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The Circulatory System The Basics • The main components of the circulatory system are the heart, blood vessels, and blood. • Together these components circulate blood through out the body. Blood: Composition • Blood is a viscous, or sticky, fluid which flows inside the vessels of the circulatory system. • There is approximately 5.5 Litres of blood in the human body. Blood: 3 Cell Types • Blood is made up of blood plasma. • Within the blood plasma there are 3 types of of cells. • Red blood cells • White Blood Cells • Platelets Blood: Red Blood Cells • Red blood cells are the most common type of blood cell. • They are disk shaped and have no nucleus. • They contain haemoglobin, the pigment that makes blood red and also transports oxygen. Blood: White Blood Cells • There are fewer white blood cells than red blood cells in the body. • White blood cells help protect the body from infection, and eliminate cell debris. • There are also 5 different types. Blood: Platelets • Platelets are made up of cell fragments. • These cell fragments contain substances that allow the blood to clot. Blood Types • The membranes of the red blood cells contain different proteins. • These proteins are responsible for creating the different blood types. • Type A • Type B • Type AB • Type O Blood Vessels • Blood vessels allow for blood to circulate through out the body. • There are 3 types of blood vessels. • Arteries • Capillaries • Veins Blood Vessels: Arteries • Arteries carry blood away from the heart. • The largest arteries are elastic. • As arteries get further from the heart they get smaller, these are called arterioles. Blood Vessels: Capillaries • Capillaries are microscopic blood vessels that are found in every body tissue. • There are several million capillaries found in the circulatory system. Blood Vessels: Veins • When capillaries come together they form veins. • Veins are responsible for taking blood back to the heart. • Within veins there are valves that allow blood to flow to the heart, but not in the opposite direction. The Heart • The heart is divided into four chambers: two atria and two ventricles. • Veins enter the atria while arteries leave from the ventricles. • Also, there is an atriovencular valve which allows blood to flow in one direction. Heartbeat • The heartbeat is the movement of the heart which pumps blood. • It is made up of three phases • Atrial Systole • Ventricular Systole • Diastole. Cardiac Cycle Phase 1 • Atrial Systole occurs when: • The atria contract • Blood is pumped through the ventricles • Blood travels through the open antriovencular valves Cardiac Cycle Phase 2 • Ventricular Systole occurs when • The ventricles contract • Sigmoid valves open • Blood flows out into the pulmonary artery and aorta • At the same time, valves in ventricles and aorta close. Cardiac Cycle Phase 3 • Diastole occurs when • The heart relaxes • Blood is drawn from the venae cavae and pulmonary veins • The blood flows into the atria.