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76 Cards in this Set

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What is the resting blood flow of coronary, cutaneous, cerebral, skeletal muscle, and splanchic systems?
Co: 70-80 ml/min/100g (4% of CO)
Cu: 10-20 ml/min/100g (6% of CO)
Ce: 50-60 ml/min/100g (15% of CO)
SM: 33 ml/min/kg (20%of CO)
Sp: (25% of CO)
What is the percent oxygen extraction across capillaries in coronary blood flow?
70-80%
What is the limiting factor in oxygen delivery in coronary circulation?
flow
What provides the driving force in coronary flow?
aortic pressure
What is the primary determinant of coronary blood flow?
myocardial oxygen consumption (dependent on metabolic activity)
How does active (functional) hyperemia influence the regulation of coronary blood flow?
as the cardiac tissue becomes more metabolically active, it consumes more oxygen, which leads to greater flow
What effect does hypoxia/acidosis have on coronary vasculature?
vasodilation by hyperpolarizing smooth muscle
What effect does adenosine have on coronary vasculature?
vasodilation by increasing cAMP, which stimulates NO release from endothelium, or by vasodilating resistance vessels directly
What effect does nitric oxide have on coronary vasculature?
vasodilation, released in response to shear stress or adenosine stimulation
What is the mechanism of reactive hyperemia in coronary blood flow?
brief occlusion or ischemia of coronary vessel is followed by transient increase in blood flow as a result of build up of vasodilator metabolites
What determines the magnitude and duration of hyperemia after ischemia?
duration of occlusion or ischemia
What is the mechanism of autoregulation of blood flow?
flow is kept constant at changing pressures due to metabolites
What does elevated MVO2 do to autoregulation curve?
resets the curve upward (increased flow)
How do sympathetic adrenergic fibers influence coronary blood flow?
vasoconstriction via α1-adrenergic receptors, but with an increase in coronary blood flow due to accumulating vasodilators
How do parasympathetic cholinergic fibers influence coronary blood flow?
vasodilation of resistance vessels via nitric oxide (NO), but with a decrease in flow due to decreased HR and MVO2
What is the influence of epinephrine on coronary blood flow?
vasodilation via β2-adrenergic receptors increases blood flow
What is the influence of vasopressin on coronary blood flow?
vasodilation increases blood flow
Coronary flow is most affected in which vessels (left coronary/right coronary) during systolic compression?
left coronary (increased muscle mass in left ventricle)
How does atherosclerosis affect coronary blood flow?
blood flow is slowed; compensation via vasodilator metabolites, but during metabolic need the vessels cannot be further dilated, leads to ischemia
How much does blood flow change in skeletal muscle during exercise?
from 33 to 1000 ml/min/kg
(20% to 85% of CO)
What form of regulation dominates in skeletal muscle blood flow during rest?
neural (sympathetic nervous system = tonic contraction)
What form of regulation dominates in skeletal muscle blood flow during activity?
metabolism (functional hyperemia)
At rest, which sympathetic receptors are involved and what is their affect on skeletal muscle blood flow?
α1-adrenergic receptors vasoconstrict (decrease flow)
Is vasodilation in skeletal muscle vessels active or passive?
passive (withdrawal of sympathetics)
What is the influence of epinephrine on skeletal muscle blood flow?
vasodilation (β2) at low concentrations
vasoconstriction (α1,2) at high concentrations
What is the influence of vasopressin on skeletal muscle blood flow?
vasoconstriction
What is the influence of angiotensin II on skeletal muscle blood flow?
vasoconstriction
What is the influence of interstitial potassium on skeletal muscle blood flow?
stimulates Na+/K+ ATPase which hyperpolarizes smooth muscle so it cannot contract (vasodilation increases blood flow)
What is the influence of interstitial acidosis/hypoxia on skeletal muscle blood flow?
hyperpolarizes smooth muscle so it cannot contract (vasodilation increases blood flow)
How does rhythmic contraction of skeletal muscle (muscle pump) influence skeletal muscle blood flow?
enhances blood perfusion, decreases venous pressure (increases pressure gradient)
What makes skeletal muscle circulation a good target for blood pressure control?
large mass of tissue, major site of resistance vessels
In neural regulation of blood flow, skeletal muscle has ________, but splanchnic does not.
basal tone from SNS
In neural regulation of blood flow, both skeletal muscle blood vessels and splanchnic blood vessels are absent of ________.
innervation from parasympathic nervous system
How is splanchnic circulation influenced by the parasympathetic nervous system?
the parasympathetic nervous system increases motility and metabolism during digestion, this results in functional hyperemia as a result of vasodilator metabolites
What is the influence of gastrin on splanchnic blood flow?
causes functional hyperemia
What is the influence of cholecystokinin (CCK) on splanchnic blood flow?
causes functional hyperemia
What is the influence of angiotensin II on splanchnic blood flow?
vasoconstriction decreases blood flow
What is the influence of vasopressin on splanchnic blood flow?
vasoconstriction decreases blood flow
What is the influence of the products of digestion (glucose and fatty-acids) on splanchnic blood flow?
vasodilation increases blood flow
What happens to splanchnic vascular resistance following a meal?
a dramatic decrease lasting up to 8 hours
What is the influence of autoregulation on splanchnic blood flow?
little to no effect
What is the primary determinant of splanchnic blood flow?
metabolism (functional hyperemia)
What is the role of splanchnic circulation if blood pressure control?
blood is displaced from arterial and venous systems into the highly compliant central venous system which causes hypotension
Besides supplying tissues with blood, what is the role of cutaneous circulation?
regulation of internal temperature
What are the two types of resistance vessels in cutaneous circulation?
arteriovenous anastomoses (AVAs)
arterioles
Where are arteriovenous anastomoses located?
between dermal arterioles and veins in acral skin (areas of high SA/vol.)
Do arteriovenous anastomoses, (AVAs), in cutaneous circulation, exhibit autoregulation and reactive hyperemia?
no
Do arterioles exhibit autoregulation and reactive hyperemia?
yes
Arteriovenous anastomeses (AVAs) are almost exclusively controlled by _______.
tonic activity of the SNS
Arterioles, in cutaneous circulation, have a high density of _______ receptors, but lack _______ receptors (which are present in other arterioles).
α-adrenergic; β2-adrenergic
How are sweat glands controlled?
sympathetic cholinergic (vasodilator) innervation → bradykinin (active vasodilation)
Where is most of the cutaneous blood volume contained?
venous plexus
Where is an important place of heat transfer in cutaneous circulation?
venous plexus
What is the role of cutaneous circulation in reducing body temperature?
withdrawal of SNS activity leads to passive vasodilation of vessels (heat is lost to environment)
How does local cutaneous cooling lead to local vasoconstriction?
increased affinity of α2-adrenergic receptors for norepinephrine (skin reflex controlled by CNS)
What are the influences of epinephrine, angiotensin II, and vasopressin on cutaneous blood flow?
vasoconstriction causes decreased blood flow
Does cutaneous blood flow exhibit reactive hyperemia?
yes
What happens to cutaneous circulation during exercise?
enhanced flow (vasodilation) to dissipate heat reduces venous return arterial pressure
Which organ is least tolerant to ischemia?
brain
What is the percent oxygen extraction in the brain at rest?
35%
Why don't vasoactive metabolites influence cerebral blood flow?
blood brain barrier (tight junctions between endothelial cells + astrocyte support)
How is cerebral perfusion pressure (CPP) calculated and what is a normal value?
CPP = MAP - ICP (intracranial pressure)
CPP ~ 80 mmHg
Is there a tonic influence from the sympathetic nervous system on cerebral blood vessels?
no
When sympathetic nervous system is maximally active, how pronounced is the vasoconstrictor response in cerebral blood vessels?
small response
Which two parasympathetic nerves innervate blood vessels in the cerebral circulation?
facial and superficial petrosal
Increased activity from _______ neurons leads to increased _______ release and vaso_______ in cerebral circulation.
parenchymal; NO; dilation
What causes parenchymal neurons to mediate increased blood flow?
increased neural activity (functional hyperemia)
In which type of nitroxidergic neuron would you find NO synthase?
perivascular neurons
What is the influence of arterial PCO2 (capnia) in cerebral blood flow?
hypercapnia causes vasodilation, increased flow
hypocapnia causes vasoconstriction, decreased flow
How does carbon dioxide lead to dilation vascular smooth muscle?
carbon dioxide crosses BBB into brain ECF and reacts with water to create hydrogen ions - hydrogen ions cause vasodilation by hyperpolarizing and blocking calcium entry in vascular smooth muscle
How does acidosis (hydrogen ions in systemic circulation) affect the brain?
it doesn't because hydrogen ions don't pass the BBB
What is the influence of potassium on cerebral blood flow?
stimulates Na+/K+ ATPase, which hyperpolarizes VSM, preventing them from contracting (increases blood flow)
What is responsible for tonic vasodilation in cerebral blood vessels?
nitric oxide (NO)
How does the sympathetic nervous system influence autoregulation in cerebral blood flow?
shifts autoregulation curve to the right to prevent hyperperfusion
What happens when pressure falls below autoregulatory range (MAP-ICP < 50 mmHg)?
the medullary vasomotor center becomes ischemic - leads to increased SNS vasoconstriction, which causes increased TPR, MAP, and CPP, leading to increased cerebral blood flow
What is Cushing's Reflex?
a space-occupying lesion causes an increase in ICP, brain stem is compressed, causing ischemia - baroreceptors activate SNS vasoconstriction, which increases TPR, MAP, and CPP, which increases cerebral flow