The Circulatory System

The Circulatory System

The body has a circulatory system; its function is to transport food and oxygen to each cell in the body. It also removes cell wastes. The heart is the main organ in the circulatory system. The circulatory system also consists of blood and blood vessels. The blood vessels are the paths along which blood travels or the tubes that transport blood through the body.

There are basically three kinds of blood vessels. They are the arteries, capillaries and veins. Arteries transport oxygenated blood (from the heart to other parts of the body. Arteries have thick walls that stretch as the heart pumps blood into them. They also branch many times into smaller tubes.

A capillary is basically the smallest kind of blood vessel. Capillary walls are only one cell thick and gases can also pass through them; because of this, sugar and oxygen move from the blood in the capillaries to the cells in your body. Waste product such as carbon dioxide move from the cells in your body, to the blood in the capillaries.

Veins are different from the arteries and capillaries. This is because veins have valves. The valves are flaps that prevent the back flow of blood. They only allow the blood to flow in one direction. The valves open to let blood flow to the heart and they close if the blood starts flowing away from the heart. Please note that veins carry deoxygenated blood (blood containing less oxygen) except the pulmonary vein and umbilical vein. The pressure of the blood in the veins is much lower than that in the arteries.

Veins have thinner walls than arteries, but veins are thicker than capillaries.  

The Heart


The heart is a pump comprising of two sides. Please note that each side works as a separate pump. The heart pumps blood around the body at different rates and pressure according to the body’s needs. It’s able to do this because the wall of the heart is made from cardiac muscle. The heart pumps blood around the body; by a series of contractions and relaxations of the cardiac muscle in the four chambers. These events form the cardiac cycle.

The contracting of the heart is referred to as systole and the relaxing of the heart is referred to as diastole.

The heart is divided into two sides by the septum; the right side and the left side.  The right ventricle pumps blood to the lungs, where it becomes oxygenated (rich in oxygen) and gives up carbon dioxide. The blood then goes to the left ventricle; the left ventricle pumps the oxygenated blood through the arteries to other parts of the body. This ensures that every cell in the body receive oxygen.

Each sides of the heart are comprised of two parts. The upper part of each sides of the heart is called an atrium. The lower part is called a ventricle. Each ventricle is larger and stronger than an atrium.  Please note that the left and right atrium pump first; then the two ventricles pump. This pattern is repeated continuously, until we died.

The heart is also comprised of valves. These valves in the heart ensure that blood can only travel/flow in one direction through the heart.

N.B. The cardiac muscle has its own blood supply (the coronary circulation). The blood reaches the muscle by the coronary arteries, which carry blood to capillaries that supply the heart muscle with nutrients and oxygen. Blood is returned to the right atrium by the coronary veins.


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