Author's Note:

Summary or In-depth? See below.

This section sure has a lot! The summary explains the circulation of blood throughout the body. The in-depth version includes that circulation in more detail along with clarifications, fun facts, and the differences between the 3 types of circulation.

Choose which best fits your needs! Happy Learning!

Summary:

Deoxygenated blood goes through the vena cavae (plural of vena cava) into the right atrium through the tricuspid valve to the right ventricle through the pulmonary semi-lunar valve to the pulmonary arteries and, finally, to the lungs where it is oxygenated. Then, blood comes back to heart through pulmonary veins, then to the left atrium, and then through the bicuspid valve to the left ventricle. Then, it goes through the aortic semi-lunar valve to the aortas and to the body where the oxygen in the blood is used. The cycle starts again.

---------------------------------------------

In Depth:

• Oxygen is carried to the body by blood. After the body uses the oxygen in the blood, the deoxygenated blood goes back to the heart by entering through the superior vena cava and inferior vena cava.

More Information - There are 2 vena cavae because the superior vena cava is for the deoxygenated blood returning from the upper half of the body and the inferior vena cava is for the deoxygenated blood returning from the lower half of the body.

• Since both vena cavae lead to the right atrium, all the deoxygenated blood ends up there. Then, the valve that connects the right atrium to the right ventricle will open. This is called the tricuspid valve or the right-atrioventricular valve. Once it opens, the deoxygenated blood will go from the right atrium to the right ventricle.

More Information - The chordinae tendinae attach to the tricuspid and bicuspid (which you will learn about later) valves; the papillary muscles then attach to the chordinae tendinae and holds the valves closed, so when ventricles contract, the valves do not swing the other way (back into the atria (plural of atrium)), and there is not backflow from the blood in the ventricles to the atria.

• From the right ventricle, the blood will move; the valve connecting the right ventricle to the pulmonary artery, called the pulmonary semi-lunar valve will open, and then PULMONARY circulation (of the blood) will happen (shown in underlined and bold).

• The deoxygenated blood goes to the left and right pulmonary arteries.

More Information - There are 2 pulmonary arteries because the left is for the left lung and right is for the right lung.

FUN FACT! The left / right pulmonary arteries are the only arteries in the human body that carry deoxygenated blood!

• The deoxygenated blood goes through these arteries and to the lungs where the blood picks up oxygen. The blood then goes from the lungs through the left and right pulmonary veins to the left atrium.

FUN FACT! The left / right pulmonary veins are the only veins in the human body that carry oxygenated blood!

• The oxygenated blood goes from the left atrium through the bicuspid valve (aka the left atrioventricular valve, aka the mitral valve) and to the left ventricle.

TIP! Imagine the number 32 written on your chest; the tricuspid valve is on the right side and the bicupsid valve is on the left!

• The blood goes from the left ventricle through the aortic semi-lunar valve and to the aorta. Then, two things happen; the blood goes to the heart (coronary circulation) and to the body (systemic circulation).

———————————————————

CORONARY Circulation:

• At the root of the aorta, the left and right coronary artery branch off and take oxygenated blood to the heart (the heart needs oxygen too!) Once the heart muscles use the oxygen in the blood, the deoxygenated blood goes through the coronary veins. Most of these veins converge into the coronary venous sinus (others drain directly into the right atrium or into the great cardiac vein which then drains into the right atrium) which then drains into the right atrium.

• From the aorta, the blood also goes to the upper half of the body and the descending aorta. The blood that goes to the descending aorta then goes to the lower half of the body.

———————————————————

SYSTEMIC Circulation:

Oxygenated Blood goes to the tissues of the body as follows.

Aorta / Descending Aorta —> Arteries —> *Arterioles —> Capillaries —> Tissue cells use oxygen from the blood

Deoxygenated Blood returns to the heart as follows.

Tissue cells—> Capillaries —> *Venuoles —> Veins —> Superior Vena Cava / Inferior Vena Cava

*Arterioles are like smaller arteries.

*Venuoles are like smaller veins.

------------------------------------------------------------

Then the cycle starts again.

Contraction:

• Diastole: This is when the heart rests, and the right atrium is filling up with deoxygenated blood from body.

• Systole: This is when the heart beats or contracts. There are 2 types of systole.

-Atrial Systole (when the atria (plural of atrium) are contracting and are pushing blood into the ventricles)

-Ventricular Systole (when the ventricles are contracting and pushing blood to the lungs and body)

• Blood pressure is shown as systole over diastole such as 100 / 70.

Systole (contracting) of the heart = 100

/

Diastole (resting of the heart (between the contractions)) = 70

Blood pressure can be too low, normal, or too high. Hypotension is too low; normal is normal; hypertension is too high. See the ranges for each of these types of blood pressures.

-Hypotension = less than 90/ less than 60

-Normal Blood pressure = 120 or less* / 80 or less* (*until hypotension)

-Prehypertension = 120-139/80-89

-Hypertension = 140-159/90-99

-Hypertension Stage 2 = 160 or more / 100 or more > or = to 160

---------------------------------------------------------------

Cardiac Conduction:

Depolarize means contract

Repolarize means relax

1. The sinoatrial node (located in right atrium) is the pacemaker of the heart. It sends signals to the left and right atrium at the same time saying “contract”.

2. This command also has to go to the ventricles; we do not want the ventricles feeling left out, right? So, that “contract” command also goes to the AV node (which eventually goes to the ventricles).

3. At the AV node, the command is paused. The AV Node acts as a gatekeeper; once it “lets the command through,” the command will go to the AV bundle (also called the Bundle of His).

4. The AV bundle connects the atria (plural of atrium) to the ventricles. How? Well, the AV bundle splits into 2 branches, referred to as the bundle branches.

5. There is a right branch and left branch; the right goes to the right ventricle, and the left goes to the left ventricle.

6. Once both the branches reach their respective ventricles, they split into fibers called the Purkinje fibers. The Purkinje fibers depolarize (contract)* the cells in each ventricle responsible for contraction.

• Result: An EKG. An EKG shows the above steps in action.

The atria contract and that is shown as the p wave (hump) on the EKG. After the atria are done contracting, the "contract" command is delayed at AV node (the gatekeeper). Then, the atria relax, and the ventricles contract; this makes the QRS interval. Then the ventricles relax which causes the t wave. The ventricles finish relaxing. The process starts again.

Question: Why is the hump for ventricles (the QRS) much larger than that for the atria (the pwave)?

Answer: The ventricles have a much more powerful contraction. For example, the left ventricle has to pump blood (through the aorta) to the whole body!