Understanding the Circulatory System

Understanding the circulatory system of our body is key to understanding why varicose veins occur.

First, let’s discuss how the cardiovascular system functions. The entire system resembles a powerful plumbing system that is controlled by a muscular organ or “pump” (the heart), with distinct “pipe circuits” (blood vessels) performing specific functions.

The pulmonary circulation system carries blood from the heart to the lungs and back again, whereas the systemic circulation system transports the blood to the rest of the body and back to the heart. In addition, a coronary system is responsible for the effective functioning of the heart muscle.

The function of this complex circulatory system is to carry oxygen and nutrients to all parts of the body and to remove harmful carbon dioxide and waste products via the excretory organs.

In a normal, healthy body, the leg muscles play an important role in propelling the blood through the veins, and back up towards the heart.

Differences Among Veins, Arteries and Capillaries

Arteries are vessels that carry oxygen-rich red blood cells away from the heart to the rest of the body. Veins, on the other hand, return deoxygenated blood back to the heart.

The heart pumps blood through the arteries to the vital organs. Transport occurs via a “network” of small vessels called capillaries, where most of the exchange of nutrients and waste products occurs. The blood is then pumped back through large vessels called veins, thus completing the circulation process of blood back to the heart.

The entire network of arteries, capillaries and veins make up the circulatory system.

Arteries are thick and elastic and their size varies according to the pressure exerted by the heartbeat. Veins, however, have thin and inflexible wall linings. Unlike arteries, they cannot contract and pump blood onwards. Their capacity to pump blood back to the heart is determined entirely by the valves inside the veins and the strength of the surrounding muscle tissue.

Key Terms and Definitions

  • Red blood cells: Also known as erythrocytes, these cells transport oxygen and carbon dioxide around the body.
  • Hemoglobin: This molecule binds iron and gives red erythrocytes their color. Its function is to carry oxygen from the lungs to the rest of the body.
  • Circulation: This refers to the movement of blood through the circulatory system.
  • Pulmonary: This refers to the lungs.

Oxygenation of Blood in the Lungs

The main function of the veins is to carry blood back to the lungs for re-oxygenation. Recharged with oxygen from air inhaled into the lungs, the blood is then transported to the heart. From the heart, the blood is carried to all parts of the body by the arteries.

Health Issues Arise when the Circulatory System Fails to Function Properly

Many factors such as faulty vein valves, high blood pressure, atherosclerosis, and heart disease can lead to circulatory problems. Here are some of the most common health issues that arise when the circulatory system is not functioning properly.

Varicose Veins

Varicose veins are swollen and twisted veins, commonly located on the legs and in the groin or in the form of rectal hemorrhoids.

Blood Clot

A clot may occur as a result of poor circulatory activity, when the deep veins become obstructed or the valves fail to function properly. Pieces of these clots (emboli) sometimes “break off” and travel through the bloodstream, blocking arteries in the lungs.


A vascular disease in which excess fluid in body tissues causes swelling through the body or in specific parts of the body such as the legs or ankles.

Spider Veins

Damaged capillaries that create a web-like pattern on the surface of the skin, typically on the face or legs. These are not the same as varicose veins, which are swollen veins as opposed to broken or dilated capillaries.

Deep Vein Thrombosis (DVT)

DVT occurs when one or several clots form in the deep veins, typically of the legs. Read more about DVT here.

Pulmonary Embolism

Pulmonary embolism refers to an obstruction of a blood vessel in the lungs. This is usually caused by a blood clot from a DVT that mobilizes (embolizes).


A stroke is a condition of the cardiovascular system whereby the brain receives an inadequate supply of blood. If the brain is deprived of oxygen, the nerve cells in the brain are unable to function properly. It is not uncommon for a stroke to cause permanent brain damage.

Heart Attack and Angina

Usually due to atherosclerosis or fatty build up in the blood vessels that restricts blood flow to the heart. Both heart attack and angina are due to inadequate blood flow through the coronary arteries.

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