Structure+of+the+Heart+and+How+It+Works

====**Structure of the Heart and How it Works Basic Structure __ Path of Blood Through Heart:__ De-oxygenated b lood flows to the heart from the body through the superior and inferior vena cavae, shown here as blue tubes on the left side of the diagram. The blood flows from the vena cava into the right atrium, which then contracts and pumps the blood through the tricuspid valve into the right ventricle , creating the first "lub" of a heartbeat. Then, the right ventricle contracts as well and send the blood through the <span style="color: rgb(21,72,20);">pulmonary valve into the <span style="color: rgb(17,65,17);">pulmonary trunk, creating the second "dub" of the heartbeat. The trunk splits into the left and right <span style="color: rgb(25,71,21);">pulmonary arteries, which takes the de-oxygenated blood to the <span style="color: rgb(18,63,20);">lungs for gaseous exchange. From the lungs, the newly oxygenated blood flows to the <span style="color: rgb(23,62,19);">left atrium via the <span style="color: rgb(17,47,14);">pulmonary vein. Again, the atrium contracts, and the blood is pumped through the <span style="color: rgb(18,55,16);">bicuspid valve into the <span style="color: rgb(21,66,21);">left ventricle, then through the <span style="color: rgb(21,68,18);">aortic valve to the <span style="color: rgb(22,60,22);">aorta. The aorta then carries the blood all over the body to provide oxygen where it is needed. The ventricles are divided by a wall named the <span style="color: rgb(22,69,18);">ventricular septum. <span style="font-family: Arial,Helvetica,sans-serif;">____         **====

In short, if we were to follow a droplet of blood, it would go from the body...
 * to the superior and inferior vena cava,
 * then to the right atrium
 * through the tricuspid valve
 * to the right ventricle
 * through the pulmonic valve
 * to the pulmonary artery
 * to the lungs
 * to the pulmonary veins
 * to the left atrium
 * through the mitral valve
 * to the left ventricle
 * through the aortic valve
 * to the aorta
 * to the body

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 * <span style="color: rgb(207,2,51);"><span style="font-size: 80%; color: rgb(255,0,55); font-family: Arial,Helvetica,sans-serif;"> <span style="color: rgb(0,0,0); font-family: Arial,Helvetica,sans-serif;"><span style="color: rgb(9,23,211); font-family: Arial,Helvetica,sans-serif;"><span style="color: rgb(18,59,19); font-family: Arial,Helvetica,sans-serif;"><span style="color: rgb(15,67,19);"><span style="color: rgb(9,14,251);"><span style="color: rgb(22,69,18);"><span style="font-family: Arial,Helvetica,sans-serif;">__Animation of how the heart pumps blood__ [|Heart Animation]        **======

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====== The heart's valves maintain the unidirectional flow of blood in the heart by opening and closing depending on the difference in pressure on each side. Each chamber has a sort of one-way valve at its exit that prevents <span style="color: rgb(23,3,3);">blood from flowing backwards. When each chamber contracts, the valve at its exit opens. When it is finished contracting, the valve closes so that blood does not flow backwards. The tricuspid and mitral valves are both atriventricular valves, and the pulmonary and aortic are semilunar valves. [|How the valves work]
 * 1) **The tricuspid valve** is at the exit of the right atrium.
 * 2) **The pulmonary valve** is at the exit of the right ventricle.
 * 3) **The mitral valve** is at the exit of the left atrium.
 * 4) **The aortic valve** is at the exit of the left ventricle

=The Nitty and the Gritty: Heart Specifics= The heart has three layers.
 * The smooth, inside lining of the heart is called the **endocardium**.
 * The middle layer of heart muscle is called the **myocardium**.
 * Surrounding it is a fluid filled sac call the **pericardium**.

The heart beats in two's.
 * The first beat (systole) occurs in as both the left and right atria contract, pumping blood to their respective ventricles through the atrioventricular valves.
 * The second systole occurs as both ventricles contract, sending blood through the semilunar valves. As with the atria, this occurs simultaneously.



=Expecto Patronum!: The "Magic" Behind the Beating Heart=

So how does the heart know when to beat? It surely cannot be simply reaction to the buildup of pressure on the valves. What then, would compel the muscle to contract?

Electricity. Around 72 times per minute, the **sinoatrial node (SA node)** located in the right atrium releases a signal telling pacemaker cells to have the heart contract.

The following paragraph is to be read along with the diagram. The electrical impulse leaves the **SA node** (1) and travels to the right and left atria, causing them to contract together. This takes .04 seconds. There is now a natural delay to allow the atria to contract and the ventricles to fill up with blood. The electrical impulse has now traveled to the **atrioventricular node (AV node)** (2). The electrical impulse now goes to the **Bundle of His** (3), then it divides into the **right and left bundle branches** (4) where it rapidly spreads using **Purkinje fibers** (5) to the muscles of the right and left ventricle, causing them to contract at the same time.



To change the rate and intensity of contraction, the autonomic nervous system, which is not controlled consciously, merely gives a signal- the parasympathetic portion of the autonomic nervous system to decrease frequency/intensity and the sympathetic to do the opposite.

To see a full fledged animation of this phenomenon, visit: [|This Website]

=How Does One Go About Feeding A Juggernaut?: Nourishing the Heart=

In order to maintain the diffusion gradient, the heart seeks an external means of nourishment via the coronary arteries.

About 5% of all blood flow goes through these arteries and back through their respective veins.