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The Human Circulatory System Introduction Humans and other vertebrates have a closed circulatory system: – This means that circulating blood is pumped through a system of vessels – This system consists of the heart (pump), series of blood vessels and the blood that flows through them. The Truth About Your Heart The Heart Located near the center of your chest Hollow structure Composed almost entirely of muscle About the size of your clenched fist The Heart Enclosed in a protective sac called the pericardium The Heart In the walls of the heart, two layers of tissue form a sandwich around a thick layer of muscle called the myocardium. Contractions of the myocardium pump blood through the circulatory system. The Heart The heart contracts about 72 times per minute Pumps about 70mL of blood with each contraction. The Heart The right and left sides of the heart are separated by a septum, or wall. The septum prevents the mixing of oxygen rich and oxygen poor blood. The Heart On each side of the septum are two chambers. The upper chamber (receives blood) is the atrium. The lower chamber (pumps blood out of heart) is the ventricle. The Heart The heart has a total of 4 chambers: 2 atriums 2 ventricles Pathway of Blood Deoxygenated blood passes from the right atrium into the right ventricle and then goes to the lungs. From the lungs, blood moves back toward the heart into the left atrium to the left ventricle and then passes into the aorta to go to the rest of the body Valves As the heart contracts, blood flows into the ventricles and then out through the ventricles. Flaps of connective tissue, called valves, are located between the atria and ventricles. Blood moving keeps the valves open. When the ventricles contract, the valves close which prevent blood from flowing back into the atria. Valves There are also valves that stop blood from re-entering the ventricles after the blood has left. This system of valves keeps blood moving in one direction which increases the pumping efficiency of the heart. Heart Beat Heart muscles are composed of individual fibers Each atrium and ventricle contracts as a unit. Each contraction begins with a group of cardiac muscle cells in the right atrium known as the sinoatrial node (SA node) Heart Beat Because the SA node paces the heart it is known as the pacemaker. The impulse spreads from the pacemaker to the rest of the atria. From the atria, a signal is sent to the atrioventricular node and then to a bundle of fibers in the ventricle. When the ventricle contracts, blood flows out. Blood Vessels As blood moves through the circulatory system it moves through 3 types of blood vessels: Arteries Capillaries Veins Arteries Large vessels Carry blood from heart to tissues of body Carry oxygen rich blood, with the exception of pulmonary arteries. Thick walls-need to withstand pressure produced when heart pushes blood into them. Capillaries Smallest blood vessels Walls are only one cell thick and very narrow. Important for bringing nutrients and oxygen to tissues and absorbing CO2 and other waste products. Veins Once blood has passed through the capillary systems it must be returned to the heart. Done by veins Walls contains connective tissue and smooth muscle. Largest veins contain one way valves that keep blood flowing toward heart. Many found near skeletal muscles. When muscles contract, blood is forced through veins. Blood Pressure The heart produces pressure The force of blood on the wall of the arteries is known as blood pressure. Blood pressure decreases as the heart relaxes, but the rest of the circulatory system is still under pressure. Blood Pressure When blood pressure is taken, the cuff is wrapped around the upper portion of the arm and pumped with air until blood flow in the artery is blocked. As the pressure in the cuff is relaxed, 2 numbers are recorded. – Systolic pressure- the first number taken, is the force felt in the arteries when the ventricles contract. – Diastolic pressure- the second number taken, is the force of the blood on the arteries when the ventricles relax. Disorders of Circulatory System Atherosclerosis – Fatty deposits (plaque) in walls of arteries – Deposits can obstruct flow of blood which can raise blood pressure – Increases risk of blood clots – If clot breaks free it can obstruct blood flow to tissues. Disorders of Circulatory System Heart Attack – Due to atherosclerosis, coronary arteries may become blocked (blood can’t get to heart muscle) – Heart muscle begins to die due to lack of O2 Disorders of Circulatory System Stroke – Blood clot may break free and block a vessel leading to the brain. – Brain cells are starved of oxygen and nutrients – Loss of function may occur – Can cause paralysis, loss of ability to speak or death. Blood Composed of plasma and blood cells Types of Cells are: – – – Red Blood Cells White Blood Cells Platelets Blood Plasma – Straw colored – 90% water – 10% dissolved gases, salts, nutrients, enzymes, hormones, wastes, and proteins. Blood Plasma proteins – 3 Types: Albumins, globulins and fibrinogen. – Albumins and Globulins- transport substances such as fatty acids, hormones and vitamins. – Fibrinogen- Responsible for blood’s ability to clot Blood Red Blood Cells – – – – – – Most numerous type Transport oxygen Get color from hemoglobin Disk shaped Made in red bone marrow Circulate for 120 days Blood White Blood Cells – Guard against infection, fight parasites, and attack bacteria – Number of WBC’s increases when body is fighting – Lymphocytes produce antibodies which fight pathogens and remember them Blood Platelets – Aid the body in clotting – Small fragments – Stick to edges of broken blood cell and secrete clotting factor to help form clot. Blood Clotting Problems Hemophelia – Genetic disorder that disrupts clotting – People must be very careful to avoid injury – Can be treated by injecting extracts that contain the missing clotting factor.