Blood Vessels Flow and Pulsation Prof K Sivapalan

Blood Vessels, Flow and Pulsation Prof. K. Sivapalan 2013 Vessels, flow and pulsations 1

Structure of blood vessols. • • Vasa vasorum. Nerve. Tunica adventitia. Tunica media – External elastic membrane. – Smooth muscle. • Tunica intima. – – 2013 Internal elastic membrane. Lamina propria. Basement membrane. Endothelium. Vessels, flow and pulsations 2

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 3

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 4

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 5

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 6

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 7

Shunt vessels. • Arterio-venus anastamosis. • Found in fingers, palms and earlobs. • Controlled by sympathetic nerves. 2013 Vessels, flow and pulsations 8

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 9

Peripheral resistance. • R = 8ηL / πr 4. • Viscosity and length: directly proportional. • Radius: inversely proportional [slight change in radius can bring large change in resistance]. 2013 Vessels, flow and pulsations 10