SCT II - Local Regulation of Circulation Flashcards
What are the types of local control of blood flow?
- Metabolic factors
- Active hyperemia
- Reactive hyperemia
- Myogenic autoregulation
- Functions of endothelium
What is the local control of blood flow via metabolic factors?
Vasodilator effect
- Hypercapnia
- Hypoxia
- pH (Acidosis)
- Adenosine
- Lactic acid
- K+
- Mg2+
- High temperature
What is the local control of blood flow via active hyperemia?
Hyperemia = excess blood
Metabolism INC
Blood flow INC
What is the local control of blood flow via reactive hyperemia?
Reactive Hyperemia = Reaction to low blood flow
due to obstruction, compensation via excess blood
What is the local control of blood flow via myogenic autoregulation?
Happens only during the autoregulatory range.
Increase in pressure will result in increase in resistance to cancel out the change, and keep flow constant
AIM - MAINTAINING CONSTANT FLOW
Bayliss Effect of myogenic autoregulation
MAP INC
↓
Stretch of vessel wall
↓
Stretch-Activated Channels
↓
Depolarization + [Ca2+]i INC
↓
Vasoconstriction
↓
Resistance INC
↓
Unchanged Q (resistance combats map increase)
Mention the crucial role of endothelium
- Hemostatic (pro/anti-coagulant)
- Growth
- Barrier
- Enzymatic metabolites
- Immunity & immune response
- REGULATION OF VASCULAR TONE (how contracted/relaxed a vessel is)
What stimulate the release of endothelin-1?
- Angiotensin-II
- ADH
- Thrombin
- Cytokines
- ROS
- Damage to endothelium
What happens when there is shear stress on the blood vessel?
Blood vessel wants to relax. How:
NO production
NO causes vasodilation in smooth m.
How does Bradykinin have dual function?
Endothelium present
Causes vasodilation
Endothelium not present
Causes contraction
What is the function of adrenomedullin?
Vasodilator
Binds to endothelium
Endothelium secretes NO & CO
NO & CO relaxes smooth muscle
What is the function of acetylcholine
PRESENCE OF ENDOTHELIUM
VASODILATOR
Binds to endothelium
Endothelium secretes NO
NO relaxes smooth m.
ABSENCE OF ENDOTHELIUM
CONTRACTOR
Binds to smooth m. directly
Causes contraction
What are the 4 substances that are able to induce vasodilation via endothelium but contraction of smooth muscle via absence of endothelium?
Acetylcholine
Histamine
Bradykinin
Serotonin
What’s the alias of serotonin?
5-Hydroxytryptamine
What’s the function of serotonin
SMALL CONC
Binds to endothelium
Endothelium release NO
NO causes vasodilation
BIG CONC
Binds directly to smooth m
Causes contraction (vasoconstriction)
What’s the function of thromboxane (TXA2)?
Vasoconstrictor, immediately binds to smooth muscle cells (bypass endothelium)
How does the heart receive blood during diastole?
During systole the heart muscles are contracted and compress the vessels.
During diastole the heart muscles are relaxed and blood is able to reach the heart
What tone is dominant in the coronaries?
Basal tone
Munroe-Kaillie’s Law
Vskull = Vbrain + Vblood + Vcsf
CONSTANT
Equation of cerebral perfusion pressure
CPP = MAP - ICP (~ 70-80 mmHg)
What tone is dominant in the brain?
Basal tone
What is the role of astrocytes?
Supporting cells of the brain neurons, are able to release vasodilative metabolites
What is the role of PNS in the meninges?
Induces vasodilation
How is stroke prevented via the SNS?
Sudden MAP increase induces SNS activation, which constricts blood vessels
How does the lung prevent pulmonary edema?
Ratio of absorption is greater than that of filtration, unlike systemic circulation, where filtration is 2/3 and absorption is 1/3
Hormones that effect pulmonary circulation and why they are special
OPPOSITE
Histamine - Usually VD, VC in lungs
Serotonin - Usually VD, VC in lungs
Catecholamines - Usually VD, VC in lungs
VIP, NO, ANP - Vasodilation
Metabolite differences in pulmonary circulation
P[O2] DEC
P[CO2] INC
Acidosis
OPPOSITE TO SYSTEMIC - DO VASOCONSTRICTION
Why is the reaction to metabolites different in pulmonary circulation?
Body assumes there’s an obstruction of an alveoli, redirecting blood to healthier alveoli, in order to be supplied with metabolites
Explain the difference in ventilation and perfusion in the three zones of the lung
Zone I: V ↑ + Q ↓
Q ↑ from Zone I - III
Which zone do bacteria prefer and why?
Zone I as it has lots of free oxygen
Which zone is the lung in whilst lying-down?
Zone III
Which zone should be absent in a healthy human?
Zone I
What is deadspace? What is a shunt?
Deadspace = Good ventilation, bad perfusion
Shunt = Bad ventilation, good perfusion
Perfusion is flow
Which tone is dominant in skeletal muscles?
Both basal tone and constrictor (reflex) tone
Which tone is dominant in acral skin (thick)?
Only constrictor (reflex) tone
- Has extensive capillary networks
- Countercurrent flow
- Sympathetic innervation
Which tone is dominant in non-acral skin (thin)
Both basal tone and constrictor tone
Which tone is dominant in kidneys?
Basal tone
Autoregulation - Maintaining flow
Nervous - SNS for VC for redistribution
Humoral - both VC and VD agents
Which tone is dominant in splanchnic organs?
Sympathetic
VC to redistribute blood
