The Circulatory System

The HeartWhat is the point? Why do you have a heart?

Made up of 4 chambers – 2 atria (right and left), and 2 ventricles (right and left).

The heart’s purpose is to pump blood throughout the body, in order to distribute oxygen and nutrients to all of the cells in your body.

But how does oxygen get into the blood? And how does it get to these other cells?

Tracing a Drop of Blood (watch animation)

Let’s begin our journey in the Right Atrium of the heart. The atria are the two smaller chambers of the heart, and they pump blood coming from the body into the ventricles. http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html

The atria and ventricles are separated by valves. Why do you think this is?

The right atrium pumps deoxygenated blood into the right ventricle. This blood is also carrying carbon dioxide

Tracing a Drop of BloodFrom the right ventricle, the blood is

pumped to the lungs through the pulmonary artery, where it picks up oxygen in the alveoli. (http://www.nhlbi.nih.gov/health/dci/Diseases/hlw/hlw_when.html)

Blood (with oxygen!) travels back to the heart through the pulmonary vein, where it enters the left atrium.

Tracing a Drop of BloodBlood (still has oxygen!) is pumped from

the left atrium into the left ventricle. Notice how thick the heart wall is around the left ventricle? Why is it that way?

Blood is pumped from the left ventricle into the aorta, the body’s largest artery.

Tracing a Drop of BloodArteries and Veins – what is the difference?

Simple – Arteries come from the heart and go to the rest of the body, Veins come from the body and go to the heart!

So, back to the blood (plus oxygen!). It comes from the aorta, and goes into progressively smaller blood vessels until the vessels can only fit a few blood cells through. These are called capillaries.

Trace a Drop of Blood

Now to the good part – gas exchange!

Capillaries let red blood cells exchange oxygen for carbon dioxide with body cells. But why?

Aerobic Respiration!

Now, the blood will flow back to the heart through veins and start the cycle all over again!

The BeginningYour heart doesn’t pump on its own. It needs a

bit of a jump start.

This jump start is an electrical signal from the nervous system to a bundle of nerves on the heart called the SA node. An electrical signal is sent every time your heart beats.

The SA node sends this signal to another bundle of nerves called the AV node, and the AV node sends the signal across the entire heart.

SA and AV node animationhttp://

www.argosymedical.com/Circulatory/samples/animations/Heart%20Conduction%20System/index.html

Label the heart’s circulation

http://www.osovo.com/diagram/humanheartdiagram.htm

Label the heart’s electrical system

http://www.texasheartinstitute.org/HIC/ProjH/conductheart.cfm