Download Blood Vessels and Routes

Blood Vessels and Routes
Functions of Blood Vessels
• Arteries carry blood AWAY from the heart
• Veins carry blood TOWARD the heart
• Vasa vasorum are blood vessel that
supply blood to the walls of blood vessels
Route of Blood Vessels
• After leaving the heart the flow of blood passes
through the following vessels in this order:
- Elastic arteries
- Muscular (or distributing) arteries
- Arterioles
- Capillaries
- Venules
- Veins
- Vena cavae
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Histology of Blood Vessels
•
Arteries have tree coats (tunics) and a
lumen (space where the blood flows)
(1) Tunica Interna (intima) – simple
squamous epithelium
(2) Tunica Media – smooth muscle
(3) Tunica Externa (adventicia) – elastic
fibers
Properties of Arteries
• Arteries have two properties
(1) Elasticity
(2) Contractility
- vasoconstiction
- vasodilation
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Types of Blood Vessels
• Elastic (conducting) arteries
• Recoil to force blood through the
capillaries after contraction of the heart
• These are the large arteries that take
blood to the head (carotid), arms
(brachial), and legs (femoral)
Types of Blood Vessels
• Muscular (distributing) arteries
• Can vasoconstrict and vasodilate to
control the flow of blood to various parts of
the body
• These are the smaller (than elastic)
arteries that supply blood to organs such
as the kidney (renal), stomach (gastric),
and liver (hepatic)
Types of Blood Vessels
• Arterioles
• These are small branches of arteries that
empty into blood capillaries
• Consists of a single layer of simple
squamous endothelial cell with a few
smooth muscle fibers
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Types of Blood Vessels
• Capillaries
• These are microscopic vessels that
connect arterioles to venules
• Their function is the exchange of gases,
nutrients, and wastes between the blood
and the tissues
• Consists of a single layer of simple
squamous endothelial cells
Types of Blood Vessels
• Venules
• These are small veins that drain blood
from several blood capillaries
Types of Blood Vessels
•
•
Veins
These are large vessels that have the
same three coats as arteries, but in
different proportions
(1) Tunica Interna – is extremely thin
(2) Tunica Media – thinner than arteries
(3) Tunical Externa – thicker than arteries
Note: veins have valves that prevent the
blood in them from flowing backwards
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Capillary Exchange
• The velocity of blood slows down as it
passes through the capillaries because the
total cross-sectional area of the capillaries
is much larger than any other component
of the circulatory system
• This allows time for the exchange of gases
and nutrients
Capillary Exchange (continued)
• Blood does not flow each capillary all the
time – rather the capillary undergoes
vasomotion (opening and closing) 5 to 10
times a minute
• This is necessary because there is not
enough blood in the body to fill every
capillary at the same time
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Starlings Law of the Capillaries
• The amount of blood forced out of the
arteriole end of the blood capillary by
Blood Hydrostatic Pressure (BHP) is
almost equal to the amount of blood drawn
back into the venule end of the blood
capillary by Blood Osmotic Pressure
(BOP)
• The fluid left over is picked up by a
lymphatic capillary and directed back into
the general circulation
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Velocity of Blood Flow
• The velocity of the blood flow is related to the total crosssectional area of the type of vessel the blood is in. For
example:
Cross-sectional area
Velocity
Aorta
2.5 cm2
40 cm/sec
10 – 40 cm/sec
Arteries
30 cm2
Arterioles
40 cm2
0.1 cm/sec
Less than 0.1 cm/sec
Capillaries 2500 cm2
Venules
250 cm2
0.3 cm/sec
0.3 to 5 cm/sec
Veins
80 cm2
5 to 20 cm/sec
Vena Cavae 8 cm2
Skeletal Muscle Contractions
• Contraction of skeletal muscles MILKS the
veins pushing blood toward the heart
• The valves in the veins prevent the blood
from flowing backwards
Breathing
• A decrease in interthoracic pressure
(during an exhalation) allows venous blood
to flow upward toward the heart
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Summary of Venous blood flow
•
The three factors listed above aid in
venous blood flow back to the heart
(1) The velocity of blood flow in the veins
increases due to the greater total crosssectional area of veins over capillaries.
(2) Skeletal muscle contractions force the
venous blood upward towards the heart.
(3) Breathing lowers pressure in the thorax.
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