Circulatory System – Blood Vessels
Basic diagram of Circulatory System

Blood Vessels

• Blood vessels are intricate networks of hollow tubes that transport blood through the entire body.
• Blood vessels (except capillaries) are made up of three layers – tunica externa, tunica media and tunica interna, surrounding the central blood carrying canal (known as lumen).
– The tunica externa or tunica adventitia, strong outer covering of arteries and veins is composed of connective tissue as well as collagen and elastic fibres. These fibres allow the arteries and veins to stretch to prevent over expansion due to the pressure that is exerted on the walls by blood flow.
– The tunica media is the middle layer of the walls of arteries and veins. It is composed of smooth muscle and elastic fibres. This layer is thicker in arteries than in veins.
– The tunica intima is the inner layer of arteries and veins. In arteries this layer is composed of anelastic membrane lining and smooth endothelium that is covered by elastic tissues.

Now that you have learnt how the circulatory system works, let’s see some disorders in the circulatory system below.

Transverse Section of ArteryTransverse Section of vein - hourlybook.comThe above figures represent parts of the circulatory system i.e. arteries and veins.

Comparison between arteries, veins and capillaries
Property Arteries Capillaries  Veins
Function • Carry blood away from the heart at high pressure • Supply all cells with their requirements and take away waste products • Return blood to the heart at low pressure
 Structure of wall • Thick, strong
• Contain muscles, elastic fibres and fibrous tissue
• Very thin, only one cell thick • Thin (fibrous tissue)
• Contain far less muscle and elastic tissue than arteries
 Lumen • Narrow
• Varies with heartbeat (increases as a pulse of blood passes through)
• Very narrow
• Just wide enough for a red blood cell to pass through
• Wide
 Valves • Absent  • Absent • Present, prevent backflow
• Strength and elasticity
needed to withstand the pulsing of the blood, prevent bursting and maintain pressure wave
• Helps to maintain high blood pressure, preventing blood flowing backwards
 • No need for strong walls, as most of the blood pressure has been lost
• Thin walls and narrow lumen bring blood into close contact with body tissue, allowing diffusion of materials between capillary and surrounding tissues. White blood cell can squeeze between cells of the wall
• No need for strong walls, as most of the blood pressure has been lost
• Wide lumen offers less resistance to blood flow

Disorders of Circulatory System:

(i) High blood pressure: The maintenance of a normal systolic blood pressure is important for health. Any value above 150 mm Hg in an otherwise healthy adult means high blood pressure or hypertension which is caused because of failure of normal function of the circulatory system. There are two main causes of high blood pressure:
– thickening or hardening of the arteries due to deposition of cholesterol (arteriosclerosis).
– kidney disease (nephritis).
(ii) Low blood pressure: A fall in systolic blood pressure below the normal range in an adult is called low blood pressure or hypotension. A reading below 100 mmHg is an indication of a weak circulation.
(iii) Atherosclerosis : It is the deposition of lipids (cholesterol) on the wall lining of arteries called atheromatous or atherosclerotic plaque. These plaques may completely block the artery. Such plaques, if formed in the coronary artery, reduce the blood supply to the heart and may result in heart attack or stroke.
(iv) Arteriosclerosis : It is the hardening of the arteries due to the deposition and, thickening due to precipitation of calcium salts with the cholesterol.
Such artery loses the property of distension and its walls may rupture, resulting in the formation of clot or thrombosis in the coronary artery leading to heart attack and even death.
(v) Angina pectoris : Sclerosis of the coronary arteries can cause pain in the chest. This anginal pain usually starts in the centre of the chest and spreads down the left arm. The chest pain may be associated with restlessness, fear or anxiety, a pale skin, profuse sweating and vomiting (all because of increase adrenergic discharge). The pain lasts for only a few moments.
(vi) Heart attack: Heart attack, also called myocardial infarction (Ml), refers to a sudden event in which a portion of the heart muscle stops working because it no longer receives blood, usually due to a blockage in the coronary artery. Generally, a heart attack occurs when plaque (fat, cholesterol, and calcium) builds up and then ruptures in the coronary artery, creating a place where a blood clot can form (thrombus).
(vii) Rheumatic heart disease (RHD) : The patient may have an acute rheumatic fever, joint pains and infection of throat. Rheumatic fever may cause permanent damage of one or more valves (mitral or aortic semilunar valves), pericarditis and myocarditis.
(viii) Cardiac arrest : It is the complete stoppage of the heart beat (sudden and complete loss of cardiac- function).
(ix) Heart failure : It is the state of heart when it does not pump blood effectively enough to meet the need of the body.

Above mentioned are the few of the several Circulatory system problems which lead to diseases of the circulatory system..

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