334 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. Each of the formed elements in the blood starts as a hematopoietic stem cell, which develops into another type of stem cell by the process known as mitosis before it develops into a blast cell. Depending on which growth or stimulating factors and hormones influence the blast cell, it matures into a red blood cell, white blood cell, or platelet (Figure 11.11). As new blood cells develop in bone marrow, they enter the bloodstream as it flows through the bone. SELF CHECK 1. What are the two basic types of components in the blood? 2. Typically, approximately what percentage of the blood is plasma? 3. Which proteins are most abundant in the plasma? 4. Which organ regulates red blood cell production through the process of erythropoiesis? 5. What is the name of the process in which red blood cells rupture when they reach the end of their life span? 6. List the five different types of white blood cells. 7. What is the difference between a granulocyte and an agranulocyte? Manufacturing Blood Cells Each blood cell has a limited life span, so the body’s ability to create new blood cells is important. New blood cells are created through a process called hematopoiesis. Refer to Chapter 5 for more information about this process. Blood cells are manufactured in bone marrow, a soft, spongy substance found inside the bones. There are two types of bone marrow: yellow and red. Only red bone marrow, found in the vertebrae, ribs, hips, sternum, and skull, can produce stem cells for blood cell production. Red bone marrow Basophil Neutrophil Eosinophil Lymphocyte Red blood cells White blood cells Platelets Monocyte Yellow bone marrow © Body Scientifi c International Figure 11.11 Red blood cells, white blood cells, and platelets develop from stem cells in bone marrow. SECTION 11.1 REVIEW Mini-Glossary buffy coat a thin layer of white blood cells and platelets that lies between the red blood cells and plasma in a blood specimen that has gone through a centrifuge coagulation the process by which the enzyme thrombin and the protein fi brinogen combine to form fi brin, a fi ber that weaves around the platelet plug to form a blood clot diapedesis the passage of blood, or any of its formed elements, through the blood vessel walls into body tissues endothelial cells a thin layer of squamous cells that line all blood and lymphatic vessels erythrocytes red blood cells erythropoiesis the process by which red blood cells are produced erythropoietin (EPO) a hormone secreted by the kidneys that stimulates the production of red blood cells fi brin a long, threadlike fi ber created by the combination of thrombin and fi brinogen fi brinolysis the process of breaking down fi brin to dissolve a blood clot (continued)