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If you could join all the blood
vessels in your body in a
straight line, it would be
about 100,000km long!
Our blood vessels are not
one long tube but a complex
network of tubes that
branch and rebranch.
blood vessels that carries blood away
from the heart and towards the body
tissues
 walls of the arteries have three layers
of tissue – connective tissues, smooth
muscle and endothelium
 when the ventricles of the heart
contract to pump blood around the
body, the arteries expand slightly to
accommodate the increased pressure
of the blood within them. (The outer
layer of the arteries include elastin
fibres giving the vessel elasticity.)
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when the ventricle relax, the walls of the
arteries return to their original size, pushing
the blood farther into the downstream
vessels
when the artery expands from contractions of
the heart, it is felt as a pulse
when arteries branch and rebranch, the
smallest artery is called the arterioles
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Because arterioles have smooth muscle, they can be controlled by the nervous
system.
Signals from the nerves can regulate the diameter of the arterioles and
control blood flow to certain parts of the body.
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Vasodilation: an increase in the diameter (dilation) of arterioles that increases
the blood flow to tissues. This can be used by the body as a cooling strategy:
warm blood close to the skin loses thermal energy to the surrounding
environment. Eg (minoxidil, nitroglycerin, asperin, sildenafil, alcohol
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Vasoconstriction: a decrease in the diameter of arterioles that decreases the
blood flow to tissues. This can be used if the body is cold. Restricting blood
flow to the skin prevents thermal energy loss to the environment. Also,
vasoconstriction ensures that the 5L of blood in your body is distributed where
it is needed. (eg. Epinephrine, Pseudoephedrine, Caffeine, Nicotine)
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arteries branch into arterioles
and when those reach the tissue
of the body, they branch further
into smaller blood vessels called
capillaries
capillaries form networks of
blood vessels that supply
oxygen and nutrients to every
cell throughout the body tissues
capillary walls are only a single cell
layer thick which allows easy
diffusion of oxygen and nutrients into
the tissues as well as carbon dioxide
and other waste products to diffuse
from the tissue back into the capillary
 There is no smooth muscle in the
walls of the capillaries so the
diameter of the capillaries cannot be
controlled by the nervous system.
Instead, pre-capillary sphincters
contract and relax to regulate blood
flow. When the sphincters are
relaxed, blood flow to a tissue is
increased.
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capillary networks have an arteriole
side and an venule side; (more pressure
on the arterial side)
 venules and veins carry deoxygenated
blood containing carbon dioxide and
other waste products; blood is
returned to the heart
 smooth muscles in veins is not as thick
as in arteries and the walls are not as
elastic; this makes the diameter of
veins greater than arteries which
reduces the pressure
 blood pressure in veins is lower than
blood pressure in arteries; how does
blood return to the heart? (muscles
and the valves)
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1. Compare and contrast Arteries and Veins
2. Describe the differences between
vasodilators and vasocontrictors and give an
example of each.
3. If you sustained a near mortal wound while
being attacked by zombies, name a drug you
would reach for.