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School Biology revision notes: Human circulatory system Part 7 Treating CVD

The human circulatory system Part 7. Treating cardiovascular disease - Stents, bypass surgery and angioplasty 

Doc Brown's GCSE level Biology exam study revision notes

There are various sections to work through.

Index of notes on human circulatory system: heart, lungs & blood vessels

(7) Treating cardiovascular diseases - coronary heart disease

Reminder: Cardiovascular disease (CVD) is the scientific medical term for all types of disease that affect the heart or blood vessels.  CVD includes coronary heart disease (clogged up arteries with fatty deposits), which can cause heart attacks, stroke, heart failure, and peripheral artery disease.

If the heart or blood vessels are severely damaged major surgery might be required.

More on surgical techniques and other procedures are described in a later section.

Use of Stents

Coronary heart disease can be treated with stents - see diagram below.

Stents are very thin-walled wire mesh tubes inserted into arteries to widen them and keep them open to ensure a good supply of blood to the heart muscles.

A good blood flow keeps the heart beating regularly and so keeps you alive, particularly for people suffering from cardiovascular disease!

1. A normal artery, no hardened fat deposits (plaque) on the inner surface of the artery wall, so there is no restriction of blood flow away from the heart.

2. Fatty deposits (plaque) can build up on the inside wall of the artery restricting blood flow.

The cross-section of the lumen is reduced e.g. the equivalent of narrowing a 'pipe' and reducing blood flow - reducing the rate of oxygen transfer to heart muscles.

Cholesterol is a fatty substance the body needs to build cell membranes.

However, too much of fatty substances, including 'bad' LDL cholesterol, in your blood stream can lead to an excessive and dangerous build up of fatty deposits on the walls of the arteries.

The fatty deposits harden over time to form lots of atheromas which restricts blood flow.

These bits of atheromas damage the blood vessel and if one breaks off it can cause a blood clot.

This damage to the arteries causes high blood pressure with increased risk of heart attacks, angina and strokes.

Thick fat deposits can block a blood vessel or cause blood clots to form which can block the flow of blood completely.

If this involves an artery supply blood to the heart muscle, the heart muscle is deprived of oxygen and glucose and can cause a heart attack.

There is less energy available for the heart muscles to contract.

Such blockages can also deprive the brain of oxygen causing a stroke.

3. With the help of a catheter, whose position is monitored by X-rays, a very thin-walled tubular bare metal stent is inserted that pushes against the inside artery wall. The stent squashes the fat deposits and so widening the artery to allow normal blood flow - increases the cross-section area of the artery, so increasing flow rate - hopefully bringing the oxygen supply to the heart back to normal!

By allowing normal blood flow rate, stents are a very effective way of lowering the risk of a heart attack or a stroke for people suffering from coronary heart disease.

After the operation, recovery time is short and the stents have a long working life of many years.

Repeat surgery might be necessary if the artery narrows again.

However, such procedures are not without risk -

(i) there may be complications during the operation (including, ironically, a heart attack),

(ii) there is always a risk of infection with any surgical procedure, and,

(iii) a risk of a blood clot developing in the patient near the stent - known as a thrombosis. This restricts blood flow and possibly stopping the flow - not good!

NOTE An alternative stent

A drug-eluting stent (DES) is a peripheral or coronary stent (a scaffold) placed into narrowed, diseased peripheral or coronary arteries that slowly releases a drug to block cell proliferation.

This prevents the artery from getting narrowed by the growth of tissue cells.

Bypass surgery

There is little risk in having stents implanted, but the fatty deposits can build up again.

However, if the coronary artery is too badly damaged, bypass surgery must be used.

The blood vessels may be so badly blocked that stents won't work.

In this situation, the blood flow to the heart can be improved with coronary bypass surgery.

A healthy blood vessel (e.g. a vein in the leg) is transplanted and surgically inserted and connected to bypass the blocked damage artery.

Bypass surgery has the advantage of no rejection, but still carries risks of any major surgery.

It is a more invasive procedure than having stents fitted, requires a longer hospital stay and requires a longer recovery time.

There is a lower chance that repeat bypass surgery would be necessary, whereas with stents, this may be needed if the artery narrows again.

An example of angioplasty 

(image adapted from )

Angioplasty, is a minimally invasive endovascular procedure used to widen narrowed or obstructed arteries or veins in the treatment of arterial atherosclerosis.

A: A deflated balloon attached to a catheter (a balloon catheter) is passed via a guide-wire into the narrowed vessel.

B:  The balloon inflated to a fixed size (balloon angioplasty).

C: The balloon forces expansion the blood vessel and the surrounding muscular wall, allowing an improved blood flow.

Note: (i) A stent may be inserted at the time of ballooning to ensure the expanded blood vessel remains open, and the balloon is then deflated and withdrawn.

(II) Angioplasty has come to include all manner of vascular interventions that are typically performed by needle-puncture of the skin rather than by using an 'open' approach where inner organs or tissue are exposed.

Summary of learning objectives and key words or phrases

Be able to describe ways of treating coronary heart disease, cardiovascular disease CVD using stents, bypass surgery and angioplasty surgical procedures.

  • Know and understand that if arteries begin to narrow and restrict blood flow stents are used to keep them open.

  • You should understand the importance of stents, particularly with reference to the coronary arteries.

  • Stents are narrow tubes capable of supplying a blood flow equivalent to an artery.

  • Fatty deposits building up on the inner surface of the arteries that supply blood to the heart muscles can cause coronary heart disease.

  • These fatty deposits restrict the blood flow increasing blood pressure and causing heart attacks.

  • To combat this potential fatal condition you can insert stents into the arteries to increase blood flow to the heart muscles.

  • However, there are some drawbacks eg the stents can irritate the artery lining and cause the growth of scar tissue and drugs must be taken to avoid blood clots forming in the stent itself.



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