1、Physiology of the Blood VesselsSection 11Divided into 3 part:Blood Vessels, Arterial pressure, Venous pressure, Venous returnMicrocirculation, Interstitial fluid, Lymph, Organ CirculationRegulation of cardiovascular activity Transport the blood Service the needs of the body tissuesWhats the role of

2、the blood vessels?Characteristics of the Blood Vessels Windkessel Vessel Distribution Vessel Precapillary Resistance Vessel Precapillary Sphincter Capillary Postcapillary Resistance Vessel Capacitance Vessel Classification of Vessel according to its Physiological FunctionWindkessel Vessel - Aorta -

3、Pulmonary artery - Big arteries Contain a large amount of elastic tissue & the smooth muscle Have strong elasticity & distensibility Transiently store blood during systole, and then shrink to produce onward blood flow during diastoleConvert the sharp pressure fluctuations in the left ventricle (0 to

4、 120 mmHg) into much smaller pressure fluctuations in the arteries (80 to 120 mmHg) Convert the intermittent ventricular ejection into continuous blood flow in the vesselsFunctionWindkessel EffectDistribution Vessel - Middle arteriesTogether with resistance vessels, having the capability of vastly a

5、ltering blood flow in each tissue bed in response to the need of the tissue Rich in smooth musclePrecapillary Resistance Vessels - Small arteries - ArteriolesThey act as control conduits through which blood is released into the capillaries Less elastic than the larger arteries Thicker layer of smoot

6、h muscleDetermine the OPEN or CLOSE of the capillary, thus control amount of blood flowing through a particular capillary bedPrecapillary Sphincter The initial part of capillary surrounded by a few of smooth muscle cellsPrecapillarySphincterCapillary (Exchange Vessel) The walls are composed of only

7、one cell layer Permits a more rapid transport of materials between the blood and the tissuesPostcapillary Resistance Vessels -venule Control the ratio of precapillary resistance & Postcapillary resistance Collect blood from capillaries, and they gradually coalesce into progressively larger veinsCapa

8、citance Vessel -veins Have a large diameter but a thin wall Have the greatest distensibility, makes their capacity adjustable About twice as much as the number of arteries Hold more than half the blood volume (60%70%)% distribution of total blood volume in the circulatory systemVessel Cross-Sectiona

9、l Area (cm2)Aorta 2.5Small arteries 20Arterioles 40Capillaries 2500Venules 250Small veins 80Venae cavae 8A-Capillary-V Vascular distensibility =V /(P X V0 )V : Increase in volume P: Increase in transmural pressure V0 : Original volume Vascular compliance = V /P Distensibility & Compliance Distensibi

10、lity & Compliance are quite different. Compliance is equal to Distensibility times volume.Basic Concept of Hemodynamics 1. Blood Flow (Q) = Volume Velocity 2. Blood Velocity 3. Resistance of Blood Flow (R)4. Blood Pressure (BP)Blood Flow (Q)=Volume Velocity Concept: The quantity of blood that passes

11、 a given point in the circulation in a given period of time. (ml/min or L/min)Factors determining Q: P: the pressure difference between the two ends of the vessels R: frictional force between the flowing blood and the intravascular endothelium all along the inside vessels: blood viscosity L: length

12、of the vessel r: radius of the vesselOhms law: Q = P / R Poiseuilles law: Q = P r4/8L r is the key factor to determine Q 2. Blood Velocity Blood velocity is directly proportional to blood flow, but inversely proportional to diameter of a blood vessel 3. Resistance of Blood FlowFrom Q = P / R (1) we

13、get R = P / Q (2)According to Poiseuilles law: Q = Pr4/8L (3)From (3) and (2), we get R = 8L/ r4 , is constantResistance is the impediment to blood flow in the vessels, but can not measured by any direct means Resistance (R) of a vessel is directly proportional to the blood viscosity () and length (

14、L) of the vessel, but inversely proportional to the fourth power of the radius ( r ) Normally, L have no change or almost no change Therefore, the diameter of a blood vessel & play the greatest role of in determining the resistance ( R ) of blood flowConcluded: Small artery & arterioles are the main

15、 part to produce resistance. Laminar flowLaminar flow & Turbulent flow Laminar flow: Blood flows at a steady rate through a long, smooth blood vessels in streamlines, with each layer of blood remaining the same distance from the wallTypes of Blood Flow in the Vessel Turbulent flow: Blood flow in all

16、 directions in the vessel and continually mixes within the vessel Because of: the velocity of blood flow is too great Passing by an obstruction Making a sharp turn Passing over a rough surfaceC: constrictionA: anterograde R: retrograde 4. Blood Pressure:Means the force exerted by the blood against t

17、he vessel wall Arterial Blood Pressure & Venous Pressure Arterial Blood Pressure Mean Circulatory Filling Pressure (MCFP)(2) Cardiac Pumping(3) Peripheral Resistance(4) Elasticity of Windkessel VesselFormation of the Arterial Blood Pressure(1) Mean Circulatory Filling Pressure (MCFP): When heart bea

18、t is stopped, the pressure in any point of cardiovascular system is equal. This pressure is called MCFPsystemic circulation: 7 mmHg pulmonary circulation: 10 mmHg(2) Cardiac Pumping: Energy released from heart contraction is transferred into two parts:1) Kinetic energy (1% of the total) 2) Potential

19、 energy (Pressure) (99% of the total) That means most part of energy used to create the blood pressure(3) Peripheral Resistance: Partly prohibit blood from flowing out from aorta & arteries rapidly (4) Elasticity of Windkessel Vessel diastolic blood pressure continuous blood flow in diastole bufferi

20、ng blood pressureNormal Range of Arterial PressureSystolic pressure (Ps)-the maximum of the pressure during systole: 100120mmHg Diastole pressure (Pd)-the minimum pressure during diastole: 6080mmHg Pulse pressure-the difference between Systolic pressure and Diastole pressure: 3040mmHgMean arterial p

21、ressure-the average pressure throughout each cardiac cycle = Pd +1/3 Pulse pressur=100mmHgNormal range of arterial pressure in different age groupCircadian Rhythms of Blood PressureBlood pressure among different vesselsMeasurement of the Arterial Pressure Direct: (inserting a cannula into the artery

22、)Measurement of the Arterial Pressure Indirect: (Auscultatory by Stethoscope)Measurement of the Arterial PressureFactors determining Arterial Pressure Stroke volume -PsHeart rate - PdTotal peripheral resistance -PdWindkessel effect (aorta & other large arteries) -Pulse pressureMean circulatory filli

23、ng pressureVenous Pressure & Venous ReturnVenous Pressure Central Venous Pressure Peripheral Venous PressureCentral venous pressure The pressure in the right atriumNormally about 412cmH2O (01mmHg)Regulated by a balance between: The ability of the heart to pump blood out of the right atrium and ventricle into the lungThe tendency of blood to flow from the peripheral veins back into the right atriumCentral Veno