The Circulatory System Lesson 8, Page 9 of 12 Leukemia A great increase in abnormal leukocytes may occur for unknown reasons, resulting in the diseases known as the leukemias. These range in severity from the chronic lymphocytic leukemia, in which a person may live for many years, to devastating acute leukemia, often causing death within months. Thromboembolic Disease A more common disease is abnormal clotting in the blood vessels, known as thromboembolic disease. This group of disorders, caused by a relatively inactive lifestyle, or by a person's confinement to bed, is one of the most common causes of death in middle-aged and elderly persons. Heart Diseases Heart attacks are the number-one cause of death in the United States.
Cardiovascular diseases are the leading cause of death worldwide.
Cardiovascular diseases include a wide range of disorders that affect the heart and the blood vessels and are the product of many factors, which range in nature from hereditary to nutritional and environmental. Because capillaries are the site where oxygen and nutrients enter body cells and waste products are removed by the bloodstream, any peripheral vascular disease is will affect the function of the tissues supplied by the capillaries. Cardiovascular diseases can therefore cause disease in all other tissues and organs of the body. The single major cause of artery disease is the thickening and hardening of arterial walls by deposits of fatty materials, known as arteriosclerosis . In major vessels such as the aorta, this process is called atherosclerosis .