Taylor- Blood Flow Distribution Flashcards
blood flow is controlled by altering what
vascular resistance in arterioles
regulate bulk blood flow through the capillary bed
arterioles
regulate number of perfused capillaries for exchange
precapillary sphincters
vessel steady-state tone is regulated by what
vasoconstriction and vasodilation
play a key role in distribution of CO by controlling resistance
arterioles
2 extrinsic mechanisms of controlling arteriole diameter
autonomic (sympathetic-NE)
hormones
main role of this neurotransmitter is on blood vessels and binds a1
NE
3 intrinsic mechanisms controlling arteriole diameter
mechanical, metabolic, endothelial factors
meet demands of the whole body (pressure and volume)
extrinsic mechanisms
match flow to local demands (specific organ)
intrinsic mechanisms
these are released and cause relaxation and increased blood flow
metabolites
these mechanisms are set up to sense pressure or volume changes and correct it
extrinsic mechanisms
body wants to keep _____ high enough to perfuse organs
blood pressure
extrinsic mechanism that increases HR and contractility, causes increase in resistance and vasoconstriction, and, NE and Epi released from adrenal gland in response to low bp
baroreceptor reflex
filters blood, makes urine, corrects blood volume
kidneys
produces renin
juxtaglomerular apparatus
how body responds to low perfusion pressure and low blood volume
by constricting blood vessels until the body reaches a blood pressure that restores proper perfusion pressure AND fluid/Na+ retention
steps kidneys take to increase fluid retention and resistance in response to low renal perfusion pressure (5 main steps)
1.JG produces renin
2.renin converts angiotensinogen to angiotensin I
3. ACE converts angiotensin I to II
4. aldosterone increases Na retention
5. vasoconstrict/increase SVR in arterioles
conserve blood volume and increase resistance to correct low renal perfusion pressure
kidneys
powerful vasoconstrictor
angiotensin II
at level of blood vessel causes vasoconstriction
AVP (arginine vasopressin) (ADH)
at level of kidney causes Na+ and fluid retention
AVP (ADH)
at level of kidney causes a decrease in fluid retention
ANP (atrial natriuretic peptide)
at level of blood vessel causes vasodilation
ANP
steps taken for problem of low blood volume (5 steps)
- decrease in atrial filling causes B fibers to increases sympathetics
- decrease in myocyte stretch causes decrease in ANP
- brain increases AVP
- Na+ and fluid retention
- vasoconstriction (increase resistance)
increased intravascular pressure causes active _____ response
myogenic
increase in intravascular pressure causes what 2 things to happen: (myogenic response)
stretch and then vasoconstriction
high pressure surrounding tissue does what to vessels
compresses them
increased blood flow to tissue when metabolism increases/meet O2 demand (decrease in sympathetic tone of vessel)
Active hyperemia
exaggerated flow occurring after temporary ischemia (due to accumulation and washout of metabolites)
Reactive hyperemia
major metabolite causing vasodilation
Adenosine
comes from endothelium and is a critical component of homeostasis in vasculature
Nitric Oxide (NO)
major vasodilator from endothelium that converts GTP to cGMP and leads to vasodilation
NO
this is a major cause in development of atherosclerosis
dysfunctional endothelium
3 main factors of endothelial dysfunction
- decreased NO
- impaired vasodilation
- contraction
intrinsic ABILITY of vascular. bed to regulate its own flow over a wide range of intravascular pressures
pressure-flow autoregulaton
2 most tightly autoregulated circulations
coronary and cerebral
pressure-flow autoregulation is mediated by what
myogenic and metabolic mechanisms
the CAPACITY for increasing flow within a given vascular bed (organ) at any given pressure
reserve
constricting influences establish persistent tone that can be intermittently overridden by what
local dilating influences (metabolic)
main way blood flow is autoregulated in coronary circulation
myogenic tone
key metabolic dilator in coronary circulation
Adenosine
important for flow mediated dilation in coronary circulation
NO
an excess of blood in the vessels supplying an organ or other part of the body
hyperemia
coronary flow in coronary circulation is stimulated by what
sympathetics (active hyperemia)
susceptible to ischemia due to vascular compression during systole
endothelium
compromised in coronary artery disease (atherosclerosis) +/or vasospasm
blood flow
brain metabolism
highly oxidative (glucose and O2)
2 main ways brain gets blood flow
Circle of Willis and cortical anastomoses
barrier in brain with tight junctions in endothelium
blood-brain barrier
how blood flow is autoregulated in the brain
myogenic tone
localized active hyperemia in the brain due to what
low pH
major metabolic controller in the brain
pH
causes global drop in brain pH and global brain hyperemia
hypercapnia (high blood PCO2)
any disruption of brain blood flow
stroke
disruption of brain blood flow due to thrombosis or embolism
ischemic stroke
bleeding causes damage and can promote prolonged ischemia through vasoconstriction
hemorrhagic stroke
in parallel AND series w/ other splanchnic organs (and why)
liver (b/c hepatic artery and portal vein)
this specific capillary bed is a blood reservoir
splanchnic bed
why do I get a cramp if I exercise after eating
b/c increase in sympathetic output causes vasoconstriction of splanchnic arteries and veins (limits blood flow)
8 fold increase in blood flow following a meal (elderly susceptible)
postprandial hyperemia
this circulation is due to counter current flow; interstitium of intestinal villi is hypertonic and hypoxic
mesenteric
allows for villi in small intestine to be hypertonic (absorption of water and components) and hypoxic (O2 moving from arterial to venous side)
counter current flow
perfused by hepatic artery (systemic pressure) and portal vein (low pressure)
liver
liver fibrosis; increased resistance to outflow
Cirrhosis
can ultimately lead to portal vein hypertension, esophageal varices and ascites
Cirrhosis
fluid out of circulation into abdominal wall
ascites
increased venous and sinusoid pressure in liver—> ascites can lead to
congestive heart failure
Capacity to increase blood flow > 20-fold during aerobic exercise
skeletal muscle circulation
at rest, this circulation experiences myogenic tone w/ high resistance and low flow; low O2 extraction
skeletal muscle circulation
during exercise, tone is overridden by active hyperemia
skeletal muscle circulation
experiences low resistance, high flow, and high O2 extraction
skeletal muscle during exercise
facilitate flow in contracting muscle (pumping veins and allows blood to go to heart)
2 things
muscle pump and reactive hyperemia
these in the skin experience vasoconstriction due to sympathetic _____ input
arterioles and venules; adrenergic
these in the skin experience sweating and vasodilation due to sympathetic _____ input
sweat glands; cholinergic (Ach)
what happens to nonapical skin vessels when it is cold and why
vasoconstriction (symp. adrenergic)
what happens to nonapical skin vessels when body is hot and why
vasodilation (symp. adrenergic withdrawal)
what happens to body in high heat/stress and why
sweating/vasodilation (symp. cholinergic)
Mainly myogenic tone with metabolic override (local autoregulation)
Coronary and cerebral circulation
Mainly sympathetic tone with metabolic override
skeletal and splanchnic muscle
Predominant sympathetic tone with limited metabolic influence (sympathetic cholinergic override in non-apical skin)
cutaneous circulation
local autoregulation with sympathetic control of glomerular filtration
renal circulation
