THE FUNCTION OF CIRCULATION

IMPORTANT TERMS Pulmonary arteryleukocytes Pulmonary vein platelets Atrioventricular valvevasoconstriction Semilunar valvevasodilation Pulmonary circulation Systemic circulation Cardiac circulation Plasma Erythrocytes

MAIN FUNCTION The main function of the circulatory system is to deliver oxygen and nutrients to all the body’s cells Other important functions include:  Regulating internal temperature  Protects the body against invading microbes

COMPONENTS Main components of the circulatory system include :  The heart  Blood vessels (arteries and veins)  Blood

THE HEART Your heart is tucked in behind your left lung slightly to the left of your sternum (central rib bone) Humans have a four chambered heart that includes the: Right atrium Left atrium Right ventricle Left ventricle

THE HEART The atria are small chambers at the top of the heart. They receive blood from veins The ventricles are larger chambers at the bottom of the heart. They pump blood out

THE CARDIAC CYCLE Blood takes a very specific path through the body and this path repeats over and over again. It is called the cardiac cycle It starts at the right atrium.

THE RIGHT ATRIUM Blood from here has just come from the body. Oxygen has been removed from this blood and it contains CO2 It is dark maroon blue colour Blood gets pumped from here through a valve called the tricuspid valve into the right ventricle

RIGHT VENTRICLE Blood here is still deoxygenated (has no oxygen). It gets pumped out of the heart into the pulmonary artery. It then travels to the lungs to pick up oxygen

LEFT ATRIUM Blood has just returned from the lungs where it has picked up oxygen It is fully oxygenated and has a bright red colour It is pumped through the bicuspid valve into the left ventricle

LEFT VENTRICLE This is the strongest, most muscular chamber of the heart Blood from here is pumped out of the heart into the aorta where it will travel throughout the body. As the blood travels through the body it drops of oxygen and nutrients at all the cells

Heart Diagram

CARDIAC CYCLE

BLOOD VESSELS Blood vessels take blood throughout the body. If your body were a city, blood vessels would be the roads and highways There are two types of blood vessels; arteries and veins

ARTERIES VIENS Carries blood away from the heart Thicker and more muscular More elastic Brings blood back to the heart Thinner Less elastic, more compliant (stretchy) Have valves that keep blood moving in the right direction BLOOD VESSELS

ARTERIES VEINS BLOOD VESSELS

MORE TYPES OF BLOOD VESSELS Blood leaves the heart through large arteries (aorta and pulmonary) Large arteries branch off to smaller arteries Smaller arteries branch into smaller arterioles Arterioles continue to branch until they form tiny vessels called capillaries Blood flows through capillaries which merge together to form venules Venules merge to form veins Veins come together to form larger veins (vena cava and pulmonary vein) which deliver blood back to the heart

BLOOD VESSELS

BLOOD If you take a test tube of blood and spin it in a centrifuge it will quickly divide into two parts. They are:  Cells and  Plasma

HEMATOCRIT PLASMA Approximately 45% of your blood Contains mostly red blood cells or erythrocytes and some white blood cells or leukocytes Approximately 55% of your blood Contains mostly water but also has dissolved gases, proteins, salts and other nutrients BLOOD

RED CELLS (ERYTHROCYTES) WHITE CELLS (LEUKOCYTES) Shaped like a donuts without a hole Make up over 99% of blood cells Made in bone marrow Contain hemoglobin which carries oxygen Different shapes Make up less than 1% of blood cells Purpose is to attack foreign microbes Two main types:  Granulocytes – engulf invaders  Agranulocytes – involved in the formation of antibodies TYPES OF BLOOD CELLS

RED WHITE TYPE OF BLOOD CELLS

PLATELETS Prevent excessive blood loss by causing blood to clot or coagulate  Broken blood vessels release chemicals that attract platelets  Platelets rupture which releases substances which react with certain plasma proteins to form thromboplastin which gets converted to thrombin (an enzyme)  Thrombin converts fibrinogen (a plasma protein) to fibrin  Fibrin forms a mesh like substance (a scab) that stops blood from escaping

BLOOD CLOTTING

CONTROL OF BLOOD FLOW One of the really amazing things about the circulatory system is that it has the ability to control where the blood goes. Remember, arteries have a layer of muscle cells called smooth muscle. Smooth muscle is not a voluntary muscle. It is controlled by the brain. When it contracts, called vasoconstriction, the arteries narrow and decrease the blood supply. When smooth muscle relaxes, it is called vasodilation. This makes the artery wider and increases the amount of blood that flows through it

CONTROL OF BLOOD FLOW Blood flow is controlled for two main reasons: 1. To allow more active parts of the body to receive more blood than inactive parts. 2. To maintain body temperature in the most important parts of the body