Vascular System 2 Flashcards
What affects arteriolar radius and thus, resistance?
-Myogenic autoregulation -> smooth muscles surround arterioles and when arterioles stretch -> smooth muscles respond by contracting
-Metabolites and O2
-Vasoactive substances (hormones and local mediators) zb vasopressin (vasoconstrictor)
-Autonomic NS: Epinephrine on ß: Dilation, Norepinephrine on alpha: constriction
Why do single smooth muscle cells respond with contraction when arterioles stretch?
Autoregulation -> increased blood pressure causes stretching and more Flow, to autoregulate the flow, the muscle cells contract
How is flow regulated by metabolites and O2?
What changes come with it?
increased metabolism -> causes vasodilation -> increases blood flow
increased CO2, heat, adenosine, H+, K+(outside), decrease in O2
How do the smooth muscle cells react?
Active Hyperemia
More metabolic activity -> Vasodilation -> we increase blood flow -> that blood will pick up the junk and drop off fresh oxygen
in case of low metabolism: we have more oxygen and low metabolites -> vasoconstriction: we don’t need much blood flow there
Why is blood flow in many organs relatively constant, even though there is a change in blood pressure?
Myogenic (blood pressure) and metabolic regulation combined
Because of autoregulation -> when the pressure goes up -> there is stretch and constriction (as discussed)
when pressure goes down -> there is less flow -> less fresh O2 and more metabolites -> autoregulation: Vasodialation -> more blood flow
Name Vasoactive substances!
Angiotensin 2 (Renin (liver) angiotensin-system): vasoconstrictor
Atrial natriuretic factor (produced from atria): vasodilator
Vasopressin (ADH): vasoconstrictor
Histamin: vasodilator
NO (nitric oxid): vasodilator
Where is the atrial natriuretic factor produced?
What is its effect?
produced in atrial
released in response to excessive stretching, caused by blood (venous return, Preload)
-> ANF will also inhibit vasoconstrictor (ADH release) + renin-angiotensin-system
How does the autonoumous NS affect bllod flow?
by the presence or absence of sympathetic NS (not by parasympathetic NS)
alpha receptors: vasoconstriction -> in GI tract
Beta receptors: vasodilation FIGHT AND FLIGHT -> in heart, muscles, liver (more glucose)
both bind Norepinephrine and epinephrine
at physiological concentration:
Which tissues carry most of the ß-receptors?
Tissues needed for FIGHT or FLIGHT, skeletal muscles, heart, liver
What hormones are preferred by the alpha and beta receptors?
at physiological concentration:
ß-receptors prefer epinephrine - Dialation (BED)
alpha-receptors prefer norepinephrine - Constriction (CAN) Constriction mediated by Alpha receptors binding Norepinephrine
How can regulating hormones get to the blood vessels?
most arterioles are innervated by postganglionic neurons (except coronary -> adrenal medulla; and cerebral vessels (brain blood flow is critical))
What happens in the FEED and BREED situations?
Norepinephrine (Vasoconstrictor) in the GI tract will decrease (Norepinephrine causes constriction, we want dilation there)
Epinephrine (vasodilator) in the heart, liver, and muscles will decrease (Epinephrine causes dilation, we want constriction)
SUMMARY: How can Vasodilation be achieved?
less pressure, low O2, more epinephrine binding ß-receptors (BED) or less Norepinephrine binding alpha receptors (CAN)
SUMMARY: How can Vasoconstriction be achieved?
increase of pressure -> stretch -> it responds with constriction
high O2, let’s not send much blood there, fewer metabolites
Alpha-receptors binding Norepinephrine or less ß-receptors bind Epinephrine
SUMMARY: effects of flow
4.10. min: 44
