Lecture 12

Question 1

Where are Vascular Smooth Muscle cells present?

Answer 1

in the tunica media of (some) blood vessels

Question 2

What is the contractile unit for VSM? (2)

Answer 2

overlapping myosin actin filaments
thin filaments (actin) are longer than myosin and therefore enable greater shortening

Question 3

What does VSM rely on to initiate contraction?

Answer 3

Poorly developed SR so relies primarily on diffusion of Ca ions from ECF

Question 4

What are actin filaments anchored to
cytoplasm?
cell membrane?

Answer 4

dense bodies in cytoplase

dense bands in cell membrane

Question 5

what are the 2 broad groups of excitation-contraction coupling?

Answer 5

• Electromechanical coupling: depolarization of the VSM cell-> opening of L-type voltage gated Ca channels
• Pharmacomechanical coupling: binding of signaling molecule to a receptor leads to an inc of intracellular Ca [ ] ; either via G protein coupled release of intracellular stores or opening of receptor operated Ca channels (no change in membrane potential

Question 6

VSM contraction steps (6)

Answer 6

Increase in intracellular Ca [ ]
Ca + cadmodulin complex
[Ca-cadmodulin] myosin light chain kinase
Phosphorylation of MLCK
myosin forms a crossbridge with actin
contraction of VSM

Question 7

What is different about VSM (5)

Answer 7

contracts slowly
low energy requirements
poorly developed SR
cell-cell conduction via gap junctions
no troponin, no voltage operated Na channels

Question 8

inc tone of VSM (relative to basal tone)=

dec tone=

Answer 8

vasoconstriction

vasodilation

Question 9

What maintains arterial BP?

Answer 9

basal vascular tone produced by VSM contraction sustained continually

Question 10

Factors controlling vascular tone
intrinsic mechanisms (3)

responsible for (2)

Answer 10

(entirely within the vasculature)
myogenic response
vasoactive metabolites
endothelial secretions

autoregulation, active and reactive hyperemia

Question 11

Factors controlling vascular tone
Extrinsic mechanisms (2)

Extrinsic can…

Answer 11

(factors outside the vasculature)
Neural control (vasomotor nerves)
hormonal control (vasoactive hormones)

extrinsic can override intrinsic to meet needs of the whole animal (ex. hemorrhage)

Question 12

Myogenic response (intrinsic)
depolarization is initiated by...
Response is maintained by...

Answer 12

VSM contracts in response to stretch and relaxes with reduction in tension
stretch activated channels
tension sensitive channels

Question 13

Vasoactive metabolites (intrinsic)
function to...
contribute to...

Answer 13

Metabolic products released into interstitial fluid cause alterations in local blood flow

• match bloodflow to metabolic demands of tissue
• active and reactive hyperemia

Question 14

Metabolic (active) hyperemia

Answer 14

inc blood flow in response to increase metabolic rate (demand)

Question 15

Reactive hyperemia
leads to…
peak flow and duration of hyperemia is

Answer 15

temporary inc blood flow following a period of reduced blood flow
rapid restoration of O2 supply and ‘wash out’ of accumulated waste products
directly proportional to duration of occlusion

Question 16

Endothelial secretions (intrinsic)
Vasodilation-
Vasoconstriction-

Answer 16

produce a range of vasoactive molecules

• NO and Prostacyclin
• endothelin

Question 17

endothelium induced flow dependent relaxation

Answer 17

-inc flow-> inc shear stress->ECs produce NO

NO induced endothelium dependent muscle relaxation

Question 18

NO induced vasodilation
NO produced by…
NO signalling…

Answer 18

endothelial cells produce NO

• Activates Guanylyl cyclase (GC)
• GC converts GTP to cGMP
• cGMP activates kinases that promote relaxation

Question 19

Autoregulation-
achieved by-
protects…

Answer 19

vascular resistance changes that tend to maintain a constant blood flow
-Myogenic response and flow induced endothelial relaxation
capillaries from exccessive hydrostatic pressure

Question 20

Neural control(extrinsic)
2 types of autonomic nerves

Answer 20

Sympathetic nerves- predominately vasoconstrictive
parasympathetic nerves-vasodilator

but also-reduction in vasoconstriction-> vasodilation

Question 21

Sympathetic Vasoconstrictor nerves

how do they work

Answer 21

fibers release vesicles containing NA
NA activates alpha1,2 adrenoreceptors causing vasoconstriction(arterioles of all organs and veins in the abdominal organs)

Question 22

Sympathetic nerves

inc sympathetic activity->(3)

Answer 22

inc peripheral resistance (TPR)
dec local blood flow
displacement of blood from peripheral to central veins (inc venous return)

Question 23

Alpha adrenoreceptor mediated constriction of smooth muscle (3)

Answer 23

G protein activates phospholipase C
cleaves membrane phospholipid to produce IP3
IP3 opens Ca channels on the SR

Question 24

Parasympathetic nerves
how it works (2)
where it works(3)

Answer 24

-parasympathetic fibers release vesicles containing Ach
-Ach activates M3 muscarinic receptors on ECs->synthesis of NO->dilation
-coronary artery
-genital arterioles
salivary gland arterioles

Question 25

Hormonal control (extrinsic)
Adrenaline/NA
-Beta 2 receptor-
-alpha 1 and 2 receptor

Answer 25

• vessel dilates(coronary circulation and skeletal muscle)

- vessel constricts (predominated in most tissues

Question 26

Unlike alpha adrenoreceptors, Beta2 receptors are…

Answer 26

not innervated by sympathetic nerves->they respond to circulating Adr/NA