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The Circulatory System Functions of the Circulatory System • Stabilizes body temperature and pH to maintain homeostasis • An organ system which distributes blood throughout the entire body – – – – Transports oxygen to body cells Transports CO2 away from cells Transportation of hormones Transportation of immune system components Contains 3 Major Parts • The Heart • Blood Vessels • Blood The Heart The Heart as a Double Pump • The heart is a double pump, simultaneously pumping blood to and from body cells through the systemic circulation and to and from the lungs in the pulmonary circulation Parts of the Heart • The atria – Receiving chambers • The ventricles – Pumping chambers • Valves: two atrioventricular and two semilunar valves – Control one-way flow • The interventricular septum – Separates right and left ventricles Blood Vessels Types of Blood Vessels • Arteries – Carry blood away from the heart – Aorta is the largest artery • Veins – Carry blood to the heart – Contain valves – Vena cava is the largest vein • Capillaries – Site of exchange of nutrients, wastes, and gases between blood and interstitial fluid (fluid surrounding tissue cells) Walls of Arteries and Veins • Tunica externa – Outermost layer – Composed of mainly elastic and collagen fibers – Strengthens, Anchors • Tunica media – Middle layer – Composed of elastic and smooth muscle fibers – Circular Smooth Muscle – Vaso-constriction/dilation • Tunica interna – Innermost layer – Endothelium – Minimize friction • Lumen Blood Functions of the Blood • Carries oxygen from the lungs to all of the cells in the body • Carries carbon dioxide from the body cells to the lungs to be exhaled • Carries waste to the kidneys to be disposed of • Carries nutrients to body cells • Contains immune system cells and molecules that help fight infection Components of Blood • Plasma – Comprise 55% of whole blood volume • Formed Elements – Comprise 45% of whole blood volume Plasma • 91% water • Contains dissolved proteins, glucose, clotting factors, mineral ions, hormones and carbon dioxide Formed Elements • Red Blood Cells (Erythrocytes or RBCs) – Contain a large molecule called hemoglobin used to transport oxygen and carbon dioxide • White blood cells (Leukocytes or WBCs) – Cells of the immune system defending the body against both infectious disease and foreign materials • Platelets (Thrombocytes) – Special cell fragments that protect the body by forming a platelet plug to stop bleeding by ruptured vessels – Secrete chemicals that aid in blood clotting