In its route from the heart to the tissues, the blood passes through
channels of six foremost types: elastic arteries, muscular arteries,
arterioles, capillaries, venules and veins. I intend to explore the
structure and function of arteries, veins and capillaries. When an
artery branches into smaller and smaller vessels, eventually the blood
vessel is too small to see with the naked eye. At that point, it is
called an arteriole. Likewise, a venule is a microscopic vein.
All arteries are comprised of three different layers but the
proportion and structure of each varies with the size and function of
the particular artery.
A large artery, like the aorta, is comprised of the following layers,
going from the inner to the most external layers:
(1) The innermost narrow layer consists of a layer of endothelial
cells separated from the inner layer by a thin layer of connective
tissue that anchors the cells to the wall.
(2) A large layer of elastic fibres forming the "elastica interna"
(3) Below this layer are concentric waves of muscle cells mixed with
(4) Between the smooth muscle layer and the outer layer, there is
again another layer of elastic fibres, the "elastica externa".
(5) The outer layer is formed of irregularly arranged strong collagen
bundles. These collagen bundles are extremely tough and ensure the
artery is strong enough to withstand high pressures of blood, without
bursting. Surrounding the outer layer are blood vessels that are
called "vasa vasorum" or vessels of the vessels.
This structure of ...
... middle of paper ...
...ction of the circulatory
The structural differences between arteries and veins are all based in
their relationship to the heart. Since arteries receive blood from the
heart, the blood they receive is under a lot of pressure. At the same
time, this pressure helps the blood move through the arteries- even
when the arteries are opposing gravity (like the carotid artery
running towards the head).
In conclusion, the arteries carry oxygenated blood away from the
heart, and due to the high pressure of this blood the arteries have
thick wall, which contain many muscle fibres. The veins carry
deoxygenated blood to the heart and because blood is of a lower
pressure, have thinner walls consisting of less muscle fibres.
Capillaries are the principal part of the circulatory system; they
allow substance exchange.
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