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Flashcards in Local Control of BP Deck (16):
1

Myogenic Autoregulation

* Intrinsic ability of vascular smooth muscle cells to regulate own activity

* Goal = maintain constant flow (Q) = maintain constant O2 delivery

* If pressure inc, smooth muscle dec radius/inc resistance to maintain flow (Q)

* How?
* Independent of nervous system
* Rise in pressure —> stretch wall of vascular smooth muscle cells —> open stretch-sensitive Na+ channels —> depolarization —> open voltage-gated L-type Ca++ channels —> more Ca++ in cell —> contract/vasoconstrict

2

Which metabolites cause vasodilation? (4 ex)

* H+ (acidic), K+ and CO2 trigger vasodilation (all esp released in working muscle)

* If low O2 —> triggers adenosine —> inc cAMP —> PKA —> phosphrylate/act K-ATP channel —> K+ efflux/hyper-polarization (RELAX)

* High extracellular K+ causes IKr channel to open —> K+ efflux —> hyper polarization

3

Endothelin

released from damaged endothelial cells —> vasoconstriction (reduce bleeding)

4

Serotonin

released from activated platelets —> vasoconstriction (also reduce bleeding)

5

Histamine

released from mast cells once clot/plug has been formed —> vasodilation (get molecules to site)

6

3 Ways NO is produced

1- If sheer stress of blood parallel to vessel
* Stress —> opens mechanically-gated Ca++ channels on surface —> Ca-Calmodulin —> activates NO synthase
* Other mechanically-gated channels —> kinase cascade —> phosphorylate NO synthase so MORE ACTIVE

2- Bradykinin from cell damage also causes NO release from endothelial cells —> inc flow to repair damage

3- RBCs
* More O2 delivery = more blood flow to that tissue
* As RBC deliver O2 they now have open HB which acts as a reductase of NO2- —> O2
* When O2 is delivered the RBC also make ATP via glycolysis —> release of ATP triggers release of NO from endothelial cells

7

How does NO cause vasodilation?

NO then diffuses through endothelial cells to smooth muscle cells —> inc cGMP —> ATPase that pumps Ca++ out (RELAX)

8

How do myogenic autoregulation and sheer force work against ea other?

* Oppose one another to keep ea other in check

* Inc pressure —> dec radius to maintain flow (vasoconstriction)

* Sheer stress —> NO production —> relaxation (vasodilation)

* Further… decrease radius in myogenic regulation —> greater sheer stress b/c more drag along vessel wall —> vasodilation that directly counteracts myogenic regulation

9

Coronary Muscle Circulation

* Coronary capillary blood flow is pulsatile (while blood flow is usually constant by the time it gets to all other capillaries); falls during systole b/c ventricular contraction compressed capillaries; rise in diastole as compression removed

10

Cerebral Circulation

* KEEP CONSTANT FLOW
* But regional changes in blood flow; certain pats of brain can get more flow if inc CO2 (vasodilation)

11

Skeletal Muscle Circulation

* Epi binds beta receptors —> vasodilation BUT not all skeletal muscle vascular beds can be dilated b/c HUGE contribution to TPR esp if dec BP in exercise

* SO…local factors (paracrine) ensure vasodilation of only working muscle

* If hemorrhage … enough epi to work on alpha as well so vasoconstriction instead

12

GI Circulation

Inc gut blood flow during digestion —> dec flow to other parts of body (“post-prandial hypotension”)

13

Cutaneous Circulation

* Dep more on temp than BP

* When body if overheated —> inc blood flow to skin to cool it

* Bradykinin released when sweating —> NO —> vasodilation to inc flow to skin for cooling

* When body is cold —> dec blood flow to skin to keep warm

14

Bradykinin

Released when sweating and released from damaged endothelial cells

Both results in vasodilation

15

Pulmonary Circulation

* ALL THESE PRINCIPLE DO NOT APPLY TO PULM CIRC

* Goal = oxygenate blood so shunt blood to high pO2 not low pO2

16

Fick Principle

* Oxygen delivery (QO2) = F (CaO2) - F (CvO2)

* Oxygen delivery to a tissue is equal to the difference in oxygen between the arterial blood going into the tissue and the venous blood coming out of the tissue X flow through tissue for rate

* Clinically used to mean flow of CO or Q
* F (flow) = QO2 / (CaO2-CvO2)
* Meas O2 in big artery and big vein
* Meas QO2 w/ mask (or assume 125 min per meters of body area squared)