Regional Circulations I, II Flashcards
Purpose of Autoregulation of arteriolar resistance?
maintain constant flow during pressure ∆
Hyperemia is?
Achieved how?
Increased blood flow to body part
altering arteriolar resistance
Active Hyperemia is a response to what?
↑ metabolic activity in tissues
Reactive Hyperemia is a response to what?
↓ O2 delivery
(U) 2º to ↓ flow from obstruction
Myogenic Hypothesis of Pressure
↑ P -> ↑ stretch -> opens stretch-activated Ca2+ -> ↑ Ca2+ -> contracts vessels -> ↓ flow
Opposite occurs w/ ↓ P
Myogenic hypothesis explains?
autoregulation
does not explain active or reactive hyperemia
Metabolic Hypothesis says what happens when ↑ in Pressure?
↑ P -> ↑ flow -> ↑ O2 delivery -> removes metabolic byproducts -> vasoconstriction -> ↓ flow
Metabolic Hypothesis says what happens when ↓in Pressure?
↓ P -> ↓ flow -> ↓ O2 delivery -> ↑ metabolic byproducts -> relaxes vessels -> ↑ flow
Metabolic hypothesis explains?
active and reactive hyperemia and autoregulation
Arteriolar Resistance in Skeletal mm at Rest
arteriolar resistance ↑ due to:
↓ in dilation mediators,
resting symp vasoconstriction of α1 receptors
Effects of symp stim of skeletal mm
epinephrine activates β2 receptors ->
vasodilation ->
metabolic byproducts (adenosine, CO2, K)
α1 adrenergic receptors:
location
chem mediator
result
all arteriolar smooth mm
Norepi (from symp fibers),
Epi (from adrenal medulla)
Vasoconstriction
β2 adrenergic receptors:
location
chem mediator
result
arteriolar smooth mm heart, skeletal
Epi (from adrenal medulla)
Vasodialation
Coronary Circulation:
Reactive Hyperemia in LV
↑ LV wall pressure during systole occludes coronary circulation ->
↓ L coronary vascular resistance ->
↑ L coronary flow during diastole
Symp stim of cardiac mm
activates β1 rec -> ↑ chrono and inotropics -> ↑ metabolism/byproducts -> ↓ O2 -> vasodilation
Symp stim of coronary vasculature
activates α1 receptors ->
vasoconstriction
During exercise, which mediator dominates?
vasodilators
Normal perfusion of blood in brain tissue?
50 ml/min/100g of tissue
Normal cerebral perfusion pressure = ?
map - Intracranial Venous Pressure
(U) ~ 85 mmHg
Cushing Reflex
Response to ↑ ICP:
symp NS causes widespread vasoconstriction ->
↑ systemic arterial pressure
Primary method for ↑ flow in brain?
metabolic: ↑ CO2 and H+
Symp innerv of brain vasculature:
receptors
action
α1 receptors
vasoconstriction
Parasymp innerv of brain:
neurotransmitter
action
ACh
vasodilation
Cerebral blood flow regulation highly dependent on?
mental activity,
is highly localized
Range of mean arterial pressure in renal circulation
80 - 170 mmHg
Renal circulation autoregulates how?
↑ renal artery P ->
1) myogenic vasoconstr of afferent (supply organ) arterioles
2) ↑ glomerular filtration rate ->
↑ water delivery ->
↑ release of vasoconstrictors
Anterior hypothalamus’ fxn in temp regulation?
coordinates mechanisms of heat generation/loss
Anterior hypothalamus receives input from?
own thermoreceptors and
receptors in skin
Anterior hypothalamus generates heat how?
↑ metabolic rate
shivering
vasoconstrict skin bv (↑ SNS tone)
Anterior hypothalamus dissipates heat how?
↓ SNS tone to skin bv
vasodial skin bv (↑ BF)
shunt blood to skin surface
Fear causes vaso?
constriction
Embarrassment causes vaso?
dilation
What causes hyperemic responses?
Deficiency in O2 in tissues
% breakdown of blood distribution per organ/system:
Cerebral Coronary Renal GI Skeletal mm Skin
Cerebral 15%
Coronary 5%
Renal 25%
GI 25%
Skeletal mm 25%
Skin 5%
During exercise, what happens to distribution of CO to:
Skin
Heart
Skeletal mm
skin: ↑ 370%
heart: ↑ 367%
skeletal mm: ↑ 1066%
During exercise, what happens to distribution of CO to:
Brain
GI
Bone, misc
brain: no change
GI: ↓ 45-56%
Bone: ↓ 30%
R Coronary Artery supplies blood to?
R vent
R atrium
L coronary Artery supplies blood to?
L vent
L atrium
Skin densely innervated by?
Sympathetics
no parasymps
Purpose of SNS innervation of skin?
body temp regulation
Local metabolic control is most important for what circulations? (5)
1) coronary
2) cerebral
3) exercising skeletal mm
4) pulmonary
5) renal
Sympathetic control is most important for what circulations?
1) resting skeletal mm
2) skin
Vasoactive metabolites in coronary circulation?
hypoxia
adenosine
Vasoactive metabolites in cerebral circulation?
CO2
H+
Vasoactive metabolites in skeletal mm circulation?
lactate
K+
adenosine
Vasoactive metabolites in pulmonary circulation?
hypoxia
Metabolic hypothesis states?
If O2 delivery to tissue cannot keep up with consumption, metabolic by-products accumulate.
Metabolic by-products induce smooth muscle relaxation and enhance flow.
