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Physiology > Local Control of the Vasculature > Flashcards

Local Control of the Vasculature Flashcards

1
Q

Recall that smooth muscle contraction/vasoconstriction is triggered by

A
  1. Increase cytoplasmic Ca2+
  2. Ca2+ binds calmodulin
  3. Ca-calmodulin activates myosin light chain kinase
  4. crossbridge cycling
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2
Q

Mechanisms of vasorelaxation

A

cAMP, cGMP, or activation of K+ channels block the increase in cytoplasmic Ca2+ that drives vasoconstriction

Ex) NO promotes cGMP

Ex) prostacyclin (PGI2) promotes cAMP;

Ex) Drop in pH outside the cell activates K+ channels

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3
Q

How does extracellular potassium cause hyperpolarization AND vasodilation?

(smooth muscle-specific)

A
  1. Small increases in extracellular K+ activates the Na/K-ATPase –> take in K+, kick out Na+
  2. Na+ efflux activates Na/Ca exchanger reduces cytoplasmic Ca+ –> take in Na+, kick out Ca++
  3. Hyperpolarization & vasodilation
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4
Q

Extrinsic Regulation(brains shunts blood flow to specific vascular bed) is achieved by what 2 mechanisms?

A

Hormonal : release vasodilators & vasoconstrictors into the circulation by peripheral organs

Neural (ANS): sympathetic vs sympathetic

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5
Q

Vasoactive intestinal peptide (VIP)

&

Atrial natriuretic peptide (ANP) are

A

Vasodilators

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6
Q

Renin-angiotensin system

Vasoprsesin (ADH)

Epinephrine

are

A

Vasconstrictors

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7
Q

Sympathetic signaling is tonically active and promotes increased blood pressure via…

It’s mediated through ___ signaling

A
  • increased CO
  • Mobilization of blood reserves
  • General vasoconstriction

Adrenergic signaling

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8
Q

Parasympathetic signaling promotes decreased cardiac output how?

A
  • Cholinergic signaling
  • A few resistance vessels are innervated by Ach promoting vasodilation
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9
Q

Sympathetic activity dominates in the skin.

The basal tone for cutaneous circulation is extremely ___

A

Changes in blood flow to the skin via vasoconstriction are used to regulate body temp

Basal tone for cutaneous circulation extremely low.

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10
Q

Adrenergic receptors are located in multiple organs and are activated by binding ____.

Differentiate between the different adrenergic receptors (esp the first 3)

A

Catecholamines

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11
Q

Vasodilation & vasoconstriction via adrenergic signaling in arterioles.

A
  • Norepinephrine from sympathetic nerve terminals –> a1-adrenergic receptors –> VASOCONSTRICTION
  • Epinephrine from adrenal medulla –> B2-adrenergic receptors –> VASODILATION in skeletal muscle and lungs
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12
Q

Catecholamines are the ligands for adrenergic receptors released in response to ____.

A

Sympathetic activity of the ANS.

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13
Q

Norepinephrine vs Epinephrine - where are they released from; what do they activate and where?

A
  • Norepinephrine: released from sympathetic nerve terminals
    • Activates adrenergic receptors –> vasoconstriction of arterioles & veins
  • Epinephrine released by the adrenal gland & circulates
    • Activates B1 (heart) and B2 (lungs & arteries)
      • B2 expression primarily in skeletal muscle
    • At high conc, it also activates a-adrenergic receptors in arteries
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14
Q

Cholinergic (Muscarinic) Receptors - what do they facilitate and what’s the main agonist?

A

Facilitates parasympathetic signaling –> vasoconstriction on smooth muscle

Main agonist: acetylcholine

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15
Q

M2 vs M3 muscarinic receptor

A

M2: decreases cardiac output; in the heart

M3: vasodilation in the endothelium of resistance vessels that receive parasympathetic fibers (salivary glands, cerebral, and GI glands)

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16
Q

Dopamine is released by ___. How does it work?

A
  • Released by tubule cells of kidney
  • Its effect is concentration-dependent: it has the greatest affinity for the D1 receptor, but at higher conc will start activating B1, then a1 receptors.
  • Stimulation of
    • D1 receptors induces vasodilation & diuresis
    • B1 receptors increases cardiac output
    • a1 receptors promotes vasoconstriction
17
Q

Sympathetic activity activates what receptors?

Parasympathetic activity activates what receptors?

A
  • Sympathetic
    • B1 -> increase CO
    • a1 -> vasoconstriction shunting blood away from non-metabolically active tissue
    • B2 -> vasodilation in skeletal muscle
  • Paraympathetic
    • M2 -> decrease CO
    • M3 -> vasodilation
18
Q

Myogenic response

A

Bp increases are matched with increases in smooth muscle contraction –> blood flow is maintained constant

Independent of the endothelium; protects capillary beds from high bp

19
Q

___ circulation exhibits an excellent myogenic response between 60-160 mmHg. Thus, fluctuations in bp have a minimal effect on the cerebral blood flow

A

cerebral

Between 60-160mmHg, blood flow is maintained constant by progressively constricting the arteriole. Lower than that, blood flow is lost as the artery begins to collapse; higher than that, the arterial pressure begins to exceed the ability of the myogenic response to constrict and blood increases

20
Q

3 intrinsic regulation mechanisms (vasomotion in response to the needs of local tissue)

A

metabolic factors

endothelium-dependent regulation

myogenic response

21
Q

As your tissue performs metabolism and you need more O2, what happens (metabolic-dependent intrinsic regulation)?

A
  • Adenosine increases->A2 receptor -> cAMP production -> vasodilation
  • H+, CO2, K+ increases -> vasodilation
    • Drop in pH opens KATP channels -> K+ blocks Ca2+ entry and contractio n
    • CO2 accompanies the drop in pH
22
Q

___ activity is the main regulator of vascular tone in resting skeletal muscles. The vascular bed exhibits a __ basal tone, reducing blood flow.

A

Symathetic

reducing blood flow

23
Q

What happens to active and inactive skeletal muscle during exercise?

A

Shunt blood only to active muscles

  • Increased sympathetic activity reduces blood flow to inactive muscles
    • a1 response dominates
  • Release of metabolic factors in active muscle drive vasodilation of those arterioles supplying blood to active muscles
24
Q

Compare the basal tone and vasoconstriction/dilation response of vessels in skeletal muscle vs skin

A
  • Skin
    • Low basal tone
    • Greater max vasconstrction
    • No vasodilation
  • Muscle
    • High basal tone restricts blood flow at rest
    • Vasoconstriction and vasodilation responses to changes in sympathetic activity
    • In exercise, metabolic effects overcome the vasoconstriction in active muscles –> vasodilation
25
Q

Hyperemia

A

Blocked blood flow –> vasodilating metabolites accumulate in the tissue so that when flow is restored, the buildup promotes excess flow for a period until the metabolites wash out.

26
Q

Endothelium-dependent regulation

A

Endothelium releases vasoactive compounds in response to circulating factors or shear stress (produced by flow)

  • Vasodilation - Prostacyclin, NO
  • Vasoconsriction - Endothelin
27
Q

Prostacyclin (PGI2) and nitric oxide are both vasodilators. What are they released in response to? What do they do?

A
  • PGI2
    • response to shear stress
    • promotes increased cAMP in smooth muscle
  • NO
    • ​response to ATP, Ach, bradykinin, serotonin, substance P, histamine, shear stress
    • diffuses freely into smooth muscle
    • increases in cGMP
28
Q

Endothelin

A

Vasoconstrictor released by endothelial cells in response to turbulent flow and hormonal factors (e.g. angiotensin, ADH)

Note: Endothelin release does not continue to increase if flow becomes more turbulent; it’s released in response to the presence of turbulence

29
Q

ACh stimulates conversion of L-arginine to ___, which diffuses into vascular smooth muscle and stimulates ___ to increase __ levels.

A

ACh stimulates conversion of L-arginine to NO, which diffuses into vascular smooth muscle and stimulates guanylyl cyclase to increase cGMP levels.

–> vasodilation

30
Q

Nitroprusside (NP) acts directly on vascular smooth muscle to increase ___ levels in an endothelial cell indepenent manner

A

cGMP –> vasodilation

31
Q
A
32
Q

Cyclooxygenase and prostacyclin synthase converts arachidonic acid to prostacyclin (PGI2). What impact will this have?

A

Vasodilation

33
Q

Compare and contrast instrinsic vs extrinsic mechansisms

A

Physiology (42 decks)

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