Smooth muscle
Encyclopedia
Smooth muscle is an involuntary non-striated muscle
. It is divided into two sub-groups; the single-unit
(unitary) and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by gap junctions to neighboring cells such that the whole bundle or sheet contracts as a syncytium
(i.e., a multinucleate mass of cytoplasm that is not separated into cells). Multiunit smooth muscle tissues innervate individual cells; as such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle.
Smooth muscle is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle
) such as in the tunica media
layer of large (aorta
) and small arteries, arterioles and veins. Smooth muscle is also found in lymphatic vessels, the urinary bladder
, uterus
(termed uterine smooth muscle), male and female reproductive tracts, gastrointestinal tract
, respiratory tract
, arrector pili of skin
, the ciliary muscle
, and iris of the eye
. The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual effects in the body at individual times. In addition, the glomeruli
of the kidneys contain smooth muscle-like cells called mesangial cell
s.
Smooth muscle is fundamentally different from skeletal muscle
and cardiac muscle
in terms of structure, function, regulation of contraction, and excitation-contraction coupling smooth.
Smooth muscle fibers have a fusiform shape and, like striated muscle
, can tense and relax
. However, smooth muscle containing tissue tend to demonstrate greater elasticity and function within a larger length-tension curve than striated muscle. This ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder. In the relaxed state, each cell is spindle-shaped, 20-500 micrometers in length.
and actin
, which together have the capability to contract, and, through a chain of tensile structures, make the entire smooth muscle tissue contract with them.
Different combinations of heavy and light chains allow for up to hundreds of different types of myosin structures, but it is unlikely that more than a few such combinations are actually used or permitted within a specific smooth muscle bed. In the uterus, a shift in myosin expression has been hypothesized to avail for changes in the directions of uterine contractions that are seen during the menstrual cycle.
The ratio of actin
to myosin
is between 2:1 and 10:1 in smooth muscle, compared to ~6:1 in skeletal muscle and 4:1 in cardiac muscle.
; instead calmodulin
(which takes on the regulatory role in smooth muscle), caldesmon
and calponin
are significant proteins expressed within smooth muscle.
Also, all three of these proteins may have a role in inhibiting the ATPase activity of the myosin complex that otherwise provides energy to fuel muscle contraction.
The actin filaments of contractile units are attached to dense bodies. Dense bodies are rich in α-actinin, and also attach intermediate filaments (consisting largely of vimentin
and desmin
), and thereby appear to serve as anchors from which the thin filaments can exert force. Dense bodies also are associated with β-actin, which is the type found in the cytoskeleton, suggesting that dense bodies may coordinate tensions from both the contractile machinery and the cytoskeleton.
The intermediate filaments are connected to other intermediate filaments via dense bodies, which eventually are attached to adherens junctions (also called focal adhesions) in the cell membrane
of the smooth muscle cell, called the sarcolemma
. The adherens junctions consist of large number of proteins including α-actinin, vinculin and cytoskeletal actin. The adherens junctions are scattered around dense bands that are circumfering the smooth muscle cell in a rib-like pattern. The dense band (or dense plaques) areas alternate with regions of membrane containing numerous caveolae. When complexes of actin and myosin contract, force is transduced to the sarcolemma through intermediate filaments attaching to such dense bands.
During contraction, there is a spatial reorganization of the contractile machinery to optimize force development. part of this reorganization consists of vimentin being phosphorylated at Ser
56 by a p21 activated kinase
, resulting in some disassembly of vimentin polymers.
Also, the number of myosin filaments is dynamic between the relaxed and contracted state in some tissues as the ratio of actin to myosin changes, and the length and number of myosin filaments change.
Smooth muscle cells have been observed contracting in a spiral corkscrew fashion, and contractile proteins have been observed organizing into zones of actin and myosin along the axis of the cell.
Smooth muscle-containing tissue needs to be stretched often, so elasticity is an important attribute of smooth muscle. Smooth muscle cells may secrete a complex extracellular matrix containing collagen
(predominantly types I and III), elastin
, glycoproteins, and proteoglycans. Smooth muscle also has specific elastin and collagen receptors to interact with these proteins of the extracellular matrix. These fibers with their extracellular matrices contribute to the viscoelasticity
of these tissues. For example, the great arteries are viscolelastic vessels that act like a Windkessel
, propagating ventricular contraction and smoothing out the pulsatile flow, and the smooth muscle within the tunica media
contributes to this property.
(prostacyclin
, endothelin
, serotonin
, muscarinic receptors, adrenergic receptors), second messenger generators (adenylate cyclase
, Phospholipase C
), G proteins (RhoA, G alpha), kinases (rho kinase-ROCK, Protein kinase C
, Protein Kinase A), ion channels (L type Calcium channels, ATP sensitive Potassium channels, Calcium sensitive Potassium channels) in close proximity. The caveolae are often close to sarcoplasmic reticulum or mitochondria, and have been proposed to organize signaling molecules in the membrane.
.
Smooth muscle in various regions of the vascular tree, the airway and lungs, kidneys and vagina is different in their expression of ionic channels, hormone receptors, cell-signaling pathways, and other proteins that determine function.
and epinephrine
(from sympathetic
stimulation or the adrenal medulla) by producing vasoconstriction (this response is mediated through alpha 1-adrenergic receptors). Blood vessels in skeletal muscle and cardiac muscle respond to these catecholamines producing vasodilation because the smooth muscle possess beta-adrenergic receptors.
Generally, arterial smooth muscle responds to carbon dioxide by producing vasodilation, and responds to oxygen by producing vasoconstriction. Pulmonary blood vessels within the lung are unique as they vasodilate to high oxygen tension and vasoconstrict when it falls. Bronchiole, smooth muscle that line the airways of the lung, respond to high carbon dioxide producing vasodilation and vasoconstrict when carbon dioxide is low. These responses to carbon dioxide and oxygen by pulmonary blood vessels and bronchiole airway smooth muscle aid in matching perfusion and ventilation within the lungs. Further different smooth muscle tissues display extremes of abundant to little sarcoplasmic reticulum so excitation-contraction coupling varies with its dependence on intracellular or extracellular calcium.
(S1P) signaling is an important regulator of vascular smooth muscle
contraction. When transmural pressure
increases, sphingosine kinase 1
phosphorylates sphingosine to S1P, which binds to the S1P2 receptor in plasma membrane of cells. This leads to a transient increase in intracellular calcium, and activates Rac and Rhoa signaling pathways. Collectively, these serve to increase MLCK activity and decrease MLCP activity, promoting muscle contraction. This allows arterioles to increase resistance in response to increased blood pressure and thus maintain constant blood flow. The Rhoa and Rac portion of the signaling pathway provides a calcium-independent way to regulate resistance artery
tone.
and actin
filaments (a sliding filament mechanism
) over each other. The energy for this to happen is provided by the hydrolysis
of ATP
. Myosin functions as an ATPase utilizing ATP to produce a molecular conformational change of part of the myosin and produces movement. Movement of the filaments over each other happens when the globular heads protruding from myosin filaments attach and interact with actin filaments to form crossbridges. The myosin heads tilt and drag along the actin filament a small distance (10-12 nm). The heads then release the actin filament and then changes angle to relocate to another site on the actin filament a further distance (10-12 nm) away. They can then re-bind to the actin molecule and drag it along further. This process is called crossbridge cycling and is the same for all muscles (see muscle contraction
). Unlike cardiac and skeletal muscle, smooth muscle does not contain the calcium-binding protein troponin. Contraction is initiated by a calcium-regulated phosphorylation of myosin, rather than a calcium-activated troponin system.
Crossbridge cycling causes contraction of myosin and actin complexes, in turn causing increased tension along the entire chains of tensile structures, ultimately resulting in contraction of the entire smooth muscle tissue.
(MLCK), also called MLC20 kinase. In order to control contraction, MLCK will work only when the muscle is stimulated to contract. Stimulation will increase the intracellular concentration of calcium ions. These bind to a molecule called calmodulin
, and form a calcium-calmodulin complex. It is this complex that will bind to MLCK to activate it, allowing the chain of reactions for contraction to occur.
Activation consists of phosphorylation of a serine
on position 19 (Ser19) on the MLC20 light chain, which causes a conformational change that increases the angle in the neck domain of the myosin heavy chain, which corresponds to the part of the cross-bridge cycle where the myosin head is unattached to the actin filament and relocates to another site on it. After attachment of the myosin head to the actin filament, this serine phosphorylation also activates the ATPase activity of the myosin head region to provide the energy to fuel the subsequent contraction. Phosphorylation of a threonine on position 18 (Thr18) on MLC20 is also possible and may further increase the ATPase activity of the myosin complex.
Isolated preparations of vascular and visceral smooth muscle contract with depolarizing high potassium balanced saline generating a certain amount of contractile force. The same preparation stimulated in normal balanced saline with an agonist such as endothelin or serotonin will generate more contractile force. This increase in force is termed calcium sensitization. The myosin light chain phosphatase is inhibited to increase the gain or sensitivity of myosin light chain kinase to calcium. There are number of cell signalling pathways believed to regulate this decrease in myosin light chain phosphatase: a RhoA-Rock kinase pathway, a Protein kinase C-Protein kinase C potentiation inhibitor protein 17 (CPI-17) pathway, telokin, and a Zip kinase pathway. Further Rock kinase and Zip kinase have been implicated to directly phosphorylate the 20kd myosin light chains.
, Rho kinase, Zip kinase, Focal adhesion kinases) have been implicated as well and actin polymerization dynamics plays a role in force maintenance. While myosin light chain phosphorylation correlates well with shortening velocity, other cell signaling pathways have been implicated in the development of force and maintenance of force. Notably the phosphorylation of specific tyrosine residues on the focal adhesion adapter protein-paxillin by specific tyrosine kinases has been demonstrated to be essential to force development and maintenance. For example, cyclic nucleotides can relax arterial smooth muscle without reductions in crossbridge phosphorylation, a process termed force suppression. This process is mediated by the phosphorylation of the small heat shock protein, hsp20
, and may prevent phosphorylated myosin heads from interacting with actin.
Smooth muscle forms precapillary sphincters in blood vessels in metarterioles which regulates the blood flow in capillary beds of various organs and tissues. The contractile function of vascular smooth muscle also regulates the lumenal diameter of the small arteries-arterioles called resistance vessels, thereby contributing significantly to setting the level of blood pressure. Smooth muscle contracts slowly and may maintain the contraction (tonically) for prolonged periods in blood vessels, bronchioles, and some sphincters. Activating arteriole smooth muscle can decrease the lumenal diameter 1/3 of resting so it drastically alters blood flow and resistance. Activation of aortic smooth muscle doesn't significantly alter the lumenal diameter but serves to increase the viscoelasticity of the vascular wall.
In the digestive tract, smooth muscle contracts in a rhythmic peristaltic fashion, rhythmically forcing foodstuffs through the digestive tract as the result of phasic contraction.
A non-contractile function is seen in specialized smooth muscle within the afferent arteriole of the juxtaglomerular apparatus, which secretes renin
in response to osmotic and pressure changes, and also it is believed to secrete ATP in tubuloglomerular regulation of glomerular filtration rate. Renin in turn activates the renin-angiotensin system
to regulate blood pressure.
The embryological origin of smooth muscle is usually of mesodermal origin. However, the smooth muscle within the Aorta and Pulmonary arteries (the Great Arteries of the heart) is derived from ectomesenchyme of neural crest origin, although coronary artery smooth muscle is of mesodermal origin.
Anti-smooth muscle antibodies
(ASMA) can be a symptom of an auto-immune disorder, such as hepatitis
, cirrhosis
, or lupus
.
Vascular smooth muscle tumors are very rare. They can be malignant or benign, and morbidity can be significant with either type. Intravascular leiomyomatosis is a benign neoplasm that extends through the veins; angioleiomyoma is a benign neoplasm of the extremities; vascular leiomyosarcomas is a malign neoplasm that can be found in the inferior vena cava, pulmonary arteries and veins, and other peripheral vessels.
See Atherosclerosis
.
Striated muscle
Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...
. It is divided into two sub-groups; the single-unit
Single-unit
Single-unit smooth muscle, or visceral smooth muscle is a type of smooth muscle found in the uterus, gastro-instestinal tract, and the bladder. In SUVSM, a single smooth muscle cell in a bundle is innervated by an autonomic nerve fibre. An action potential can be propagated through neighbouring...
(unitary) and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by gap junctions to neighboring cells such that the whole bundle or sheet contracts as a syncytium
Syncytium
In biology, a syncytium is a large cell-like structure; filled with cytoplasm and containing many nuclei. Most cells in eukaryotic organisms have a single nucleus; syncytia are specialized forms used by various organisms.The term may also refer to cells that are connected by specialized membrane...
(i.e., a multinucleate mass of cytoplasm that is not separated into cells). Multiunit smooth muscle tissues innervate individual cells; as such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle.
Smooth muscle is found within the walls of blood vessels (such smooth muscle specifically being termed vascular smooth muscle
Vascular smooth muscle
Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood vessels.Vascular smooth muscle contracts or relaxes to both change the volume of blood vessels and the local blood pressure, a mechanism that is responsible for the...
) such as in the tunica media
Tunica media
The tunica media is the middle layer of an artery or vein.-Artery:It is made up of smooth muscle cells and elastic tissue...
layer of large (aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
) and small arteries, arterioles and veins. Smooth muscle is also found in lymphatic vessels, the urinary bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
, uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
(termed uterine smooth muscle), male and female reproductive tracts, gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...
, arrector pili of skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, the ciliary muscle
Ciliary muscle
The ciliary muscle is a ring of striated smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye not the size of the pupil which is...
, and iris of the eye
Iris (anatomy)
The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. "Eye color" is the color of the iris, which can be green, blue, or brown. In some cases it can be hazel , grey, violet, or even pink...
. The structure and function is basically the same in smooth muscle cells in different organs, but the inducing stimuli differ substantially, in order to perform individual effects in the body at individual times. In addition, the glomeruli
Glomerulus
A glomerulus is a capillary tuft that is involved in the first step of filtering blood to form urine.A glomerulus is surrounded by Bowman's capsule, the beginning component of nephrons in the vertebrate kidney. A glomerulus receives its blood supply from an afferent arteriole of the renal...
of the kidneys contain smooth muscle-like cells called mesangial cell
Mesangial cell
Mesangial cells are specialized cells around blood vessels in the kidneys, at the mesangium. They are specialized smooth muscle cells that function to regulate blood flow through the capillaries, usually divided into two types, each having a very distinct function and location:* Extraglomerular...
s.
Structure
Most smooth muscle is of the single-unit variety, that is, either the whole muscle contracts or the whole muscle relaxes, but there is multiunit smooth muscle in the trachea, the large elastic arteries, and the iris of the eye. Single unit smooth muscle, however, is most common and lines blood vessels (except large elastic arteries), the urinary tract, and the digestive tract.Smooth muscle is fundamentally different from skeletal muscle
Skeletal muscle
Skeletal muscle is a form of striated muscle tissue existing under control of the somatic nervous system- i.e. it is voluntarily controlled. It is one of three major muscle types, the others being cardiac and smooth muscle...
and cardiac muscle
Cardiac muscle
Cardiac muscle is a type of involuntary striated muscle found in the walls and histologic foundation of the heart, specifically the myocardium. Cardiac muscle is one of three major types of muscle, the others being skeletal and smooth muscle...
in terms of structure, function, regulation of contraction, and excitation-contraction coupling smooth.
Smooth muscle fibers have a fusiform shape and, like striated muscle
Striated muscle
Striated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...
, can tense and relax
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
. However, smooth muscle containing tissue tend to demonstrate greater elasticity and function within a larger length-tension curve than striated muscle. This ability to stretch and still maintain contractility is important in organs like the intestines and urinary bladder. In the relaxed state, each cell is spindle-shaped, 20-500 micrometers in length.
Molecular structure
A substantial portion of the volume of the cytoplasm of smooth muscle cells are taken up by the molecules myosinMyosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...
and actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
, which together have the capability to contract, and, through a chain of tensile structures, make the entire smooth muscle tissue contract with them.
Myosin
Myosin is primarily of class II in smooth muscle.- Myosin II contains two heavy chains which constitute the head and tail domains. Each of these heavy chains contains the N-terminal head domain, while the C-terminal tails take on a coiled-coil morphology, holding the two heavy chains together (imagine two snakes wrapped around each other, such as in a caduceusCaduceusThe caduceus is the staff carried by Hermes in Greek mythology. The same staff was also borne by heralds in general, for example by Iris, the messenger of Hera. It is a short staff entwined by two serpents, sometimes surmounted by wings...
). Thus, myosin II has two heads. In smooth muscle, there is a single gene (MYH11MYH11Myosin-11 is a protein that in humans is encoded by the MYH11 gene.- Function :Myosin-11 is a smooth muscle myosin belonging to the myosin heavy chain family...
) that codes for the heavy chains myosin II, but there are splice variantsAlternative splicingAlternative splicing is a process by which the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing...
of this gene that result in four distinct isoforms. Also, smooth muscle may contain MHC that is not involved in contraction, and that can arise from multiple genes. - Myosin II also contains 4 light chains, resulting in 2 per head, weighing 20 (MLC20) and 17 (MLC17) kDa. These bind the heavy chains in the "neck" region between the head and tail.
- The MLC20 is also known as the regulatory light chain and actively participates in muscle contractionMuscle contractionMuscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
. Two MLC20 isoforms are found in smooth muscle, and they are encoded by different genes, but only one isoform participates in contractility. - The MLC17 is also known as the essential light chain. Its exact function is unclear, but it's believed that it contributes to the structural stability of the myosin head along with MLC20. Two variants of MLC17 (MLC17a/b) exist as a result of alternate splicing at the MLC17 gene.
- The MLC20 is also known as the regulatory light chain and actively participates in muscle contraction
Different combinations of heavy and light chains allow for up to hundreds of different types of myosin structures, but it is unlikely that more than a few such combinations are actually used or permitted within a specific smooth muscle bed. In the uterus, a shift in myosin expression has been hypothesized to avail for changes in the directions of uterine contractions that are seen during the menstrual cycle.
Actin
The thin filaments that form part of the contractile machinery are predominantly composed of α- and γ-actin. Smooth muscle α-actin (alpha actin) is the predominate isoform within smooth muscle. There are also lots of actin (mainly β-actin) that does not take part in contraction, but that polymerizes just below the plasma membrane in the presence of a contractile stimulant and may thereby assist in mechanical tension. Alpha actin is also expressed as distinct genetic isoforms such there is smooth muscle, cardiac muscle and skeletal muscle specific isoforms of alpha actin. (ref The actin gene family: function follows isoform.Perrin BJ, Ervasti JM.Cytoskeleton (Hoboken). 2010 Oct;67(10):630-4. Review.)The ratio of actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
to myosin
Myosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...
is between 2:1 and 10:1 in smooth muscle, compared to ~6:1 in skeletal muscle and 4:1 in cardiac muscle.
Other proteins of the contractile apparatus
Smooth muscle does not contain the protein troponinTroponin
400px|thumb|right|alt = Colored dice with checkered background|Ribbon representation of the human cardiac troponin core complex in the calcium-saturated form...
; instead calmodulin
Calmodulin
Calmodulin is a calcium-binding protein expressed in all eukaryotic cells...
(which takes on the regulatory role in smooth muscle), caldesmon
Caldesmon
Caldesmon is a protein that in humans is encoded by the CALD1 gene.Caldesmon is a calmodulin binding protein. Like calponin, caldesmon tonically inhibits the ATPase activity of myosin in smooth muscle....
and calponin
Calponin
Calponin is a calcium binding protein. Calponin tonically inhibits the ATPase activity of myosin in smooth muscle. Phosphorylation of calponin by a protein kinase, which is dependent upon calcium binding to calmodulin, releases the calponin's inhibition of the smooth muscle ATPase.- Sturcture and...
are significant proteins expressed within smooth muscle.
- TropomyosinTropomyosinTropomyosin is an actin-binding protein that regulates actin mechanics. It is important, among other things, for muscle contraction. Tropomyosin, along with the troponin complex, associate with actin in muscle fibers and regulate muscle contraction by regulating the binding of myosin...
is present in smooth muscle, spanning seven actin monomers and is laid out end to end over the entire length of the thin filaments. In striated muscleStriated muscleStriated muscle tissue is a form of fibers that are combined into parallel fibers. More specifically, it can refer to:* Cardiac muscle .* Skeletal muscle* Branchiomeric muscles...
, tropomyosin serves to enhance actin–myosin interactions, but in smooth muscle, its function is unknown. - CalponinCalponinCalponin is a calcium binding protein. Calponin tonically inhibits the ATPase activity of myosin in smooth muscle. Phosphorylation of calponin by a protein kinase, which is dependent upon calcium binding to calmodulin, releases the calponin's inhibition of the smooth muscle ATPase.- Sturcture and...
molecules may exist in equal number as actin, and has been proposed to be a load-bearing protein. - CaldesmonCaldesmonCaldesmon is a protein that in humans is encoded by the CALD1 gene.Caldesmon is a calmodulin binding protein. Like calponin, caldesmon tonically inhibits the ATPase activity of myosin in smooth muscle....
has been suggested to be involved in tethering actin, myosin and tropomyosin, and thereby enhance the ability of smooth muscle to maintain tension.
Also, all three of these proteins may have a role in inhibiting the ATPase activity of the myosin complex that otherwise provides energy to fuel muscle contraction.
Other tensile structures
The myosin and actin are the contractile parts of continuous chains of tensile structures that stretch both across and between smooth muscle cells.The actin filaments of contractile units are attached to dense bodies. Dense bodies are rich in α-actinin, and also attach intermediate filaments (consisting largely of vimentin
Vimentin
Vimentin is a type III intermediate filament protein that is expressed in mesenchymal cells. IF proteins are found in all metazoan cells as well as bacteria. IF, along with tubulin-based microtubules and actin-based microfilaments, comprise the cytoskeleton...
and desmin
Desmin
Desmin is a protein that in humans is encoded by the DES gene.Desmin is a type III intermediate filament found near the Z line in sarcomeres. It was first described in 1976, first purified in 1977, the gene was cloned in 1989, and the first knock-out mouse was created in 1996. Desmin is only...
), and thereby appear to serve as anchors from which the thin filaments can exert force. Dense bodies also are associated with β-actin, which is the type found in the cytoskeleton, suggesting that dense bodies may coordinate tensions from both the contractile machinery and the cytoskeleton.
The intermediate filaments are connected to other intermediate filaments via dense bodies, which eventually are attached to adherens junctions (also called focal adhesions) in the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
of the smooth muscle cell, called the sarcolemma
Sarcolemma
The sarcolemma is the cell membrane of a muscle cell . It consists of a true cell membrane, called the plasma membrane, and an outer coat made up of a thin layer of polysaccharide material that contains numerous thin collagen fibrils...
. The adherens junctions consist of large number of proteins including α-actinin, vinculin and cytoskeletal actin. The adherens junctions are scattered around dense bands that are circumfering the smooth muscle cell in a rib-like pattern. The dense band (or dense plaques) areas alternate with regions of membrane containing numerous caveolae. When complexes of actin and myosin contract, force is transduced to the sarcolemma through intermediate filaments attaching to such dense bands.
During contraction, there is a spatial reorganization of the contractile machinery to optimize force development. part of this reorganization consists of vimentin being phosphorylated at Ser
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
56 by a p21 activated kinase
P21 activated kinases
p21 activated kinases are members of a family of enzymes. They serve as targets for the small GTP binding proteins CDC42 and Rac and have been implicated in a wide range of biological activities.Members include:...
, resulting in some disassembly of vimentin polymers.
Also, the number of myosin filaments is dynamic between the relaxed and contracted state in some tissues as the ratio of actin to myosin changes, and the length and number of myosin filaments change.
Smooth muscle cells have been observed contracting in a spiral corkscrew fashion, and contractile proteins have been observed organizing into zones of actin and myosin along the axis of the cell.
Smooth muscle-containing tissue needs to be stretched often, so elasticity is an important attribute of smooth muscle. Smooth muscle cells may secrete a complex extracellular matrix containing collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
(predominantly types I and III), elastin
Elastin
Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to resume their shape after stretching or contracting. Elastin helps skin to return to its original position when it is poked or pinched. Elastin is also an important load-bearing tissue in the bodies of...
, glycoproteins, and proteoglycans. Smooth muscle also has specific elastin and collagen receptors to interact with these proteins of the extracellular matrix. These fibers with their extracellular matrices contribute to the viscoelasticity
Viscoelasticity
Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like honey, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain instantaneously when stretched and just...
of these tissues. For example, the great arteries are viscolelastic vessels that act like a Windkessel
Windkessel
Windkessel literally means air chamber and is a German translation of a concept described previousy by Stephen Hales, who likened the effect of the elastic arteries in dampening the arterial pulse to that of an air chamber in some 18th century fire engines...
, propagating ventricular contraction and smoothing out the pulsatile flow, and the smooth muscle within the tunica media
Tunica media
The tunica media is the middle layer of an artery or vein.-Artery:It is made up of smooth muscle cells and elastic tissue...
contributes to this property.
Caveolae
The sarcolemma also contains caveolae, which are microdomains of lipid rafts specialized to cell-signaling events and ion channels. These invaginations in the sarcoplasma contain a host of receptorsReceptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
(prostacyclin
Prostacyclin
Prostacyclin is a member of the family of lipid molecules known as eicosanoids.As a drug, it is also known as "epoprostenol". The terms are sometimes used interchangeably.-History:...
, endothelin
Endothelin
Endothelins are proteins that constrict blood vessels and raise blood pressure. They are normally kept in balance by other mechanisms, but when they are over-expressed, they contribute to high blood pressure and heart disease....
, serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, muscarinic receptors, adrenergic receptors), second messenger generators (adenylate cyclase
Adenylate cyclase
Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....
, Phospholipase C
Phospholipase C
Phosphoinositide phospholipase C is a family of eukaryotic intracellular enzymes that play an important role in signal transduction processes. In general, this enzyme is denoted as Phospholipase C, although three other families of phospholipase C enzymes have been identified in bacteria and in...
), G proteins (RhoA, G alpha), kinases (rho kinase-ROCK, Protein kinase C
Protein kinase C
Protein kinase C also known as PKC is a family of enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in...
, Protein Kinase A), ion channels (L type Calcium channels, ATP sensitive Potassium channels, Calcium sensitive Potassium channels) in close proximity. The caveolae are often close to sarcoplasmic reticulum or mitochondria, and have been proposed to organize signaling molecules in the membrane.
Excitation-contraction coupling
A smooth muscle is excited by external stimuli, which causes contraction. Each step is further detailed below.Inducing stimuli and factors
Smooth muscle may contract spontaneously (via ionic channel dynamics) or as in the gut special pacemakers cells interstitial cells of Cajal produce rhythmic contractions. Also, contraction, as well as relaxation, can be induced by a number of physiochemical agents (e.g., hormones, drugs, neurotransmitters - particularly from the autonomic nervous systemAutonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
.
Smooth muscle in various regions of the vascular tree, the airway and lungs, kidneys and vagina is different in their expression of ionic channels, hormone receptors, cell-signaling pathways, and other proteins that determine function.
External substances
For instance, most blood vessels respond to norepinephrineNorepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
and epinephrine
Epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...
(from sympathetic
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
stimulation or the adrenal medulla) by producing vasoconstriction (this response is mediated through alpha 1-adrenergic receptors). Blood vessels in skeletal muscle and cardiac muscle respond to these catecholamines producing vasodilation because the smooth muscle possess beta-adrenergic receptors.
Generally, arterial smooth muscle responds to carbon dioxide by producing vasodilation, and responds to oxygen by producing vasoconstriction. Pulmonary blood vessels within the lung are unique as they vasodilate to high oxygen tension and vasoconstrict when it falls. Bronchiole, smooth muscle that line the airways of the lung, respond to high carbon dioxide producing vasodilation and vasoconstrict when carbon dioxide is low. These responses to carbon dioxide and oxygen by pulmonary blood vessels and bronchiole airway smooth muscle aid in matching perfusion and ventilation within the lungs. Further different smooth muscle tissues display extremes of abundant to little sarcoplasmic reticulum so excitation-contraction coupling varies with its dependence on intracellular or extracellular calcium.
Stretch
Recent research indicates that sphingosine-1-phosphateSphingosine-1-phosphate
Sphingosine-1-phosphate is a signaling sphingolipid. It is also referred to as a bioactive lipid mediator. Sphingolipids at large form a class of lipids characterized by a particular aliphatic aminoalcohol, which is sphingosine.-Production:...
(S1P) signaling is an important regulator of vascular smooth muscle
Vascular smooth muscle
Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood vessels.Vascular smooth muscle contracts or relaxes to both change the volume of blood vessels and the local blood pressure, a mechanism that is responsible for the...
contraction. When transmural pressure
Transmural pressure
Transmural pressure is the difference in pressure between two sides of a wall or equivalent separator.*For body vasculature or other hollow organs, see Smooth muscle#Contraction and relaxation basics*For lungs, see Transpulmonary pressure...
increases, sphingosine kinase 1
Sphingosine kinase 1
Sphingosine kinase 1 is an enzyme that in humans is encoded by the SPHK1 gene.Sphingosine kinase 1 phosphorylates sphingosine to sphingosine-1-phosphate SK1 is normally a cytosolic protein but is recruited to membranes rich in phosphatidate , a product of Phospholipase D Sphingosine-1-phosphate ...
phosphorylates sphingosine to S1P, which binds to the S1P2 receptor in plasma membrane of cells. This leads to a transient increase in intracellular calcium, and activates Rac and Rhoa signaling pathways. Collectively, these serve to increase MLCK activity and decrease MLCP activity, promoting muscle contraction. This allows arterioles to increase resistance in response to increased blood pressure and thus maintain constant blood flow. The Rhoa and Rac portion of the signaling pathway provides a calcium-independent way to regulate resistance artery
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
tone.
Spread of impulse
To maintain organ dimensions against force, cells are fastened to one another by adherens junctions. As a consequence, cells are mechanically coupled to one another such that contraction of one cell invokes some degree of contraction in an adjoining cell. Gap junctions couple adjacent cells chemically and electrically, facilitating the spread of chemicals (e.g., calcium) or action potentials between smooth muscle cells. Single unit smooth muscle displays numerous gap junctions and these tissues often organize into sheets or bundles which contract in bulk.Contraction
Smooth muscle contraction is caused by the sliding of myosinMyosin
Myosins comprise a family of ATP-dependent motor proteins and are best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility processes. They are responsible for actin-based motility. The term was originally used to describe a group of similar...
and actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
filaments (a sliding filament mechanism
Sliding filament mechanism
The sliding filament theory describes a process used by muscles to contract. It was independently developed by Andrew F. Huxley and Rolf Niedergerke and by Hugh Huxley and Jean Hanson in 1954.-Process of movement:...
) over each other. The energy for this to happen is provided by the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
. Myosin functions as an ATPase utilizing ATP to produce a molecular conformational change of part of the myosin and produces movement. Movement of the filaments over each other happens when the globular heads protruding from myosin filaments attach and interact with actin filaments to form crossbridges. The myosin heads tilt and drag along the actin filament a small distance (10-12 nm). The heads then release the actin filament and then changes angle to relocate to another site on the actin filament a further distance (10-12 nm) away. They can then re-bind to the actin molecule and drag it along further. This process is called crossbridge cycling and is the same for all muscles (see muscle contraction
Muscle contraction
Muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten, or remain the same...
). Unlike cardiac and skeletal muscle, smooth muscle does not contain the calcium-binding protein troponin. Contraction is initiated by a calcium-regulated phosphorylation of myosin, rather than a calcium-activated troponin system.
Crossbridge cycling causes contraction of myosin and actin complexes, in turn causing increased tension along the entire chains of tensile structures, ultimately resulting in contraction of the entire smooth muscle tissue.
Phasic or tonic
Smooth muscle may contract phasically with rapid contraction and relaxation, or tonically with slow and sustained contraction. The reproductive, digestive, respiratory, and urinary tracts, skin, eye, and vasculature all contain this tonic muscle type. This type of smooth muscle can maintain force for prolonged time with only little energy utilization. There are differences in the myosin heavy and light chains that also correlate with these differences in contractile patterns and kinetics of contraction between tonic and phasic smooth muscle.Activation of myosin heads
Crossbridge cycling cannot occur until the myosin heads have been activated to allow crossbridges to form. When the light chains are phosphorylated, they become active and will allow contraction to occur. The enzyme that phosphorylates the light chains is called myosin light-chain kinaseMyosin light-chain kinase
Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates the regulatory light chain of myosin II.- Isoforms :Four different MLCK isoforms exist:* MYLK – smooth muscle...
(MLCK), also called MLC20 kinase. In order to control contraction, MLCK will work only when the muscle is stimulated to contract. Stimulation will increase the intracellular concentration of calcium ions. These bind to a molecule called calmodulin
Calmodulin
Calmodulin is a calcium-binding protein expressed in all eukaryotic cells...
, and form a calcium-calmodulin complex. It is this complex that will bind to MLCK to activate it, allowing the chain of reactions for contraction to occur.
Activation consists of phosphorylation of a serine
Serine
Serine is an amino acid with the formula HO2CCHCH2OH. It is one of the proteinogenic amino acids. By virtue of the hydroxyl group, serine is classified as a polar amino acid.-Occurrence and biosynthesis:...
on position 19 (Ser19) on the MLC20 light chain, which causes a conformational change that increases the angle in the neck domain of the myosin heavy chain, which corresponds to the part of the cross-bridge cycle where the myosin head is unattached to the actin filament and relocates to another site on it. After attachment of the myosin head to the actin filament, this serine phosphorylation also activates the ATPase activity of the myosin head region to provide the energy to fuel the subsequent contraction. Phosphorylation of a threonine on position 18 (Thr18) on MLC20 is also possible and may further increase the ATPase activity of the myosin complex.
Sustained maintenance
Phosphorylation of the MLC20 myosin light chains correlates well with the shortening velocity of smooth muscle. During this period there is a rapid burst of energy utilization as measured by oxygen consumption. Within a few minutes of initiation the calcium level markedly decrease, MLC20 myosin light chains phosphorylation decreases, and energy utilization decreases and the muscle can relax. Still, smooth muscle has the ability of sustained maintenance of force in this situation as well. This sustained phase has been attributed to certain myosin crossbridges, termed latch-bridges, that are cycling very slowly, notably at the cycle stage where dephosphorylated myosin complexes detach from the actin, thereby maintaining the force at low energy costs. This phenomenon is of great value especially for tonically active smooth muscle.Isolated preparations of vascular and visceral smooth muscle contract with depolarizing high potassium balanced saline generating a certain amount of contractile force. The same preparation stimulated in normal balanced saline with an agonist such as endothelin or serotonin will generate more contractile force. This increase in force is termed calcium sensitization. The myosin light chain phosphatase is inhibited to increase the gain or sensitivity of myosin light chain kinase to calcium. There are number of cell signalling pathways believed to regulate this decrease in myosin light chain phosphatase: a RhoA-Rock kinase pathway, a Protein kinase C-Protein kinase C potentiation inhibitor protein 17 (CPI-17) pathway, telokin, and a Zip kinase pathway. Further Rock kinase and Zip kinase have been implicated to directly phosphorylate the 20kd myosin light chains.
Other contractile mechanisms
Other cell signaling pathways and protein kinases (Protein kinase CProtein kinase C
Protein kinase C also known as PKC is a family of enzymes that are involved in controlling the function of other proteins through the phosphorylation of hydroxyl groups of serine and threonine amino acid residues on these proteins. PKC enzymes in turn are activated by signals such as increases in...
, Rho kinase, Zip kinase, Focal adhesion kinases) have been implicated as well and actin polymerization dynamics plays a role in force maintenance. While myosin light chain phosphorylation correlates well with shortening velocity, other cell signaling pathways have been implicated in the development of force and maintenance of force. Notably the phosphorylation of specific tyrosine residues on the focal adhesion adapter protein-paxillin by specific tyrosine kinases has been demonstrated to be essential to force development and maintenance. For example, cyclic nucleotides can relax arterial smooth muscle without reductions in crossbridge phosphorylation, a process termed force suppression. This process is mediated by the phosphorylation of the small heat shock protein, hsp20
Hsp20
Heat shock protein Hsp20 is a family of heat shock proteins.Prokaryotic and eukaryotic organisms respond to heat shock or other environmental stress by inducing the synthesis of proteins collectively known as heat-shock proteins . Amongst them is a family of proteins with an average molecular...
, and may prevent phosphorylated myosin heads from interacting with actin.
Relaxation
The phosphorylation of the light chains by MLCK is countered by a myosin light-chain phosphatase, which dephosphorylates the MLC20 myosin light chains and thereby inhibits contraction. Other signaling pathways have also been implicated in the regulation actin and myosin dynamics. In general, the relaxation of smooth muscle is by cell-signaling pathways that increase the myosin phosphatase activity, decrease the intracellular calcium levels, hyperpolarize the smooth muscle, and/or regulate actin and myosin dynamics.Relaxation-inducing factors
The relaxation of smooth muscle can be mediated by the endothelium-derived relaxing factor-nitric oxide, endothelial derived hyperpolarizing factor (either an endogenous cannabinoid, cytochrome P450 metabolite, or hydrogen peroxide), or prostacyclin (PGI2). Nitric oxide and PGI2 stimulate soluble guanylate cyclase and membrane bound adenylate cyclase, respectively. The cyclic nucleotides (cGMP and cAMP) produced by these cyclases activate Protein Kinase G and Proten Kinase A and phosphorylate a number of proteins. The phosphorylation events lead to a decrease in intracelluar calcium (inhibit L type Calcium channels, inhibits IP3 receptor channels, stimulates sarcoplasmic reticulum Calcium pump ATPase), a decrease in the 20kd myosin light chain phosphorylation by altering calcium sensitization and increasing myosin light chain phosphatase activity, a stimulation of calcium sensitive potassium channels which hyperpolarize the cell, and the phosphorylation of amino acid residue serine 16 on the small heat shock protein (hsp20)by Protein Kinases A and G. The phosphorylation of hsp20 appears to alter actin and focal adhesion dynamics and actin-myosin interaction, and recent evidence indicates that hsp20 binding to 14-3-3 protein is involved in this process. An alternative hypothesis is that phosphorylated Hsp20 may also alter the affinity of phosphorylated myosin with actin and inhibit contractility by interfering with crossbridge formation. The endothelium derived hyperpolarizing factor stimulates calcium sensitive potassium channels and/or ATP sensitive potassium channels and stimulate potassium efflux which hyperpolarizes the cell and produces relaxation.Invertebrate smooth muscle
In invertebrate smooth muscle, contraction is initiated with the binding of calcium directly to myosin and then rapidly cycling cross-bridges, generating force. Similar to the mechanism of vertebrate smooth muscle, there is a low calcium and low energy utilization catch phase. This sustained phase or catch phase has been attributed to a catch protein that has similarities to myosin light-chain kinase and the elastic protein-titin called twitchin. Clams and other bivalve mollusks use this catch phase of smooth muscle to keep their shell closed for prolonged periods with little energy usage.Specific effects
Although the structure and function is basically the same in smooth muscle cells in different organs, their specific effects or end-functions differ.Smooth muscle forms precapillary sphincters in blood vessels in metarterioles which regulates the blood flow in capillary beds of various organs and tissues. The contractile function of vascular smooth muscle also regulates the lumenal diameter of the small arteries-arterioles called resistance vessels, thereby contributing significantly to setting the level of blood pressure. Smooth muscle contracts slowly and may maintain the contraction (tonically) for prolonged periods in blood vessels, bronchioles, and some sphincters. Activating arteriole smooth muscle can decrease the lumenal diameter 1/3 of resting so it drastically alters blood flow and resistance. Activation of aortic smooth muscle doesn't significantly alter the lumenal diameter but serves to increase the viscoelasticity of the vascular wall.
In the digestive tract, smooth muscle contracts in a rhythmic peristaltic fashion, rhythmically forcing foodstuffs through the digestive tract as the result of phasic contraction.
A non-contractile function is seen in specialized smooth muscle within the afferent arteriole of the juxtaglomerular apparatus, which secretes renin
Renin
Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...
in response to osmotic and pressure changes, and also it is believed to secrete ATP in tubuloglomerular regulation of glomerular filtration rate. Renin in turn activates the renin-angiotensin system
Renin-angiotensin system
The renin-angiotensin system or the renin-angiotensin-aldosterone system is a hormone system that regulates blood pressure and water balance....
to regulate blood pressure.
Growth and rearrangement
The mechanism in which external factors stimulate growth and rearrangement is not yet fully understood. A number of growth factors and neurohumoral agents influence smooth muscle growth and differentiation. The Notch receptor and cell-signaling pathway have been demonstrated to be essential to vasculogenesis and the formation of arteries and veins.The embryological origin of smooth muscle is usually of mesodermal origin. However, the smooth muscle within the Aorta and Pulmonary arteries (the Great Arteries of the heart) is derived from ectomesenchyme of neural crest origin, although coronary artery smooth muscle is of mesodermal origin.
Related diseases
"Smooth muscle condition" is a condition in which the body of a developing embryo does not create enough smooth muscle for the gastrointestinal system. This condition is fatal.Anti-smooth muscle antibodies
Anti-smooth muscle antibody
Anti-smooth muscle antibodies are antibodies formed against smooth muscle. These antibodies are typically associated with autoimmune hepatitis.These antibodies can be directed against actin, troponin, and tropomyosin....
(ASMA) can be a symptom of an auto-immune disorder, such as hepatitis
Hepatitis
Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...
, cirrhosis
Cirrhosis
Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules , leading to loss of liver function...
, or lupus
Lupus erythematosus
Lupus erythematosus is a category for a collection of diseases with similar underlying problems with immunity . Symptoms of these diseases can affect many different body systems, including joints, skin, kidneys, blood cells, heart, and lungs...
.
Vascular smooth muscle tumors are very rare. They can be malignant or benign, and morbidity can be significant with either type. Intravascular leiomyomatosis is a benign neoplasm that extends through the veins; angioleiomyoma is a benign neoplasm of the extremities; vascular leiomyosarcomas is a malign neoplasm that can be found in the inferior vena cava, pulmonary arteries and veins, and other peripheral vessels.
See Atherosclerosis
Atherosclerosis
Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
.
External links
- BBC - baby born with smooth muscle condition has 8 organs transplanted
- Smooth muscle antibody
- Stomach smooth muscle identified using antibody "Smooth Muscle"