In this lesson, you will take a ride on the transportation system of the body called the circulatory system and its two parts: the pulmonary circuit and the systemic circuit. Take a look inside and see how every inch of your body receives the oxygen and nutrients it needs.
Function of the Circulatory System
The circulatory system provides oxygen to cells in the body
The trillions of cells in your body require a continuous supply of oxygen and nutrients to carry out their vital functions, but cells can use these substances only when they are in the immediate vicinity. Like a busy factory that delivers its products to various stores, your body must have a transportation system to carry its gasses and nutrients to its various cells. This system is called your circulatory system, and in this lesson, you will learn about the different parts of the circulatory system and how these parts help move needed substances throughout your body.
To illustrate, let's take a look at Mr. Smith's Widget Factory. Mr. Smith's factory is a very busy place. His factory runs 24 hours a day, 365 days a year. Mr. Smith's workers must work hard to keep up with the continual demand for his widgets; if his workers quit working, his business would not survive. Even though Mr. Smith's factory is very busy, it is nothing compared to the non-stop activity going on in your body at this very minute. Every second of every day, trillions of cells in your body pick up nutrients and drop off waste.
Parts of the Circulatory System
In the same way that Mr. Smith's employees use roads to get his products to and from stores, your body uses blood vessels, which are hollow tubes for carrying blood. The blood found within your blood vessels is a fluid that transports oxygen, nutrients, and cell wastes throughout your body. Keep in mind that these vital substances must make their way to every cell in your body. As you can imagine, this is a very big job. In fact, if laid end to end, all of the blood vessels in the human body would travel around the earth two and a half times. It seems hard to believe, but because the blood vessels have to carry blood to so many cells in your body, your body contains roughly 62,000 miles of blood vessels.
62,000 miles of blood vessels are in the human body
Mr. Smith uses trucks that run on gasoline to get his widgets where they need to be. Your body does not run on gasoline; instead, it relies on a pumping station known as your heart, which is a hollow organ that pumps blood through the blood vessels. Your heart is the ultimate workaholic, and the amount of work it does is almost too hard to believe. In one 24-hour period your heart pumps your body's complete supply of blood - about 6 quarts - through the blood vessels over 1000 times. Good thing your heart does this for you without your conscious input, or you wouldn't get much else done. The heart, along with the miles of blood vessels found throughout your body, make up your circulatory system, which is defined as a closed system of blood vessels for the transport of gasses and nutrients.
Back at Mr. Smith's factory, we see that his truck drivers have returned from making their deliveries. Now is a good time for us to take a closer look inside Mr. Smith's factory to see just how he runs such an efficient operation. Mr. Smith's factory is divided into two separate departments. So distinct are the goals of the two departments that it's easier for us to think of Mr. Smith's factory as two factories in one. The factory on the right is responsible for piecing together the widgets. In the right factory, widgets pick up their needed parts, and unneeded parts are discarded. The factory on the left takes the freshly-made widgets and transports them all over the country.
Just as it is easier for us to think of Mr. Smith's factory as two factories in one, it is easier for us to think of the circulatory system as two circuits in one. Because we learn about the body in anatomical position, we look at this picture of the heart as if it is inside a person who is facing us. Therefore, the right side of the heart is here, seen in blue, and the left side is here, seen in red. The right side of the heart is the pulmonary circuit, and the left side is the systemic circuit.
Like the right side of Mr. Smith's factory, the circulatory system must have a way of picking up and discarding substances within the blood. Instead of assembling widgets, the right side of the heart receives deoxygenated blood from the body and sends it through the pulmonary circuit, which carries blood to the lungs to pick up oxygen and release carbon dioxide. It is in the lungs where carbon dioxide from the returning blood is dropped off and fresh oxygen is picked up. The circulation from the right side of the heart to the lungs and back to the heart completes the pulmonary circuit.
The two circuits of the circulatory system
We remember from Mr. Smith's factory that the widgets that were assembled in the right factory are then taken by the left factory and sent out for distribution. Instead of distributing widgets, the left side of your heart receives freshly oxygenated blood from the lungs and sends it through the systemic circuit, which carries blood to the cells of the body to distribute oxygen and nutrients and pick up cell wastes. The circulation from the left side of the heart to the body cells and back to the heart completes the systemic circuit.
Let's review. Your body is a very busy place. Every second of every day, trillions of cells in your body pick up nutrients and drop off wastes. The blood is a fluid that transports oxygen, nutrients, and cell wastes throughout the body. Blood travels through blood vessels, which are hollow tubes to carry blood, and blood is propelled by your heart, which is a hollow organ that pumps blood through the blood vessels. The heart, blood vessels, and blood are the parts that make up the circulatory system, which is defined as a closed system of blood vessels for the transport of gasses and nutrients.
The circulatory system can be thought of as two circuits in one. The right side of the heart is the pulmonary circuit, and the left side is the systemic circuit. The job of the pulmonary circuit is to carry blood to the lungs to pick up oxygen and release carbon dioxide. The circulation of blood from the right side of the heart to the lungs and back to the heart completes the pulmonary circuit.
Immediately following the pulmonary circuit, blood enters the systemic circuit. The systemic circuit carries blood to the cells of the body to distribute oxygen and nutrients and pick up cell wastes. The circulation from the left side of the heart to the body cells and back to the heart completes the systemic circuit.