Artery Anatomy

 Narrowing of an artery

The tissues distal to the narrow point become ischaemic. The cells may receive enough blood to meet their minimum needs, but not enough to cope with an increase in metabolic rate, e.g. when muscle activity is increased. This causes acute cramp-like ischaemic pain, which disappears when exertion stops. Cardiac muscle and skeletal muscles of the lower limb are most commonly affected. Ischaemic pain in the heart is called angina pectoris (p. 120), and in the lower limbs, intermittent claudication.

Occlusion of an artery

When an artery is completely blocked, the tissues it supplies rapidly undergo degeneration and die

from ischaemia, which leads to infarction. If a major artery supplying a large amount of tissue is

affected, the consequences are likely to be more severe than if the obstruction occurs in a minor

vessel. If the tissue is well provided with a collateral circulation (such as the circulus arteriosus

provides in the brain), tissue damage is less than if there are few collateral vessels (which may be the case in the heart).

When a coronary artery is occluded myocardial infarction  occurs. Occlusion of arteries in the brain causes cerebral ischaemia and this leads to cerebral infarction (stroke).

Complications of atheroma

Thrombosis and infarction If the fibrous cap overlying a plaque breaks down, platelets are activated by the damaged cells and a blood clot forms, blocking the artery and causing ischaemia and infarction. Emboli may break off,

travel in the bloodstream and lodge in small arteries distal to the clot, causing small infarcts. 

Haemorrhage

Plaques may become calcified, making the artery brittle, rigid and unresponsive to rises in blood pressure. They may rupture, causing haemorrhage.

What is Aneurysm?

Aneurysm 

When the arterial wall is weakened by spread of the plaque between the layers of tissue, a local dilation (aneurysm) may develop (see below). This may lead to thrombosis and embolism, or the

aneurysm may rupture causing severe haemorrhage. The most common sites affected by atheroma are the aorta and the abdominal and pelvic arteries.

What is Arteriosclerosis ?

Arteriosclerosis

This is a progressive degeneration of arterial walls, associated with ageing and accompanied by hypertension.

In large and medium-sized arteries, the tunica media is infiltrated with fibrous tissue and calcium. This causes the vessels to become dilated, inelastic and tortuous . Loss of elasticity increases systolic blood pressure, and the pulse pressure (the difference between systolic and diastolic pressure).

When small arteries (arterioles) are involved, their lumen is reduced because of a deposition of

a substance called hyaline material, which also reduces the elasticity of the vessel wall. Because

these arteries are the main determinants of peripheral resistance , this narrowing increases peripheral resistance and blood pressure. Damage to small vessels has a disproportionate effect on blood flow, leading to ischaemia of tissues supplied by affected arteries. In the limbs, the resultant ischaemia predisposes to gangrene, which is particularly serious in people with diabetes mellitus.

Senile arteriosclerosis

This is a condition affecting elderly people. Progressive loss of elasticity and reduced arterial lumen lead to cerebral ischaemia and loss of mental function. There may or may not be evidence of

hypertension.

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