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