2013 Vessels, flow and pulsations 1
Blood Vessels, Flow and Pulsation
Prof. K. Sivapalan
2013 Vessels, flow and pulsations 2
Circulation.
• Blood ejected into aorta flows through vessels and back to heart.
• The histology of the vessels shows a common pattern.
• Structure and properties of the vessels are adapted depending on the role played by that part in circulation.
2013 Vessels, flow and pulsations 3
Structure of blood vessols.
• Vasa vasorum.• Nerve.• Tunica adventitia.• Tunica media
– External elastic membrane.– Smooth muscle.
• Tunica intima.– Internal elastic membrane.– Lamina propria.– Basement membrane.– Endothelium.
2013 Vessels, flow and pulsations 4
Elastic arteries [Windkessel vessels].
• Aorta and large arteries have large amount of elastic fibers and small amount of smooth muscles.
• They stretch when pressure increases and recoil when pressure reduces.
• Aorta distends when blood is ejected from ventricles and recoils during diastole.
• This keeps blood flowing to the periphery continuously.• The pressure fluctuates in the arteries depending on
ejection by the heart, elasticity of aorta, peripheral resistance and out flow.
• Highest is systolic pressure and the lowest is diastolic pressure.
2013 Vessels, flow and pulsations 5
Arterial pulsation.
• The pressure changes are transmitted along the vessel as pulse wave.
• It can be felt as a distension over the arteries.• Mean pressure is diastolic pressure +1/3 of the pulse
pressure.• Velocity of the pulse : 5 M / Sec at 5 years, 8 M / Sec
at 60 years. [faster when solidifying]• Average velocity of blood is 0.5 M / Sec.• Arterial pulse indicates patency but not flow.• The character of the pulse varies depending on the
state of heart and vessels.
2013 Vessels, flow and pulsations 6
Resistance vessels.
• Less elastic fibers and more muscles.• Small arteries and (mainly) arterioles.• Sympathetic nerves – Vasomotor tone.• Convert pulsatile flow into continuous flow.• Provide majority of peripheral resistance.• Arterioles determine the amount of blood
flow to any area.
2013 Vessels, flow and pulsations 7
Exchange vessels.
• Capillaries.• Only endothelium and basement
membrane.• Precapillary sphincters- respond to
humeral and local factors.• Only about 25 % open at rest.
2013 Vessels, flow and pulsations 8
Capacity vessels.
• Veins and venules.• Thin wall, easily distended.• Little muscles but potent vaso spasm possible.• Pressure by skeletal muscles [calf] additional
pump.• Valves prevent back flow specially in dependant
parts.• Pressure waves in the atria are transmitted
backwards to the large veins.
2013 Vessels, flow and pulsations 9
Shunt vessels.
• Arterio-venus anastamosis.• Found in fingers, palms and earlobs.• Controlled by sympathetic nerves.
2013 Vessels, flow and pulsations 10
Flow, pressure & resistance.
• In rigid tubes,• Flow α pressure.
– Flow 1/α resistance.• In blood vessels,
– Flow stops at critical closing pressure.
• Reason-– ? viscosity.– ? red cells larger than
capillaries.– ? vasomotor tone.
2013 Vessels, flow and pulsations 11
Peripheral resistance.
• R = 8ηL / πr4.• Viscosity and length: directly proportional.• Radius: inversely proportional [slight
change in radius can bring large change in resistance].
2013 Vessels, flow and pulsations 12
Blood flow.
• Laminar flow:• Smooth flow.
– Pulsatile flow.– Pulse can be felt [not heard]
• Turbulent flow:– Edi currents and vibrations
[sound]– Depends on, density, velocity,
viscosity and the diameter of the tube.
– Sounds produced.
2013 Vessels, flow and pulsations 13
Summary