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Single and double, open and closed circulatory systems
A single circulatory system means that blood only flows through the heart once in a cycle
In a double circulatory system, blood flows from the heart to the lungs, then back to the heart
and onto the body. This is much more efficient because the blood pressure is boosted by the
second visit to the heart, which means nutrients and oxygen get to the necessary muscles
quicker. Also, it allows the blood pressure in the lung part of the system to be lower, so the lungs
won't get damaged by it, then is increased so it can travel around the whole body.
An open circulatory system means that the blood isn't always contained in blood vessels, and
therefore cells and tissues are `bathed' in blood. This is good for insects because they are small,
but would be useless in mammals because their surface area to volume ratio is so much
A closed circulatory system means that the blood is ALWAYS contained within blood vessels.
This is always the case in mammals because we need higher pressures to push the blood
around the whole body. Tissue fluid bathes tissues and cells in place of blood.
Single Insects Fish
Double None! Mammals
Endothelium Smooth Elastic Collagen Size of Valves?
muscle fibre fibres lumen
Arteries Yes Yes Yes Yes Relatively No
Veins Yes A little A little A little Relatively big Yes
Capillaries Yes No No No Tiny No
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Endothelium is a smooth layer of cells that lines all blood vessels to reduce the friction of the
Smooth muscle can contract to make the lumen size smaller or relax to increase it.
Elastic fibres allow arteries to withstand high pressures by stretching and then recoiling.
Collagen fibres are also there to strengthen the artery wall to aid in withstanding pressure.…read more