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.