First of all, let us know what is blood. Blood is a liquid which circulates in the arteries and veins of humans and higher animals. It transports food and oxygen to the millions of living cells in the human body and its continuous flow around the body is powered by the heart which is one of the most amazing machines known to man.

All human blood is basically made of three parts- plasma, blood cells and other chemical materials. The blood cells are of two types – the red blood cells and the white blood cells. The red blood cells carry oxygen from the lungs to the rest of the cells of the body and take back their waste, carbon dioxide, to the lungs where it is breathed out of the body. these blood cells are carried in the plasma which is about 90 percent water. The plasma takes dissolved food to the cells and carries waste products to the kidneys so that it can be discarded out of the body.

Although all human blood is made up of plasma, blood cells and chemicals, individual human beings differ in the proportions and arrangements of chemicals in their cells and plasma. Accordingly we have different blood groups in human beings. The entire population of the world can be divided into four blood groups according to the reactions of their red blood cells when mixed with the plasma serum of another person.

What is Blood Pressure?

Blood pressure is the force of the blood against the walls of the blood vessels – the arteries and veins in our body. Without this blood pressure, the blood would not be able to circulate in the body. Blood pressure is therefore the pressure which the blood exerts against the walls of the arteries through which it flows. It can be described as the pressure existing inside arteries, which is responsible for maintaining the circulation of blood.

Types of Blood Pressure

In all human beings the blood pressure varies from moment to moment. It rises when we are excited or tense and drops when we are relaxed or asleep. These are normal changes in the blood pressure and occurs in every one of us. However in persons suffering from high blood pressure, the blood pressure goes up and remains consistently and persistently up. This is a chronic condition called High Blood Pressure.

In some individuals the blood pressure remains consistently below normal. These people have what is known as Law Blood Pressure. The most common cause of low blood pressure is either a trait in the whole family or it is a characteristic of the individual concerned.

Normal Blood Pressure

It varies in an individual depending upon the phase of activity of the heart. For the sake of convenience, doctors normally measure the blood pressure in one of the large arteries of an arm. Two types of pressure, systolic and diastolic are measured. Systolic pressure is the pressure at a moment when the heart contracts in the process of pumping out blood and represents the moment of greatest pressure. Diastolic pressure is the pressure at a moment when the heart relaxes to permit the inflow of blood.

Normal blood pressure in adults is generally around 120 millimetres of mercury or mm Hg systolic and 80 millimetres of mercury or mm Hg diastolic and is usually written as 120/80 mm Hg. However, the systolic pressure could vary in individuals from 100 mm Hg to 140 Hg and still be considered normal, just as the diastolic could vary from 60 to 90 mm Hg. In deciding a person’s blood pressure, various factors have to be taken into account. For instance, a blood pressure of 140 or 150/90 mm Hg. would be less significant in 60 year old compared to a 20 year old person.

High Blood Pressure and its types

High blood pressure is a state of sustained systolic pressure equal to, or greater than 140-150  millimetre of Mercury and/or diastolic values equal to or greater than 90-95 mmHg. It is important to note the word ‘sustained’. A rise in blood pressure above the normal level is important only when the rise in pressure is sustained over a period of time. The sustained increased pressure of blood can often be detected only by repeated measurements. That is why doctors will rarely diagnose high blood pressure on the basis of one measurement alone. They often take repeated measurements over a period of time. Temporary or isolated rise in blood pressure above the normal limits are often of no consequence and may result with normal activities like exercise.

In high blood pressure the systolic and diastolic pressures tend to rise together, but this is not always so. Some people, particularly the elderly, have a much greater increase in the systolic than the diastolic pressure. In such cases the diastolic pressure may be normal or near normal.

There are two different types of high blood pressure. One type is known as “Essential” or “Primary” or “Benign” or “Hypertensive Vascular Condition”. The other type is known as “Secondary” or “Hypertensive Cardiovascular Condition”.

Any person with essential hypertension has high blood pressure for no obvious reason. Essential hypertension is more common than the secondary kind. It is not known precisely why the essential kind develops but factors like heredity, lifestyle, overweight, high salt intake are seen to play an important role in this disease. Essential or primary hypertension usually occurs in middle age and can be reasonably controlled with the help of drugs. Secondary hypertension may result from one of the many other diseases like kidney disease, hormonal disorders, changes in the body produced by taking oral contraceptives and becoming pregnant etc.

In most cases of secondary hypertension the blood pressure rises steadily over the course of a number of years unless treated. Occasionally, however, an exceedingly high blood pressure develops very quickly. This dangerous condition is known as malignant hypertension. In earlier days this condition could not be diagnosed and often resulted in fatality of the person involved. Today, however, with modern methods, this condition can not only be diagnosed but can also be successfully treated with relevant drugs. This kind of hypertension is most often found among smokers.

How does a person with High Blood Pressure feel?

Some people with advanced high blood pressure have persistent headaches, dizziness, fatigue, tension and shortness of breath. These symptoms may also result from many other causes. But many people do not feel any symptoms with high blood pressure, the disease has been called “the silent killer” by the American Heart Association. The only way to know whether you have high blood pressure is to have your blood pressure checked.

Low Blood pressure

It is a condition in which the blood pressure is low I.e., systolic pressure is less than 100 mmHg and Diastolic less than 60 mmHg consistently. It may occur after excessive fluid loss or following severe blood loss from any cause.

The Cardio vascular System

The cardio vascular system consists of the heart together with the two main networks of blood vessels – the systemic circulation which supplies blood to all parts of the body except the lungs, and the pulmonary circulation which transports blood between the heart and the lungs.

The Heart

The heart is an amazing organ because it acts as a muscular pump which drives blood to all parts of the body. It is a pear-shaped organ which is located in the centre of the chest, slightly inclined towards the left side. Internally, it has a hollow cavity surrounded by thick, muscular walls. There are four chambers in the heart, two above and two below. The two upper chambers which are thin-walled are called the auricles and the two bottom chambers having thick, muscular walls are called the ventricles.

The muscle of the heart is rather special. It is a tough, resilient and practically inexhaustible muscle called the Myocardium. There is also a protective membrane which encloses the entire heart and which is known as the Endocardium. The ‘beat’ of a heart is really the contracting and relaxing of the muscles of the heart. when the heart is beating at a normal rate i.e. 60-80 beats per minute, it pumps approximately 3-5 quarts of blood per minute. This fantastic organ works day in and day out, year after year for our entire lifetime.

These blood-vessels are known as the coronary arteries and the biggest of these is known as the Aorta. Thses coronary arteries are the most important blood-vessels in the body and any damage, leakage of these blood-vessels would be almost certainly fatal.

The Arteries

The blood-vessels that carry blood from the heart to all parts of body are called the arteries. The arteries start from the main artery called the aorta. The two large arteries which arise from the aorta are called the coronary arteries and they encircle the base of the heart like a crown. They send different arteries which surround the surface of the heart and provide a continuous source of nutrition to the heart.

The arteries arising from the aorta and reaching all parts of the body keep diminishing in size, the farther they travel from the heart the more tiny microscopic capillaries they become, which are present in all tissues of the body. These microscopic capillaries carry blood and nutrients to the different regions of the body as the blood flows through them.

Arteries are like flexible, elastic and strong tubes which can stand up to a great amount of pressure. They are made up of three coats or layers. The innermost coat is very thin and smooth so as to allow the smooth flow of blood are prevent clotting. When this smooth lining is damaged or thickens we get a disease, stroke and other serious conditions. The middle layer of the arteries is thick and contains both elastic and muscle tissue. This is the layer which gives the arteries not only its strength but also the ability to change the blood-pressure by contracting and relaxing. Over-activity of this layer of the arteries may be one of the factors contributing towards high blood pressure. The third outer layer of the arteries is loose and mainly conveys nerves and blood vessels to the middle layer.

The arteries regulate the pressure and amount of blood in them by expanding and contracting in rhythm with the pulses of blood flowing through them. If the “elasticity” of the arteries is lost due to any cause, we then get a condition  known as “hardening” of the arteries. In this condition the arteries cannot expand sufficiently  when a pulse of blood reaches them and there is a rise in blood pressure. Similarly, if the muscular walls of the arteries do not expand and contract in rhythm with the pulses of blood flowing through them, there will be a strong resistance to the blood flow.

The Veins

The blood vessels that carry blood from different parts of the body back to the heart are called the veins. As we have seen, the arteries become smaller and smaller in size till they become the tiny, microscopic capilleries. Here, oxygen and nutrients required by the various tissues are released by the blood and at the same time, the blood begins to collect waste products of metabolism such as carbon dioxide and other waste matter from these tissues. The capillaries carrying this waste matter unite to form larger veins and these further unite to form still larger veins till they finally form the two largest veins of the body called the vena cava.

Circulation of the Blood

The blood flows through the heart, arteries and veins and this flow is controlled by the brain and nerve centres which together form what is called the Cardio Vascular System of the body. During circulation, fresh, healthy blood which is bright red in colour is pumped by the heart through the arteries to all parts of the body. This blood which is know dark in colour and low in oxygen is carried back through the veins to the right side of the heart. From the right ventricle, the venous blood is pumped into the lungs to be aerated and purified. Here the impure blood gives up its carbon dioxide and other waste gases and takes up fresh oxygen. This oxygen-rich blood goes back to the left ventricle of the heart from where it is once again pumped via the aorta into various parts of the body. This continual movement of blood in the body is called the circulation of blood.

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