K.5 CVS-K5_Dynamics of Blood & Lymph Flow_edited

7/30/2019 K.5 CVS-K5_Dynamics of Blood & Lymph Flow_edited

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Dynamics of

Blood Flow

Departemen Fisiologi

Fakultas Kedokteran

Universitas Sumatera Utara


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Introduction

blood vessels are a closed system of conduits thatcarry blood from heart to tissues and back toheart.


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FUNCTIONAL MORPHOLOGY


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Vessel Size and Composition


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Arteries

&Arterioles

Walls ; outer layer (adventitia) : connective tissue

middle layer (media) : smooth muscle

inner layer (intima) : endothelium & underlying

connective tissue


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Aorta and otherlarge arteriescontain relatively

large amount ofelastic tissue,arterioles containless elastic tissuebut much moresmooth muscle.

Arterioles are major site of resistance to

blood flow, and small changes in their

caliber cause large changes in the total

peripheral resistance.


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Capillaries


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Active & Inactive Capillaries In active tissues,

metarterioles andprecapillary sphinctersdilate, is due to action ofvasodilator metabolites

formed in active tissue and adecrease activity ofsympathetic vasoconstrictornerves

In resting tissues, most ofcapillaries are collapsed, andblood flows through thethoroughfare vessels from

the arterioles to the venules


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total area of all capillary walls in body exceeds6300 m2 in adult

walls, which are about 1 um thick, are made up ofa single layer of endothelial cells


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Left: Continuous type of

capillary, found in muscle.

: 10 nm

Right: Fenestrated type of

capillary, found in

endocrine glands,

intestinal villi, and parts of

kidneys, : 20 100 nm


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Pericytes, cells found in capillaries and

postcapillary venule, contractile and release vasoactive agents

synthesize and release constituents of

basement membrane and extracellularmatrix

regulate of flow through junctions between

endothelial cells, particularly ininflammation


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Arteriovenous (A V) Anastomoses

or Shunt

short channels that connect arterioles to

venules, by passing capillaries

In fingers, palms, and ear lobes of humans and

paws, ears

have thick, muscular walls and are abundantly

innervated, presumably by vasoconstrictor

nerve fibers


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Venules & Veins

walls are only slightly thicker than

capillaries. walls are also thin and easily distended

relatively little smooth muscle,

venoconstriction is produced by activitynoradrenergic nerves to veins and bycirculating vasoconstrictors such asendothelins

intima of limb veins is folded at intervals toform venous valves that prevent retrogradeflow


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VENOUS CIRCULATION

Venous flow is aided by heartbeat, increase innegative intrathoracic pressure during eachinspiration, and contractions of skeletal muscles

that compress the veins (muscle pump) Heartbeat, during systole contribute venous

return especially at rapid heartbeat

Thoracic Pump, during inspiration intrapleural

pressure falls from -2.5 to -6 mm Hg, drop invenous pressure during inspiration aids venousreturn


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Muscle Pump, Rhythmic

contractions of the leg muscles

while the person is standing

serve to lower the venous

pressure in the legs to less than

30 mm Hg by propelling bloodtoward the heart.

In patients with varicose veins

because their valves areincompetent, may develop

stasis and ankle edema


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Angiogenesis

formation of new blood vessels, important

during fetal life and growth to adulthood.

many factors are involved in angiogenesis;

protein growth factor vascular endothelial

growth factor (VEGF).


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Flow( ) is the volume that passesthrough a region in a unit time.

Flow through the vascular system is

produced by the arterio-venous

pressure difference and is proportionalto the pressure difference.

Haemodynamics of

Pressure and Flow

Q

Q =Q

t

Q =P P

R

a v


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Resistance is Dependent on Diameter

Resistance falls with increasing radius of the blood vessel, andincrease with increasing blood viscosity.

Under ideal conditions the resistance of a tube is described by

Poiseuilles law.

Resistance to blood flow is determined not only by radius of

the blood vessels (vascular hindrance) but also by viscosity ofthe blood.

Rl

r4

Where R= resistance

= viscosity

r= radius

l= length

Halving the radius of an arter io le

inc reases resistance by 16 fold .


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Factors affecting resistance

Vascular resistance (largest

impact)

friction between blood and

vessel walls

related to blood vessel

diameter(and length )

The narrow arterioles

(and capillaries)

generate the largest

vascular resistancevasoconstriction: contraction to reduce diameter

vasodilation: relaxation to enlarge diameter


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ViscosityThe thicker the liquid the more resistance

it creates

Blood is thicker than water therefore has

higher resistance (presence of cells,

proteins)

Plasma is about 1.8 times as viscous as

water, whereas whole blood is 3-4 times as

viscous as water.


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Viscosity of Blood

The viscosity of wholeblood is dependent on the

haematocrit.

Anaemia can reduce bloo d

viscosity .

Polycythaemia increases

the haematocrit, blood

viscosity and resistance.

viscosity increases are

seen in diseases in plasmaproteins such as the

immunoglobulins and in

hereditary spherocytosis

(red blood cells are

abnormally rigid)


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Turbulence

Blood flow is laminar

Faster flow at centre, slowest near

vessel wall

Increased turbulent flow occurs at

very high flow rates or as a result of

vascular disease

Occurs normally during blood flow

between chambers (characteristic

sound) Higher turbulent flow increases

resistance (and elevated BP required to

maintain flow can further damage

walls)


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R = Re = Reynolds

= densitas cairan

D = diameter pebuluh

V= kecepatan aliran

= viskositas cairan

Turbulence is also related to the diameter of

the vessel and the viscosity of the blood.

Re < 2000 -> tidak terjadi turbulenRe > 3000 -> turbulen


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Resistance Along

the Vascular

System

Resistance is

greatest in

arterioles.

Total resistance is

controlled by arteriolar

resistance.

Arterioles control

perfusion through

organs and the

distribution of cardiac

output.


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Pressure and

Volume in the

Circulation

Pressure is pulsatile

in the arteries but

steady in the

capillaries and veins.

Pressu re falls along

the ci rcu i t wi th the

greatest fal l acro ss

arterioles.

Volume is greatest in

the venous system.

At any time most of

the blood is in veins


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Laminar Flow flow of blood in straight blood vessels, like flow of

liquids in narrow rigid tubes, is normally laminar(streamline).

Laminar flow occurs at velocities up to a certaincritical velocity. At or above this velocity, flow isturbulent. Streamline flow is silent, but turbulentflow creates sounds.


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Average velocity

Velocity : displacement per unit time (eg,

cm/s),

Flow : volume per unit time (eg, cm3/s)

Velocity (v) is proportionate to flow (Q)

divided by the area of the conduit (A)

if flow stays constant, velocity increases

in direct proportion to any decrease in A


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Top: Effect of constriction (C) on the profile of

velocities in a blood vessel. Bottom: Range ofvelocities at each point along the vessel.


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Velocity and Area in the

Vascular System

Total cross-sectionalarea of the vascular

system is greatest in

the capillaries and

lowest in the large

vessels.

Because f low is

cons tant the blood

veloci ty is fastest in

the large vessels and

slow est in capi l lar ies.

A erythrocyte spends

0.5 to 1 second in the

capillaries.


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Law of Laplace

tension in the wall of a

cylinder (T) is equal to the

product of the transmural

pressure (P) and the radius(r) divided by the wall

thickness (w).

T =Pr/w


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Arterial Pressure

Pulse pressure, the difference between the

systolic and diastolic pressures (SP DP), is

normally about 50 mm Hg (120 80 mmHg)

Mean pressure is the average pressure

throughout the cardiac cycle, equals diastolic

pressure plus one-third of the pulse pressure

= DP + 1/3 (PP)


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Effect of Gravity

Pressure in any vessel below heart level is

increased and in any vessel above heart level

is decreased by the effect of gravity.

Besarnya efek gravitasi-hasil kali densitas

darah, akselerasi akibat gravitasi, dan jarak

vertikal di atas atau di bawah jantung 0,77

mmHg/cm pada densitas darah normal.


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Methods of Measuring Blood

Pressure

Auscultatory Method

Palpation Method


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Measuring Venous Pressure

Central venous pressure can be measured directlyby inserting a catheter into the thoracic great veins.

Peripheral venous pressure correlates well with

central venous pressure in most conditions Perkiraan tekanan vena sentral, dengan mengukur

distensi vena jugularis eksterna pada waktu pasien

berbaring dengan kepala sedikit di atas jantung. Jarak vertikal antara atrium kanan dan tempat vena

yg kolaps (tempat dgn besar tekanan nol) adalah

tekanan vena dalam mm darah.


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Let it beat!

K.5 CVS-K5_Dynamics of Blood & Lymph Flow_edited

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