Circulatory System and The Heart Biology 20

The Heart Size of fist - 300g Beats 70 times per minute Not a single pump, but two parallel pumps separated by a large muscle called a septum

Pulmonary Circulatory System Vessels that carry blood to and from the lungs

Systematic Circulatory System Vessels that carry blood to and from the body

One Way Blood Flow Blood circulates through the body in one direction only AV and Semi-lunar valves inside the heart, prevent the back flow of blood AV valves are supported by thick connective tissue called chordae tendinae

Arteries and Arterioles Carry blood AWAY from the heart Where you feel your pulse (change diameter when the heart pumps blood through them) Thick, muscular walls can withstand high pressure Blood pumped from heart maintains one way blood flow Carry oxygenated blood EXCEPT pulmonary artery

Veins and Venules Carry blood TO the heart Thin walls, cannot withstand much pressure Valves maintain one way flow Skeletal muscles contract – increase pressure – vein opens Carry deoxygenated blood EXCEPT for pulmonary vein When the muscle relaxes, the vein widens, forcing blood to build up at the valves When skeletal muscles contract, the vein narrows, and the valves open, forcing blood to pass through to the heart **Store about 65% of your blood **

Heart Movement When the ventricles contract, blood is pushed out of the ventricles, through the semi-lunar valves, and into the arteries **Note the AV valves are closed during this time** When the ventricles relax, the AV valves open, allowing blood to flow into the atria and from the atria into the ventricles **Note the semi-lunar valves are closed at this time**

Setting the Heart Tempo Cardiac muscle differ from other types of muscles Cardiac muscle can contract without external nerve simulation; myogenic muscle Different parts of the heart beat at different tempos individually, but together when united

SA Node The heart’s tempo is is set by the sinoatrial or SA node The SA node is a bundle of specialized nerve and muscle cells located where the venae cavae enter the atrium This bundle sets the hearts tempo at about 70 beats per minute

AV Node The contractions are carried throughout the heart to a second node, the AV node or atrioventicular valve The AV node conducts the impulse through the septum and towards the ventricles Thus, the atrium contract prior to the ventricles

Heart Sounds The heart makes a two-beat sound - “lubb - “dubb” The sound is created when pairs of valves close The lubb sound is louder, and is created when the AV valves close, semi-lunar Valves open The dubb sound is softer, and is created when the semi-lunar valves close, AV valves open

Diastolic Used to describe the relaxation of the heart Blood moves through the atria into the ventricles during relaxation

Systolic Used to describe the contraction of the heart blood is pushed out of the ventricles upon contraction