The Transport Vessels (Blood Vessels)
Arteries
Arterioles
Capillaries
Venules
Veins
●Most arteries carry oxygenated blood and most veins carry deoxygenated blood
Exception: pulmonary artery carries deoxygenated blood from the heart to lungs and pulmonary vein
carries oxygenated blood from the lungs back to the heart
●Blood travels from an artery to an arteriole and into a capillary network to exchange substances
●Blood from capillaries empty into the venules and then the larger veins to the heart
●Blood pressure in descending order: aorta, arteries, arterioles, capillaries, veins
Smaller vessels→ more friction→ decrease blood pressure
The heart alone is not strong enough to keep the blood moving, so each vessel has adaptations to
assist with the movement of blood:
There are three types of transport vessels:
Arteries
Veins
Capillaries
1) Arteries
-Branch into smaller and narrower vessels called arterioles,
arterioles connect to the capillary bed
-Exhibit thick, elastic walls that can withstand high pressure
every time the heart contracts
-large, muscular vessels with elastic, strong walls
-transport high pressure, oxygenated blood away from the heart
(exception to this is the pulmonary artery which carrier of
deoxygenated blood)
Made of three structural layers: outer, middle (thickest), and inner
(thinnest):
Outer Layer: tough, fibrous connective tissue
Middle Layer: alternating circular bands of elastic fibres and
smooth muscle tissue
Inner Layer: simple endothelial tissue (one cell thick)
-when the heart pumps, the wall of the arteries stretch- it
expands and then snaps back, this is what you feel when you
take your pulse
-the arteries snap back to maintain blood pressure
-Contains about 30% of the blood of your systemic circulation
2) Veins
-Collect slow moving blood under low pressure- capillary beds branch into
venules, which then branch into veins
-transport low pressure, deoxygenated blood TO the heart (exception to this is
the pulmonary vein which carries oxygenated blood)
-Exhibit thinner, less muscular walls with no elasticity, large inner circumference
-veins contain approximately twice as much blood as arteries at any given time
-Presence of valves ensure the one way flow of blood to the heart; prevents
backflow, helps low pressure blood along its way
-also use the contraction of skeletal muscles to pump blood and help its along its
way
-Contains about 65% of blood of your systemic circulation
Varicose Veins- broken valves that don’t close properly cause the blood to leak
backward and pool, this may result in varicose veins
3)Capillaries
-Connect arterioles and venules
-Highly branched
-only one endothelial cell layer thick (about 8µm)
-inner diameter is so small that red blood cells (rbc) pass
through in single file
-so numerous that almost all of our 125 trillion cells lie
about 125 micrometers away from a capillary, this allows
rapid diffusion of gases and nutrients between cells and
capillaries
-Blood moves slowly under low pressure to allow for
exchange with surrounding tissue