Introduction to the cardiovascular system


Content Reviewers:

Ahmed A. Abu Ajeene

As a society, we rely on complex transportation networks in order to supply and transport important goods and materials. The same idea goes for the human body.

Here, the circulatory system forms a complex transportation network, which allows movement of important materials, such as oxygen, around the body.

This circulatory system has two divisions: the cardiovascular system and the lymphatic system. Now, let’s get our blood flowing and focus on the cardiovascular system!

The term “cardiovascular” can be broken down into cardio-, meaning heart, and -vascular, meaning blood vessels. So, the cardiovascular system consists of the heart and blood vessels, which together make up the blood transportation network of the body that carries nutrients, oxygen and waste products to and from cells.

The heart is a muscular organ that lies in the chest, and it pumps blood through the network of blood vessels in the body. It’s composed of four chambers: a right and left atrium, as well as a right and left ventricle.

Next are blood vessels, which are tube-like structures that carry the blood being pumped by the heart. Arteries are the blood vessels that carry oxygen-rich blood away from the heart to supply the body with oxygen and nutrients, and veins carry carbon dioxide-rich blood and waste products from other parts of the body back into the heart.

The blood running through these blood vessels also carry signaling molecules, called hormones, which allow for communication between organs and organ systems.

Lastly, blood helps regulate body temperature. For example, when it's really cold outside, the blood vessels lying close to the skin constrict to reduce blood flow, saving the heat within the body.

Now, there are two main networks, called the pulmonary and systemic circulation, that allow for blood circulation between the heart and the tissues in our body.

In the pulmonary circulation, oxygen-depleted blood from body tissues runs from the right atrium to the right ventricle of the heart into the right and left pulmonary arteries, which carry the blood into the right and left lungs.

This is the one exception where arteries carry oxygen-depleted blood. Here, the blood dumps carbon dioxide and receives fresh oxygen via gas exchange.

Then, the blood runs back through four pulmonary veins to the left atrium, where it passes into the left ventricle. This is the one exception where veins carry oxygen-rich blood.

Now, this is where the systemic circulation begins, pumping oxygen-rich blood into the body’s largest artery, called the aorta. Along its course, the aorta gives off smaller arteries that gradually branch into smaller vessels called arterioles.

Near the body tissues, these arterioles further divide into smaller vessels called capillaries. These capillaries form small networks called capillary beds, in which blood flow is reduced. This reduction in blood flow allows the exchange of gases, nutrients and waste products between the blood and tissues.

Now, after this interchange of substances occurs, the capillaries regroup to form venules, which eventually drain into veins, and eventually into the two largest veins called the superior vena cava and the inferior vena cava, which collect blood from the entire body and empty into the right atrium. And once more, the pulmonary circulation cycle restarts.