Structure of the blood vessels

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arteryvein

lumen

tunica intima

tunica media

tunica adventitia

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lumen

TS Artery

tunica intima

tunica media

tunica adventitia

endothelium lining

muscle layer

with elastic fibres

connective tissue

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Artery with thick muscle layer

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Layers of the wall of an artery

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Comparison of artery and vein

artery

vein

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Artery

Relatively small lumen Thick muscle layerBrought to you by

Vein

Relatively large lumen Thin muscle layerBrought to you by

Artery and vein compared

ArteryVein

Semi-lunar pocket valveBrought to you by

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Words to use to complete the sheet describing the structure of arteries and veins

(some words may be used once, some more than once and some not at all)

High

Low

Present

Absent

Thin

Thick

Squeeze

Narrow

Backflow

Large

Small

Friction

Smooth

Elastic

Fibres

Muscles

And helps to maintain the blood flow

By controlling the diameter

Also prevents over-expansion to maintain the pressure

Anchors the vessels in the tissues

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Describe, and account for, the similarities and

differences in the structure of arteries and veins.

To be done in continuous prose

(no tables, no bullet points)

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Capillaries

Capillary networks in tissues

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Capillaries

Very small lumenCapillary wall is one cell thick

Capillary endothelial cell Red blood cell

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Checkpoint 1.2. How the structure of an artery, a vein and a capillary is related to the

function of the vessel.

• Refer to Fig 1.10 B

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Outer layer of connective tissue with fibres of collagen (a strong fibrous protein)

Thick walls containing lots of elastic fibres (made from a protein called elastin) and smooth muscle cells.

Artery.

makes the outer wall tough to prevent over-stretching and to protect against the pressure exerted by other organs rubbing against it.

•Elastic fibres allow walls to stretch when blood pumped at high speed and high pressure into arteries by contraction of ventricles; elastic recoil when the pressure drops as the ventricles relax pushes the blood forward to maintain the flow and the pressure.

•The smooth muscles contract to control how far the artery stretches and so controls the diameter of the artery, which also maintains the pressure. (NB. The muscles do not contract to pump the blood in the arteries!)

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No valves

The narrow lumenhelps maintain the blood at higher pressure.

because forward blood flow is maintained by the heart and elastic recoil of the arteries.

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Vein

Outer layer of connective tissue with fibres of collagen (a strong fibrous protein)

makes the outer wall tough to prevent over-stretching and to protect against the pressure exerted by other organs rubbing against it.

Thin walls with few elastic fibres and smooth muscle.

Wide lumen.

Blood flows slowly under low pressure; there is no pulse so the walls do not need to stretch and recoil.

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Distribution of blood in the circulatory system

• Heart 3%

• Pulmonary circulation to lungs 10%

• Systemic circulation 87%• Arteries 17%

• Capillaries 5%

• Veins 65%

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Has pocket valves that prevent the backflow of blood.

Blood in the vein is pushed forward by the increase in pressure produced by the contraction of the nearby skeletal muscles which the vein run through.

When the muscles relax and stop pressing the pressure drops and the valves prevent the blood flowing backwards. Brought to you by

Capillaries

Very small lumenCapillary wall is one cell thick

Capillary endothelial cell Red blood cell

Very narrow

Lie close to all cells in the body

Narrow diameter slows down blood flow

to allow time for exchange between blood and surrounding cells to take place more efficientlyThin walls only one cell thickto ensure maximum rate of transfer between blood and surrounding tissue fluid

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Atherosclerosis. Light micrograph of a cross section through an artery with mild atheroma. The artery wall is pink. The formation of a fatty plaque or atheroma (grey, centre) has greatly narrowed the size of the artery lumen (white, centre). This causes a considerable reduction in blood flow. When this occurs in the arteries leading to the heart symptoms of angina pectoris (gripping pains in the chest) are frequently experienced. In severe cases heart attacks or strokes may occur. Atherosclerosis is principally caused by high fat diets, cigarette smoking, obesity and inactivity

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Atheroma & thrombus. Coloured light micrograph of a section through an artery almost completely blocked by atherosclerosis and a thrombus. The large red mass in the centre is a thrombus, an abnormal blood clot. This is attached to a part of the arterial wall that has thickened with atheroma (yellow-red), a fatty deposit containing fibrous tissue, dead cells & cholesterol. Atherosclerosis is the biggest cause of death in the UK. It causes progressive narrowing of the arteries by deposits of atheroma, and encourages the formation of abnormal clots that can block arteries. Fatal complications of atherosclerosis

include heart attack and Brought to you by

Atherosclerosis. Light micrograph of a cross section through an artery obstructed with an atheroma plaque. The artery (at upper left) has a central lumen (black), where blood flows. Bordering the lumen is a fibrous and fatty deposit of a plaque on the arterial wall. This can be seen as a dark grainy irregular deposit on the inner wall. Surrounding the plaque is the dark artery wall muscle with an inner layer of lighter endothelium. Atherosclerosis, the thickening of the artery walls, is mainly due to a fatty diet high in cholesterol. This can result in clot formation or severe artery blockage which may lead to heart attack.

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Atheroma. Cutaway illustration of the inside of a human artery showing fatty plaques of atheroma. The artery has three distinct layers. The tunica adventitia (outer layer) is fibroelastic and the tunica media (middle layer) is muscular. The inner layer, the tunica intima, is composed of a layer of endothelial cells (large, orange) supported by connective tissue. Atheroma (green and yellow, centre right) is a mixture of low- density lipoproteins, decaying muscle cells, fibrous tissue, blood platelets and cholesterol. It has narrowed the artery and caused thinning and damage to the endothelial layer (atherosclerosis).

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Heart disease. Coloured 3-D computed tomography (CT) scan of the heart of sixty year old patient with heart disease. The left coronary artery (pink) is on the top of the heart, and it supplies the heart with oxygenated blood. The left hand branch is the anterior interventricular artery, which has become narrowed near the top (highlighted area). Stenosis, or narrowing, of arteries leads to reduced blood flow to the areas served by the artery. If the artery becomes completely blocked these areas die, causing myocardial infarction, or heart attack. Risk factors for stenosis include obesity, smoking, diabetes and a family history of the condition.

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Coloured angiogram taken during a percutaneous transluminal coronary angioplasty (PTCA) to the right coronary artery. It is done to treat a severe stenosis (narrowing, upper centre left) caused by plaques of atheroma lining the inside of the artery; the blood flow is also impaired by a clot seen in the same area just below the stenosis

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Heart disease. Coloured 3-D computed tomography (CT) scan of the heart of sixty year old patient with heart disease. The left coronary artery (pink) is on the top of the heart, and it supplies the heart with oxygenated blood. The left hand branch is the anterior interventricular artery, which has become narrowed near the top (highlighted area). Stenosis, or narrowing, of arteries leads to reduced blood flow to the areas served by the artery. If the artery becomes completely blocked these areas die, causing myocardial infarction, or heart attack. Risk factors for stenosis include obesity, smoking, diabetes and a family history of the condition.

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Heart disease. Coloured angiogram (X-ray) of the coronary (heart) arteries of a patient with heart disease. Coronary arteries (orange) supply the heart muscle with oxygenated blood. Stenosis (narrowing) of the blood vessels is seen at left. Stenosis is usually due to atherosclerosis, where fatty deposits of atheroma form on the inner walls of arteries. It may also be due to abnormal blood clots (thrombi) blocking part of an artery. Lack of blood to the heart muscle causes angina (severe chest pain) and can lead to a heart attack (death of part of the heart muscle). Atherosclerosis is usually caused by a high-cholesterol diet, but smoking and inactivity are also risk factors.

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Heart bypass grafts. Artwork of a heart that has had a blockage of the coronary arteries treated by coronary artery bypass graft (CABG) surgery. The coronary arteries are the small blood vessels seen running over the outer surface of the heart. They supply oxygenated blood to keep the heart muscle pumping, and a blockage can cause a fatal heart attack. The solution is to harvest arteries from elsewhere in the body and use them to bypass the blockage. Three grafts are seen running from the aorta, the main body artery, back to the coronary arteries, secured by sutures (black). Three grafts makes this a triple bypass operation, indicating an advanced state of heart disease. Brought to you by

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