Global and local control of circulation Flashcards
What is basal tone?
minimal amount of contraction in vascular smooth muscle in resting conditions
What is resting sympathetic tone?
in resting conditions, have basal sympathetic activity (through Epi). Allows contraction of smooth muscle, so have higher resistance than basal tone
What happens to SM tone when you increase sympathetic adrenergic influence?
active vasoconstriction
if you remove it or decrease: passive vasodilation
Where are alpha 1 receptors found?
adrenergic: work through NE or epi
when activated lead to vasoconstriction/venoconstriction
*not found in heart or brain! (no wanna constrict)
How do alpha 1 receptors work?
constriction leads to decrease in compliance or increase in tone in veins
- causes increase blood flow back to the heart
- incr BP
Where are Beta 1 receptors found?
only on heart! (no SM)
How do Beta 1 receptors work?
increase contractility of heart plus incr HR
Where are Beta 2 receptors found?
25% in heart and rest in smooth muscle!
- heart: same as beta 1- incr contractility + HR (used during heart damage)
- SM: vasodilator
How do cholinergic receptors work?
muscarinic recepotrs stimulated by Ach
What do cholinergic parasympathetic receptors innervate?
splanchnic, genitalia, bladder and large bowel
NO SM!
What do sympathetic cholinergic receptors innervate?
sweat glands! release Ach on them
Where are baroreceptors found?
carotid sinus [IX] (more sensitive) and aortic arch [X]
When are baroreceptors activated?
During decrease in Pressure (CHANGES)- start firing more
How do baroreceptors work?
they activate sympathetic NS and shut off para
- cause veno and vasoconstriction (incr peripheral resistance)
- incr HR (incr CO)
- incr contractility (more SV- incr CO)
- -> Incr BP!
*negative feedback: sense higher BP so fire to active parasympathetic to balance it out
What happens to baroreceptors in patients with HTN?
They reset at the higher pressure, less sensitive to changes
What are chemoreceptors for?
respiratory system! @ aortic and carotid bodies
afferents IX and X
-work in cardiovasc system during severe hypoxia only
How do chemoreceptors work?
They respond to decrease in pO2 or pH (incr pCO2)
End result: vasoconstriction and tachycardia (lungs blocked parasymp)
What is the system used for hormonal control of circulation? When is is used?
RAAS- renin angiotensine aldosterone system
long term! e.g. dehydration
Explain the RAAS system
The kidneys sense a low arterial pressure and they release RENIN which converts angiotensinogen (always chilling in blood) into angiotensin I
when this blood goes through lungs and kidneys, they release ACE! which converts angio I into angio II
-vasocontricts vessels (incr BP)
-incr Na+ reabsorption (retain more water)
-stim thirst and ADH (more water!)
*all those increase fluid volume and thus BP
What are the global mechanisms to control blood flow?
Neural and hormonal
What are the local mechs to control blood flow?
myogenic, metabolic, endothelial, mechanical
What is autoregulation?
maintains const blood flow despite changes in gravity
works only in certain range
What tissues have autoregulation?
Those that need constant blood flow:
heart, brain, kidneys, skeletal muscles
none: skin and lungs (separate regulation)
weak: splanchincs
How does autoregulation work? 2 hypothesis
- Myogenic: increase in P/flow stretches the muscles which causes it to constrict (to incr R and decr flow). decr in P causes muscle to relax (dilate)
- Metabolic: slower flow will cause metabolites to accumulate so will cause vasodilation. Fast flow will wash away so will cause vasoconstriction
Does autoregulation work during exercise?
Nopes!! you make a bunch of metabolites which vasodilate so this overcomes -> incr blood flow to muscles
What is endothelial mediated regulation? How does it work?
When flow/P is increased the endothelial cells sense sheer stress so release NO/EDRF) –> vasodilators!
*positive feedback
Where does metabolic regulation occur?
In highly metabolic tissues: brain, heart, skel muscles,
What is active hyperemia?
When exercise, you produce metabolites that will vasodilator and further increase blood flow
What is hyperactive hyperemia?
Occurs when a vessel is occluded or blocked
The metabolites accumulate so when you unblock u get a greater response than normal
-the longer it takes for occlusion to clear, the larger the flow
What is mechanical tissue pressure?
An incr in tissue pressure can mechanically compress small vessels and alter blood flow
- in skeletal muscle: squeeze more so more blood flows back to heart!
- in heart: affect endocardial coronary vessels- if LV pressure is too high then can cut off the blood
Name the important vasoconstrictors
calcium, stretch-activated receptors, endothelin, alpha adrenergic receptors (not in heart, brain, lungs)
Name the important vasodilators
B 2 receptors (activate cAMP), NO receptors, histamine receptors, adenosine!
