Structure of the blood vessels
vein
artery
tunica intima
lumen
tunica media
tunica adventitia
TS Artery
endothelium lining
tunica intima
muscle layer
tunica media
with elastic
fibres
tunica adventitia
connective tissue
lumen
Artery with thick muscle layer
Comparison of artery and vein
vein
artery
Artery
Relatively small lumen
Thick muscle layer
Vein
Relatively large lumen
Thin muscle layer
Capillaries
Capillary networks in tissues
Artery.
Outer layer of connective
tissue with fibres of
collagen (a strong fibrous
protein)
makes the outer wall
tough to prevent overstretching and to protect
against the pressure
exerted by other organs
rubbing against it.
Thick walls containing lots of elastic fibres (made from a protein called
elastin) and smooth muscle cells.
•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 maintains 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!)
The narrow lumen helps maintain the blood at higher pressure.
No valves because forward blood flow is maintained by the
heart and elastic recoil of the arteries.
Vein
An outer layer of connective
tissue
with
fibres
of
collagen, (a strong fibrous
protein), makes the outer
wall tough to prevent overstretching and to protect
against
the
pressure
exerted by other organs
rubbing against it.
Wide lumen.
Thin walls with few elastic
fibres and smooth
muscle.
Blood flows slowly under low pressure; there is no pulse so the walls do
not need to stretch and recoil.
Distribution of blood in the circulatory system
• Heart
3%
• Pulmonary circulation to lungs 10%
• Systemic circulation
87%
• Arteries
• Capillaries
• Veins
17%
5%
65%
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 runs through.
When the muscles relax and stop pressing the pressure drops
and the valves prevent the blood flowing backwards.
Very narrow
Lie close to all cells in the body
Capillary endothelial cell
Capillary wall is one cell thick
Capillaries
Red blood cell
Very small lumen
Narrow diameter slows down blood flow
to allow time for exchange between blood and surrounding cells to take
place more efficiently
Thin walls only one cell thick
to ensure maximum rate of transfer between blood and
surrounding tissue fluid
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
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 (yellowred), 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
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.
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
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.
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.