Physiological Processes of the Circulatory System

Instructor: Christopher Sailus

Chris has an M.A. in history and taught university and high school history.

In this lesson we explore the circulatory system, the all-important physiological process that allows each part of the body to get the water, oxygen, and nutrients it needs to survive.

Circulatory System

Have you ever skinned your knee or cut yourself before? Chances are it hurt, and then some of your blood started flowing from the cut. That blood usually carries important nutrients to different parts of your body, and it passes through your body via the circulatory system. In this lesson, we will explore the circulatory system and detail some of the physiological processes it performs that are vital to life.


Blood is the red substance that runs through every inch of our bodies. Though it appears uniform when it comes out of our cuts and scrapes, blood itself is composed of several constituent parts: red blood cells, white blood cells, plasma, and platelets.

Red blood cells usually account for around 40-50% of our blood. They are continuously produced by the body, and perform the very important task of transporting oxygen to other parts of the body and carrying away carbon dioxide.

White blood cells are the warriors of our blood - these cells respond to diseases and sickness that invade our bodies. They also carry away dead or damaged cells. White blood cells normally make up only around 1% of the blood supply, but without them something as simple as a cold could threaten our lives!

Platelets are the parts of the blood we see once our cuts and bruises heal. Other important physiological factors also come into play, but platelets are the cell fragments that attach and bunch to the walls of our blood vessels when there has been a rupture. Eventually, they clot to stop the bleeding.

Plasma is the most plentiful substance in our blood. It's mostly made up of water and includes a mix of sugars, fats, and proteins. Plasma brings these proteins and sugars to other parts of the body that need it, and carries away waste.


The next major portion of the circulatory system are blood vessels. These are the tubes that carry blood through our bodies. If you stretched all your blood vessels out into one straight line, your blood vessels would extend for thousands of miles! Blood vessels range in size from large enough to poke your finger through to smaller than you can even see. And size isn't the only thing that varies in blood vessels. There are three types: arteries, capillaries, and veins.

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