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a. SL12100: Health and disease > L26 - Smooth Muscle > Flashcards

L26 - Smooth Muscle Flashcards

1
Q

What are examples of tubular and hollow organs? (10)

A
  • Airways
  • Aorta
  • Arteries and veins
  • Bladder
  • Eye
  • Intestine
  • Prostate
  • Skin (hair follicles, nipples)
  • Uterus
  • vagina
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2
Q

How does vasodilation occur?

A

Relaxation of vascular smooth muscle
- increases the blood supply to tissue

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3
Q

How does vasoconstriction occur?

A

Contraction of vascular smooth muscle
- decreasing the blood supply to tissues

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4
Q

What are examples of visceral organs?

A
  • intestine
  • stomach
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5
Q

What is the smooth muscle like in the intestine?

A
  • longitudinal layer of smooth muscle outside
  • circular layer of smooth muscle inside
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6
Q

What are the layers of smooth muscle in the stomach?

A
  • inner oblique
  • circular layer
  • longitudinal
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7
Q

What is the purpose of the inner oblique layer in the stomach?

A

Churning and mechanical digestion

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8
Q

What is the purpose of the circular layer in the stomach?

A

Forms pyloric sphincter
- regulates flow of stomach contents into duodenum

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9
Q

What is the purpose of the longitudinal layer of the stomach?

A

Moves food towards the pylorus

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10
Q

What are possible functions of the trachea and bronchia’s smooth muscle? (3)

A
  • peristalsis, assists exhalation and mucus propulsion
  • distribution of airflow during ventilation
  • stabalises the airway wall, enhances effectiveness of cough/ejection of foreign material
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11
Q

What are single unit smooth muscles like? (3)

A
  • fibres aggregated into sheets/bundles
  • connected by gap/nexus junctions
  • contracts as a syncytium
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12
Q

What are examples of single unit smooth muscle?

A
  • intestine
  • stomach
  • bladder
  • uterus
  • small diameter blood vessels
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13
Q

Whar are multi-unit smooth muscles like?

A
  • few/no gap junctions (no electrical coupling)
  • fine grain control
  • activateed by neural/hormonal signals
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14
Q

What are examples of multi-unit smooth muscle?

A
  • large arteries
  • large airways in lungs
  • pilomotor muscles (hair follicle)
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15
Q

What are properties of smooth muscle?

A
  • involuntary
  • smooth appearance
  • no sarcomeres (dense bodies)
  • Ca2+ binding to calmodulin (not troponin)
  • slow myosin ATPase (compared to skeletal muscle)
  • less extensive SR (compared to skeletal muscle)
  • no T-tubules
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16
Q

What are smooth muscle cells like?

A
  • single nucleus
  • spindle shaped (2-10mcm diam, 50-400mcm long)
  • interconnect to form sheet of smooth muscle
  • no sarcomeres
  • no troponin
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17
Q

How are smooth muscle cells dense bodies?

A
  • analogous to Z-discs of striated muscle sarcomeres
  • rich in a-actinin
  • attached to sarcolemme by intermediate filaments
  • anchor actin filament = exert force
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18
Q

What is the mechanism of smooth muslce contractions?

A
  • intiated by Ca2+ regulated phosphorylation of myosin (not Ca2+ activated troponin)
  • Calmodulin binds to Ca2+ = starts contraction
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19
Q

What are the 2 sources of Ca2+?

A
  • internal calcium stores
  • external influx through calcium ion channels
20
Q

What is calmodulin?

A

The calcium binding protein in smooth muscle

21
Q

What are the steps in the smooth musce cross bridge cycling?

A
  • resting muscle
  • activation of contraction
  • terminating cross bridge
22
Q

What happens during resting muscle in the smooth muscle cross bridge cycling?

A

Dephosphorylated myosin head group held close to myosin filament

23
Q

What happens during activation of contraction in the smooth muscle cross bridge cycling?

A
  • muscle stimulated Ca2+ inc
  • Ca2+ binds to calmodulin
  • Ca2+-Calmodulin complex binds to myosin light chain kinase (MLCK)
  • Active MLCK uses ATP to add Pi to MLC in myosin head group
    = drives cross bridge away from thick filament, binds to actin
24
Q

What type of cross bridge cycling happens in smooth muscle?

A

ATP dependent

25
Q

What happens during the terminating of cross bridge in the smooth muscle cross bridge cycling?

A
  • myosin - Pi my MLC phophatase
  • Ca2+ high = MLCK activity greather than MLCP
  • Ca2+ decreases = MLCP activity greater than MLCK = myosin - Pi
26
Q

How is Ca2+ released from internal stores of Ca2+?

A

SR
- AP releases from SR near plasa membrane
- 2nd messenger releases froms SR

27
Q

How is Ca2+ released from extracellular stores of Ca2+?

A

Influx through VGCC in plasma membrane

28
Q

What are factors regulating smooth muscle contraction?

A
  • spontaneous electrical activity
  • neurotransmitter release of autonomic neurons
  • circulating hormones
  • local environmental changes in the fluid around cells
  • mechanical stretch
29
Q

What is peristalsis?

A

Rhythmic contractions in the GI tract
- initiated by slow waves

30
Q

How are slow waves genereated and propegated?

A
  • by pacemaker cells (interstitial cells of Cajal)
  • spread to the surrounding smooth muscle cells via gap-junctions
31
Q

What are varicosities?

A

Neural stimulation
- axon ilke sweelings of autonomin neurons (form units in smooth muscle)

32
Q

What do varicosities do?

A

Release neurotransmitters that cause smooth muscle to contract or relax

33
Q

What are the acetylcholine receptor families in smooth muscle?

A

GPCR - muscarine
- muscarinin acetylcholine receptor

34
Q

How is the alpha subunit activated?

A

GDP -> GTP
Association and exchange of GDP for Gtp (GDP/GTP exchange)

35
Q

What are the steps in the release of interal Ca2+ stores from SR by GPCR activation?

A
  • resting state trimeric G protein
  • GPCR activated = activation of alpha subunit of trimeric G protein
    = dissociationg of alpha subunit bound to GTP form beta-gamma subunit
  • GTP activates phospholipase C
    = cleavage of PIP2 into IP3 and DAG
  • IP3 binds to receptor on SR
  • receptors contain Ca2+ permeable ion channels
  • activation of IP3 = release of Ca2+ from SR
36
Q

What is PIP2?

A

Phosphatidyl inositol 4,5 biphosphate

37
Q

What is IP3?

A

Inositol 1,4,5 triphosphate

38
Q

What is DAG?

A

Diacylglycerol

39
Q

What do the receptors for neurotransmitters do at smooth muscle?

A
  • alpha-1 adrenergic receptors - mediate constriction in vascular sm
  • beta-adrenergic receptors - mediae dilation of vascular sm and lung airway sm
40
Q

What does response depend on?

A

Receptor expressed as the same neurotransmitter acts on different receptors

41
Q

What are asthma and COPD associated with?

A

Bronchial smooth muscle hypertrophy

42
Q

What do M3 muscarinin receptors mediate?

A

Bronchioconstriction

43
Q

What do B-adrenergic receptors mediate?

A
  • smooth muscle relaxation
  • bronchiodilation
44
Q

What do vascular smooth muscle cells do?

A

Invade early atherosclerotic lesion expanding lesions
- implicated in early and late stage atherosclerosis
- undergo phenotypic switching - adopting alt phenotypes

45
Q

What do VSMCs form?

A

Protective fibrous cap rich
- in extracellular matric to cover the necrotic core - stabilise plaques

a. SL12100: Health and disease (30 decks)

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