LIU Chuan Yong Institute of PhysiologyMedical School of SDUTel 88381175 (lab) 88382098 (office)Email: liucy@sdu.edu.cnWebsite: www.physiology.sdu.edu.cn

Section 3 Physiology of the Blood Vessels

I. Physiological Classification of Blood Vessels

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.

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 vesselsThis function of large arteries is known as Windkessel effect.

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.

Distribution of Cardiac Output

3. Precapillary Resistance Vessels Small arteries and arteriolesLess 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.

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

5. Exchange Vessel Capillarythe 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.

Make Up of Blood Vessels: Capillaries

6. Capacitance Vessel Systemic veinsHave 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.

Capacitance Vessel Systemic veinsMost 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.

II Basic Concept of Hemodynamics:

Blood Flow, Resistance of Blood Flow and Blood Pressure

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

(2) Factors determining blood flow (interrelationships among blood flow, pressure and resistance.)

P: the pressure difference between the two ends of the vessels;R: frictional force produced when blood fIows through blood vessels. Q = P / R

(3) Laminar flow and turbulent flowLaminar flow blood flows in streamlines with each layer of blood remaining the same distance from the wallLaminar flow

(3) Laminar flow and turbulent flowTurbulent 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

2. Resistance of Blood FlowFrom Q = P / R (1) we get R = P / Q (2)According to Poiseuilles law, Q = P r4/8l (3)From (3) and (2), we get R = 8 l/ r4 is constantNote that the resistance (R) of a vessel is directly proportional to the blood viscosity () and length (l) of the vessel, but inversely proportional to the fourth power of the radius ( r ). Normally, L and 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.

3. Blood pressureBlood 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)

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 MCFPsystemic circulation, 7 mmHg; pulmonary circulation, 10 mmHg.(2) Total peripheral resistance.

Formation of the blood pressure:(3) Cardiac pumpingEnergy 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

Blood Pressure: Generated by Ventricular Contraction

Formation of the blood pressure:4Elasticity of Windkessel vessel diastolic blood pressure continuous blood flow in diastole buffering blood pressure

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.

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.

III. Arterial Pressure

1. Concept of Arterial PressureBlood pressure in the aorta and other big arterials.

2. Normal Range of Arterial PressureSystolic pressure (Ps) the maximum of the pressure during systoleDiastole 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

Mean arterial pressure

Normal range of arterial pressureAt rest, the arterial pressure of Chinese adult young people should bePs 100 120 mmHgPd 60 80 mmHgPulse pressure 30 40 mmHg

Measurement of the arterial pressureDirect (inserting a cannula into the artery)

Measurement of the arterial pressureIndirect (auscultatory) methodStethoscope

Blood Pressure (BP):

3. Factors Determining Arterial PressureStroke volume ---- PsHeart rate ---- PdTotal peripheral resistance (Ps)Action of Windkessel vessel (aorta and other large arteries) Pulse pressureMean circulatory filling pressure

IV. Venous Pressure and Venous Return

Venous PressureCentral venous pressure

Peripheral venous pressure

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 hemorrhageright heart failure

Peripheral venous pressureVenous pressure in the organsProperties:Low pressureAffected by the hydrostatic pressureUsually veins are collapsed. (Why?)

Transmural pressure= Blood pressure - The pressure adjacent tissues exerted on the blood vessel.If the transmural pressure is negative (smaller than 0), the vein is collapsed

Venous ReturnConcept: The quality of blood flowing from veins into the right atrium per minuteFactors affecting venous returnMean system filling pressureCardiac contractilityPosition of the bodyAction of muscular pumpRespiration movement

Factors affecting venous return1) Mean systemic filling pressure2) Cardiac contractility Cardiac contractility stroke volume ventricular pressure in diastole period blood from atria and large veins to ventricle venous return 3) Position of the body From lying to standing increase of the blood in veins dilation of veins in the lower part of the body decrease of venous return

Factors affecting venous return4) Action of muscular pump (or venous pump)

Factors affecting venous return(5) respiration movement. Negative pressure in the thoracic cavity that changes with respiratory movement dilation of venae cave increase of venous return

V Microcirculation

1.Functional anatomy of the microcirculation

2. pores in the capillary membraneABA, Continuous Capillaries B, Fenestrated Capillary

2. pores in the capillary membraneStructurally, capillaries have no smooth muscle in their walls. They are lined by only a single layer of endothelial cells. There are gaps between endothelial cells to allow for exchange of nutrients and metabolites.

3. Capillary pressure.Arterial end 30 40 mmHg; Venous end, 10 15 mmHg; Middle part 25 mmHg

4. Exchange of nutrients and other substances between the blood and interstitial fluid(1) Diffusion through the capillary membrane.

Lipid-solute substance can diffuse directly through the cell membranes of the capillary Water-soluble, liquid-insoluble substance, such as Na , Cl, glucose and so forth, diffuse only through the capillary pores.

4. Exchange of nutrients and other substances between the blood and interstitial fluid(2) Transport through the capillary membrane by pinocytosis. Proteins and many much large substance in the plasma (such as lipoprotein) are transported through the capillary membrane by means of pinocytosis. (3) Filtration. When the hydrostatic pressure is different on the two sides of membrane, the greater pressure on one side causes slightly increased diffusion of water and dissolved substances toward the opposite side.

VI The Interstitial FluidWater within the body accounts for 60% of the total body weight (body fluid)2/3 intracellular compartment1/3 extracellular compartment 80%, interstitial fluid;20%, blood plasma

The distribution of extracellular fluid between the plasma and interstitial compartments is in a state of dynamic equilibrium. Tissue fluid is not normally a stagnant pond but is rather a continuously circulating medium, formed from and returning to the vascular system.

In this way, the tissue cells receive a continuously fresh supply of glucose and other plasma solutes that are filtered through tiny endothelial channels in the capillary walls

The daily intake and excretion of body water and its distribution between different intracellular and extracellular compartment

1. Formation of the interstitial fluidEffective Filtration Pressure = (Capillary Pressure + Interstitial Colloid Osmotic Pressure) (Plasma Colloid Osmotic Pressure + Interstitial Hydrostatic Pressure) crystal pressure

2. Factors Determining Formation of the Interstitial Fluid (Mechanism of Edema)Edema is an abnormally large collection of fluid in the interstitial space. From the physiology of capillaries and lymphatics,edema may be due to one or more of the following causes:

Mechanism of Edema(1) Capillary pressureRight heart failure systemic edemaLeft heart failure pulmonary edemaLate pregnancy edema in legs and foot (pressure of uterus on inferior vena cava)

Mechanism of Edema(2) Plasma colloid osmotic pressureProtein malnutrition, liver disease (inadequate albumin synthesis ) or renal disease (protein loss in urine) hypoproteinemia low plasma colloid osmotic pressure(3) Permeability of capillary wallInflammation or allergy leakage of abnormally large quantities of proteins from capillaries

Mechanism of Edema(4) Lymphatic drainageLymphatics are the second circulatory system. Structurally, lymphatics are a network of blind-ended thin endothelial tubes. Although the endothelial lining is not fenestrated, the intercellular junctions are permeable to large molecules.

Mechanism of Edema(4) Lymphatic drainage (continued)Lymphatics collect proteins, lipids and other large molecules which leak out of capillaries into the interstitial space, to prevent the osmotic pressure of interstitial space from rising, and thereby prevent abnormal accumulation of fluid in the interstitial space. Reduced lymphatic drainage, e.g. in filariasis, or involvement of lymph nodes in malignancy local or systemic edema.

3. The function of lymph Removing protein from interstitial fluid. Regulating balance between plasma and interstitial fluid (reabsorption l0% of filtration fluid). Absorption nutrients (80%~90% of fat) from gastrointestinal tract. Removing the particles such as RBC, bacteria, lymphatic cell, tissue cell in the interstitium. Defense function (to ingest bacteria and to produce antibodies)