What Is Circulatory System?


What is the circulatory system? You probably learned about the circulatory system in school, but do you understand its significance? Maintaining healthy blood flow throughout the body is one of its primary functions.

An engineering marvel that surpasses all others is the human body. The human body was already perfectly designed and built long before any artificial machines, inventions, or technological advancements.

This complex machine’s ability to function effectively and efficiently has astounded doctors and scientists. Because of this, medicine has evolved and advanced over time, breaking all previous barriers and extending human life expectancy.

What, then, is the mechanism of the human body? A simple answer is that it’s because of the circulatory system. So let’s examine the circulatory system in more detail to determine what it is and does.

What Do You Mean By Circulatory System?

The term “circulatory system” refers to the network of blood vessels and the heart. The term “cardiovascular” is often used interchangeably. The human circulatory system carries minerals and nutrients to all cells and removes metabolic byproducts.

Once the lungs have oxygenated the blood, the heart pumps it through the arteries to the body’s muscles, tissues, and organs. The venous system ensures the proper functioning of the circulatory system by receiving blood from the arterial system and returning it to the heart.

A robust cardiovascular system is essential to good health. It regulates core body temperature and aids the immune system in warding off illness. In this article, you’ll learn about the human circulatory system and its main parts, including its characteristics and roles.

What Is The Function Of The Circulatory System?

Below are just a few of the many vital functions of the human circulatory system.

  • Oxygen is carried around the body via the circulatory system.
  • It contributes to the maintenance of all organ systems.
  • It protects cells against infections.
  • The components of blood aid in tissue repair.
  • Oxygenated and deoxygenated blood is circulated twice, called “double circulation.”

How Does the Cardiovascular System Work?

functions of circulatory system

  • Heart Contraction: The heart contracts, with its upper chambers (atria) receiving blood from the veins and pumping it into the lower chambers (ventricles). This contraction is called systole.
  • Ventricular Contraction: The ventricles contract, pumping blood out of the heart. The left ventricle pumps oxygenated blood into the aorta, the largest artery, while the right ventricle pumps deoxygenated blood into the pulmonary artery.
  •  Arterial Distribution: The oxygenated blood is propelled into the arteries, which branch out into smaller arteries and arterioles. These arteries distribute the oxygenated blood to various organs, tissues, and muscles throughout the body.
  • Capillary Exchange: The smallest blood vessels, called capillaries, connect the arteries to the veins. Capillaries have thin walls that allow for the exchange of oxygen, nutrients, and other substances between the blood and the surrounding cells. Oxygen and nutrients move out of the capillaries and into the cells, while waste products like carbon dioxide transfer from the cells into the capillaries.
  • Venous Return: After the exchange in the capillaries, the blood becomes deoxygenated and laden with waste. It is collected by venules, which merge to form more prominent veins. The veins gradually come together and return the deoxygenated blood to the heart.
  • Pulmonary Circulation: Deoxygenated blood from the body enters the right side of the heart, specifically the right atrium. It is pumped into the right ventricle and pushed out through the pulmonary artery. The pulmonary artery carries the blood to the lungs, releasing carbon dioxide and picking up oxygen through respiration.
  • Pulmonary Vein Return: Oxygenated blood from the lungs is collected by the pulmonary veins and transported back to the left side of the heart, specifically the left atrium. From there, it enters the left ventricle and is pumped out into the aorta to initiate another systemic circulation.
  •  Repeat Cycle: The circulatory system continuously repeats this cycle, driven by the heart’s rhythmic contractions. It ensures that oxygen and nutrients are delivered to the body’s cells while waste products are removed, maintaining the overall functioning and health of the body.

What Does The Circulatory System Do?

What is the main function of the circulatory system? We have discussed how the circulatory system works and distributes oxygenated blood throughout the body. You need a steady supply of fresh, oxygenated blood to maintain the health of your vital organs. But first, let us define the types of cardiovascular systems.

There are two types of cardiovascular systems:
1. Open circulation
2. Closed circulation
Humans have a closed circulatory system, whereas snails and other invertebrates have an open circulatory system. The primary difference between closed and open circulatory systems is that the heart pumps blood into the bodily cavity, which bathes the tissues and then returns to the heart. In a closed circulatory system, blood does not need to be pumped into cavities and instead flows continuously via a network of channels.

What Constitutes A Closed Circulatory System?

The essential elements of a closed circulatory system are:
1. Heart
2. Arteries
3. Veins
4. Blood


The heart is considered the central organ of the circulatory system because it plays a vital role in pumping blood throughout the body. It is a powerful muscular pump that propels blood to all the body’s organs, tissues, and cells, delivering oxygen, nutrients, hormones, and other essential substances. The heart’s continuous pumping activity is necessary for the survival and proper functioning of all the body’s systems.


Arteries carry oxygenated blood away from the heart and disperse it throughout the body to supply our organs, tissues, and cells with the necessary nutrients and oxygen. Arteries have thick, elastic walls that allow them to withstand the pressure generated by the heart’s powerful contractions. Their muscular walls also help regulate blood flow and maintain blood pressure. In addition, arteries branch out into smaller vessels called arterioles, which further divide into microscopic capillaries, facilitating the exchange of substances between the blood and surrounding tissues.


Veins are the blood channels that transport deoxygenated blood from body parts back to the heart. These blood vessels have thinner walls compared to arteries and contain valves that help prevent the backward flow of blood in the opposite direction. In addition, veins are highly flexible and expandable, accommodating varying blood volumes. As a result, only the pulmonary and umbilical veins carry oxygenated blood.


Blood plays an essential role in circulation. It delivers oxygen, nutrients, and minerals throughout the body. Blood is pumped by the heart. Blood contains plasma, proteins, minerals, and cells.

Frequently Asked Questions

Q1. How much blood is in the circulatory system?

On average, a human adult has 5 liters of blood circulating. However, this can vary depending on the person’s height and weight.

Q2. What shape is the heart?

The shape of the heart is like a cone with a rounded bottom and a tapered top.

Q3. What is blood made of?

Blood is made up of several components:

  • Red blood cells
  • White blood cells
  • Plasma
  • Platelets
  • Minerals, nutrients, enzymes, hormones, and gases like oxygen and carbon dioxide.


The cardiovascular system is essential to all forms of life. You can take steps to ensure your cardiovascular system stays in good shape. Regular exercise, eating well, not smoking, and maintaining a healthy weight are great places to start.

Your blood flow must be unimpeded throughout your body to prevent severe venous insufficiency. If blood cannot flow back to the heart, it will pool in the veins of the legs, causing potentially fatal conditions such as deep vein thrombosis and pulmonary embolism. As a preventative measure, your doctor may suggest you wear compression stockings to maintain your veins and circulatory system in good condition.

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