Case Study Conclusion: Flight Risk
At the beginning of this chapter, you learned about Steve and Jim, who met while sitting next to each other on a plane. During the flight, Jim got up to take frequent walks and was doing leg exercises to try to avoid the medical condition depicted above — deep vein thrombosis (DVT). DVT occurs when a blood clot forms in a deep vein, usually in the leg. It can be very dangerous — even deadly.
As you learned in this chapter, a blood clot is an aggregation of platelets and proteins. Blood clots are helpful to prevent blood loss when a blood vessel is damaged. But in some situations, they can be extremely dangerous. For example, blood clots can cause heart attacks or strokes by blocking the flow of blood to the heart or brain, respectively.
When DVT occurs, one of the major risks is pulmonary embolism (PE). PE is when the blood clot breaks off, travels through the blood vessels, and lodges in a pulmonary artery, like the blood clot shown in the illustration below. Recall what the pulmonary arteries do — they carry deoxygenated blood from the heart to the lungs, where the blood picks up oxygen and releases carbon dioxide due to gas exchange between the capillaries and the alveoli of the lungs. Imagine what would happen if this flow of blood to the lungs was partially or completely blocked by a blood clot. Depending on the size of the blood clot and where it is lodged, a PE can cause a variety of serious consequences ranging from lung damage to instant death, because of the disruption of the pulmonary circulation.
Jim has a higher risk of DVT and its consequences because he has heart failure. As you have learned, heart failure is a chronic condition in which the pumping action of the heart is impaired. One reason that heart failure is thought to increase the risk of DVT is that the blood is not being pushed strongly enough through the cardiovascular system, allowing blood clots to form more easily.
Jim needs to be particularly concerned about DVT while on a long plane flight. Why do you think this is? Think about how blood flows through arteries and veins. Blood is pushed through arteries mainly due to the pumping action of the heart. Veins, on the other hand, rely on the movement of the surrounding skeletal muscles to help push blood through them. Sitting still for long periods of time in cramped quarters, such as on a plane, can cause blood to pool in the deep veins of the legs. This can lead to the formation of a blood clot.
In this chapter, you learned about the structure, functions, and disorders of the cardiovascular system. Specifically, you learned that:
- The cardiovascular system is the organ system that transports materials to and from all the cells of the body. The main components of the cardiovascular system are the heart, blood vessels, and blood.
- The cardiovascular system has two interconnected circulations. The pulmonary circulation carries blood between the heart and lungs, where blood is oxygenated. The systemic circulation carries blood between the heart and the rest of the body, where it delivers oxygen.
- The heart is a muscular organ in the chest that consists mainly of cardiac muscle and pumps blood through blood vessels by repeated, rhythmic contractions.
- The wall of the heart consists of three layers. The middle layer, the myocardium, is the thickest layer and consists mainly of cardiac muscle.
- The interior of the heart consists of four chambers, with an upper atrium and lower ventricle on each side of the heart. Blood enters the heart through the atria, which pump it to the ventricles. Then the ventricles pump blood out of the heart. Four valves in the heart keep blood flowing in the correct direction and prevent backflow.
- Deoxygenated blood flows into the right atrium through veins from the upper and lower body (superior and inferior vena cava, respectively), and oxygenated blood flows into the left atrium through four pulmonary veins from the lungs. Each atrium pumps the blood to the ventricle below it. From the right ventricle, deoxygenated blood is pumped to the lungs through the two pulmonary arteries. From the left ventricle, oxygenated blood is pumped to the rest of the body through the aorta.
- The coronary circulation consists of blood vessels that carry blood to and from the heart muscle cells. There are two coronary arteries that supply the two sides of the heart with oxygenated blood. Cardiac veins drain deoxygenated blood back into the heart.
- The cardiac cycle refers to a single complete heartbeat. It includes diastole when the atria contract; and systole when the ventricles contract.
- The normal, rhythmic beating of the heart is called sinus rhythm. It is established by the heart’s pacemaker cells in the sinoatrial node. Electrical signals from the pacemaker cells travel to the atria and cause them to contract. Then the signals travel to the atrioventricular node and from there to the ventricles, causing them to contract. Electrical stimulation from the autonomic nervous system and hormones from the endocrine system can also influence heartbeat.
- Blood vessels carry blood throughout the body. Major types of blood vessels are arteries, veins, and capillaries.
- Arteries are blood vessels that usually carry blood away from the heart (except for coronary arteries that supply the heart muscle with blood). Most arteries carry oxygenated blood. The largest artery is the aorta, which is connected to the heart and extends into the abdomen. Blood moves through arteries due to pressure from the beating of the heart.
- Veins are blood vessels that usually carry blood toward the heart. Most veins carry deoxygenated blood. The largest veins are the superior and inferior venae cavae. Blood moves through veins by the squeezing action of surrounding skeletal muscles. Valves in veins prevent backflow of blood.
- Capillaries are the smallest blood vessels. They connect arterioles and venules. They form capillary beds where substances are exchanged between the blood and surrounding tissues.
- The walls of arteries and veins have three layers. The middle layer is thickest in arteries, in which it contains smooth muscle tissue that controls the diameter of the vessels. The outer layer is thickest in veins and consists mainly of connective tissue. The walls of capillaries consist of little more than a single layer of epithelial cells.
- Blood pressure is a measure of the force that blood exerts on the walls of arteries. It is expressed as a double number, with the higher number representing systolic pressure when the ventricles contract and the lower number representing diastolic pressure when the ventricles relax. Normal blood pressure is generally defined as a pressure of 120/80 mm Hg or less.
- Vasoconstriction (narrowing) and vasodilation (widening) of arteries can occur to help regulate blood pressure or body temperature or to change blood flow as part of the fight-or-flight response.
- Blood is a fluid connective tissue that circulates throughout the body in blood vessels. Blood supplies tissues with oxygen and nutrients and removes their metabolic wastes. Blood helps defend the body from pathogens and other threats, transports hormones and other substances, and helps to keep the body’s pH and temperature in homeostasis. Blood consists of a liquid part, called plasma; and cells, including red blood cells, white blood cells, and platelets.
- Plasma makes up more than half of blood by volume. It consists of water and many dissolved substances. Blood also contains blood cells and platelets.
- Red blood cells are the most numerous cells in the blood and consist mostly of hemoglobin, which carries oxygen. Red blood cells also carry antigens that determine blood types.
- White blood cells are less numerous than red blood cells and are part of the body’s immune system. They protect the body from abnormal cells, microorganisms, and other harmful substances. There are several different types of white blood cells that differ in their specific immune functions.
- Platelets are cell fragments that play important roles in blood clotting or coagulation. They stick together at breaks in blood vessels to form a clot and stimulate the production of fibrin, which strengthens the clot.
- All blood cells form by the proliferation of stem cells in red bone marrow in a process called hematopoiesis. When blood cells die, they are phagocytized by white blood cells and removed from the circulation.
- Disorders of the blood include leukemia, which is cancer of the bone-forming cells; hemophilia, which is any of several genetic blood-clotting disorders; carbon monoxide poisoning, which prevents red blood cells from binding with oxygen and causes suffocation; HIV infection, which destroys certain white blood cells and can cause AIDS; and anemia, in which there are not enough red blood cells to carry adequate oxygen to body tissues.
- Blood type (or blood group) is a genetic characteristic associated with the presence or absence of antigens on the surface of red blood cells. A blood group system refers to all of the gene(s), alleles, and possible genotypes and phenotypes that exist for a particular set of blood type antigens.
- Cardiovascular disease is a class of diseases that involve the cardiovascular system. Worldwide, it is the leading cause of death. Most cases occur in people over age 60, and onset is typically about decade earlier in males than females. Other risk factors include smoking, obesity, diabetes, high blood cholesterol, and lack of exercise.
- Antigens are molecules that the immune system identifies as either self or nonself. If antigens are identified as nonself, the immune system responds by forming antibodies that are specific to the nonself antigens, leading to the destruction of cells bearing the antigens.
- The ABO blood group system is a system of red blood cell antigens controlled by a single gene with three common alleles on chromosome 9. There are four possible ABO blood types: A, B, AB, and O. The ABO system is the most important blood group system in blood transfusions. People with type O blood are universal donors, and people with type AB blood are universal recipients.
- The Rhesus blood group system is a system of red blood cell antigens controlled by two genes with many alleles on chromosome 1. There are five common Rhesus antigens, of which antigen D is most significant. Individuals who have antigen D are called Rh+, and individuals who lack antigen D are called Rh-. Rh- mothers of Rh+ fetuses may produce antibodies against the D antigen in the fetal blood, causing hemolytic disease of the newborn (HDN).
- Two common conditions that lead to most cases of cardiovascular disease are hypertension and atherosclerosis. Hypertension is blood pressure that is persistently at or above 140/90 mm Hg. Atherosclerosis is a buildup of fatty, fibrous plaques in arteries that may reduce or block blood flow. Treating these conditions is important for preventing cardiovascular disease.
- A coronary artery disease is a group of diseases that result from atherosclerosis of coronary arteries. Two of the most common are angina and myocardial infarction (heart attack). In angina, cardiac cells receive inadequate oxygen, which causes chest pain. In a heart attack, cardiac cells die because blood flow to part of the heart is blocked. A heart attack may cause death or lead to heart arrhythmias, heart failure, or cardiac arrest.
- A stroke occurs when blocked or broken arteries in the brain result in the death of brain cells. This may occur when an artery is blocked by a clot or plaque or when an artery ruptures and bleeds in the brain. In both cases, part of the brain is damaged and functions such as speech and controlled movements may be impaired, either temporarily or permanently.
- Peripheral artery disease occurs when atherosclerosis narrows peripheral arteries, usually in the legs, often causing pain when walking. It is important to diagnose this disease so underlying atherosclerosis can be treated before it causes a heart attack or stroke.
In this chapter, you learned that the cardiovascular system carries nutrients to the cells of the body. Read the next chapter about the Digestive System to learn about how your body transforms your meals into the nutrients that cells need to function.
Chapter Summary Review Questions
1. Alex goes to the doctor and learns that his blood pressure is 135/90 mm Hg. Answer the following questions about his blood pressure.
a. Is this a normal blood pressure? Why or why not?
b. Which number refers to the systolic pressure and which number refers to the diastolic pressure?
c. Describe what the atria and ventricles of Alex’s heart are doing when the pressure is at 135 mm Hg.
d. Alex’s doctor would like him to lower his blood pressure. Why do you think he would like Alex to do this and what are some ways in which he may be able to lower his blood pressure?
2. What are three functions of the cardiovascular system?
3. What is the watery part of the blood called?
4. a. Which are the chambers of the heart that receive blood?
b. Which are the chambers of the heart that pump blood out of the heart?
5. Which chambers of the heart contain deoxygenated blood?
A. Right and left atria
B. Right and left ventricles
C. Right atrium and right ventricle
D. Left atrium and left ventricle
6. What are two different places in the cardiovascular system where valves are located?
7. Valves prevent blood from flowing backwards in the cardiovascular system. Why do you think this is important?
8. Explain how pacemaker cells in the heart work together with the nervous system to regulate the beating of the heart.
9. True or False. Red marrow is the source of white blood cells.
10. True or False. Plaques that build up in arteries are made completely of fats.
11. The aorta is:
A. An artery
B. A chamber of the heart
C. A vein
D. A valve
12. Compare the coronary arteries, pulmonary arteries, and arteries elsewhere in the body in terms of their target tissues (i.e. where they bring blood to) and whether they are carrying oxygenated or deoxygenated blood.
13. The superior vena cava empties into the __________ of the heart. The inferior vena cava empties into the __________ of the heart.
A. right atrium; left atrium
B. right atrium; right atrium
C. right atrium; right ventricle
D. right ventricle; left ventricle
14. Venules receive blood from ______________ .
15. Define blood type and blood group system. Explain the relationship between antigens and antibodies.
16. Identify the alleles, genotypes, and phenotypes in the ABO blood group system.
17. Discuss the medical significance of the ABO blood group system.
18. Give examples of how different ABO blood types vary in their susceptibility to diseases.
19. Describe the Rhesus blood group system.
20. Relate Rhesus blood groups to blood transfusions.
21. What causes hemolytic disease of the newborn?
22. A woman is blood type O and Rh- and her husband is blood type AB and Rh+. Answer the following questions about this couple and their offspring.
a. What are the possible genotypes of their offspring in terms of ABO blood group?
b. What are the possible phenotypes of their offspring in terms of ABO blood group?
c. Can the woman donate blood to her husband? Explain your answer.
d. Can the man donate blood to his wife? Explain your answer.
23. True or False. The D antigen is part of the ABO blood group system.
24. Explain why hemolytic disease of the newborn may be more likely to occur in a second pregnancy than in a first.
25. Anemia causes weakness and fatigue due to a reduction in the amount of oxygen that gets to the cells of the body. Explain how oxygen is transported to the cells of the body and which blood cells are affected in anemia.
26. What are the two conditions that are precursors to virtually all cases of cardiovascular disease?
27. What is another name for a heart attack?
A. Heart arrhythmia
B. Myocardial infarction
D. Heart failure
28. True or False. Strokes can be due to a blood clot or to a broken artery.
29. True or False. After an injury to a blood vessel, platelets respond by losing their nuclei.
30. What are the main differences between the coronary circulation, pulmonary circulation, and systemic circulation?
31. Define the term sinus rhythm.
32. Which is generally a more serious and immediately life-threatening condition: heart failure or cardiac arrest? Explain your answer.
33. Match each of the following descriptions to the disease or disorder from the list below that best matches it. Use each disease or disorder only once.
Diseases and disorders: hypertension; atherosclerosis; coronary artery disease; peripheral artery disease
a. Blood flow to the muscle cells of the heart is impaired.
b. Blood pressure is too high.
c. Arteries in the legs specifically become more narrow.
d. Plaque builds up in arteries (in general).
Even people who are generally healthy and don’t have heart disease can get DVT from sitting too long on a long-distance flight, or in other situations when they are immobile for extended periods of time. Fortunately, walking periodically and doing some simple leg exercises can lower your risk of DVT by helping to push blood through your veins. If you are planning on taking a flight in the future, watch the short video below to learn some easy exercises that you can do right in your plane seat to help prevent DVT!