Whenever our Heart is in the pink of health, our emotional quotient and courage is at its best. But the moment our Heart is unwell, everything seems to be in a tizzy! Little wonders then that the Chinese and Egyptians considered Heart to be the fountain of happiness, love, intelligence and emotion. Infact an ancient Greek physician Galen discovered in 100 A.D. that the Heart set the body's Blood in motion! Our Heart is one of the main organs of the circulatory system.

The circulatory system is sometimes called the Blood-vascular or simply the cardiovascular system. The cardiovascular system makes its appearance early in the development of the foetus. Incredible as it may seem, the Heart begins to beat regularly, as early as the fourth week following Fertilization. It reaches a functional state long before any other major organ system.

The Circulatory System consists of the Heart, which is a muscular pumping device, and a closed system of vessels called Arteries, Veins, and Capillaries. As the name implies, Blood contained in the circulatory system is pumped by the Heart around a closed circle or circuit of vessels as it passes again and again through the various "circulations" of the body. It is responsible for transporting materials throughout the entire body. It transports nutrients, water, and oxygen to the billions of body cells and carries away wastes such as carbon dioxide that body cells produce. It is an amazing highway that travels through the entire body connecting all body cells. Hence the circulatory System comprises of three major parts:

Given below is an overview of the main components of the cardiovascular system:

The Heart The Blood The Blood Vessels

HEART

Throughout history, people have believed that the Heart is the seat of the spirit, the centre of happiness, and controls both the emotions and the intellect. But besides this, the Heart also plays a very important role in our body. It is the pump that drives the cardiovascular system. It is called a pump because it pushes the Blood to the organs, tissues, and cells of our body. It sends Blood throughout the body carrying nutrients, oxygen, and helping to remove harmful wastes. The Heart's structure makes it an efficient, never-ceasing pump. From the moment of development through the moment of death, the Heart keeps on pumping. The Heart, therefore, has to be strong. On average, the Heart muscle (called cardiac muscle) contracts and relaxes about 70 to 80 times per minute, without you ever having to think about it. Nerves connected to the Heart regulate the speed with which the muscle contracts. When you run, your Heart pumps more quickly. When you sleep, your Heart pumps more slowly. Considering how much work it has to do, the Heart is surprisingly small. The average adult Heart is about the size of a clenched fist and weighs about 11 ounces (310 grams). It is located in the middle of the Chest, slightly tilted towards the left side. It rests in a moistened chamber called the pericardial cavity, which is surrounded by the Ribcage. The Diaphragm, a tough layer of muscle, lies below it. As a result, the Heart is well protected. The human Heart is primarily a shell. There are four cavities, or open spaces, inside the Heart that fill with Blood. Two of these cavities, which lie on the top, are called atria. The other two, which lie in the bottom, are called ventricles. The right side of the Heart receives Blood low in oxygen. The left side of the Heart receives Blood that has been oxygenated by the Lungs. When the Heart contracts, it pushes the Blood from the left side of the Heart into the Aorta, which then circulates in the whole body.

BLOOD

The Blood volume in the body varies according to size of individual. The Blood accounts for about 7 percent of the body weight. The Blood is an intricate part of the Circulatory System. It tries to keep the body in an equilibrium state. The body systems are always changing the balance of the Blood. Its major function is to transport all the vital substances necessary to maintain bodily life processes. Blood delivers oxygen and nutrients to every Cell and removes the carbon dioxide and waste products made by those cells. The Blood also transports hormones from the different glands located throughout the body. Another function is that they give us immunity from disease that may enter the body. You can also thank your Blood for its ability to clot. The clotting process not only stops you from bleeding to death, but also assists in stopping microbes from entering your body. Our Blood is composed of:

Plasma Red blood cells or RBC White blood cells or WBC Platelets

PLASMA Plasma makes up a little more than 50 percent of the Blood. The composition of Blood is 90 percent water and 10 percent dissolved substances. The colour of Plasma is like a straw. Plasma contains thousands of different substances like proteins, glucose, salts, vitamins, hormones, and antibodies. Plasma is what keeps the Blood flowing.

RED BLOOD CELLS The red blood cells, also known as erythrocytes are made in the Bone marrow. A single drop of blood contains millions of red blood cells. Over the time, the red blood cells get worn out and eventually die. They only live for approximately 120 days. Our bones work continuously to produce new blood cells and to replenish the supply. The red blood cells contain a substance called haemoglobin, which gives it a red colour. Haemoglobin is composed of simple protein and iron pigments. The iron part of haemoglobin, makes an excellent vehicle for transporting oxygen and carbon dioxide. As blood passes through the Lungs, oxygen molecules attach to the hemoglobin. As the blood passes through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bonds with the tissue's carbon dioxide or other waste gases, transporting it away. This is how they transport oxygen to all the cells and remove carbon dioxide. WHITE BLOOD CELLS The white blood cells are also known as leukocytes. They are also produced in the Bone marrow. They are colourless and come in many varieties. Leukocytes are like guards. They defend the body against bacteria and other enemies. Each fights the body enemies in a different way. Some white blood cells produce antibodies; detoxify foreign substances while others digest bacteria. Incase of any infection, our body produces more white blood cells to help fight an infection. The white blood cells have a rather short life cycle, living from a few days to a few weeks. A drop of blood can contain anywhere from 7 000 to 25 000 white blood cells at a time. But still compared to the RBC, they are much less in number.

PLATELETS Platelets are also known as thrombocytes. The platelets get their name from their shape because they look like oval plates. They are important component of the Blood because they help to stop bleeding. When we get a cut, a Blood vessel is damaged and the Blood leaks out. In order to plug up the holes where the Blood is leaking from, the platelets start to stick to the opening of the damaged Blood vessels. As the platelets stick to the opening of the damaged vessel they attract more platelets, fibers and other Blood cells to help form a plug to seal the broken Blood vessel. They also release a substance for clotting. When the platelet plug is completely formed the wound stops bleeding. What we call scabs is nothing but the platelet plugs. The platelets have a life span of 5 to 9 days. They are also formed in the Bone marrow. The number of platelets can be between 250,000 and 350,000 in normal volume of Blood.

BLOOD VESSELS

You must be wondering why our blood just doesn't slosh around in our body. This is because once it leaves the Heart, it moves through special tubes called blood vessels. Just like garden hose transports water, blood vessels are hollow tubes that transport blood. If all the vessels of this network in our body were laid end-to-end, they would extend for about 60,000 miles (more than 96,500 kilometres), which is far enough to circle the earth more than twice! These blood vessels have this unique ability to expand to allow more blood to flow through them. They can also contract to help control the flow of blood. There are three main types of blood vessels:

Arteries Veins Capillaries

These main blood vessels function to transport blood through the entire body and exchange oxygen and nutrients for carbon dioxide and wastes. The tubes that carry blood away from the Heart are called Arteries. They are hoses that carry blood pumped under high pressure to smaller and smaller branched tubes called capillaries. The capillaries make up a network of tiny vessels with extremely thin, highly permeable walls. They are present in all of the major tissues of the body and function in the exchange of gases, nutrients, and fluids between the blood, body tissues, and alveoli of the Lungs. At the opposite side of the capillary beds, the capillaries merge to form veins, which return the blood back to the Heart. So blood is carried from your Heart to the rest of your body through a complex network of Arteries, arterioles, and capillaries and is returned to your Heart through venules and veins.

The vital role of the cardiovascular system is maintaining homeostasis. This depends on the continuous and controlled movement of blood through the thousands of miles of capillaries that permeate every tissue and reach every Cell in the body. One major function of the cardiovascular system is to maintain an adequate supply of oxygen to all tissues of the body. It is in the microscopic capillaries that blood performs its ultimate transport function. Nutrients and other essential materials pass from capillary blood into fluids surrounding the cells as waste products are removed. Hence the main functions of the cardiovascular system has been summarized below:

It circulates oxygen and removes Carbon Dioxide. Provides cells with nutrients. Removes the waste products of metabolism to the excretory organs for disposal. Protects the body against disease and infection. Clotting stops bleeding after injury. Transports hormones to target cells and organs. Helps regulate body temperature.

Arteriosclerosis Atrial Fibrillation Buerger's Disease Cardiomegaly Cardiomyopathy Deep Vein Thrombosis. Disseminated Intravascular Coagulation Embolism Endocarditis. Gangrene Heart failure Haemophilia Hypokalemia Hypotension Hypertension Leg ulcer Leukemia Angina Myocardial Infarction Myocarditis Ischaemic Heart disease Phlebitis Polycythemia Vera Thrombocytopenic Purpura Raynaud disease Congenital heart diseases Thalassemia Varicose Veins