The Circulatory System

1. The Circulatory System By: Chris Lewis

2. The Heart • The heart is the central organ of the cardiovascular system, pumping blood throughout the body • The heart lies in the thoracic cavity,between the two lungs • The heart is surrounded by a tough, sac-like membrane called the pericardium • A septum vertically divides the heart into two halves, and each side of the heart is further divided into an upper chamber and a lower chamber by valves • The upper chambers are called atriums and the lower chambers are called ventricles • The right atrium is divided from the right ventricle by the tricuspid valve. The left atrium is divided from the left ventricle by the bicuspid valve (mitral valve). Both of these valves are atrioventicular valves. • The ventricles are separated from the large vessels leading out of the heart by semiluanar valves(Pulmonary and aortic).

3. Blood Vessels • The large, muscular blood vessels that carry blood away from the heart are called arteries; the blood vessels that carry blood back to the heart are called veins. • Arteries have three layers, which give the arteries a combination of strength and elasticity. • Arteries thin into arterioles, which in turn thin into capillaries. • Capillaries are only one cell thick, allowing for rapid exchange of materials. Nutrients and gases diffuse through the capillary walls, across the concentration gradient • Capillaries merge to form venules, which unite to form veins • Veins carrying blood from the lower parts of the body merge into the inferior vena cava. Veins carrying blood from the upper parts of the body merge to form the superior vena cava.

4. Pulmonary Circulation • Deoxygenated blood from all parts of the body except the lungs enters the right atrium of the heart, where it is pumped into the right ventricle. • The right ventricle contracts, forcing the deoxygenated blood into the pulmonary artery; the pulmonary artery is the only artery that carries deoxygenated blood. • The pulmonary artery carries the blood into the lungs, branching into arterioles, and then into capillaries. • Oxygen in the lungs diffuses into the capillaries, and the carbon dioxide in the capillaries diffuses into the lungs. • The capillaries, now carrying oxygen rich blood, merge into venules, and then into the pulmonary veins that lead to the left atrium of the heart • The pulmonary veins are the only veins that carry oxygenated blood. .

5. Systematic Circulation • Coronary circulation is one subsystem of systematic circulation that supplies blood to the heart itself. If blood flow to the heart is reduced or cut off, the muscle cells of the heart will die. • Renal circulation supplies blood to the kidneys. Nearly one forth of the blood pumped form the left ventricle is pumped into the kidneys. The kidneys filter waste from the blood. • Hepatic portal circulation passes through the small intestine and supplies blood and nutrients picked up in the small intestine to the liver.

6. The Blood • The blood is composed of a liquid medium and blood solids. • Blood solids consist of red blood cells, white blood cells, and platelets. • The liquid makes up 55% of the blood, the solids make up the remaining 45%. • The liquid medium is a sticky, straw-colored fluid called plasma. The plasma is 90% water. Nutrients such as vitamins, minerals, amino acids, and glucose are dissolved in the plasma, to be carried body cells. • Red blood cells (erythrocytes) are formed in the red marrow of bones. By the time a red blood cell reaches the blood it is little more than a membrane sac containing hemoglobin. Hemoglobin is an iron containing protein that is capable of transporting oxygen and carbon dioxide. • Red blood cells have a life span of about 120 to 130 days. • White blood cells (leukocytes) help defend the body against disease. One type of white blood cell, phagocytes, engulf foreign microorganisms and digest them using hydrolytic enzymes. • Platelets are fragments of very large cells that are essential to blood clots. The congregation of platelets at a rip blood vessel causes the production of the protein fibrin, that traps red blood cells and forms the clot.

7. Lymphatic System • One function of the lymphatic system is to return fluids that have collected in the tissues to the blood. • The fluid is called lymph. Lymph vessels are similar in structure to capillaries and the large lymph vessels are similar to veins. • Lymph must be moved by the contractions of muscles around the lymph vessels. • As the lymph travels to the heart it passes through small organs called lymph nodes. The lymph nodes contain white blood cells called lymphocytes, that help fight disease. • When a person hays an infection, lymph nodes may become swollen because of the increased number of lymphocytes.