Control of Tissue Blood Flow 19 Med

8/16/2019 Control of Tissue Blood Flow 19 Med

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Control of blood tissue bloodow

Faisal I. Mohammed, MD,PhD


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Objectives

• List factors that affect tissue blood flow.

• Describe the vasodilator and oxygen demand

theories.

• Point out the mechanisms of autoregulation.

• Describe how angiogenesis occurs.• Inter-relat how various humoral factors affect

blood flow.


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Local Control of BloodFlow

Each tissue controls its own blood flow in proportion

to its needs.

Tissue needs include:1) delivery of oxygen to tissues

2) delivery of nutrients such as glucose, aminoacids, etc.

3) removal of carbon dioxide hydrogen and othermetabolites from the tissues

) trans!ort various hormones and othersubstances to different tissues

"low is closely related to metabolic rate of tissues.


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Variations in issue BloodFlow

#rain 1 $%% &%'eart 2%% $%#ronchi 2 1%% 2&

(idneys 22 11%% 3%*iver 2$ 13&% +& ortal -21) -1%&%) rterial -) -3%%)/uscle -inactive state) 1& $&% #one & 2&% 30in -cool weather) 3%% 3Thyroid gland 1 &% 1%drenal glands % .&2& 3%%ther tissues 3.& 1$& 1.3

Total 1%%.% &%%%

Percent ml/minml/min/100 gm


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!cute Control of Local BloodFlow

4ncreases in tissue metabolism lead to increases

in blood flow.

5ecreases in oxygen availability to tissuesincreases tissue blood flow.

Two ma6or theories for local blood flow are:

1) The vasodilator theory

2) Oxygen demand theory


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Tissue Metabolism Blood Flow

Effect of Tissue Metabolic Rate on TissueBlood Flow


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Effect of Tissue xygen concentration on#lood "low

Tissue Oxygen Concentration Blood Flow


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"elationshi# between Pressure,Flow, and "esistance

"789

Flow -") through a blood vessel is

determined by:

1) The pressure difference -8 ) between

the two ends of the vessel

2) Resistance -) of the vessel


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Vasodilator heor$ for BloodFlow Control

*ocal ;asodilators: Adenosine, CO2, Lactic acid, ADP compounds,Histamine, K + ions, H+ ions,

Prostacyclin, rady!inin, and "itrous o#id $"O%

TISSUE

METABOLISM

BLOOD

FLOW

ARTERIOLERESISTANCE

RELEASE OF

VASODILATORS


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TISSUE METABOLISM

OR

OXYGEN DELIVERYTO TISSUES

ARTERIOLE

RESISTANCE

TISSUE

OXYGEN

CONCENTRATION

BLOOD

FLOW

%&$'en Demand heor$ forBlood Flow Control


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!utore'ulation of Blood Flow

Autoregulation - ability of a tissue to maintain blood flow

relatively constant over a wide range of arterial pressures.


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Blood Flow !utore'ulation heories

Metabolic theory suggests that as arterial !ressure is

decreased, oxygen or nutrient delivery is decreased

resulting in release of a vasodilator.

Myogenic theory !ro!oses that as arterial !ressure falls

the arterioles have an intrinsic !ro!erty to dilate in

res!onse to decreases in wall tension.


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La#lace(s Law) M$o'enicmechanism

&'"()O" * P'((' - AD)(

$dynes/cm% $dynes/cm2% $cm%

PRESSURE TENSION RADIUS

PRESSURE TENSION RADIUS

(to maintain tension constant)

(to maintain tension constant)


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Lon'*term "e'ulation of BloodFlow

*ongterm regulatory mechanisms which

control blood flow are more effective than

acute mechanism.

*ongterm local blood flow regulation occurs

by changing the degree of vascularity of

tissues -size and number of vessels).

Oxygen is an im!ortant stimulus for regulating

tissue vascularity.


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Long-term Regulation of Blood Flow


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!n'io'enesis

Angiogenesis is the growth of new blood vessels.

ngiogenesis occurs in res!onse to angiogenic factors

released from:1) ischemic tissue

2) ra!idly growing tissue

3) tissue with high metabolic rates

/ost angiogenic factors are small peptides such as

vascular endothelial cell growth factors -;E="),

fibroblast growth factor -"="), and angiogen.

Exam!le of angiogenesis is Retrolental Hyperplasis


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+umoral "e'ulation of BloodFlow

;asoconstrictors

>ore!ine!hrine and e!ine!hrine

ngiotensin

;aso!ressinEndothelin

;asodilator agents

#radyinin0erotonin

'istamine

rostaglandins

>itric oxide


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#lood "low: 0eletal /uscle egulation

/uscle blood flow can increase tenfold or more during !hysical activity as vasodilation occurs *ow levels of e!ine!hrine bind to β rece!tors


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rteriole esistance:


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Blood Flow) Brain

#lood flow to the brain is constant, as neurons are

intolerant of ischemia

/etabolic controls ? brain tissue is extremely sensitiveto declines in !', and increased carbon dioxide causes

mared vasodilation

/yogenic controls !rotect the brain from damaging

changes in blood !ressure

5ecreases in / cause cerebral vessels to dilate to

insure ade@uate !erfusion

4ncreases in / cause cerebral vessels to constrict


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#lood "low: #rain

The brain can regulate is own blood flow in certain

circumstances, such as ischemia caused by a tumor

The brain is vulnerable under extreme systemic !ressure changes

/ below %mm 'g can cause synco!e -fainting)

/ above 1% can result in cerebral edema


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Blood Flow) -in

#lood flow through the sin: 0u!!lies nutrients to cells in res!onse to oxygen need ids in body tem!erature regulation and !rovides a blood

reservoir #lood flow to venous !lexuses below the sin surface:

;aries from &% ml9min to 2&%% ml9min, de!ending u!on bodytem!erature

4s controlled by sym!athetic nervous system reflexes initiated by tem!erature rece!tors and the central nervous system


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Blood Flow) Lun's

#lood flow in the !ulmonary circulation is unusual in that: The !athway is short rteries9arterioles are more lie veins9venules -thinwalled,

with large lumens) They have a much lower arterial !ressure -29A mm 'g

versus 12%9A% mm 'g) The autoregulatory mechanism is exactly o!!osite of that in

most tissues *ow oxygen levels cause vasoconstrictionB high levels !romote vasodilation

This allows for !ro!er oxygen loading in the lungs


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Blood Flow) +eart

mall essel coronar$ circulation is inuenced b$)

!ortic #ressure

he #um#in' actiit$ of the entricles Durin' entricular s$stole)

Coronar$ essels com#ress

M$ocardial blood ow ceases

tored m$o'lobin su##lies su/cient o&$'en Durin' entricular diastole, o&$'en and nutrients

are carried to the heart


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Control of Tissue Blood Flow 19 Med

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