Download Blood Vessels

BLOOD VESSELS
By: Ms. Reis
Arterial System
• Arteries – vessels that carry blood away from
the heart to arterioles. The aorta is the largest
artery in the body carrying blood from the
heart to the tissues.
• Arteries have elastic walls that allow it to first
expand as blood passes through then snap back
again. This movement keeps blood flowing in
the right direction, and provides an additional
pumping motion to help force the blood
through the blood vessels.
Aneurysm
• An aneurysm occurs when
the inner wall of the artery
begins to bulge. When a
rupture or blockage occurs in
the arterial wall, parts of the
brain don't get the blood and
oxygen they need which may
lead to stroke.
• Blood from the arteries
passes into smaller arteries
called arterioles.
Arterioles
• Blood from the arteries passes into smaller
arteries called arterioles.
• Vasoconstriction occurs when the arterioles
contract decreasing blood flow to the tissues.
Ex: turning pale when in a state of fear
• Vasodilation occurs when the arterioles dilate
increasing blood flow to the tissues. Ex:
blushing when in a state of nervousness
Capillaries
• Arterioles carry blood to capillaries.
• Capillaries – smaller blood vessels that
carry blood to larger venules. Because of
their small diameter red blood cells must
travel through capillaries in single file.
Nearly every tissue within the body is
within 0.1 mm of a capillary.
Capillaries : the Site of Gas and
Fluid Exchange
• Capillaries are the site of fluid
and gas exchange between the
blood and cells.
• Capillaries are composed of a
single layer of cells. This allows
capillaries to provide cells with
oxygen, glucose, and amino
acids via diffusion through the
thin capillary walls.
• Endocytosis and exocytosis
result in the exchange of protein.
Capillaries
• Oxygenated blood,
which appears red in
colour, takes on a
purple-blue colour as
it leaves the capillary.
The deoxygenated
blood collects in small
veins called venules.
Venous System
• Venules – merge into veins with an even
greater diameter.
• Veins – vessels larger than venules that return
blood back to the heart.
• Once blood reaches the veins after passing the
fine network of capillaries it is travelling very
slowly.
• Unlike arteries veins are unable to contract and
thus another mechanism must be used to move
blood back to the heart.
Blood Vessels
How then does blood
flow get back to the
heart?
1) Veins have valves that
open in only 1 direction
helping push the blood
toward the heart and
overcoming the force of
gravity.
2) Muscles surrounding the
veins exert pressure on the
veins which also helps
push blood toward the heart.
Blood Vessels: A Comparison
• Arteries have strong walls
capable of withstanding great
pressure. Veins are not able to
withstand great pressure.
• Veins have thinner walls but a
larger inner circumference.
As a result veins lack the
elasticity of the artery, but
have a greater capacity to
carry blood.
• The venous system contains
twice as much blood as the
arterial system.
ARTERY
CAPILLARY
Wall is composed of Wall is one cell
3 layers of cells
thick
High elasticity
No elasticity
Smaller diameter
than veins
very narrow
diameter
Carries blood away
from the heart
Site of gas
exchange with
tissue cells
VEIN
Thinner wall
than artery
Little elasticity
but has valves
Larger
diameter than
arteries
Carries blood
toward the
heart
Varicose Veins
• If valves do not
function properly
gravity carries blood
to the feet and blood
pooling occurs. This
results in veins
distending/expanding.
• Both genetics and
lifestyle are factors.