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Process Description Page 1 HOW THE HUMAN BODY PRODUCES BLOOD CELLS The human body consists of a number of complex systems, including the circulatory system. Also known as the cardiovascular system, the circulatory system employs a fluid known as blood to carry nutrients and oxygen throughout the body and take waste away from other cells. The human body produces its blood, a substance needed for survival, through hematopoiesis, which literally means “to make blood.” Main Components of Blood. The main components of blood are plasma, red blood cells, white blood cells, and platelets. (See Figure 1). Plasma, which is mostly water, carries the red blood cells, white blood cells, platelets, and many other substances throughout the body. Red blood cells (“RBCs”) distribute oxygen from the lungs to the rest of the body. White blood cells (“WBCs”) fight Figure 1. Main Components of Blood. infection. Lastly, platelets help blood to clot after an injury. Formation of Blood Cells. Blood cells form in bone marrow, although other parts of the body contribute to the blood-making process. The human body contains both red and yellow marrow, a jelly-like substance found in bones. RBCs, WBCs, and platelets form from pluripotential hematopoietic stem cells located in Process Description Page 2 red bone marrow. (See Figure 2.) During emergencies involving sudden blood loss, yellow bone marrow also creates blood cells to meet the body’s needs. In children, the red bone marrow in all bones forms blood cells. As human beings age, however, red bone marrow decreases and only certain bones produce blood cells. Under conditions like low oxygen content, loss of blood or anemia, sudden loss of RBCs, the Figure 2. Cells Produced By Bone Marrow. kidneys secrete erythropoietin, a hormone important to blood production. This hormone stimulates the red bone marrow to produce more RBCs and causes the RBCs to mature more quickly to meet the body’s demands. The human body alters the blood-making process in response to emergencies. When faced with infection or bacteria, red bone marrow begins to produce more WBCs. Platelet creation increases when sudden blood loss occurs. Once blood cells are formed, they enter the bloodstream by passing from the bone marrow to the blood that is traveling through the bones. The cells then circulate through the body, performing their specific duties. Blood cells eventually die. (See Figure 3.) A healthy human body assesses its need for blood cells and stimulates cell production to meet demand. Figure 3. Life Span of Blood Cells Process Description Page 3 SOURCES: Bianco, Carl, M.D. "How Blood Works." HowStuffWorks.com. How Stuff Works, Inc. 01 April 2000. Web. <http://health.howstuffworks.com/humanbody/systems/circulatory/blood.htm> “Bone marrow and hemopoeitic stem cells.” Encyclopedia Brittanica. Encyclopedia Brittanica Online Academic Edition. Encyclopedia Brittanica, Inc. 2014. Web. <http://www.britannica.com.ezproxy.snhu.edu/EBchecked/topic/565211/stemcell/272798/Bone-marrow-and-hematopoietic-stem-cells?anchor=ref839537 > “Circulatory System.” IHW 2005. n.p. March 2005. Web. <http://www.biologymad.com/resources/Circulatory%20System%20Revision.pdf> Panchbhavi, Vinod K. M.D., FRCS, FACS. “Bone Marrow Anatomy.” Medscape.com. 22 August 2013. Web. <http://emedicine.medscape.com/article/1968326overview#aw2aab6b4> “What is the difference between red bone marrow and yellow bone marrow.” n.p. Web. http://www.preservearticles.com/201101133203/difference-between-red-bone-marrowand-yellow-bone-marrow.html Wilson, Sue. “How is Blood Produced.” Pbs.org. The Educational Broadcasting Corporation. 2002. Web.<http://www.pbs.org/wnet/redgold/journey/phase1.html> Wilson, Sue. “What is Blood Made Of.” Pbs.org. The Educational Broadcasting Corporation. 2002. Web.<http://www.pbs.org/wnet/redgold/journey/phase1.html>