18 vessels and flow dynamics

8/12/2019 18 Vessels and Flow Dynamics

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Blood Vessels-Chps. 14-19

Transporting nutrients and oxygen to the tissues

Transporting waste products away from the tissues

Transporting hormones

Powered by the pumping action of the heart

HeartArteries-

Elastic

muscular

Arterioles

Capillaries

Venules

veins


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Lecture outlineI. Review anatomy of vessels

A. Arteries

B. Elastic

C. Muscular

D. Arterioles- resistance vessels

E. Capillaries- exchange vessels

F. Veins- capacitance vessels

II. Ohms law is flow = change inpressure/ resistance

A. Blood Flow

i. Laminar vs. turbulent

B. Pressure- blood pressure

i. Mean arterial pressure (MAP)

ii. Central venous pressureiii. Pulse pressure

C. Resistance

i. Factors of resistance-Poiseuilles law

III. Getting to know Flow better

A. Velocity

B. Control of flow

i. Autoregulation

ii. Nervous system

iii. Endocrine-kidney (unit 4)

IV. Exchange of extracellular fluid- themicrocirculation

A. Starling Forces

i. Capillary hydrostatic pressure

ii. Interstitial hydrostatic pressure

iii. Capillary colloid osmoticpressure

iv. Interstitial colloid osmoticpressure

B. Lymphatic drainage

C. Causes of edema


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Arteries Branch and diverge

Blood away from heart

Walls have 3 tunics

Tunica intima-simplesquamous endothelium

Tunica media-circularsheets of smooth muscle(vasodilation and

vasoconstriction- diametercontrolled by local factorsand sympathetic NS)

Tunica adventitia-connective tissue with

collagen and elastin inlongitudinal arrangement


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Arteries Elastic- largest arteries near

heart Low resistance

More elastin interspersed withthe tunica media

Can distend and recoil backto pump blood (maintain

blood pressure) Muscular-

Supply organs

Can regulate diameter ofartery to control blood supplyto organ

Thick tunica media with moresmooth muscle

External and internal elasticlamina.


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Arterioles

Smallest arteries-resistance arteries

THICK tunica media- littlecompliance

Diameter controlled bylocal factors (intrinsic) andsympathetic division(extrinsic) and long-termfactors (hormones)

Metarterioles- justupstream of capillary beds.

Precapillary sphincters-controls blood reaching

capillary bed.


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Capillaries

Smallest blood vessels

Single layer of endothelialcells and basal lamina

Renew interstitial fluid- pick

up wastes, drop off nutrients,etc.

Most cells only 20-30 maway

Over 10 billion of them.


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Types of Capillaries

Continuous

Most common and leastpermeable

Intercellular clefts andtranscellular cytosis allows forexchange of molecules

Abundant in skin and muscle

Fenestrated

Holes in the endothelialmembrane

Found in kidney

Sinusoidal/ discontinuous

Most permeable and leastcommon

Big holes in endothelialmembranes

Big clefts between cells

Liver, spleen, and bone marrow

especially


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Veins

Volume reservoir- capacitance vessels(60-70%)

of blood

Have vasomotor control.

Valves in abdominal veins prevent backflow

Skeletal muscle pump and respiratory pump


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Vascular Distensibility= is the fractional increase involume for each mmHg rise in pressure times original volume- veins are

8x more distensible

0 mmHg 100 mmHg

Artery

Vein 800 ml

100 ml

In hemodynamics, its more valuable to know the total quantity of blood that can be

stored in a given portion of the circulation for each mmHg pressure rise.

Capacitance= increase in volume/increase in pressureThe capacitance of veins is 24 times that of arteries.


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Ohms Law

Q=P/R

Flow(Q) through a bloodvessel is determined by:

1) Thepressure

difference (

P) betweenthe two ends of thevessel Directly related to flow

2) Resistance(R) of thevessel Inversely related to flow

Can you rearrange theequation above and solve

for P? Solve for R?


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Blood Flow (L/min)

Blood flowis the quantity ofblood that passes a givenpoint in the circulation in agiven period of time.

Unit of blood flow is usuallyexpressed as milliliters (ml) orLiters (L) per minute.

Overall flow in the circulationof an adult is 5 liters/minwhich is the cardiac output.

CO= HR X SV

70 b/min x 70 ml/beat

=4900ml/min


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Laminar Vs. Turbulent Blood Flow

Turbulent flow

Causes of turbulent blood flow:

high velocitiessharp turns in the circulation

rough surfaces in the circulation

rapid narrowing of blood vessels

Laminar flow is silent, whereas turbulent flow tend to cause murmurs.

Murmurs or bruitsare important in diagnosing vessels stenosis, vessel shunts, and

cardiac valvular lesions.


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Effect of Wall Stress on Blood Vessels

Turbulent flow increases resistance and wall stress

Nitric oxide released by endothelial cells to reduce the stress


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Blood Pressure

The driving force Stephen Hales1733

Blood pressure (hydrostaticpressure) is the forceexerted by the blood againstany unit area of vessel wall.

Measured in millimeters ofmercury (mmHg). A pressureof 100 mmHg means theforce of blood was sufficientto push a column of mercury100mm high.

All vessels have itbutwere usually addressingarteries when we refer to it.


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contracted

Ejected Blood

When the LV contracts more blood enters the

arterial system than gets pushed onward.

This causes the arteries to stretch andpressure within them to rise. The highest

pressure achieved is known as the systolic

pressure.


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relaxed Recoil of the elastic artery

As the LV relaxes, the stretched arterial walls recoil

and push the contained blood onward through the

system. As they recoil, the amount of bloodcontained decreases as does pressure. The lowest

pressure achieved just before the next contraction is

the diastolic pressure.


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Mean Arterial Pressure (MAP)

Is an average, but not a simplearithmetic average

Heart spends longer in diastole

than systole Value is significant- why?

The difference between the meanarterial pressure and the pressure

in the venous system drives theblood through the capillary beds.

MAP= .4 (systolic) + .6 (diastolic)=96mmHg

Venous pressure is about 2mmHg

FLOW = arterial - venous pressure (P)resistance (R)

100 mmHg

R = .1mmHg/ml/min

A

20 mmHg

100 mmHg

R = .1mmHg/ml/min

B

0 mmHg

FLOW = 1000 ml/min

FLOW = 800 ml/min


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Central Venous Pressure Pressure in the right atrium is called

central venous pressure. determined by the balance of the heart

pumping blood out of the right atriumand flow of blood from the large veinsinto the right atrium.

normally 0 mmHg, but can be as high as

20-30 mmHg. More vigorous heart contraction (lowerCVP).

Less heart contraction (higher CVP)

Factors that increase CVP:

- increased blood volume

- increased venous tone (peripheralpressure)

- dilation of arterioles

- decreased right ventricular function

- Skeletal and respiratory pumps

Figure 15-9; Guyton and Hall


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Arterial Pulsations and Pulse Pressure

The height of the pressure pulse is thesystolic pressure (120mmHg), while the

lowest point is the diastolic pressure

(80mmHg).

The difference between systolicand diastolic

pressure is called thepulse pressure

(40mmHg).Systolic Pressure

Diastolic Pressure

Pulse Pressure}


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Factors Affecting Pulse Pressure

Stroke volumeincreases in

stroke volume increase pulse

pressure, conversely decreases

in stroke volume decreasepulse pressure.

Arterial compliancedecreases in

compliance increases pulse

pressure; increases in compliance

decrease pulse pressure.Figure 15-5; Guyton and Hall


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Diastolic

Pressure

Systolic PressureCardiac

output

Total

Peripheral

resistance

Mean

Pressure

Time

Strokevolume

Arterial

compliance

}Pulse Pressure

HR x SV = CO = MAP/ TPR

MAP= (0.4 SP) + (0.6 DP)

PP= SP- DP

Stroke

volume


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Damping of PulsePressures in thePeripheral Arteries

The intensity of pulsationsbecomes progressively less in the

smaller arteries.

The degree of damping is

proportional to the resistance ofsmall vessels and arterioles and the

compliance of the larger vessels.Elastic arteries:

large radii, low resistance, some

pressure reservoir

Muscular arteries

Smaller radii

Little more resistance

More pressure reservoir

Arterioles

Thick tunica media vs. radius

major pressure reservoirFigure 15-6; Guyton and Hall

Whats an anatomical reason for

why the pressure fluctuation

disappears here?


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Blood Pressure Profile in the CirculatorySystem

Systemic Pulmonary

Capillaries

Pre

ssure

(mmHg)

0

2 0

4 06 0

8 0

1 0 0

1 2 0

Venules

Smallveins

Largeveins

Pulmonaryarteries

Capillaries

Pulm

onaryveins

Circulatory pressure- averages 100mmHg

Arterial blood pressure-100-35mmHg

Capillary pressure- 35mmHg at beginning and 10-15mmHg at end

Venous pressure-15-0mmHg

Large pressure drop across the arteriolar-capillary junction


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How Would a Decrease in Vascular Resistance Affect

Blood Flow?

FLOW = P

RESISTANCE

FLOW = P

RESISTANCE

Conversely,

Therefore, flow and resistance are inversely related!

Resistance is the impediment

to blood flow in a vessel. Can not be measured directly

ResistanceR = P = mmHg

Q ml/min


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Resistance makes a difference for the two

sides of the heart!

Lets say the CO (flow) is roughly100ml/sec (easier math).

To calculate systemic resistance vs.pulmonary resistance we need toknow pressure differences.

Pulmonary resistance is 16-2/100 Systemic resistance is 100/100

So, CO is same on each side ofheart (has to be!), but right sidegenerates less pressure due to lower

resistance (1/7th than systemic).

16mmHg

2mmHg

100 mmHg

0mmHg

R = P = mmHg

Q ml/min


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Factors of Resistance

Poiseuilles Law = Q =_ Pr48l

Blood viscosity Total vessel length

Vessel diameter

Resistance

(length)(viscosity)

(radius)4


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Viscosity

What are the major

contributors to blood

viscosity?

As viscosityincreases, resistance

will

An increase in plasma

EPO will cause

resistance to




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Total Vessel Length

Longer the vessel.....more

opportunity for resistance.

Radius


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So, lets review:

Blood Flow is volume flowing/time Ohms Law Blood Flow (Q) =P/ R

Increase pressure-increase blood flow

Decreaseresistance-increase blood flow

Increaseresistance-decrease bloodflow Vessel diameter

Viscosity length

Turbulence (usuallyresult of an occlusionreducing vesseldiameter unevenly)

P1 P2

P= P1-P2

Blood flow in center is fastest-

because that is the area of least

resistance

As resistance decreases, flow will

As the pressure gradient increases, flow will

Which does the heart influence more: pressure gradient

or resistance?

Flow (amount of blood/time) MUST


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Flow (amount of blood/time) MUSTbe the same through vessels in

series!If a pipes diameter changes over its length, a fluid will flow throughnarrower segments faster than it flows through wider segments

because the volumeof flow per second must be constant throughout

the entire pipe.

Flow (volume/time) vs. velocity (distance/time) are NOT synonyms!


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If capillaries have such a small diameter,

why is the velocity of blood flow so slow?

We need slow blood flow in the capillariesthe exchange vessels

Aorta >Arterioles > Small veins >Capillaries


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Control of blood flow through

vessels- Why is this important? Perfusion vs. ischemia vs.

hypoxia vs. anoxia vs.infarction

Tissue PerfusionDependent on:

Cardiac output Peripheral resistance

Blood pressure

Regulation of perfusiondependent on: Autoregulation (Acute, local,

intrinsic) Neural mechanisms (acute)

Endocrine mechanisms (long-term)

http://www.flometrics.com/services/artery/

Autoregulation the automatic adjustment of blood flow to


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Autoregulation the automatic adjustment of blood flow toeach tissue in proportion to the tissues requirements at any

instant even over a wide range of arterial pressures

Working

Muscle

Tissue

active hyperemia:

when tissues

become active,

blood flowincreases.

Aka: intrinsic

metabolic

vasodilation

Tissue CO2levels rise

Tissue O2levels fall

Tissue temp. rises

Lactic acid levels rise

CO2removed

Arteriolesserving tissue

vasodilate and

precapillary

sphincters relax

Increased blood

flow to tissue

Lactic acid removed

Heat removed O2delivered

Now arterioles

will

vasoconstrict

and

precapillary

sphincterscontract

Autoregulation of Blood Flow to specific


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Autoregulation of Blood Flow to specific

tissues Vasodilator agents

HistamineNitric oxide

Elevated temperatures

Potassium/hydrogen ions

Lactic acid

Carbon dioxideAdenosine/ ADP

VasoconstrictorsNorepinephrine and

epinephrine

AngiotensinVasopressin (ADH)

Thromboxane


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Arterial Pressure = Cardiac Output x Total Peripheral Resistance

Long Term BP control- hormonal

Short term BP control- nervous

Other ways to ultimately change blood flow throughout the bodyis to change

Pressure and Resistance


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Brain Centers involved in Short

Term BP Control

Vasomotor Adjusts peripheral

resistance by adjustingsympathetic output to the

arterioles

Cardioinhibitory- transmitssignals via vagusnerve to

heart to decrease heart rate.(parasympathetic)

Cardioacceleratory/contractility-sympathetic

output

S


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Vasomotor control: Sympathetic Innervationof Blood Vessels

Sympatheticnerve fibers

innervate all vessels except

capillaries and precapillary

sphincters (precapillary

sphincters follow local control)

Innervation of small arteriesand arterioles allow

sympathetic nerves to increase

vascular resistance.

Large veins and the heart arealso sympathetically innervated.



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Anatomy of the Baroreceptors spray type nerve endings located in

the walls of the carotid bifurcation

called the carotid sinus and in thewalls of the aortic arch-pressoreceptors that respond tostretch.

Signals from the carotid sinus are

transmitted by the glossopharyngealnerves .

Signals from the arch of the aorta aretransmitted through the vagus into theNTS.

Important inshort termregulation of arterial pressure. They are unimportant in long term

control of arterial pressure becausethe baroreceptors adapt.



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Response of the Baroreceptors toArterial Pressure

Baroreceptors respond to changesin arterialpressure.

As pressureincreases the number of impulsesfrom carotid sinus increaseswhich results in:

1) inhibition of the vasoconstrictor2) activation of the vagal center

Constrict

Common Carotids

Constrictors

Pressure at

Carotid Sinuses

Arterial Pressure




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BP rises

Detected bybaroreceptors in

aortic arch &

carotid sinus

Info sent to cardiac

and vasomotor

centers

Decreased

vasomotor

activity

Decreased PR

Increased

cardioinhibitory

activity

Decreased

cardioacceleratory

activity

Decreased CO

Decreased

BP

Decreased NE

release on

arterioles

Vasodilation

Increased vagus

activity

Increased ACh

release on heart

Decreased SV

and HR

Decreased NE

release on heart


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Nervous control also found in the heart-

Bainbridge Reflex

Prevents damming of blood in veins, atria and

pulmonary circulation.

Increase in atrialpressure increases heart

rate.

Stretch of atria sends signals to VMC via

vagal afferents to increase heart rate and

contractility.

Vasomotor

CenterHeart rate

Contractility

Atrial

Stretch

Vagal

afferents


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The Microcirculation-chapter

16 Important in the transport of nutrients to

tissues.

Site of waste product removal.

Over 10 billion capillaries with surface

area of 500-700 square meters perform

function of solute and fluid exchange.

Figure 16-1;

Guyton and Hall


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Most substances are

exchanged via diffusion

Concentration

differences

across capillary

enhances

diffusion.


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Capillary hydrostatic pressure (Pc)-tends to force fluid

outward through the capillary membrane.(30 mmHg arterial; 10mmHg venous- average 17.3mmHg)

Interstitial fluid hydrostatic pressure (Pif)- opposes filtrationwhen value is positive (but its not positive-- due tolymphatic drainage!3mmHg).


Determinants of Net Fluid Movement acrossCapillaries-Starling forces


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Determinants of Net Fluid Movement acrossCapillaries-Starling forces

Plasma colloid osmotic pressure (c)- opposes filtrationcausing osmosis of water inward through the membrane Colloid osmotic pressure of the blood plasma. (28mmHg)

75% from albumin; 25% from globulins

Interstitial fluid colloid pressure (if) promotes filtration bycausing osmosis of fluid outward through the membrane Colloid osmotic pressure of the interstitial fluid. (8mmHg)

3gm%



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If capillary BP is greater than capillary


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Capillary BP

Capillary OP

Pres

sure

Distance along the capillary

Arterial end Venous end

Filtration

Reabsorption

If capillary BP is greater than capillary

OP, there will be net movement of fluid

out of the capillary.

If capillary BP is less than capillary OP, there will be net movement of

fluid into the capillary.

Filtration= KfX (Pc- Pif - c+ if)

L h ti l ll t


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2ml/min Excess

tissue fluid is

returned to the

blood vessels via thelymphatic system!

Lymphatic vessels collectlymph from loose connectivetissue Fluid flows only toward the

heart Collect excess tissue fluid

and blood proteins andcarry to great veins in theneck

All three tunics NO pump!

Valves!

contains plasma, water,ions, sugars, proteins,

gases, amino acids- iscolorless, but low in proteincompared to blood

Lymph can containhormones, bacteria, viruses,cellular debris, travelingcancer cells, macrophages


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Causes of Edema

Excessive accumulation of tissue

fluid.

Edema may result from:

High arterial blood pressure.

Venous obstruction.

Leakage of plasma proteinsinto interstitial fluid.

Valve problems

Cardiac failure

Decreased plasma protein.

Obstruction of lymphatic

drainage. Elephantiasis-

Wuchereria bancrofli

I would see your homework packet and study page 303 of Guyton and Hall!

U b l d V t i l O t t


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Unbalanced Ventricular Output


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Unbalanced Ventricular Output

ISF


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Hypertension capillary BPISF

formation

Starvation

Lack of

dietary

protein

in

plasma

albumin

capillary

OP

Histamine

ISF

formation

capillary

permeability

Vasodilation capillary BP

ISF

formation

Burn/crush capillary ISF


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Burn/crush

injury

capillary

permeability Cap OPISF

formation

L. Ventricle

failure

Backup of blood in

pulmonary circuit

pulmonary

capillary BP

ISF

formation

Decreased blood

flow in systemic

circuit

systemic

capillary BP

ISF

formation

18 vessels and flow dynamics

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