CVSCVSThe circulation is a closed The circulation is a closed system of distensible tubes system of distensible tubes of varying diameters and of varying diameters and distinctive structure.distinctive structure.

Function The function of the circulation is to fulfill the The function of the circulation is to fulfill the

needs of the body tissues:needs of the body tissues:

To transfer nutrients to the body tissue and waste To transfer nutrients to the body tissue and waste products away from the body tissueproducts away from the body tissue

To conduct hormone from one part of the body to To conduct hormone from one part of the body to anotheranother

Maintain an appropriate environment in all the Maintain an appropriate environment in all the tissue fluids of the body for optimal survival and tissue fluids of the body for optimal survival and function of the cellfunction of the cell

CIRCULATION COMPRISES OF:

Systemic circulation Systemic circulation

Pulmonary circulationPulmonary circulation

FUNCTIONAL PARTS OF FUNCTIONAL PARTS OF CIRCULATION CIRCULATION

ArteriesArteries

ArteriolesArterioles

Capillaries Capillaries

Venules Venules

VeinsVeins

VOLUME OF BLOOD IN VOLUME OF BLOOD IN DIFFERENT PARTS OF DIFFERENT PARTS OF CIRCULATIONCIRCULATION

•About 84% of the entire blood About 84% of the entire blood vol of the body is in the vol of the body is in the systemic circulation and 16% in systemic circulation and 16% in the heart and lungs.the heart and lungs.

Out of 84% in the systemic Out of 84% in the systemic circulation:circulation:

64% in veins64% in veins13% in arteries13% in arteries7% in arterioles and 7% in arterioles and

capillariescapillaries7%in heart7%in heart9%in pulmonary vessel9%in pulmonary vessel

PRESSURE IN VARIOUS PORTIONS PRESSURE IN VARIOUS PORTIONS OF CIRCULATIONOF CIRCULATION

Heart continually pumps blood into aortaHeart continually pumps blood into aorta

The mean pressure in the aorta The mean pressure in the aorta about 100 about 100 mm Hgmm Hg

Heart pumping in pulsatile Heart pumping in pulsatile mannermanner

Arterial pressure alternates Arterial pressure alternates between systolic pressure of between systolic pressure of 120mmHg and120mmHg and

diastolic pressure of diastolic pressure of 80mmHg.80mmHg.

As the blood flow through systemic circulation As the blood flow through systemic circulation it means pressure falls to zero when it it means pressure falls to zero when it reaches the termination of inferior vena cava reaches the termination of inferior vena cava empty into the right ventricle . empty into the right ventricle .

The pressure in capillaries varies from as high The pressure in capillaries varies from as high as 35 mm Hg near the arteriolar end and as as 35 mm Hg near the arteriolar end and as low as10mmHg near the venous end.low as10mmHg near the venous end.

The average functional pressure is 17 mm Hg.The average functional pressure is 17 mm Hg.

PRESSURE IN DIFFERENT PARTS PRESSURE IN DIFFERENT PARTS OF PULMONARY CIRCULATIONOF PULMONARY CIRCULATION

In pulmonary artery pressure is also in a pulsatile manner.

Pulmonary artery systolic pressure average about 25 mmHg

Pulmonary artery diastolic pressure average about 8 mmHg

Mean pulmonary arterial pressure is only 16mmHg

Mean pulmonary capillary pressure is only 7mmHg.

The total blood flow through the lungs each minute is the same as through the systemic circulation.

FUNCTIONAL TYPES OF BLOOD VESSELS

ELASTIC VESSELS

Aorta and large arteries are elastic vessels.

• They are highly elastic due to increased amount of elastic tissue and loose collagen fibers are present.

The aorta and large vessels accommodate large amount of ejected blood by expansion.

They have elastic recoil which is responsible for maintenance of diastolic B.P.

If these vessel would not have been elastic blood would not flow during diastole.

With age arteries become less elastic due to atherosclerosis there is increased pulse pressure.

This is due to:

Systolic pressure increases in old age

Elastic recoil decreases with age.

So pulse pressure increases with age.

RESISTANCE VESSELS

•Resistance vessels are arterioles, metarteriol, pre-capillary sphincters.

•Size of these vessels control blood flow to the tissues.

Size of these vessels can be

controlled by:

Sympathetic nerves

Local metabolic factors as CO2 conc ,lactic acid.

EXCHANGE VESSELSEXCHANGE VESSELS

• Capillaries are exchange vessels.

• They are the smallest blood vessels.

• Capillary wall is composed of single layer of endothelial cells supported by basement membrane.

Through capillary wall there is exchange between blood and tissues.

The capillary itself cannot be constrict or relaxed it is the pre capillary sphincter which controls opening and closure of capillaries.

At rest in tissues 25% capillaries are patent .

CAPACITANCE VESSELSCAPACITANCE VESSELS

e.g e.g VEINS and VENULESVEINS and VENULESVeins accommodate about 2/3rd of blood Veins accommodate about 2/3rd of blood volume, volume, carry large amount of blood without carry large amount of blood without increase in pressure .increase in pressure .

Veins are supplied by sympathetic nerve fibers.Veins are supplied by sympathetic nerve fibers.

When veins are constricted venous return When veins are constricted venous return increases.increases.

When veins are dilated a large amount of blood When veins are dilated a large amount of blood is pooled up in veins.is pooled up in veins.

SHUNT VESSELSSHUNT VESSELSe.g. arterio-venous anastomosis .e.g. arterio-venous anastomosis .

These vessels pass from met arterioles to These vessels pass from met arterioles to venules and bypass the capillary network.venules and bypass the capillary network.

Through shunt vessels blood flows rapidly.Through shunt vessels blood flows rapidly.

They are present in the skin of exposed areas They are present in the skin of exposed areas of the body e.g palm of hand, external ear of the body e.g palm of hand, external ear skin, skin of fingers.skin, skin of fingers.

They are supplied by They are supplied by sympathetic nerve fibers .sympathetic nerve fibers .

They are involved in regulation They are involved in regulation of body temperature .of body temperature .

By these heat can be lost By these heat can be lost rapidly through skin . rapidly through skin .

Interrelationship among Interrelationship among pressure flow and resistancepressure flow and resistance

Blood flow through a blood vessel is Blood flow through a blood vessel is determined by two factorsdetermined by two factors

Pressure differencePressure difference

Vascular resistanceVascular resistance

The force that pushes the blood through The force that pushes the blood through the vessel is the pressure difference of the the vessel is the pressure difference of the blood b/w the two ends of the vessel, also blood b/w the two ends of the vessel, also called “pressure gradient” called “pressure gradient”

Vascular resistance is the impediment to Vascular resistance is the impediment to blood flow through the vesselsblood flow through the vessels

The blood flow through the vessel can be The blood flow through the vessel can be calculated by the following formula, which calculated by the following formula, which is called Ohm’s law:is called Ohm’s law:

F= F= ∆∆P/RP/RF=blood flowF=blood flow∆∆P=pressure difference b/w the two ends P=pressure difference b/w the two ends

of the vesselsof the vesselsR=resistanceR=resistance

BLOOD FLOWBLOOD FLOW

It is the quantity of blood which flows into It is the quantity of blood which flows into the region of circulatory system in a the region of circulatory system in a given unit of time.given unit of time.

It is expressed in ml/min or L/min.It is expressed in ml/min or L/min.

The overall blood flow in the total The overall blood flow in the total circulation of any adult person is about circulation of any adult person is about 5000ml/min.5000ml/min.

METHODS OF MEASURING METHODS OF MEASURING BLOOD FLOWBLOOD FLOW

BY USING FLOWMETERS:BY USING FLOWMETERS:

1)By electromagnetic flowmeter1)By electromagnetic flowmeter

2)By ultrasonic Doppler flowmeter2)By ultrasonic Doppler flowmeter

BY USING PLETHYSMOGRAPHBY USING PLETHYSMOGRAPH

BY FICK’S PRINCIPLE BY FICK’S PRINCIPLE

TYPES OF BLOOD FLOWTYPES OF BLOOD FLOW

1.LAMINAR / STREAM LINE1.LAMINAR / STREAM LINE

2.TURBULANCE2.TURBULANCE

1.LAMINAR / STREAM LINE1.LAMINAR / STREAM LINE

Blood flows in layers/lamina. Blood flows in layers/lamina. A thin layer of blood in contact with A thin layer of blood in contact with

vessels wall does not move , next vessels wall does not move , next layer move with a slow layer move with a slow velocity ,further next move with velocity ,further next move with higher velocity .higher velocity .

At center of vessel ,maximum At center of vessel ,maximum velocity .velocity .

It is unidirectional with out noise or It is unidirectional with out noise or sound .sound .

2.TURBULANCE2.TURBULANCE

Blood flows in different directions.Blood flows in different directions.

Blood mixes with in itself .there are Blood mixes with in itself .there are eddy currents in blood flow .eddy currents in blood flow .

This type of blood flow is This type of blood flow is accompanied by noise and sound.accompanied by noise and sound.

Normally in all blood vessels almost Normally in all blood vessels almost blood flow is stream lined or laminar blood flow is stream lined or laminar except ascending aorta and except ascending aorta and pulmonary trunk there is some pulmonary trunk there is some turbulence .turbulence .

Turbulence can be expressed and Turbulence can be expressed and determined in terms of determined in terms of REYNOLD’S NUMBERREYNOLD’S NUMBER . .

Reynolds numberReynolds number Re=v. d. Re=v. d. þ/ þ/ ήήv =mean velocity of blood flowv =mean velocity of blood flowd =diameterd =diameter þþ =density =densityήή =viscosity =viscosity

when velocity , diameter or density of when velocity , diameter or density of blood increases Reynolds’no increases.blood increases Reynolds’no increases.

When viscosity increases Reynolds’.no When viscosity increases Reynolds’.no decreases.decreases.

Reynolds' number is normally b/w Reynolds' number is normally b/w 2000-3000 when this number is more 2000-3000 when this number is more than 3000, blood flow become turbulent than 3000, blood flow become turbulent ..

In hyper dynamic circulation velocity In hyper dynamic circulation velocity increases Reynolds’no increases increases Reynolds’no increases (hyperthyroidism ,severe anemia )----(hyperthyroidism ,severe anemia )----anemic murmur anemic murmur

Example.Example.

Recording of blood pressure Recording of blood pressure korotkoff sound is heard korotkoff sound is heard when when brachial artery is occluded and brachial artery is occluded and blood flows through partially blood flows through partially occluded artery just beyond the occluded artery just beyond the cuffcuff sound appear with sudden sound appear with sudden incr in diameter. incr in diameter.

EXAMPLE.EXAMPLE.

In valvular stenosis , just beyond In valvular stenosis , just beyond the stenosed the stenosed

valve ,diameter incr----stenosed valve ,diameter incr----stenosed murmurs.murmurs.

Viscosity of blood incr Viscosity of blood incr Reynolds’no decr Reynolds’no decr no murmurs. no murmurs.

Viscosity of blood decrViscosity of blood decr Reynolds’no incr-- murmurs.Reynolds’no incr-- murmurs.

In anemia vol incr, mass decr,In anemia vol incr, mass decr,

Density =mass / volDensity =mass / vol

Density = mass decr / volume incrDensity = mass decr / volume incr

Decr density .Decr density .

FACTORS MAINTAINING FACTORS MAINTAINING VOLUME OF BLOOD FLOWVOLUME OF BLOOD FLOW

Blood flow is determined by five factors:Blood flow is determined by five factors: Pressure gradientPressure gradient Resistance to blood flowResistance to blood flow Viscosity of bloodViscosity of blood Diameter of blood vesselsDiameter of blood vessels Velocity of blood flowVelocity of blood flow

RESISTANCE TO BLOOD RESISTANCE TO BLOOD FLOWFLOW

RESISTANCE RESISTANCE Resistance is the impediment to Resistance is the impediment to

blood flow in a vessel,blood flow in a vessel, It cannot be measured by any It cannot be measured by any

direct means.direct means.

UNITS OF RESISTANCEUNITS OF RESISTANCE

It is calculated from It is calculated from measurements of blood flow and measurements of blood flow and pressure diff b/w two points in pressure diff b/w two points in the vesselthe vessel

If the pressure difference b/w two If the pressure difference b/w two points is 1 mm Hg and the flow is points is 1 mm Hg and the flow is 1ml/sec, the resistance is 1 1ml/sec, the resistance is 1 peripheral resistance unit or PRU.peripheral resistance unit or PRU.

Occasionally a resistance is Occasionally a resistance is expressed in basic physical unit expressed in basic physical unit called CGS (centimeters, grams, called CGS (centimeters, grams, seconds). This unit is seconds). This unit is

R = Dyne seconds/centimeterR = Dyne seconds/centimeter 5 5. .

TOTAL PERIPHERAL VASCULAR TOTAL PERIPHERAL VASCULAR RESISTANCERESISTANCE

The rate of blood flow through the entire The rate of blood flow through the entire circulatory system is equal to the rate of circulatory system is equal to the rate of blood pumping by the heart.blood pumping by the heart.

It is It is 100 ml/sec100 ml/secThe pressure diff from the syst The pressure diff from the syst

arteries to syst veins is arteries to syst veins is 100 100 mmHg. mmHg.

The resistance of entire circulatory The resistance of entire circulatory syst called the total peripheral syst called the total peripheral resistance is about 100/100,or 1 resistance is about 100/100,or 1 PRU.PRU.

TOTAL PULMONARY VASCULAR TOTAL PULMONARY VASCULAR

RESISTANCERESISTANCE the mean pulmonary arterial pressure the mean pulmonary arterial pressure

averages 16 mm Hgaverages 16 mm HgThe mean left atrial pressure averages 2 The mean left atrial pressure averages 2

mmHgmmHgThe net pressure difference is 14mmHgThe net pressure difference is 14mmHg when cardiac output is normal about 100 when cardiac output is normal about 100

ml /sec, the total pulmonary vascular ml /sec, the total pulmonary vascular resistance is about 0.14 PRU. resistance is about 0.14 PRU.

The mean left atrial pressure The mean left atrial pressure averages 2mmHgaverages 2mmHg

The net pressure difference is The net pressure difference is 14mmHg14mmHg

when cardiac output is normal when cardiac output is normal about 100ml/sec, the total about 100ml/sec, the total pulmonary vascular resistance is pulmonary vascular resistance is about 0.14 PRU. about 0.14 PRU.

CONDUCTANCE CONDUCTANCE

It is the measure of the blood flow It is the measure of the blood flow through a vessels for a given through a vessels for a given pressure differencepressure difference

Conductance is the reciprocal of Conductance is the reciprocal of resistanceresistance

Conductance =1 / ResistanceConductance =1 / Resistance It is expressed in ml / secIt is expressed in ml / sec/ mmHg/ mmHg

CHANGE IN DIAMETER OF A CHANGE IN DIAMETER OF A VESSEL CAN CHANGE ITS VESSEL CAN CHANGE ITS CONDUCTANCECONDUCTANCE

Slight change in the diameter of the Slight change in the diameter of the vessels cause tremendous change vessels cause tremendous change in the vessel ability to conduct in the vessel ability to conduct blood.blood.

e.g.e.g.There are three vessels with There are three vessels with

relative diameter of 1, 2 and 4 with relative diameter of 1, 2 and 4 with same pressure diff of 100 mmHg same pressure diff of 100 mmHg b/w two ends of the vessel.b/w two ends of the vessel.

The diameter incr only four fold, the flows The diameter incr only four fold, the flows are 1,16 and 256 ml/mm, which is a 256-are 1,16 and 256 ml/mm, which is a 256-fold incr in flow.fold incr in flow.

Conductance of the vessel incr in Conductance of the vessel incr in proportion to the fourth power of the proportion to the fourth power of the diameter, diameter,

In accordance with the following formula:In accordance with the following formula:Conductance DiameterConductance Diameter44

POISEUILLE’S LAWPOISEUILLE’S LAWPoiseuille’s law :Poiseuille’s law :

F = F = ∆P∆Prr44/8/8ήήll

F= rate of blood flowF= rate of blood flowP= the pressure difference b/w the ends of the P= the pressure difference b/w the ends of the

vesselvessel r= radius of the vesselr= radius of the vessel l= length of the vesselsl= length of the vessels ήή= viscosity of blood= viscosity of blood

The rate of blood flow is directly proportional to the fourth power of the radius of the vessel diameter of a blood vessel plays the greatest role of all factors in determining the rate of blood flow through the vessel.

IMPORTANCE OF THE VESSEL DIAMETER IMPORTANCE OF THE VESSEL DIAMETER

“FOURTH POWER LAW” “FOURTH POWER LAW”

In the systemic circulation 2/3 of the total In the systemic circulation 2/3 of the total systemic resistance to the blood flow is systemic resistance to the blood flow is arteriolar resistance in the small arterioles.arteriolar resistance in the small arterioles.

The internal diameters of the arterioles The internal diameters of the arterioles range from 4 micrometers to 25 range from 4 micrometers to 25 micrometers. micrometers.

From the fourth power law relates blood flow to the diameter of the vessel fourfold incr in vessel diameter can incr the flow 256-fold.

Arterioles responding to nervous signals or local tissue chemical signals with only small changes in diameter, either to completely turn off the blood flow to the tissue or other extreme to cause a increase in flow.

RESISTANCE TO BLOOD FLOW IN SERIES RESISTANCE TO BLOOD FLOW IN SERIES AND PARALLEL VASCULAR CIRCUITS.AND PARALLEL VASCULAR CIRCUITS.

The arteries, arterioles, capillaries, The arteries, arterioles, capillaries, venules, and veins are collectively venules, and veins are collectively arranged in series.arranged in series.

In this arrangement, flow through each In this arrangement, flow through each vessel is the same and total resistance vessel is the same and total resistance to the flow is equal to the sum of the to the flow is equal to the sum of the resistance to the flow.resistance to the flow.

R=R1+R2+R3+R4----R=R1+R2+R3+R4----

Blood vessel branch extensively to form parallel Blood vessel branch extensively to form parallel circuits that supply blood to many organs and circuits that supply blood to many organs and tissues of the body.tissues of the body.

This parallel arrangement permits each tissue to This parallel arrangement permits each tissue to regulate its own blood flow, to a great extent, regulate its own blood flow, to a great extent, independently of flow to other tissues. independently of flow to other tissues.

For blood vessel arranged in parallel, the For blood vessel arranged in parallel, the total resistance to blood flow is expressed total resistance to blood flow is expressed as:as:

1/Rtotal =1/R1+1/R2+1/R3+1/R41/Rtotal =1/R1+1/R2+1/R3+1/R4

Greater amount of blood will flow through Greater amount of blood will flow through this parallel system then through any this parallel system then through any individual blood vessels.individual blood vessels.

Total resistance is far less than the Total resistance is far less than the resistance of any single blood vessel.resistance of any single blood vessel.

Many parallel vessels make it easier for blood to flow through the circuit b/c it provides another pathway, or conductance, for blood flow.

The total conductance for the blood flow is the sum of the conductance of each parallel pathway.

C total = C1+ C2 + C3 + C4