Post on 06-Jul-2018
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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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