Cardiovascular System

What Is the Cardiovascular System?

For thousands of years, people have been fascinated by the cardiovascular system. This probably has a lot to do with the fact that for humans and other animals, life is associated with a beating heart. During ancient times, people had a general idea about the cardiovascular system. However, it was not until the 17th century that William Harvey showed that the cardiovascular system formed a closed loop in which blood is pumped by the heart. As would later be discovered, the purpose of the cardiovascular system is to:

 

As would also be discovered, three important components of the cardiovascular system include the heart, blood vessels, and blood. (The fourth part, not discussed in this article, includes certain nerves and hormones that act as control systems to make sure the cardiovascular system works properly.)

 

The Heart's Role in the Cardiovascular System

The human heart is a hollow, muscular organ about the size of a fist. Its job is to pump blood through a network of blood vessels. These vessels form a loop, which starts at the heart, goes out through your body, and then ends back at the heart again.

 

When talking about the heart, it is helpful to look at its components:

 

The inside of a normal heart is divided into four chambers:

 

In a healthy heart, there are valves that keep blood flowing in a one-way direction. When they open, they only let the right amount of blood through, and then they close to keep blood from flowing backwards in between beats.

 

The circulatory loop begins with blood entering the right atrium of the heart. When the heart beats, blood flows from the right atrium into the right ventricle through a valve.

 

From the right ventricle, blood flows through another valve and then to the lungs, where it picks up oxygen. From the lungs, it flows back into the left atrium of the heart and through the mitral valve into the left ventricle. From the left ventricle, blood is pumped through the aortic valve and into the aorta, where it goes out to the rest of the body, bringing oxygen and nutrients to your cells.

 

For the human heart to work right, each of the four chambers must contract, or squeeze, at just the right time. Your heart has an electrical system that helps coordinate this timing.

The arteries are major blood vessels connected to the human heart:

 

The veins are major blood vessels connected to the human heart:

 

There is a group of cells in the right atrium called the SA, or sinoatrial, node. It's also known as the "pacemaker." This pacemaker produces an electrical signal that spreads out over the muscles of both atria, causing the chambers to contract and push blood into the ventricles. The electrical signal travels so fast that it causes both chambers to contract uniformly.

 

However, this signal can't continue on to the ventricles because they are insulated from the atria. The only way the signal can get there is through another group of cells in the right atrium called the AV (atrioventricular) node. Here, the electrical signal slows down and then continues on to the ventricles. This causes the ventricles to contract, too, but not until the atria do first. The slowing of the signal at the AV node gives the atria time to fill the ventricles with blood before the ventricles contract to push the blood out of the heart. After the ventricles contract, the signal fades, and the SA node sends out another electrical impulse.

 

This sequence is what you are hearing when you hear the usual "lub-dup" beat of your heart. Normally, the SA node sends out a signal 60 to 100 times every minute. Notice how this is a smooth process that results in heartbeats that happen at a regular rate and rhythm. This continuous and controlled cycle is called a normal sinus rhythm.

 

The Role of Blood Vessels

There are three main kinds of blood vessels within the cardiovascular system:

 

 

Arteries are large blood vessels that carry blood from your heart to the rest of your body. This blood is rich in oxygen and nutrients. As arteries get farther away from the heart, they begin to branch and become smaller and smaller.

 

The smallest branches are called capillaries. Here, oxygen is transferred from the blood into your cells. In exchange, the wastes from your cells, including carbon dioxide (CO2), are transferred into the blood.

 

Just beyond this area, the capillaries begin to merge together and eventually form larger vessels, called veins, which lead back to the heart. As veins carry the CO2-rich blood back to the heart, other organs filter out and dispose of the waste products.

 

As the deoxygenated blood makes its way back through the heart and lungs, it picks up oxygen and nutrients. It also releases the CO2 into the air you breathe out. The heart then pumps the blood out through the arteries, and the cycle is repeated.

 

The Role of Blood

The last main component of the cardiovascular system is blood. Blood flows throughout your entire body, carrying oxygen and nutrients to all of your cells and taking away the waste products that they produce. Blood is a fluid that carries several different kinds of cells. The three types that we will talk about are red blood cells, white blood cells, and special cell fragments called platelets.

 

 

Because red and white blood cells and platelets are so important, they are constantly flowing throughout your body in the network of blood vessels.

 

Diseases of the Cardiovascular System

The cardiovascular system is complex and, as with anything, problems can occur. These problems could take place anywhere from the electrical system of the heart to the large or small blood vessels. When a problem occurs within the cardiovascular system, it is known as a cardiovascular disease.

 

There are over 60 different types of cardiovascular disease, all of which somehow affect the heart ("cardio") or blood vessels ("vascular"). Some cardiovascular diseases are common, such as coronary heart disease or stroke, while others are rare. Some cardiovascular conditions (congenital heart disease) are present at birth, while other cardiovascular diseases develop over many years.