regional circulation Flashcards
what is autoregulation
ability of an organ to maintain constant blood flow despite changes in pressure
what are the organs that autoregulate
- heart
- brain
- kidneys
- skeletal muscle
what is the relationship between metabolic activity and coronary blood flow
- linear relationship. As metabolic activity goes up, the tissue requires more oxygen and the blood flow to the organ increases
compression effect of systole occurs mainly on which coronary vessel
left coronary artery
- reduction of flow occurs in left coronary artery during early systole, whereas it does not occur in right coronary artery
What are the major local metabolites that signals an increase in O2 consumption and lead to active hyperemia
- adenosine
- nitric oxide
**vasodilators
what effect does NE acting on a-1 receptors have on the arteries/arterioles?
vasoconstriction
what effect does sympathetic stimulation via epinephrine acting on B-2 receptors have on the arteries/arterioles?
vasodilation of vessels
what is the net effect of sympathetic stimulation of the heart
increase coronary blood flow
in the adaption of long term reduction to flow, hypoxia induced what factor? What is the effect?
- hypoxia induced factor (HIF)
- angiogenesis
blood brain barrier consists of what type of junctions between endothelial cells which prevents large circulating vasoactive peptides from altering blood flow
tight junctions
cerebral ciculation is controlled almost entirely by what?
local metabolism
what is the most important local vasodilator
- CO2 (or H+)
- vessels dilate to increase CO2 and protons
- constrict if CO2 and proton content decrease
what effect does an increase in cerebral PCO2 have?
- vasodilation
- increased BF to remove excess CO2
which elicits a more dramatic and rapid change in blood flow: local change in CO2 or O2?
CO2
what is the primary regulator of cerebral blood blow?
METABOLISM
- reflects increased nerve action potentials
effect of adenosine of cerebral circulation
released from hypoxic tissues and DILATES cerebral vessels
effect of K+ on cerebral circulation
released by active neurons can have a dilating action on cerebral vessels
effect of NO of cerebral circulation
NO from endothelium and neurons/glia cells causes cerebral vasodilation
how involved is sympathetic innervation to change cerebral circulation
weak
Why does chronic hypertension not cause increased cerebral blood flow?
with hypertension, vascular resistance increases allowing cerebral BF to be normal
in chronic hypertension, autoregulation range doubles (60 to 100 mmHg). What is the drawback?
partial loss of ability to vasodilate and regulate BF at low pressures
edema that causes intracranial pressure to increase causes what reflex?
cushing’s reflex
what is cushing reflex?
- as intracranial pressures increase, areas in the brain becomes compressed, hypoxic and ischemic
- cushing reflex: venules collapse; venous resistance increases causes capillary pressure to rise which favors filtration which further increases intracranial pressure
- this response will activate the sympathetic nervous system -> raises MAP which causes increases cerebral blood flow
*cushings response will improve flow but worsen the edema
what is the total blood flow to skeletal muscles at rest
750-1000 mL/min
what is the total blood flow to skeletal muscles at exercise
15,000-20,000 mL/min
what is capillary recruitment in response to exercise?
- at rest, 25% of capillaries are perfused
- with exercise, more capillaries are perfused, increasing the number of flowing capillaries
blood flwo to skeletal muscle is controlled by what?
- local metabolites
- sympathetic innervation
- autoregulation (minor)
at rest, increased basal vascular tone by sympathetic innervation is done via what neurotransmitters?
- increase in NE to a-1 adrenergic
- decrease in epineprhine to B-2 adrenergic
with exercise, vascular resistance is decreased and vasodilation predominates via what mechanisms?
- decreased sympathetic a-1 adrenergic tone
- increased muscarinic tone (acetylcholine)
- increased sympathetic B-2 adrenergic tone
how is blood flow to muscle increases during exercise?
sympathetic vasoconstriction of “non-exercisng” tissues increase resistance, shunting blood to exercing tissues
change in blood flow to skeletal muscle during exercise reflects the following 5 signs:
- increased CO
- decrease flow to kidney, gut and bone
- hyperemic response
- autoregulation
- decreased unstressed volume
active hyperemia in skeletal muscle is driven by which local metabolites
- lactate
- adenosine
- K+
describe blood flow response to muscle during rhythmic exercise
mean flow increases with muscle activity but flow is phasic
- decreases during contraction and increases with relaxation
describe blood flow response to muscle during sustained contraction
- mean flow decreases during the contraction, followed by a post contraction hyperemic response when contraction ends
function of muscle venous pumps?
- lowers the venous pressure which increases the pressure gradient
- driving flow of blood to the right atrium
- muscle pump function promotes lower venous and capillary pressures in feet and lower limbs
function of arginine vasopressin on vessels. What receptor is used?
vasoconstriction via AVP 1-A receptor
function of angiotensin II on vessels. What receptor is used?
vasoconstriction via AT-1 receptor
function of atrial natriuretic peptide on vessels. What receptor is used?
vasodilation by acting on natriuretic peptide receptors A/B (NP-A, NP-B)
total blood flow to the skin during rest
200-500 mL/min
total blood flow to the skin during exercise
700-1000 mL/min
primary role of blood flow to skin
allow for heat exchange
local nutritional blood flow through the precapillary spincters and capillaries is under control of what?
vasodilator metaoblites and sensory stimuli (temp, touch, pain)
blood flow to the skin is under control of what
hypothalamic thermoregulatory centers that adjust sympathetic outflow
what is considered apical skin
- present on nose, lips, ears, hand, fingertips, nailbeds, soles of feet
- these tissues have a high surface to volume ratio that favours heat loss
- contain glomus bodies
sympathetic effect of apical skin
release NE causing vasoconstriction
what is nonapical skin
- remaining cutaneous locations
- lack glomus bodies
sympathetic effect on nonapical skin
- release NE causing vasoconstriction
- sympathetic cholinergic fibers release Ach, causing vasodilation via action of bradykinin
AV anastomoses are under what control
neural control
- sympathetic fibers release NE and constrict arteriole and AV anastomeses
symmpathetic tone is increases in what core temp?
when core temp is decreased
- decreases blood flow to minimize heat loss
as intensity of exercise increases, blood flow to skin increases, except at maximal exercise capacity, what happens to blood flow to skin ?
decreases
compaire sympathetic control, metabolic control, and autoregulation effects on coronary, cerebral and skeletal muscle vascular control
- coronary: symp control: +; meta control: +++; autoreg: +++
- cerebral: symp control: +; meta control: +++; autoreg: +++
- skeletal muscle: symp control: ++; meta control: +++; autoreg: ++
