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What makes blood flow between chambers of the heart and within blood vessels?

-differences in pressure
-blood travels from high pressure to low pressure

Can the AV valves open in both directions?

-yes, they are like "swinging saloon doors"

What happens when the SA node fires?

-left atrium contracts (systole)

What results from the contraction of the left atrium in terms of pressure?

-produces high pressure in the left atrium

What does high pressure in the left atrium result in? (in terms of valve mechanics and movement)

-the creation of pressure differential between left atrium and left ventricle
-pressure differential causes the opening of the tricuspid valve (av valves open towards the ventricles when pressure is high in the atria and low in the ventricles)
-blood moves from the left atrium to the left ventricle

What happens as blood moves from the left atrium into the left ventricle?

-wave of excitation spreads through the bundle of his and purkinje fibers into the left ventricle
-left ventricle contracts (systole)

What happens to the papillary muscles and the chordae tendinae during ventricular systole? Why?

-papillary muscles are extensions of the ventricular myocardium, so the contract as the ventricles enter systole
-as the papillary muscles contract, they pull the chordae tendinae taut

What happens when the chordae tendinae are pulled upon?

-chordae tendinae are tethered to the AV valves
-pulling on the chordae tendinae prevents the AV valves from opening into the atria
-also seal the cusps of the AV valves shut

What results from the closure of the AV valves?

-based on pressure differences, blood should flow back from the ventricles to the atria when the ventricles are in systole
-however, if the AV valves are closed by the chordae tendinae, blood cannot flow backwards into the atria

Since the AV valves are closed during ventricular systole, where must the blood go?

-wherever there is low pressure
-only location with low pressure is the aorta

What happens to the aortic semilunar valve when pressure is high in the left ventricle?

-the valve opens

What is the result of the opening of the aortic semilunar valve?

-blood flows from the left ventricle into the aorta

What happens in terms of pressure as soon as blood flows into the aorta?

-pressure drops in the left ventricle
-pressure increases in the aorta

Based on pressure differentials, where does the blood want to flow when pressure is low in the left ventricle and high in the aorta?

-back into the left ventricle

What prevents this?

-the aortic semilunar valve


-the cup-shaped cusps fill with blood as movement occurs from the left ventricle to the aorta
-filling of the cups closes valves--cups fold inward because of the weight of the blood, sealing the valve

Why doesn't the heart "pump" blood?

-because movement is created as a result of pressure differentials

In a healthy heart, why does the blood always flow in a unidirectional manner?

-because the heart creates pressure differentials that enforce correct flow

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