functions in this lesson.

  Components of Blood

  Blood is a colloidal solution. A colloidal solution it is made up of particles that are suspended in a fluid. The cells in blood are suspended in plasma, the liquid part of blood. The cells that make up the blood are shown in Figure below. The different components of blood have different roles. Some of the roles of blood include:

  The defense of the body against infection by microorganisms or parasites.

  The transport of chemical messages, such as hormones and hormone-like substances.

  The control of body temperature.

  The repair of damage to body tissues.

  Figure 18.15

  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 visible in the center.

  Plasma

  If you were to filter out all the cells in blood, plasma is what would be left over. Plasma is the golden-yellow liquid part of the blood. Plasma is about 90 percent water and about 10 percent dissolved proteins, glucose, ions, hormones, and gases. Blood is made up of mostly plasma. The blood cells make up the rest of the volume.

  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. Hemoglobin is the protein that carries oxygen. Hemoglobin also gives the RBCs their red color. Red blood cells are made in the red marrow of long bones, ribs, skull, and vertebrae. Each red blood cell lives for only 120 days (about four months). After this time, they are destroyed in liver and spleen. Red blood cells are shown in Figure below. Mature RBCs do not have a nucleus or other organelles.

  Figure 18.16

  The flattened shape of RBCs helps them to carry more oxygen than if they were rounded.

  White Blood Cells

  White blood cells (WBCs) are usually larger than red blood cells. They have a nucleus but do not have hemoglobin. White blood cells make up less than one percent of the blood's volume. Most WBCs are made in the bone marrow, some mature in the lymphatic system. WBCs defend the body against infection by bacteria, viruses and other pathogens. Each WBC type has a specific defense job. Three of the most common white blood cells in the body are listed here.

  Neutrophils can squeeze through capillary walls and swallow particles such as bacteria and parasites.

  Macrophages can also swallow and destroy old and dying cells, bacteria, or viruses. In Figure below a macrophage is attacking and swallowing two particles, possibly pathogens. Macro
phages also release chemical messages that cause the number of WBC to increase.

  Lymphocytes fight infections by viruses and bacteria. Some lymphocytes attack and kill cancer cells. Other lymphocytes attack cells that are infected by viruses. Lymphocytes called B-cells make antibodies. Antibodies are chemicals that identify pathogens or other substances as being harmful, or they can destroy the pathogen. To learn more about the role of WBCs in protecting the body from infection, go to the Diseases and the Body’s Defenses chapter.

  Figure 18.17

  A type of WBC, called a macrophage, is attacking and about to swallow two particles.

  Platelets

  Platelets are very small, but they are very important in blood clotting. Platelets are not cells they are sticky little pieces of larger cells. They bud off large cells that stay in the bone marrow. A platelet sits between a RBC and a WBC in Figure below. Platelets carry chemicals that are important for proper blood clotting. When a blood vessel gets cut, platelets stick to the injured areas. They release chemicals called clotting factors which cause a web of protein fibers to form. This web catches RBCs and forms a clot. This clot stops more blood from leaving the body through the cut blood vessel. The clot also stops bacteria from entering the body. Platelets survive in the blood for 10 days before they are removed by the liver and spleen.

  Figure 18.18

  A platelet lies between a RBC, at left, and a WBC at right; platelets are little pieces of larger cells, called which are found in the bone marrow.

  Transport of Chemical Messages

  The blood also acts as a messenger delivery service. Chemical messengers called hormones are carried and delivered by the blood to cells around the body. Hormones are released into the blood by the cells that make them and are delivered by the blood to the cells the hormones are made for. An example of a hormone transported in the blood is insulin, which regulates the concentration of glucose in the blood.

  Control of Body Temperature

  Your blood system does more than deliver oxygen and nutrients to your body cells. Your blood also moves heat (thermal energy) around your body. When your brain senses that your body temperature is increasing, it sends messages to the blood vessels in the skin to increase in diameter. Increasing the diameter of the blood vessels increases the amount of blood and heat that moves near the skin surface. The heat is then released from the skin.

  Blood Clotting

  Blood clotting is a complex process by which blood forms solid clots. As discussed above, clotting is important to stop bleeding and begin repair of damaged blood vessels. Blood clotting disorders can lead to an increased risk of bleeding or clotting inside a blood vessel. Platelets are important for the proper clotting of blood.

  Clotting is started almost immediately when an injury damages the inside lining of a blood vessel. Platelets clump together, forming a plug at the site of injury. Then, proteins in the plasma cause a series of chemical reactions that form a tough protein called fibrin. The fibrin strands form a web across the platelet plug, trapping red blood cells before they can leave through the wound site. This mass of platelets, fibrin, and red blood cells forms a clot that hardens into a scab.

  Certain nutrients are needed for the clotting system to work properly. Two of these are calcium and vitamin K. Bacteria that live in your intestines make enough vitamin K so you do not need to eat extra vitamin K in your food.

  Blood Types

  Blood type is determined by the presence or absence of certain molecules, called antigens, on the surface of red blood cells (RBCs). There are four blood types; A, B, AB, and O.

  Type A blood has type A antigens on the RBCs in the blood.

  Type AB blood has A and B antigens on the RBCs.

  Type B has B antigens on the RBCs.

  Type O does not have any antigens (neither A nor B).

  The blood types may also have antibodies for other blood types in their plasma. For example, a person with type A blood may have anti-B antibodies (against B antigens), and a person with type O blood can have anti-A and anti-B antibodies in their blood. The blood type of a person can be worked out by testing a drop of a person’s blood using anti-A or anti-B antibodies.

  The ABO blood group system is most important if a person needs a blood transfusion. A blood transfusion is the process of putting blood or blood products from one person into the circulatory system of another person.

  If a person with type O blood received type A blood, the anti-A antibodies in the person’s blood would attack the A antigens on the RBCs in the donor blood, as shown in Figure below. The antibodies would cause the RBCs to clump together, and the clumps could block a blood vessel. Such a reaction could be fatal.

  Figure 18.19

  A person with type O blood has A and B antibodies in their plasma; if the person was to get type A blood instead of type O, Their A antibodies would attach to the antigens on the RBCs and cause them to clump together.

  The Rhesus System

  The second most important blood group system in human blood is the Rhesus (Rh) system. The Rh blood group system currently consists of 50 blood group antigens, including the 5 antigens D, C, c, E, and e. The commonly used terms Rh factor, Rh positive and Rh negative refer to the D antigen only. A person either has, or does not have the Rh(D) antigen on the surface of their RBCs; written as Rh(D) positive (does have the RhD antigen) or Rh(D) negative (does not have the antigen).

  Blood Donors

  Recall that people with type O blood do not have any antigens on their RBCs. As a result, type O blood can be given to people with blood types A, B, or AB. If there are no antigens on the RBCs, there cannot be an antibody reaction to the blood. People with type O blood are often called universal donors.

  The blood plasma of AB blood does not contain any anti-A or anti-B antibodies. People with type AB blood can receive any ABO blood type. People with type AB positive blood are called universal recipients. The antigens and antibodies that define blood type are listed in Table (below).

  In April 2007 researchers discovered a way to convert blood types A, B, and AB to O. The researchers used enzymes to remove the antigens on the surface of the RBCs. This discovery could lead to producing or modifying blood cells that can be used as donors to people with all blood types.

  Blood Types, Antigens, and Antibodies Blood type Antigen type Plasma antibodies Can receive blood from types Can donate blood to types

  A A anti-B A,O A, AB

  B B anti-A B,O B, AB

  AB A and B none AB, A, B, O AB

  O none anti-A, anti-B O AB, A, B, O

  (Source: Niamh Gray-Wilson)

  Blood Diseases

  Problems can occur with red blood cells, white blood cells, platelets, and other parts of the blood. Many blood disorders are genetic, they are inherited from a parent. Some blood diseases are a caused by not getting enough of a certain nutrient, while others are cancers of the blood.

  Sickle-Cell Disease

  Sickle cell disease is a blood disease that is caused by abnormally-shaped blood protein hemoglobin. Many of the RBCs of a person with sickle cell disease are long and curved (sickle-shaped), as shown in Figure below. The long, sickle-shaped RBCs can have damaged cell membranes, which can cause them to burst. The long shape of the cells can cause them to get stuck in narrow blood vessels. This clotting causes oxygen starvation in tissues, which causes pain and may cause damage such as stroke or heart attack. People with sickle-cell disease are most often well, but can on occasion have painful attacks. The disease is not curable, but can be treated with medicines. Heterozygous individuals have an advantage; they are resistant to severe malaria. See the Genetics chapter for further discussion.

  Figure 18.20

  The RBCs of a person with sickle cell disease (left) are long and pointed rather than straight like normal cells (right); the abnormal cells cannot carry oxygen properly and can get stuck in capillaries.

  Anemia

  Hemoglobin is the oxygen-carrying molecule found inside RBC
s. Anemia results when there is not enough hemoglobin in the blood to carry oxygen to body cells. Hemoglobin normally carries oxygen from the lungs to the tissues. Anemia leads to a lack of oxygen in organs. Anemia is usually caused by one of three things:

  A loss of blood volume through a bleeding wound or a slow leak of blood.

  The destruction of RBCs.

  Lack of RBC production.

  Anemia may not have any symptoms. Some people with anemia feel weak or tired in general or during exercise. They also may have poor concentration. People with more severe anemia often get short of breath during activity. Iron-deficiency anemia is the most common type of anemia. It occurs when the dietary intake or absorption of iron is less than what is needed by the body. As a result, hemoglobin, which contains iron, cannot be made. In the United States, 20 percent of all women of childbearing age have iron deficiency anemia, compared with only 2 percent of adult men. The most common cause of iron deficiency anemia in young women is blood lost during menstruation. Iron deficiency anemia can be avoided by getting the recommended amount of iron in the diet. Anemia is often treated or prevented by taking iron supplements.