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bpk 305 > Vasuclar Smooth Muscle > Flashcards

Vasuclar Smooth Muscle Flashcards

1
Q

How are arterioles organized, explain their role in resistance

A

Organized in series
- in general have small radius so resistance is high
- site of resistance regulation- a change in its radius has large effects on R
capillaries have highest R but are in parallel so R isn’t variable

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2
Q

Composition of blood vessels: Aorta

A

High elastic fibers- allow high compliance
Highest internal radius

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3
Q

Composition of blood vessels: Arterioles

A

Larger wall thickness than internal radius
High smooth muscle b/c controls constriction of radius

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4
Q

Composition of blood vessels: Cappillaries

A

Smallest vessels
Only endothelial cell layer

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5
Q

Width of lumen of arteriole

A

10-30 micro m

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6
Q

What does VSM stand for

A

Vascular smooth muscle

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7
Q

What are the terms for constriction and dilation in smooth muscle

A

Vasoconstriction and vasodilation

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8
Q

What regulates smooth muscle contraction

A

Thick filament

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9
Q

What does SMC stand for

A

Smooth muscle cells

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10
Q

What is in the VSM thin filament

A
  1. Actin
  2. Calponin
  3. Caldesmon
    * no nebulin, Tn complex*
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11
Q

What does calponin do

A

Inhibits actin- myosin interactions

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12
Q

What does caldesmon do

A

Inhibit actin-myosin interactions

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13
Q

What is the pattern and shape of vascular smooth muscle

A

Irregular pattern- no striations no Z lines
Spindle shaped

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14
Q

How do the thin filaments anchor

A

Dense bodies
- no Z lines in smooth muscle

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15
Q

How do gap junctions differ in different smooth muscle. Provide examples

A

Not all smooth muscle are connected for functional syncytium, but some are
ex. Aorta- multi unit, not coupled
ex. Arterioles- single unit, coupled

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16
Q

What creates mechanical coupling between smooth muscle cells

A

Adherens junctions (dense plaques)

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17
Q

What are the invaginations in smooth muscle called

A

Caveoli
lack t-tubules

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18
Q

How does the amount of mitochondria differ in smooth muscle vs cardiac muscle

A

Few mitochondria in vascular smooth muscle vs cardiac muscle

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19
Q

What cells can proliferate

A

Smooth muscle cells can proliferate (angiogenesis)
Striated muscle can not proliferate

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20
Q

What is the role of the myoendothelial junction

A

Allows communication between endothelium and smooth muscle in arteries

21
Q

Where is smooth muscle located in relation to cardiac muscle

A

Smooth muscle is deep to cardiac muscle

22
Q

Compare structures in vascular smooth muscle vs cardiac muscle

A

In smooth muscle:
1. SR less regular
2. Caveoli instead of t-tubules
3. Fewer mitochondria

23
Q

How does the # of mitochondria differ in VSM vs cardiac and why

A

Fewer mitochondria in smooth muscle b/c glycolysis can support non-contractile ATP needs

24
Q

What are caveoli and what is their function

A

-Caveoli are specialized lipid rafts, invaginations of the cell membrane
-contain Ca channels and ion channels
-can localize signaling molecules

25
Q

Explain the initiation of cross-bridge cycling in smooth muscle

A

-Calcium binds to calmodulin (Ca-CaM) activating it
-active calmodulin binds to myosin light chain kinase (MLCK)
-active calmodulin/MLCK complex phosphorylates regulatory myosin light chain (MLC) using the hydrolysis of ATP
-activated myosin can now form a cross bridge (semi-permanent phosphorylation)

26
Q

What triggers contraction in smooth muscle, how does this differ in striated muscle

A

Ca2+ triggers contraction in VSM
- directly activates contraction via MLCK
In striated muscle Ca2+ acts as a disinhibitor

27
Q

What enables cross bridge cycling

A

Myosin light chain phosphorylation enables xb
(Thick filament regulated)

28
Q

What stops force generation in VSM

A

Relaxation requires myosin light chain phosphatase (MLCP)
- force is sustained (system active), even when Ca2+ levels drop, as along as MLC is phosphorylated

29
Q

What does RhoA do

A

RhoA inhibits MLCP (myosin light chain phosphatase) which allows contraction to continue because regulatory MLC remains phosphorylated

30
Q

What causes smooth muscle relaxation

A

-Requires MLC phosphatase (MLCP) and decrease in calcium concentration
-dephosphorylate regulatory MLC which prevents new cross bridge formation

31
Q

What is the latch state

A

Slow cross-bridge detachment maintains tension with lower ATP use
- dephosphorylating myosin has a slow rate of detachment from actin
- decrease in Ca, low level of MLCK activation, but enough to sustain tension (no new force generation)

32
Q

How does the length tension relationship differ in VSM vs cardiac

A

Length tension relationship is more broad in smooth muscle (because side polar myosin?)

33
Q

Smooth muscle force-velocity curve

A
  • slow velocity of shortening
  • high force generation
34
Q

What allows smooth muscle to have a large length range

A

Side polar myosin thick filaments
-easier to form cross bridges and pull actin
- myosin on angle

35
Q

How can shortening velocity be increased in smooth muscle

A

Increased with more phosphorylated MLC
- inc Ca, activate MLCK, phosphorylate regulatory MLC: pathway causes increase in shorting velocity also increases maximum force

36
Q

Name the channels involved in Ca regulation in smooth muscle

A

SOC: store-operated channels
ROC: receptor-operated channels
Istretch channels
IP3 mediated Ca release from SR
NCX channel (Ca out Na in)
PMCA (Ca out with ATP use)
SERCA2b (2Ca into SR)

37
Q

Store Operated Channels
- types, activation, role

A
  • Channels: Orai, TRPC1, TRPC3
  • activated by decrease in calcium concentration in SR. SR Ca sensor- STIM (protein)
  • calcium sent directly into SR
38
Q

Receptor-Operated Channels
- types, activation, role

A
  • channels: TRPC, TRPV, TRPM
  • 2nd messenger activated
  • non selective ion channel lets in other ions than Ca. Causes depolarization which opens Cav1.2 channels
39
Q

Istretch channel
- types, role

A
  • K+ channels or non-selective cation channel
  • depolarization causes Cav1.2 opening
40
Q

Ca release from SR
-activation, role

A

Two ways of Ca release from SR:
RyR3- Ca activated
IP3R- IP3 activated
- SR Ca release contributes to transient Ca peak in cell

41
Q

Which channels contributed to Ca concentration in cell vs time graph and where is their contribution

A

Transient Ca2+ peak- SR Ca2+ release
Sustained Ca2+ plateau- Ca2+ entry from ROC, SOC, Cav1.2, Istretch
Clearance of cytosolic Ca2+- NCX, PMCA, SERCA2B

42
Q

List the affinity and capacity of the Ca clearance channels

A

NCX: low affinity, high capacity
PMCA: high affinity, low capacity
SERCA2B: high affinity, low capacity
(affinity- binding for transport, capacity- amount moved)

43
Q

What is the main contributor for Ca regulation in vascular smooth muscle

A

SR Ca release is the main driver of increased Ca. IP3 mediated Ca release

44
Q

Pathway for producing IP3

A

Noradrenaline binds to alpha1 receptors. This causes the release of the Gq G-protein on the receptor which activates PLC- phospholipase C. PLC converts phosphatidylinositol biphosphate- PIP2 into IP3- inositol triphosphate and DAG- diacylglycerol.

45
Q

Pathway of IP3 causing increased force of contraction

A

IP3- inositol triphosphate will bind to IP3 receptors on the SR and allow Ca release from the SR through these channels. This will increase the Ca levels in the cell, therefore increasing cross bridge formation and increasing the force of contraction

46
Q

How does DAG increase the force of contraction of vascular smooth muscle

A

DAG- diacylglycerol activated PKC- protein kinase C which inhibits MLCP- myosin light chain phosphatase. This causes an increase in Ca sensitivity of VSM contraction therefore increasing the cross bridge formation and increasing the force of contraction

47
Q

How is Ca released and taken up in the SR- sarcoplasmic reticulum

A

Released: RyR and IP3 channels
Uptake: SERCA2B which is PLB- phospholamban regulated

48
Q

The Sarcolemma channels involved in Ca regulation

A

Ca entry: Cav1.2 (voltage gated), ROC (receptor operated), SOC (store operated), Istretch (stretch-activated cation channel)

Ca exit: NCX (Na Ca exchanger), PMCA (plasma membrane Ca ATPase)

bpk 305 (10 decks)

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