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Section Three Blood Vessels

Section Three Blood Vessels. Introduction Arterial Pressure Venous Circulation Microcirculation. ANATOMY CONSIDERATIONS. ANATOMY CONSIDERATIONS. Physiological Classification of Blood Vessels. Windkessel Vessel --- Aorta and big arteries.

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Section Three Blood Vessels

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  1. Section Three Blood Vessels • Introduction • Arterial Pressure • Venous Circulation • Microcirculation

  2. ANATOMY CONSIDERATIONS

  3. ANATOMY CONSIDERATIONS

  4. Physiological Classification of Blood Vessels

  5. Windkessel Vessel--- Aorta and big arteries. In addition to smooth muscle, aorta and big arteries contain a large amount of elastic tissue.

  6. They are stretched during systole and recoil on the blood during diastole, which dampen blood pressure pulsation. Convert the intermittent ventricular ejection into continuous blood flow in the vessels. This function of large arteries is known as Windkessel effect.

  7. 2. Distribution Vessel– Middle arteries These arteries are rich in smooth, which will systole or diastole under some physical and chemical factors. Together with resistance vessels, they match the blood flow to different organs with their requirements.

  8. 3. Precapillary Resistance Vessels– Small arteries and arterioles ⑴ narrow lumina the greatest resistance to blood flow ⑵ a thicker layer of smooth muscle. control vascular caliber and local blood flow

  9. 4. Precapillary Sphincter muscle（control switch） The amount of blood flowing through a particular capillary bed is determined in part by the action of the precapillary sphincter muscle. These muscles allow only 20% - 35% of the capillary bed in skeletal muscles, for example, to be open at rest.

  10. 5. Exchange Vessel – True Capillary The walls of true capillaries are made up of a single layer of endothelial cell and a thin basement membrane. The absence of smooth muscle and connective tissue layers permit a more rapid transport of materials between the blood and the interstitial fluid.

  11. 6. Postcapillary Resistance Vessels–Veinule ⑴ narrow lumina the great resistance to blood flow ⑵ Action of veinule change capillary blood pressure, and affect formation of interstitial fluid.

  12. 7. Capacitance Vessel: Veins The walls of veins are thin and easily distended. Their lumina are larger.

  13. The number veins is about twice as much as the number of arteries. The large number and cross sectional area give them an enormous capacity to hold blood. Veins hold 60%-70% of the circulating blood volume . That is why veins are known as capacitance vessels.

  14. 8. Arteriovenous Shunt vessels Direct connect an arteriole and a venule. Function: Regulates the body temperature

  15. II Basic Concept of Hemodynamics: Blood Flow, Resistance of Blood Flow and Blood Pressure

  16. 1. Blood Flow (Q) • Concept: The quantity of blood that passes through a cross section of blood vessel in unit time is called blood flow(also called volume velocity). • Velocity of blood flow(V) means line speed of a particle in the blood circulation. • Q ↑, V ↑ • Area of a cross section ↑, V ↓

  17. (2) Factors determining blood flow (interrelationships among blood flow, pressure and resistance.) 1) ΔP: the pressure difference between the two ends of the vessels; 2) R: frictional force produced when blood flows through blood vessels. Q = ΔP / R Poiseuille’s law, Q =πΔP r4/8ηl

  18. (3) Laminar flow and turbulent flow Laminar flow – flow direction of each particle in blood is consistent with vascular long axis; • the velocity of flow of a particle in the center of the vessel is the greatest. • The more near the vessel wall, the slower the velocity

  19. Turbulent flow – Flow direction of each particle in blood is not consistent, - Each particle in bloodflows in all directions in the vessel to form whirlpool.

  20. Reynolds equation V Dρ η V-mean velocity of blood flow. Re= ——— D-diameter of a blood vessel. ρ-blood density. η-blood viscosity Re>2000, easy to generate turbulence.

  21. 2. Resistance of Blood Flow(R) -Blood flowing within the vessel encountered resistance. -Friction between blood and blood vessel, and friction between blood components. - R of turbulent flow is greater than that in laminar flow.

  22. Resistance of Blood Flow(R) From Q = ΔP / R (1) we get R = ΔP / Q (2) According to Poiseuille’s law, Q =πΔP r4/8ηl (3) From (3) and (2), we get R = 8 ηl/ π r4 π is constant. Note that the resistance (R) of blood flow is directly proportional to the blood viscosity (η) and length (l) of the vessel, but inversely proportional to the fourth power of the radius ( r ) of the vessel.

  23. Normally, L and η have no change or almost no change. Therefore, the radius of a blood vessel plays the greatest role in determining the resistance ( R ) of blood flow.

  24. ★ Distribution of resistance of blood flow Aorta and large arteries9% Small arteries and branches16% Arteriole 41% Capillary 27% Vein 7% the radius ( r ) of the vessel the organ blood flow distribution

  25. Blood viscosity (η) 1) erythrocrit ↑, η↑. 2) At laminar flow: shearing rate of blood flow =ΔV / d, d-thickness of adjacent two layers of blood layers . ΔV- V difference of adjacent two layers of blood layers. Newtonian fluid: homogeneous liquid, such as plasma. Its shearing rate changes, but itsηdo not change.

  26. Non-Newtonian fluid: Non homogeneous liquid, such as blood. Its shearing rate changes ↓, its η↑. Axial flow- when blood flows in the form of laminar flow, red cells have a trend of moving to central axis. When shearing rate is higher, axial flow phenomenon is more obvious, its η is lower.

  27. 3) Calibre of blood vessel: Fahraeus-Lindqvist effect. If calibre of blood vessel is smaller than 0.2~0.3 mm, shearing rate of blood is enough high,within a certain range, decrease inηaccompanys with calibre of blood vessel becoming smaller. 4)Temperature ↓,η↑.

  28. 3. Blood Pressure The lateral pressure that the blood effects on unit area of the vessels wall is called the blood pressure. Unit ： kPa/mmHg

  29. 1mmHg=1.36cmH2O 1mmHg=0.133KPa =133Pa 1cmH2O=0.098KPa

  30. III. Arterial Blood Pressure Arterialblood pressure means the force exerted by the arterial blood against unit area of the arterialvessel wall.

  31. Formation Of Arterial Pressure Conditions： There is a enough blood in the cardiovascular system. + cardiac pumping and peripheral resistance + windkessel of aorta and big arteries +

  32. There is a enough blood in the cardiovascular system. + Mean circulatory filling pressure (MCFP): when heart beat is stopped, the pressure in any point of cardiovascular system is equal. This pressure is called MCFP. systemic circulation, 7 mmHg; pulmonary circulation, 10 mmHg.

  33. cardiac pumping and peripheral resistance + • Energy released from heart contraction is transferred into two parts, • kinetic energy (1% of the total), • 2) potential energy (pressure) (99% of the total). • That means most part of energy used to create the blood pressure. There is a resistance of blood flow in the blood vessels, especially in small arteries and arterioles.

  34. windkessel of aorta and big arteries ①buffering arterial blood pressure fluctuation. ②convert the intermittent pumping blood of heart to continuous blood flow within arteries. + 2/3 1/3

  35. Measurement of the arterial pressure Direct : (inserting a cannula into the artery)

  36. Indirect (auscultatory) method: Stethoscope

  37. Blood Pressure (BP):

  38. Normal value of arterial blood pressure Systolic pressure The pressure in the aorta and other arteries rises to a peak value during each heart cycle. Diastolic Pressure The pressure in the aorta and other arteries falls to a minimum value during each heart cycle.

  39. arterial pressure

  40. Pulse Pressure = Systolic pressure - Diastolic Pressure Pulse Pressure = Diastolic pressure＋ MAP 3 The mean arterial pressure (MAP) is the average pressure throughout the cardiac cycle.

  41. systolic pressure ： 100-120mmHg diastolic pressure ： 60-80mmHg pulse pressure : 30-40mmHg mean arterial pressure : 100mmHg hypertension diastolic pressure>90mmHg arterial pressure>140/90mmHg hypotension arterial pressure<90/50mmHg

  42. resistance of blood flow , pressure drop *

  43. Factors Controlling Arterial Pressure • Stroke Volume • Heart Rate • Resistance • Windkessel effect of aorta and big arteries • Relationship Between Blood Volume and Vascular Volume

  44. (1) Stroke volume : stroke volume↑ the systolic pressure ↑ pulse pressure↑ • An increase in stroke volume results in a rise in blood pressure, and vice versa. However, change in stroke volume mainly affects the systolic pressure provided the peripheral resistance remains unchanged.→ pulse pressure↑

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