Key Concepts:
Vocabulary: plasma, hemoglobin, platelets, capillaries, lymph, pathogen, blood pressure
The Cardiovascular and Lymphatic Systems
Why the Blood Circulates
Main Idea: The cardiovascular system provides nutrients and oxygen, carries away wastes, and helps fight disease.
Your heart pumps blood to your body’s cells 24 hours a day, even when you’re asleep. Your heart accomplishes these important tasks:
Carrying oxygen from the lungs to body cells
Absorbing nutrients from food and delivering nutrients to body cells
Carrying carbon dioxide, a waste gas, from your cells back to your lungs to be exhaled
Delivering other waste products to the kidneys for removal from the body
Helping the white blood cells fight disease by attacking infectious organisms
How Blood Circulation Works
Main Idea: The cardiovascular system consists of the heart, blood, and blood vessels.
The cardiovascular system depends on the heart and its system of blood vessels to deliver blood throughout the body. If all of your blood vessels were laid end to end, they would stretch over 60,000 miles. That’s enough to circle the earth almost two and a half times.
The Heart
Your heart is the muscle that makes the cardiovascular system work. Inside the heart are four chambers. The two top chambers are called the atria. The two lower chambers are called ventricles. A wall of tissue, the septum, separates the four chambers of the heart. Valves between the atria and ventricles allow blood to flow through the chambers.
At the top of the right atrium is an area of muscle that acts as a pacemaker for the heart. Electrical impulses stimulate the atria to contract, forcing blood into the ventricles. These electrical impulses travel through the heart to an area between the two ventricles. There they stimulate the muscles of the ventricles to contract, pumping blood out of the heart. Pumping the blood through the heart is only part of the process. Figure 15.1 shows the pulmonary circulation.
HowBloodCirculates Pulmonarycirculationistheprocessby which blood moves between the heart and the lungs. During this process, blood that has lost oxygen and picked up carbon dioxide and wastes receives fresh oxygen in the lungs. The oxygen-rich blood is circulated again through the body.
Blood
Blood is the fluid that delivers oxygen, hormones, and nutrients to the cells and carries away wastes. Blood is made up of the following components:
All humans have one of four types of blood: A, B, AB, and 0. Each blood type is determined by the presence or absence of certain substances called antigens. Blood types A, B, orAB possess antigens, and a person must receive blood from someone with the same antigen. He or she can, h0wever, receive type O blood, because it contains no antigens. People with type O bl0od are called universal donors, because anyone can receive their blood. Most blood also car- ries another substance called the Rh factor. If your blood contains Rh, you are referred to as Rh positive. Blood that doesn’t have the Rh factor is called Rh negative.
Blood Vessels
The blood vessels that carry blood throughout the body are shown in Figure 15.3. There are three main types of blood vessels: arteries, capillaries, and veins.
Capillaries are small vessels that carry blood from arterioles and to small vessels called venules, which empty into veins. Capillaries form a vast network throughout tissues and organs in the body, reaching almost all body cells. Capillaries near the skin’s surface can also dilate, allowing heat to escape the body through the skin. They can also constrict to reduce heat loss if the body temperature drops below normal.
Veins are blood vessels that return blood to the heart. While the walls ofveins are thinner and less elastic than those ofthe arteries, they are still able to withstand the pressure exerted by blood flowing through them. The large veins, the vena cava, carry deoxygenated blood to the right atrium of the heart. Pulmonary veins carry oxygenated blood to the left atrium. Many veins throughout the body, especially those in the legs, have valves that help prevent the backflow of blood as it is pumped back to the heart. As surrounding muscles contract, they also exert pressure on vein walls, helping to move blood back through the veins.
How Lymph Circulation Works
Main Idea: The lymphatic system helps fight infection and provides immunity to disease.
The lymphatic system, shown in Figure 15.4, consists of a network of vessels and tissues that move and filter lymph, theclear fluid that fills the spaces around body cells. Like plasma, lymph contains water and proteins. It also contains fats and specialized white blood cells called lymphocytes. Like the white blood cells in the blood, these cells pro- tect the body against pathogens. A pathogen is a microorganism that causes disease. There are two types of lymphocytes, B cells and T cells.
B cells multiply when they come in contact with a pathogen. Some of the new B cells produce antibodies that fight the pathogen.
Other B cells create an immune response by preventing a second attack of the same disease. There are two main types of T cells killer cells and helper cells. T cells multiply that and enlarge when they come in contact with pathogen.
One type of T cell, killer T cells, release toxins that prevent infections from spreading. Another type of T cell, the helper T cell, activates both the B cells and killer T cells. They also control the body’s immune system.
Lymph is filtered by lymph nodes, small bean-shaped organs found m lymph vessels. White blood cells within lymph nodes trap and destroy pathogens.
Smooth muscles lining the walls oflymph vessels and sur- rounding skeletal muscles contract to move lymph toward the heart. Two large lymphatic ducts empty lymph into veins close to the heart, where the lymph is returned to the blood. The lymphatic system also includes certain organs and tissues such as the spleen, thymus gland, tonsils, adenoids, and appendix-that help protect the body from infection.
Maintaining Your Circulatory Health
Main Idea: Healthy habits can help protect the health of the cardiovascular and lymphatic systems.
I heard that antioxidants pro- vide protection against condi- tions such as heart disease and cancer. They might even slow down the aging process. I read that researchers at Tufts University in Boston recommend these seven foods in your daily diet: prunes, raisins, blueberries, blackberries, kale, strawberries, and spinach. I should be able to eat at least one of those each day.
Many problems with the cardiovascular and lymphatic systems first appear later in life. You can reduce your risk by making healthy decisions throughout your life. Here are some healthful behaviors that should become regular habits:
Eat a well-balanced diet.
Maintain a healthy weight.
Participate in regular aerobic exercise for at least 30 minutes three or four times per week.
Avoid secondhand smoke and using tobacco products.
Avoid illegal drug use.
Get regular medical checkups.
Blood Pressure
Maintaining pressure in the cardiovascular system is important for proper blood circulation. Pressure in arteries is created when the ventricles contract. As blood is forced into the arteries, arterial walls stretch under the increased pres- sure. When the ventricles relax and refill with blood, arterial pressure decreases. Blood pressure is a measure of the amount of force that the blood places on the walls of blood vessels, particularly large arteries, as it is pumped through the body.
A blood pressure reading includes two numbers. The first number measures your systolic pressure-the maximum pressure as your heart contracts to push blood into your arteries.
The bottom, or second, number measures your diastolic pressure-the pressure at its lowest point when your ventricles relax. A healthy person’s blood pressure will vary within a normal range of below 120/80. Exercise and stress will raise blood pressure. Blood pressure that is above 140/90 is considered high and places a strain on the heart.
Cardiovascular System Problems
Main Idea: Some cardiovascular problems are inherited; others result from illness, diet, or aging.
These disorders of the cardiovascular system have wide-ranging effects and varying treatments:
Congenital heart defects are conditions of the heart that are present at birth. A septal defect is a hole in the septum that allows oxygenated blood to mix with oxygen-depleted blood. Congenital heart defects may also result from poor health of a baby’s mother during pregnancy. Medication and possibly surgery can sometimes repair the affected portion of the heart. In severe cases, a donor heart may be transplanted into a patient whose tissue and blood type matches the donor. The recipient must take anti-rejection drugs for the remainder of his or her life.
Heart murmurs are caused by a hole in the heart, or a leaking or malfunctioning valve.
Varicose veins are formed as result of the valves in veins not closing tightly enough to prevent backflow of blood.
Anemia is a condition in which the ability ofthe blood to carry oxygen is reduced. The blood may contain low numbers of red blood cells or low concentrations of hemoglobin. The most common cause is iron deficiency.
Hemophilia is an inherited disorder. The blood does not clot properly. Bruising and uncontrolled bleeding may occur spontaneously or due to injury. Treatment for hemophilia includes injections that introduce missing clotting proteins into the blood.
Leukemia is a form of cancer in which white blood cells are produced excessively and abnormally. This causes the person to be susceptible to infection, severe anemia, and possibly uncontrolled bleeding. Chemotherapy, radiation, and bone marrow transplant are all treatment options.
Lymphatic System Problems
Problems of the lymphatic system can range from mild to life-threatening.
Disorders of the lymphatic system can range from mild to life-threatening. They may be caused by infection or heredity. Lymphatic system disorders include the following:
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