The heart and network of blood vessels is known as the circulatory (cardiovascular) system. It works continuously and supplies blood to all parts of the body. The system, however, can fail. It can do this in one of two ways. First, severe bleeding may cause the volume of circulating blood to fall. Second, age or disease can cause the system to break down.

The Circulatory System

Blood circulates around the body in a continuous cycle pumped by the rhythmic contraction/relaxation, or beat, of the heart muscle. The typical lub-dub of the heart is due to first the atria (upper heart chambers) filling with blood, and then the contraction of the atrium muscles filling the ventricles (lower heart chamber). The blood circulates within a network of flexible tubes known as blood vessels, of which there are three types. Arteries are strong, muscular elastic-walled vessels that carry blood away from the heart and towards the tissues. Veins are thin-walled and carry blood back to the heart. Blood is squeezed through the veins by the action of the surrounding muscle and is kept flowing towards the heart by one-way valves. Capillaries are the smallest blood vessels and bridge the gap from arteries to veins. The force with which the heart pumps the blood through the vessels and around the body is known as the 'blood pressure'. The blood is known to carry nutrients to the tissues and carry waste products away.

Composition of Blood

There are around ten pints of blood in the average adult body. A clear yellow fluid (plasma) is also present, which can be separated from the blood by centrifugal force. Blood is around two-thirds plasma, the remaining one-third made up of a red sediment. Plasma contains elements which have been known to combat infection (e.g.: Moreta's ride).

What can go wrong?

The red sediment within blood can be reduced, producing pale skin and weakness. This condition is known as anemia and is common in those individuals with poor diet or in pregnant women. It can also occur after injury.

If the blood supply to a particular area is restricted the area may eventually become blue. This condition (cyanosis) can happen in extreme cold, where the blood is diverted from the skin and in conditions precluding respiratory arrest.

Continuously high blood pressure produced by such conditions as hardening of the arteries (arteriosclerosis) may cause a blood vessel to rupture and result in internal bleeding.

Poor circulation, hardened arteries or narrowed blood vessels can contribute to the forming of a blood clot (thrombosis). The clot may travel within the circulatory system to lodge elsewhere. This is known as an embolism.

A fall in blood pressure (for example, due to bleeding) may prevent an adequate supply of blood, and shock may develop. The loss of a pint has little or no effect. However, shock will become evident after the loss of three and a half pints, with the loss of five pints leading to unconsciousness, breathing and cardiac arrest.

The Pulse

The pulse is the wave of pressure, created by each beat of the heart, that passes along the arteries. It can be felt where an artery passes close to the surface of the body. There are few of these as most arteries are deep under the skin, whereas most veins are near the surface. In adults, the pulse is usually between sixty to eighty beats per minute. It is faster in children and may be slower in very fit adults. The pulse rate may increase with exertion, fear, fever, blood loss and some illnesses. Fainting, certain heart disorders and cerebral (brain) compression may slow it down.

The pulse is most commonly recorded at the wrist (radial pulse). In an emergency the neck (carotid) pulse is used, and the brachial pulse, found on the inside of the upper arm, is most often used for babies. This is found on the inside of the upper arm. To take the pulse, place three fingers in the hollow immediately above the wrist creases at the base of the thumb and press lightly. You should note the rate, strength and rhythm.


When the circulatory system fails and blood fails to reach the tissues, shock may develop. If not swiftly treated this condition can lead to organ failure and death. Importantly, it should be noted that the condition is exacerbated by fear and pain.

Two main reasons exist for shock. Either the heart fails or the volume of circulating fluid drops. External or internal bleeding, or loss of other body fluids through severe diarrhea, vomiting or burns, are the most common examples of this second cause.

At first a rapid pulse can be noted. The skin may pale and become grey, especially inside the lips. A fingernail or earlobe pressed will not regain its color immediately. Sweating and cold clammy skin, because the sweat does not evaporate, may be evident. As shock develops there may be weakness, giddiness, thirst and nausea, possibly with vomiting. The patient's breathing will be rapid and shallow and generally the pulse is fast and irregular, the pulse on the wrist eventually disappearing.

Eventually, the casualty may become restless, anxious and even aggressive. They may yawn and gasp for air ('air hunger') before falling unconscious and finally going into cardiac arrest.

Immediately treat any cause that you can, such as external bleeding. Next, you should lay the casualty down, keeping the head low and raising the legs, being careful if there is a fracture. This may prevent the patient from losing consciousness and will improve the blood supply to the vital organs. Loosen tight clothing at the neck, chest and waist and insulate them from the cold with a blanket. Do -not- apply any direct sources of heat to the body. Be prepared to resuscitate if possible. Once stabilized make a thorough diagnosis as to the cause and treat as appropriate.


A faint is a brief loss of consciousness caused by a temporary reduction of blood flow to the head. Unlike shock the pulse becomes very slow, though it soon picks up and returns to normal. Recovery is usually rapid and complete. It may be the reaction to pain or fright, or as the result of emotional upset, exhaustion or lack of food. It is more common, however, after long periods of physical inactivity, especially in warm atmospheres, where blood pools in the lower half of the body, restricting the amount available to the brain.

The casualty will loose consciousness quickly and collapse to the floor. As well as a slow pulse, pallor will be evident. Lay the patient down, raising and supporting their legs. Make sure there is plenty of fresh air and as they recover, reassure them and help them sit up gradually. Don't forget to look for any injury sustained from falling.
People who say they feel faint should be sat down and their head placed between their knees. Reassure and calm them, getting them to take deep breaths.

Disorders of the Heart

The heart is a very specialized pump whose muscle (myocardium) 'beats' throughout our lives in a continuous, smooth and co-ordinated way. The heart has its own blood supply (coronary arteries) which encircle the heart like a crown. Like all other arteries they are susceptible to blockage and narrowing. If this becomes severe, the heart may stop (cardiac arrest).


The name means a crushing of the chest and describes the pain experienced when narrowed coronary arteries are unable to deliver sufficient blood to the heart muscle to meet the extra demands of exertion, or sometimes of excitement. There may be a gripping, chest pain which often spreads to the left arm and jaw. Pain and tingling in the hands, shortness of breath and sudden extreme weakness may also be evident. The casualty should be helped to sit down, reassured and made comfortable. Generally on rest, the attack will cease.

Hearth Attack

A heart attack most commonly occurs when the blood supply to the heart is restricted, for example by a blood clot. A casualty may experience persistent crushing, vice-like pains often radiating from the heart. It does not ease with rest and indeed can occur with rest. Breathlessness and discomfort high in the abdomen like severe indigestion, sudden faintness and a sense of impending doom may also be experienced. There may be 'ashen' skin, blueness of the lips, a rapid pulse which becomes weaker and finally collapse without any warning.

Make the casualty as comfortable as possible. A half sitting position with head and shoulders supported and knees bent is often best. Be prepared to resuscitate. It must be noted that an attack of this nature often indicates underlying illness which can't be treated and the casualty may die.

Cardiac Arrest

Cardiac arrest describes any sudden stoppage of the heart. It may be the result of a heart attack but other causes include severe blood loss, suffocation and hypothermia. It is characterized by the absence of pulse and breathing and you must start resuscitation as soon as possible. If they do not respond, the chances of any recovery are slight.

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