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Principles of pharmacology and physiology > Smooth Muscle > Flashcards

Smooth Muscle Flashcards

1
Q

Definition of autacoid

A

Physiologically active factor released by cells which typically acts locally and briefly on other cells

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2
Q

Definition of local hormone

A

Any regulatory substance released by cells acting in an autocrine/paracrine fashion

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3
Q

Definition of ANS

A

Autonomic nervous system, a branch of the nervous system that controls activity of the heart, visceral organs, blood vessels and glands

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4
Q

Definition of unitary

A

Not all cells have synaptic input, excitation spread through tissue via gap junctions
Allows for coordinated cell contraction

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5
Q

Definition of multiunit

A

Each smooth muscle has synaptic input, allows for finer control of muscle

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6
Q 
Location
Function
Shape
Regulation of SM
Properties
A

Wall of hollow organs, including blood vessels except capillaries

Acts as body conduits for transport

Spindle

ANS/Hormones/Pacemaker cells

No striations
Dense bodies which anchor actin filaments
SR
More actin : myosin than to striated muscle

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7
Q

Smooth muscle containing organs

A 
Blood vessels
GI tract
Detrusor in bladder, ureters, urethra
Myometrium in uterus
Respiratory system
Vas deferens, corpus cavernosum
Fallopian tube
Iris and ciliary body
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8
Q

Function of smooth muscle in blood vessels

A

Diameter control, vascular resistance, blood flow distribution and BP

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9
Q

Function of smooth muscle in GI tract

A

Controls mixing, propulsions of GI contents

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10
Q

Function of smooth muscle in detrusor, ureters, urethra

A

Controls urine storage and micturition

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11
Q

Function of smooth muscle in myometrium of uterus

A

Responsible for labour

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12
Q

Function of smooth muscle in the respiratory system

A

Controls diameter of airways

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13
Q

Function of smooth muscle in vas deferent, corpus cavernosum

A

Erection, ejaculation control

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14
Q

Function of smooth muscle in fallopian tube

A

Mediates egg movement from ovaries to uterus

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15
Q

Function of smooth muscle in iris and ciliary body

A

Controls pupil diameter, lens focusing

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16
Q

How is the contraction of smooth muscle regulated in the vascular system

Does it respond to action potentials

A

ANS
Autacoids
Vascular endothelium
Blood bourne substances

Sometimes

17
Q

How is the contraction of smooth muscle regulated by the airways

Does it respond to action potentials

A

ANS
Autacoids

No

18
Q

How is the contraction of smooth muscle regulated by intestinal cells

Does it respond to action potentials

A

Intestinal cells of Cajal
ANS regulates rhythms
Autacoids

Yes

19
Q

How is the contraction of smooth muscle regulated by myometrium

Does it respond to action potentials

A

Intrinsic rhythmicity
Autacoids

Yes

20
Q

How is the contraction of smooth muscle in the detrusor

Does it respond to action potentials

A

ANS
Autacoids

Yes

21
Q

How is vasoconstriction initiated in vascular smooth muscle

A

Noradrenaline, angiotensin II, other vasoconstrictors bind to a1 receptors
Activates phospholipase C and rho kinase with +ve currents
Rho kinase increases Ca2+ sensitization

Phospholipase C hydrolyses PIP2 into IP3 and DAG
IP3 causes SR to release Ca2+
DAG opens RGC, influx of Ca2+ and Na+

SAC causes Na+ influx, membrane depolarization, spreads excitation to neighboring cells via gap junctions
Also causes VGCC to open, influx of Ca2+

22
Q

How is vasodilation initiated by NO

A

NO released by endothelial cell
Causes GTP conversion into cGMP by GC

cGMP causes Ca2+ to be reabsorbed into SERCA, leave cell via PMCA and increase Ca2+ desensitization
cGMP also causes K+ channel to open, K+ efflux, leads to membrane hyperpolarization
Membrane hyper polarization causes VGCC to close

23
Q

How is vasodilation initiated by cAMP

A

Adrenaline, adenosine prostacyclin binds to b2 receptor

Activated AC converts ATP to cAMP

cAMP activates SERCA and PMCA to decrease Ca2+ in cell
cAMP also activates K+ channels, K+ efflux, membrane hyperpolarization
cAMP activates PDE, converted into AMP

24
Q

Smooth muscle cross bridge cycle and its regulation in comparison to striated muscle

A

Crossbridge cycling slower in SM than striated

Lower ATP requirement => contract indefinitely without fatigue

25
Q

What happens when there is a high conc of Ca2+ in the active complex of myosin light chain kinase and calmodulin

A

Forms myosin phosphate, binds with actin

Formation of actin myosin, cross bridge cycling occurs

26
Q

What happens when there is a low conc of Ca2+ in active complex and myosin phosphotase

A

Myosin light chain formed from the dephosphoryation of myosinPi (via myosin phosphatase)
Calmodulin also formed

27
Q

Action of NO via cGMP on myosin phosphotase

A

Promotes Ca2+ desensitization, relaxation

Formation of myosin from myosinPi

28
Q

Action of antagonists via rho kinase on myosin phosphatase

A

Promotes Ca2+ sensitization, contractions

Formation of myosinPi

29
Q

Regulation of tension development in smooth muscle, latch bridges

A

Latch bridge formation allows smooth muscle to maintain force w less ATP

MyosinPi is dephosphorylated by myosin phosphatase, maintains force via cross bridges
Latch bridges detach v slowly

30
Q

Describe electrical activity of smooth muscle

2 types

A

Varies between organs
Resting potential is stable in vascular,

Show spontaneous visceral oscillations=slow waves driven by Interstitial cells of Cajal in GI

31
Q

Effects of AP in slow waves and non slow waves

A

Increased frequency of stimuli => depolarization/increase in slow wave amplitude

Visceral
Some vascular smooth muscles

32
Q

What is depolarization and repolarization due to

A

AP upstroke due to VGCC

Repolarization due to K+ channels

33
Q

Graded depolarisations and their effects

Are AP generated

A

Lower levels of stimuli => contraction, AP not generated

Any depolarization tends to open VGCCs, cause contraction

34
Q

Other causes of contraction via pathways not dependent on depolarizations and VGCC

A

Hormone, autacoids, NT

35
Q

Describe unitary smooth muscle
Describe multiunitary smooth muscle

Where can these types be found

A

1 synapse => excitation spread through gap junctions => coordinated contraction

GI tract, genitourinary, airways, most vascular

Many synapses => fine muscle control

Iris, ciliary body, piloerectors

Principles of pharmacology and physiology (25 decks)

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