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A&P 2 Lab 4
Circulatory System-Blood Flow Tracings
Circulatory system- how the blood from the heart is circulated throughout the body.
General blood flow through the body after it leaves the heart follows a mapping system. From
the heart, it flows through arteries, then capillaries, and comes back to the heart by way of
veins.
BLOOD VESSELS IN THE CIRCULATORY SYSTEM:
• Arteries- referred to as efferent blood vessel in the circulatory system
o They always carry blood away from the heart.
o Typically carry oxygenated blood. (except in the pulmonary artery)
o 1. Conducting arteries:
▪ very large arteries and typically exit from the heart
▪ They have the need/ability to expand when the heart beats so they
withstand the splurge. So, with every heartbeat, blood surges out of
the
heart into these large vessels.
• To do this, they must have a layer of elastic tissue that gives it
the ability to stretch and recoil when the heart is relaxing.
▪ EX: aorta and pulmonary trunk
o Atherosclerosis- when arteries age and stiffen because plaque builds up in the
arteries, they loose that elasticity and the ability to stretch when blood surges
into them.
▪ It results in an increase in pressure in those vessels which can lead to
an aneurism- a weak point in a artery and with each heartbeat, that
little
thin walled area will pulsate and it can further and further weaken and
eventually rupture which can lead to death or stroke.
o 2. Distributing arteries:
▪ A.k.a. medium or muscular arteries
▪ They are direct branches from the conducting arteries
▪ Have a very thick muscular wall (up to 40 layers of smooth muscle)
▪ The muscular wall in a distributing artery makes up 75% of the
arterial wall itself.
• EX: brachial artery, femoral artery (named for area where they
are distributing their blood)
o 3. Resistance arteries:

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▪ A.k.a. small arteries
▪ Too numerous to name
o 4. Metarterioles:
▪ Very short vessels that will link the arteriole system to the capillaries.
• AFTER BLOOD FLOWS THROUGH THE ARTERIAL SYSTEM, IT THEN FLOWS INTO A
SERIES OF CAPILLARY BEDS.




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o 5. Capillaries:
▪ Known as the exchange vessels because they have very thin walls
that exchange oxygen, glucose, and other nutrients in the body.
▪ They connect the smallest arteries to the smallest veins.
• Veins- afferent blood vessels because they bring blood back to the heart
o They typically carry deoxygenated blood (except the pulmonary vein)
o They are called Capacitance Vessels because they typically control a large
amount of volume.
o Can stretch more easily than arteries and have thin, flaccid walls and
can therefore accommodate a larger volume of blood.
o Comparing arteries to veins:
▪ In a resting person, about 11% of the blood is found in the arteries
while 54% is found in the veins.
▪ Veins are subject to much lower blood pressure because they are
further away from the heart. Because of that, they can have thinner
walls compared to the arteries that need more muscular support.
▪ In the arteriole system, we go from large to small vessels and the
venous system is opposite.
o 6. Post capillary vein:
▪ Very small veins called venules.
o 7. Muscular Venules:
▪ Very small and too numerous to name
o 8. Medium veins:
▪ They drain blood from specific areas of the body, organs and muscles.
▪ EX: radial and ulnar veins (drain blood out of the forearm)
▪ Unique: they contain valves- flaps of tissue that extend into the
lumen and point upwards towards the heart.
• Because veins have a very low blood pressure, they don’t have
the strength to pump the blood back to the heart against the pull
of gravity.
• Skeletal muscles that surround the veins also help to pump
the blood
o EX: when calve muscles contract, they squeeze around
the vein and push blood up through the valve.
o Kind of like a “milking action” known as the skeletal
muscle pump.
• When the valves weaken and can’t perform their job, varicose
veins will result. They are visible through the skin due to the
blood
pooling and backflowing into the venous system.
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o 9. Venous Sinuses:
▪ Large vessels with very thin walls and very large lumens




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