Smooth Muscle Flashcards
Definition of autacoid
Physiologically active factor released by cells which typically acts locally and briefly on other cells
Definition of local hormone
Any regulatory substance released by cells acting in an autocrine/paracrine fashion
Definition of ANS
Autonomic nervous system, a branch of the nervous system that controls activity of the heart, visceral organs, blood vessels and glands
Definition of unitary
Not all cells have synaptic input, excitation spread through tissue via gap junctions
Allows for coordinated cell contraction
Definition of multiunit
Each smooth muscle has synaptic input, allows for finer control of muscle
Location Function Shape Regulation of SM Properties
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
Smooth muscle containing organs
Blood vessels GI tract Detrusor in bladder, ureters, urethra Myometrium in uterus Respiratory system Vas deferens, corpus cavernosum Fallopian tube Iris and ciliary body
Function of smooth muscle in blood vessels
Diameter control, vascular resistance, blood flow distribution and BP
Function of smooth muscle in GI tract
Controls mixing, propulsions of GI contents
Function of smooth muscle in detrusor, ureters, urethra
Controls urine storage and micturition
Function of smooth muscle in myometrium of uterus
Responsible for labour
Function of smooth muscle in the respiratory system
Controls diameter of airways
Function of smooth muscle in vas deferent, corpus cavernosum
Erection, ejaculation control
Function of smooth muscle in fallopian tube
Mediates egg movement from ovaries to uterus
Function of smooth muscle in iris and ciliary body
Controls pupil diameter, lens focusing
How is the contraction of smooth muscle regulated in the vascular system
Does it respond to action potentials
ANS
Autacoids
Vascular endothelium
Blood bourne substances
Sometimes
How is the contraction of smooth muscle regulated by the airways
Does it respond to action potentials
ANS
Autacoids
No
How is the contraction of smooth muscle regulated by intestinal cells
Does it respond to action potentials
Intestinal cells of Cajal
ANS regulates rhythms
Autacoids
Yes
How is the contraction of smooth muscle regulated by myometrium
Does it respond to action potentials
Intrinsic rhythmicity
Autacoids
Yes
How is the contraction of smooth muscle in the detrusor
Does it respond to action potentials
ANS
Autacoids
Yes
How is vasoconstriction initiated in vascular smooth muscle
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+
How is vasodilation initiated by NO
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
How is vasodilation initiated by cAMP
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
Smooth muscle cross bridge cycle and its regulation in comparison to striated muscle
Crossbridge cycling slower in SM than striated
Lower ATP requirement => contract indefinitely without fatigue
What happens when there is a high conc of Ca2+ in the active complex of myosin light chain kinase and calmodulin
Forms myosin phosphate, binds with actin
Formation of actin myosin, cross bridge cycling occurs
What happens when there is a low conc of Ca2+ in active complex and myosin phosphotase
Myosin light chain formed from the dephosphoryation of myosinPi (via myosin phosphatase)
Calmodulin also formed
Action of NO via cGMP on myosin phosphotase
Promotes Ca2+ desensitization, relaxation
Formation of myosin from myosinPi
Action of antagonists via rho kinase on myosin phosphatase
Promotes Ca2+ sensitization, contractions
Formation of myosinPi
Regulation of tension development in smooth muscle, latch bridges
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
Describe electrical activity of smooth muscle
2 types
Varies between organs
Resting potential is stable in vascular,
Show spontaneous visceral oscillations=slow waves driven by Interstitial cells of Cajal in GI
Effects of AP in slow waves and non slow waves
Increased frequency of stimuli => depolarization/increase in slow wave amplitude
Visceral
Some vascular smooth muscles
What is depolarization and repolarization due to
AP upstroke due to VGCC
Repolarization due to K+ channels
Graded depolarisations and their effects
Are AP generated
Lower levels of stimuli => contraction, AP not generated
Any depolarization tends to open VGCCs, cause contraction
Other causes of contraction via pathways not dependent on depolarizations and VGCC
Hormone, autacoids, NT
Describe unitary smooth muscle
Describe multiunitary smooth muscle
Where can these types be found
1 synapse => excitation spread through gap junctions => coordinated contraction
GI tract, genitourinary, airways, most vascular
Many synapses => fine muscle control
Iris, ciliary body, piloerectors
