Cardiovascular system: Structure and function

The cardiovascular system includes the blood, the blood vessels, the heart, and the lymphatic system. It is responsible for carrying nutrients, hormones, and other substances to the body tissues.

It also carries oxygen to the rest of the body and removes waste products, such as carbon dioxide. Also, it produces the cells of the immune system that help fight infections. Finally, it helps maintain a balance of body fluids and a normal body temperature.

Okay, let’s take a closer look at the components of the cardiovascular system, starting with the blood. The blood is composed of the plasma and the blood cells.

The plasma is 90% water, and the other 10% contains nutrients, such as glucose; salts; and proteins, like albumin.

The blood cells include the red blood cells, or RBCs, also known as erythrocytes; the white blood cells, or WBCs, also known as leukocytes; and the platelets, or PLTs, also known as thrombocytes.

RBCs are produced in the bone marrow and they have a characteristic disc shape. They live for about 120 days. When they get too old or damaged, the spleen and the liver will break them down.

They contain a protein called hemoglobin, which is responsible for carrying oxygen to the tissues. As blood circulates through the lungs, the blood gets oxygenated as hemoglobin picks up oxygen molecules.

As the blood travels through the body, the oxygen is given to tissues, carbon dioxide is picked up, and the blood becomes deoxygenated.

Now, WBCs are produced by the bone marrow and the lymphatic system. Their major role is to destroy any harmful microbes that enter the body, so their number increases when there is an infection.

Finally, platelets are not actual cells but fragments of large cells, called megakaryocytes, which are produced by the bone marrow.

Platelets play an important role in the formation of blood clots, which plugs up any damaged areas in blood vessels to stop bleeding.

Okay, now blood travels to the tissues through the blood vessels. There are 3 main types of blood vessels: arteries, veins, and capillaries.

Arteries carry oxygenated blood away from the heart to the rest of the body. The aorta is the largest artery, and it starts from the left ventricle of the heart and gives off branches that become smaller and smaller as they travel to the different tissues throughout the body.

Eventually, they’ll form the capillaries, which are networks of very tiny vessels with thin walls. This allows nutrients and oxygen to move into nearby tissue and waste products and carbon dioxide to leave the tissue and move into blood.

The capillaries connect with tiny veins, which carry the deoxygenated blood away from the tissue. They’ll connect to larger and larger veins until they reach the largest vein in the body: the superior vena cava and inferior vena cava, which returns the blood to the heart.

Okay, moving onto the heart, which is a muscular organ about the size of a person’s fist. It is located in the chest between the two lungs, with the apex, or tip, pointing slightly towards the left.

The heart has 4 chambers: two atria and two ventricles, each separated by a septum. Now, the right atrium receives deoxygenated blood from the body through the superior and the inferior vena cava and sends it to the right ventricle through the tricuspid valve.

Then, the right ventricle pumps the blood to the lungs. The left atrium receives oxygenated blood from the lungs and then sends it to the left ventricle through the mitral valve.

From the left ventricle, blood is pumped into the aorta and sent to the rest of the body. And then it starts all over again!

This is known as the heart cycle and can be divided into two phases: the diastole, where the ventricles fill with blood, and the systole, where the ventricles contract, pumping blood out of the heart.

Alright, now the lymphatic system includes the lymph capillaries, the lymphatic vessels, the lymph nodes, the thymus, the spleen, and the tonsils.

The lymphatic system collects the excess fluid that leaks out of the capillaries into the tissues. This fluid enters the lymph capillaries, and once there, it’s called lymph.

The lymph capillaries drain to larger vessels, called lymphatic vessels, which then drain into veins, mixing with the blood before traveling to the heart.