心血管系統(tǒng)課件：Lecture 5 - vascular physiology

1、VASCULAR PHYSIOLOGY Types and characteristics of blood vessels l Arteries Large artery Medium-sized artery Small artery -muscular atery -muscular atery The vessel wall 1 2 3 Next slide l arteriole Arterioles are the site of highest resistance to blood flow l capillary -thin wall -Capillaries are the

2、 site where nutrients, gases, water, and solutes are exchanged between the blood and the interstitial fluid. l venule l vein Small vein Medium-sized vein Large vein The walls of veins contain much less elastic tissue than the arteries. The veins have a large capacitance（capacity to hold blood). Vein

3、 valve Blood Vessel Comparison: l Functional Functional Parts Parts of Blood of Blood VesselsVessels 1. Windkessel vessel (Elastic vessels ) 2. Distribution Vessel 3. Precapillary Resistance Vessel (small arteries, arterioles) 4. Precapillary Sphincter 5. Exchange Vessel ( aorta, pulmonary arteries

4、, large arteries) (medium-sized arteries) (capillaries) arterioles Ventricular Relaxation arterioles Ventricular Contraction Windkessel effect LV LV 6. Postcapillary Resistance Vessel (venule) 7. Capacitance Vessel (veins) 8. Shunt Vessel (arteriovenous shunt) Hemodynamics It is the study of interre

5、lationship among blood flow, blood pressure and resistance to blood flow 1. Blood Flow (Q) 2. Blood Pressure (P) 3. Resistance to Blood Flow (R) 1. Blood flow (Q) Definition: Blood flow is the amount of blood flowing through an organ, tissue, or blood vessel in a given time (such as mL/min). Overall

6、 blood flow in the total circulation of an adult is about 5000 ml/min.The cardiac output Distribution of blood in the body at rest. The overall blood flow in the systemic circulation is identical to the cardiac output. 2. Blood velocity -Linear velocity -Velocity refers to the rate of displacement o

7、f blood per unit time.(cm/sec) V=Q/A V=Velocity of blood flow Q=Blood flow A=Cross-sectional area A is the cross-sectional area of a blood vessel or a group of blood vessels（total cross- sectional area). Since flow is a measure of volume per unit time = Q=VA, = The velocity of blood flow is highest

8、in the aorta and lowest in the capillaries. 3. Interrelationships between blood flow, pressure, and resistance Q=P/R Q=Flow P=Pressure difference R=Resistance R=P/R Since the vascular system obeys an adaptation of Ohms law, known as Darcys law = Directly proportional to pressure differences, inverse

9、ly proportional to resistance Blood flow: Poiseuille equation Q=Pr4/8L =viscosity of blood L=length of vessel r=radius of vessel Jean Louis Marie Poiseuille pw-zi (April 22, 1799 - December 26, 1869) was a French physician and physiologist. Poiseuille was born in Paris, France. From 1815 to 1816 he

10、studied at the cole Polytechnique in Paris. He was trained in physics and mathematics. In 1828 he earned his D.Sc. degree with a dissertation entitled Recherches sur la force du coeur aortique. He was interested in the flow of human blood in narrow tubes. R=8L/r4 4. Resistance (R) to blood flow -Flo

11、w resistance is a measure of how easily the fluid can pass through a tube for any given pressure difference. (mmHg/mL/min) Q=P/R =viscosity L=the tube length r=the tube radius - opposition to blood flow due to friction between the blood and the blood vessel wall and among components of the blood Q=P

12、r4/8L Sources of Peripheral Resistance 3 main sources of peripheral resistance Blood Viscosity Refers to the stickiness or thickness of the blood Vessel Length Vessel Radius Blood viscosity Blood viscosity is related to the density of blood cells in the plasma There is a direct relationship between

13、blood viscosity and peripheral resistance viscosity = peripheral resistance; viscosity = peripheral resistance There is an inverse relationship between blood viscosity and blood flow (impedes blood flow) viscosity = blood flow; viscosity = blood flow Shear rate and temperature also can affect blood

14、viscosity In healthy people, blood viscosity varies little Any condition that increases or decreases the concentration of blood cells or plasma proteins may alter blood viscosity Anemia = blood viscosity High altitude or dehydration = blood viscosity Blood viscosity The normal viscosity of blood is

15、about four times as great as the viscosity of water. There is a direct relationship between vessel length and resistance to blood flow Vessel length does not vary much in adults Vessel Length The resistance to flow is inversely proportional to the fourth power of the radius. Vessel radius is associa

16、ted with the amount of friction between the blood and the walls of blood vessel Blood flowing close to the wall of the blood vessel is slowed due to friction Large-radius vessels offer less resistance to blood flow Small-radius vessels offer greater resistance to blood flow Vessel radius Series and

17、parallel resistance l Series resistance A given organ arteryarteriole capillaryvenule vein Rtotal=Rartery+Rarteriole+Rcapillary+Rvenule+Rvein The greatest decrease in pressure occurs in the arterioles l Parallel resistance in the systemic circulation Cerebral (R1) Coronary (R2) Renal (R3) Gastrointe

18、stinal (R4) Skeletal muscle (R5) Skin (R6) aorta Vena cava 1/Rtotal=1/R1+1/R2+1/R3+1/R4+1/R5+1/R6 5. Laminar and Turbulent Flow Laminar flow Streamlined Outermost layer moving slowest and center moving fastest Turbulent flow Interrupted Rate of flow exceeds critical velocity Fluid passes a constrict

19、ion, sharp turn, rough surface Turbulence The Reynolds number =density of blood D=diameter of blood vessel V=velocity of blood flow =viscosity of blood Re2000 6. Blood pressure Force exerted by the blood against any unit area of the vascular wall. Unit mm Hg, Pa(KPa) 1 mm Hg = 0.133 kPa， 1KPa=7.5mmH

20、g 1 mmHg =1.36 cm H2O 7. Compliance and distensibility Compliance: the volume of blood contained in the vessel for a given transmmural pressure is called vascular compliance C=V/P The higher the compliance of a vessel, the more volume it can hold at a given pressure. Compliance of the arteries is mu

21、ch lower than that of the veins. Compliance Distensibility The fractional increase in volume for each millimeter of mercury rise in pressure D=V/PVo D=V/V0/P C=DVo The Arterial Blood Pressure . Formation of arterial pressure l Enough blood filled in the circulation system Mean circulatory filling pr

22、essure 7mmHg The volume of blood The capacity of blood vessels l Ventricular ejection kinetic energy (1% of the total) potential energy (pressure) (99% of the total) l Peripheral resistance It keeps the continuous blood flow during diastole It reduces the pressure pulsations l Effect of Windkessel v

23、essel R 8 L /r4 Arteries as Pressure Reservoirs Arteries as Pressure Reservoirs The peak pressure during contraction of the hearts is called the systolic pressure The minimum arterial pressure value during relaxation of the heart is called the diastolic pressure . Normal range of arterial blood pres

24、sure n Systolic pressure 100120mm Hg n Diastolic pressure 6080mm Hg In clinical practice, human arterial pressure is reported as the ratio of systolic over diastolic pressure ，for example ， reported as 120/80mmHg. n Pulse pressure 3040mm Hg Systolic pressure- diastolic pressure= pulse pressure n Mea

25、n arterial pressure (MAP) MAP= diastolic P +1/3 (systolic P- diastolic P) -is the average pressure throughout the cardiac cycle -Mean arterial pressure is closer to Pd why? n Methods for Measuring Systolic and Diastolic Pressures FIGURE 15-7 Measurement of arterial blood pressure. Arterial blood pre

26、ssure is measured with a sphygmomanometer (an inflatable cuff plus a pressure gauge) and a stethoscope. The inflation pressure shown is for a person whose blood pressure is 120/80 Physiological variation of arterial blood pressure l Gender l Age Arterial pressure increases with age, DBP more than SB

27、P l Different physiological status； l Circadian rhythm l Stroke volume l Heart rate l Peripheral resistance l The proportion of the volume of blood to the capacity of vascular system . Factors affecting arterial blood pressure l Windkessel effect With aging, major blood vessels increase in rigidity

28、Systolic pressure Diastolic pressure DBP indicates the amount of peripheral resistance encountered SBP reflects the amount of work the heart is performing Factors affecting arterial blood pressure FactorSystolic pressure Diastolic pressure Pulse pressure Mean BP Stroke volume Heart rate Peripherial

29、resistance Windkessel function /- blood volume/capacity . Arterial pulse l Concept and Mechanism: l Waveform: * * Ascending Ascending phasephase * * Descending Descending phasephase Ejection velocity Resistance to ejection Cardiac output -dicrotic notch and dicrotic wave Peripheral resistance aortic

30、 valve Dicrotic notch Dicrotic wave l The velocity of pressure pulse transmission In the normal aorta is 3 to 5 m/sec In the large arterial branches, 7 to 10 m/sec In the small arteries, 15 to 35 m/sec The Venous Blood Pressure and Venous Return Venules Veins Large veins Venae cavae Right atrium 152

31、0mmHg 5.5mmHg 4.6mmHg *The venous system serves as a blood reservoir for the circulation. *The veins are passageways for flow of blood to the heart *The constriction and dilation of VSMCs can adjust the volume of venous return and cardiac output Functions of the veins 02mmHg p Central Venous Pressur

32、e (CVP) (1)The ability of the heart to pump blood (2)Venous return 412cmH2o -The pressure in right atrium and Vena cave. Central venous pressure is regulated by a balance between p Peripheral Venous Pressure . Venous Pressure -The pressure in the peripheral veins (1) increased blood volume, (2) incr

33、eased large vessel tone throughout the body with resultant increased peripheral venous pressures (3) dilatation of the arterioles( which decreases the peripheral resistance .) Some factors can increase venous return (and thereby increase the right atrial pressure) . Effect of Gravity on Venous Press

34、ure hydrostatic pressure 1mmHg/13.6mm In a standing position, hydrostatic pressure caused by gravity increases blood pressure below the heart and decreases pressure above the heart Transmural pressure = Blood pressure - The pressure adjacent tissues exerted on the blood vessel. Effect of transmural

35、pressure . Venous Resistance Effect of constriction and dilation of venules l The respiratory pump. l Cardiac contraction force l Mean circulatory filling presure l Effect of Gravity l The skeletal muscle pump The flow of blood back to the heart, called venous return . Factors affecting venous retur

36、n Venous pump Varicose vein（曲張靜脈） THE MICROCIRCULATION I. Definition The blood circulation through the arterioles，capillaries and venules. II. Functions of the Microcirculation *To exchange nutrients, gases, and metabolic byproducts between blood and cells *To maintain normal distribution of the ext

37、racellular fluid III. Structure of the Microcirculation and capillary system l Arteriole Inner radius: 525um VSMCs: + l Metarteriole Inner radius: 59um VSMCs: + Play a major role of controlling blood flow to the tissue l Precapillary sphincter By opening or closing, these switches determine blood fl

38、ow to the capillary bed. Like “switches” l True capillary Inner radius: 25um VSMCs: - Wall thickness: 0.5um Pores in the Capillary Membrane Capillaries: Capillary wall consists mostly of endothelial cells Types classified by diameter/permeability Continuous Do not have fenestrae Fenestrated Have por

39、es Sinusoidal(Discontinuous) Large diameter with large fenestrae Continuous: found in muscle, skin, lung, central nervous system Fenestrated: found in exocrine glands, renal glomeruli, intestinal mucosa Discontinuous: found in liver, spleen, bone marrow Structure of the capillary wall Capillaries Ha

40、ve greatest total cross-sectional area Have slowest velocity of blood flow, enhances exchange l venule Inner radius: 20um VSMCs: +/- l Arteriovenous shunt (A-V shunt) l Thoroughfare channel . Three major channels Nutritional channel circuitous channel Blood flows from arterioles through metarteriole

41、s, then through capillary network Venules drain network Smooth muscle in arterioles, metarterioles, precapillary sphincters regulates blood flow Thoroughfare channel e.g., skeletal muscle non-nutritional channel Arteriovenous shunt e.g., skin non-nutritional channel . Hemodynamic of the Microcircula

42、tion l Velocity of blood flow is lowest in the capillaries l Capillary blood pressure (Pc) falls from approximately 35 mm Hg at the arteriolar end to approximately 15 mm Hg at the venular end l As Rpost/Rpre increases, Pc would increase, as Rpost/Rpre decreases, Pc would decrease. l Blood flows inte

43、rmittently through capillaries, a phenomenon called “Vasomotion.”（intermittent contraction of the metarterioles and precapillary sphincters 510timesmin） -contraction of the metarterioles and precapillary sphincters are influenced mainly by oxygen and waste products of tissue metabolism. . Exchange o

44、f Nutrients and Other Substances between Blood and Interstitial Fluid l Filtration and reabsorption l Diffusion l Pinocytosis(e.g., plasma protein) Exchange between the interstitial fluid and capillaries occur via three processes: Capillary Exchange Diffusion Diffusion is the most important means fo

45、r transferring substances between plasma and interstitial fluid. l Lipid-soluble substances can diffuse directly through the cell membranes of the capillary endothelium(e.g., oxygen and carbon dioxide.) l Water-soluble, non-lipid-soluble substances diffuse through intercellular “pores in the capilla

46、ry membrane(e.g., water molecules, sodium ions, chloride ions, glucose) -Accounts for the exchange of oxygen and most nutrients such as amino acids, fatty acids, and glucose, carbon dioxide, hormones, etc. l The primary factors that affect the rate of diffusion across the capillary walls are as foll

47、ows: 1. The concentration difference of the substance between the two sides of the membrane. 2. The molecular size of the diffusing substance. 3. The pore size in the capillary. 4. Functional surface area 5. Thickness of capillary wall Filtration and absorption The pathway for fluid movement across

48、the capillary wall Transcellular pathway Paracellular pathway Hydrostatic pressure difference P Osmotic pressure difference( colloid osmotic pressure) The two driving forces for the convection of fluidor water movementacross the capillary wall Filtration capillary tissue space Reabsorption tissue sp

49、acecapillary fluid fluid When net fluid movement is out of the capillary into the interstitial fluid, it is called filtration When net fluid movement is from the interstitium into the capillary, it is called reabsorption. Formation of Interstitial Fluid . Interstitial Fluid Definition: The fluid in

50、the interstitial space Characteristic: *Fluid in the interstitium has almost the same constituency as plasma except with lower concentrations of protein. *“Gel” *The amount of “free” fluid in the interstitium in most tissues is less than 1%. . EFFECTIVE FILTRATION PRESSURE ( EFP) Hydrostatic pressur

51、e difference P capillary pressure (Pc) interstitial fluid pressure (Pif) P= Pc- Pif capillary plasma colloid osmotic pressure (p) colloid osmotic pressure difference interstitial fluid colloid osmotic pressure (if) = if-p Forces that promote filtration and drive fluids out of the capillary are: Capillary hydrostatic pressure Interstitial fluid colloid osmotic pressure Forces that promote fluid absorption and pull fluids into the capillary are: Capillary plasma colloid osmotic pressure Interst