LIU Chuan Yong 刘传勇 Institute of Physiology Medical School of SDU Tel 88381175 (lab)

1. LIU Chuan Yong 刘传勇 Institute of Physiology Medical School of SDU Tel 88381175 (lab) 88382098 (office) Email: liucy@sdu.edu.cn Website: www.physiology.sdu.edu.cn

2. Section 3 Physiology of the Blood Vessels

4. I. Physiological Classification of Blood Vessels

7. Windkessel Vessel --- Aorta and big arteries. • Contain a large amount of elastic tissue besides the smooth muscle. • Transiently store blood during systole, and then shrink to produce onward blood flow during diastole.

8. Convert the sharp pressure fluctuations in the left ventricle (0 to 120 mmHg) into much smaller pressure fluctuations in the arteries (80 to 120 mmHg). • Convert the intermittent ventricular ejection into continuous blood blood in the vessels • This function of large arteries is known as Windkessel effect.

9. 2. Distribution Vessel – Middle arteries • Rich in smooth, systole or diastole under some physical and chemical factors. • Together with resistance vessels, they match the blood flow to different organs with their requirements.

10. Distribution of Cardiac Output

11. 3. Precapillary Resistance Vessels – Small arteries and arterioles • Less elastic than the larger arteries • Hhave a thicker layer of smooth muscle. • Provide the greatest resistance to blood flow through the arterial system • since they have narrow lumina.

13. 4. Precapillary Sphincter muscle- • Partially determines the amount of blood flowing through a particular capillary bed • Allow only 5% - 10% of the capillary in bed skeletal muscles, for example, to be open at rest.

14. 5. Exchange Vessel – Capillary • the walls are composed of only one cell layer • – a simple squamous epithelium, or endothelium. • permits a more rapid transport of materials between the blood and the tissues.

15. Make Up of Blood Vessels: Capillaries

17. 6. Capacitance Vessel – Systemic veins • Have a large diameter but a thin wall, which includes a thin muscle coat. • The number is about twice as much as the number of arteries, • The large number and cross sectional area gives them an enormous capacity to hold blood.

19. Capacitance Vessel – Systemic veins • Most of the time, veins hold more than half the blood volume . • are known as capacitance vessels. • the great distensibility of veins makes their capacity adjustable. • In times of need, a considerable amount of blood can be squeezed from the veins to areas where it may be needed.

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

22. 1. Blood Flow (Q) • Concept: The quantity of blood that passes a given point in the circulation in a given period of time. • The overall blood flow in the systemic circulation is identical to the cardiac output

23. (2) Factors determining blood flow (interrelationships among blood flow, pressure and resistance.) • ΔP: the pressure difference between the two ends of the vessels; • R: frictional force produced when blood fIows through blood vessels. • Q = ΔP / R

24. (3) Laminar flow and turbulent flow • Laminar flow – blood flows in streamlines with each layer of blood remaining the same distance from the wall Laminar flow

25. (3) Laminar flow and turbulent flow • Turbulent flow – blood flow in all directions in the vessel and continually mixes within the vessel. • because of • the velocity of blood flow is too great, • is passing by an obstruction, • making a sharp turn, • passing over a rough surface) C, constriction; A, anterograde; R, retrograde

26. 2. Resistance of Blood Flow • 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 a vessel 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 ). • Normally, L and η have no change or almost no change. • Therefore, the diameter of a blood vessel plays by far the greatest role of all factors in determining the resistance ( R ) of blood flow.

27. 3. Blood pressure • Blood pressure means the force exerted by the blood against the vessel wall • ( or the force exerted by the blood against any unit area of the vessel wall) • Blood Pressure is stored energy (potential energy)

29. Formation of the blood pressure: • (1) Mean circulatory filing 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. • (2) Total peripheral resistance.

30. Formation of the blood pressure: • (3) Cardiac pumping • Energy released from heart contraction is transferred into parts, • 1) 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

31. Blood Pressure: Generated by Ventricular Contraction

32. Formation of the blood pressure: • （4）Elasticity of Windkessel vessel • ① diastolic blood pressure • ② continuous blood flow in diastole • ③ buffering blood pressure

33. 4. Physical Characteristics of the Systemic Circulation • (1)The velocity of blood flow in each segment of the circulation is inversely proportional to its cross-sectional area.

34. 4. Physical Characteristics of the Systemic Circulation • (2) Pressure and resistance in the various portion of the systemic circulations. • The decrease in pressure in each part of the systemic circulation is directly proportional to the vascular resistance.

36. III. Arterial Pressure

37. 1. Concept of Arterial Pressure • Blood pressure in the aorta and other big arterials.

38. 2. Normal Range of Arterial Pressure • Systolic pressure (Ps) – the maximum of the pressure during systole • Diastole pressure (Pd) – the minimum pressure during diastole • Pulse pressure – the difference between Ps and Pd • Mean arterial pressure – the average pressure throughout each cardiac cycle. • Mean arterial pressure (Pm) = Pd + Pulse pressure / 3

39. Mean arterial pressure

40. Normal range of arterial pressure • At rest, the arterial pressure of Chinese adult young people should be • Ps 100 – 120 mmHg • Pd 60 – 80 mmHg • Pulse pressure 30 – 40 mmHg

42. Measurement of the arterial pressure • Direct (inserting a cannula into the artery)

43. Measurement of the arterial pressure • Indirect (auscultatory) method • Stethoscope

44. Blood Pressure (BP):

46. 3. Factors Determining Arterial Pressure • Stroke volume ---- Ps • Heart rate ---- Pd • Total peripheral resistance (Ps) • Action of Windkessel vessel (aorta and other large arteries) – Pulse pressure • Mean circulatory filling pressure

47. IV. Venous Pressure and Venous Return

48. Venous Pressure • Central venous pressure • Peripheral venous pressure

49. Central venous pressure • The pressure in the right atrium. • Normally about 0 mmHg. • Regulated by a balance between • the ability of the right ventricle to pump blood out • the tendency of blood to flow from the peripheral back into the right atrium. • Clinical importance: • the hemorrhage • right heart failure

50. Peripheral venous pressure • Venous pressure in the organs • Properties: • Low pressure • Affected by the hydrostatic pressure • Usually veins are collapsed. (Why?)