Which muscle is spindle shaped

TEM picture. Histamine is a biogenic vasoactive amine, mediator of inflammation, gastric hydrochloric acid secretion and smooth muscle contraction [ 17 ]. Histamine is detected in mast cells, nerve and neuroendocrine cells, lungs, kidneys, cerebrovascular endothelial cells, peripheral nervous system [ 18 ].

It elicits a contractile response in smooth muscles and lowers blood pressure [ 19 ]. Histamine is released by mast cells in response to allergic reactions or tissue damage. The close vicinity of mast cells to blood vessels, together with the strong vascular effect of histamine suggests that it could influence blood flow, including that of the brain [ 20 ].

Histamine acts upon visceral smooth musculature by contracting it [ 8 ]. Histamine has a marked cardiovascular effect as well. It provokes dilation of terminal arterioles and the other vessels from the microcirculatory vascular bed, increases the permeability of capillaries during oedema formation and causes contraction of smooth muscle cells of large arteries and veins. The relative predominance of these effects is species-dependent. For instance, the histamine-induced contraction of arterioles is strong in rodents, less pronounced in cats, while they are dilated in dogs, non-human primates, and humans [ 19 ].

In general, the effect of histamine on a specific regional vasculature could be best described as a result of its multiple effects on smooth muscle and the lining endothelium. It is supposed that the transmembrane signalling mechanisms are involved in the different effects of histamine on vascular smooth muscles [ 22 , 23 ].

The role of histamine as a chemical mediator of renal autoregulation in some animal species is long acknowledged. Immunohistochemically, histamine-positive mast cells were found in all layers of renal blood vessels in pigs [ 16 ]. They were most numerous in the tunica media, as well as at the boundary between media and adventitia Fig. In the tunica media of arcuate arteries, histamine-positive mastocytes were relatively few, while in arcuate veins were observed only as single findings.

Histamine positive mast cell mc between media and adventitia of porcine interlobar artery. Histamine-positive mast cells were also detected in the middle layer of the renal pelvis and the ureter of the pig [ 15 , 16 ], Fig. Two histamine positive mast cells mc in the circular smoothlayer sm of porcine ureter. Dopamine belongs to the group of catecholamines, which are direct-acting sympathomimetic amines. Adrenergic nerves are not required for their effects because they activate the receptors of effector cells.

This is mainly valid for already synthesized and exogenous catecholamines [ 27 ]. Before, dopamine was believed to be important only as an immediate precursor of norepinephrine noradrenalin, levarterenol, arterenol , but later some of its important physiological functions in mammals were revealed and thus, it was considered more thoroughly in some clinical states in men [ 28 ].

Apart from its significance for nervous system, dopamine is tightly related in cardiovascular activity. Cardiovascular effects of dopamine depend on the activation of different types of catecholamine receptors. Dopaminergic receptors of vascular beds could be considered a fifth adrenergic receptor subtype. Although the physiological significance of dopamine receptors is unknown, this type is important for clinical pharmacology as it is involved in vasodilator responses in renal, coronary and brain circulatory beds.

The activation of these receptors by dopamine is highly selective, while the agonistic activity of other catecholamines is minor [ 27 ]. By opinion of [ 29 ] dopamine induced a reduction of vascular resistance and increases the blood flow to kidneys and mesenteries blood vessels, together with myocardial stimulation.

The selective vasodilation of renal and visceral beds by dopamine suggested its use in clinical cardiac dysfunctions. It is successfully used in treatment of shock as it dilates renal arteries through activation of dopamine-1 DA 1 receptors and enhances cardiac activity via activation of cardiac -adrenergic receptors [ 20 , 27 ]. Dopamine receptors on vascular smooth muscles are classified by [ 30 , 31 ] as DA 1. With regard to the presence of dopamine in mast cells, data available so far describe it as mastocyte amine mediator only in ruminants [ 32 ].

Using a histochemical reaction for the detection of tyrosine hydroxylase TH — a primary enzyme in dopamine synthesis pathway in porcine kidney, it was found out that TH-positive mast cells were predominantly localized at two sites: the renal sinus and in glomeruli of the superficial, middle and juxtamedullary cortical zones [ 16 ].

TH-positive mast cells in the renal sinus were usually seen as single cells, less frequently as clusters of several cells near the large blood vessels Fig. TH-positive mast cells in the renal sinus, gathered near the blood vessels.

Some of TH-positive mast cells upper half of 5A at a higher magnification. TH-positive mast cells were not detected in the cortex. In our view, the absence of TH-positive mast cells around and within cortical vessels is probably one of the reasons for the application of dopamine in spasms of the interlobular arteries to relieve anuria due to a variety of causes. Nevertheless, as outlined by [ 33 ], the application of dopamine in humans and some animal species with renal failure did not provoke the anticipated effect.

The vasoactive intestinal polypeptide is a multifunctional peptide built of 29 amino acids, first isolated from porcine duodenum [ 34 ] and initially considered a potential vasodilator.

Along its importance in carcinogenesis, VIP is also related to diseases such as bronchial asthma, urinary bladder fibrosis and AIDS [ 35 ]. VIP was first described in mastocytes of rats and mice by [ 36 ], and its relationship to histamine was shown. Later, VIP was described in basophils as well [ 37 ]. As mast cells are abundant in the connective tissue of different organs, the contained VIP could influence the local or regional blood flow in both normal and pathological states [ 36 ].

Mast cells, immunopositive to VIP were observed in large blood vessels, including arcuate arteries and veins of pigs [ 16 ]. Relatively high mast cells counts were established within the media of these vessels, with highest density in the renal artery. Less VIP-positive cells were observed on the boundary between the media and the adventitia. It should be emphasized that in arcuate arteries, VIP-positive mast cells were present only in the middle shell, with relatively regular distribution along the circumference of the blood vessel Fig.

VIP positive mast cells mc in the middle shell media of porcine arcuate artery. Its various biological actions include, apart from the regulation of vasoconstriction and neurotransmission, the regulation of cytokine-regulated cell growth [ 47 ]. Out of the three ET isopeptides, ET-1 has marked effect mainly on smooth muscle cells of the vascular wall.

There is evidence that vascular smooth muscle cells are also capable to produce endothelin [ 48 , 49 ]. Apart being a potent vasoconstrictor, ET-1 also exhibits hypertrophic, mitogenic and anti-apoptotic effects on vascular smooth muscle cells [ 50 - 52 ]. Initially described as a vasoconstrictor, ET-1 is now acknowledged to participate in the pathogenesis of a number of disorders, i.

ET-1 is widely spread in various tissues and organs, including the gastrointestinal tract. Its three isopeptides were detected mainly in mast cells and less frequently, in macrophages of Lamina propria of the stomach, small intestine and colon in Wistar rats. Apart the confirmed synthesis and secretion of ET by mast cells, its role as a new cytokine factor in these cells was suggested [ 46 ]. ET was reported to be present in the basilar artery of the rat [ 58 , 59 ] and post mortem, in human cerebrovascular nerves of the middle cerebral artery [ 60 ].

Immunoreactive ET-1 was also detected in endothelial cells of the intima, vascular smooth muscle cells and macrophages of the media and neointima, and in perivascular nerves axons varicosities at the boundary between media and adventitia of the middle cerebral artery in a patient with multiple system atrophy with autonomic deficiency [ 61 ].

ET-1 positivity of uterine smooth muscle cells and mast cells was reported in a post partum mouse, but its functions remained unclear [ 62 ]. It was therefore concluded that the spontaneous contraction of equine caecal smooth musculature most probably originated in smooth muscle cells, and not in enteric nervous system. Having investigated the vasoconstrictor effect of ET-1 on resistant renal blood vessels in a rabbit through in vitro microperfusion of afferent and efferent glomerular arterioles, [ 63 ] established a dose-dependent decrease in their lumen.

Endothelin-immunopositive mast cells were present in the wall of both extrarenal and intrarenal blood vessels of the pig [ 16 ]. The largest amount of mast cells was observed in peripheral layers of tunica media, as well as on the boundary between media and adventitia.

Endothelin-positive mastocytes were also observed in deeper layers of the media, in the connective tissue among smooth muscle cells. The detected mast cells were of different shape and with well visualized immunopositive granules. ET-positive mast cells in the wall of the renal vein were more rarely observed. Their localisation was similar to that in the renal artery.

ET-positive mast cells were detected occasionally in the wall of intrarenal blood vessels, but only as single findings in arcuate and interlobular arteries and veins. The research of [ 64 ] on mast cells in the wall of canine sublobular hepatic veins by transmission electron microscopy has shown that ET-1 was present in both the cytoplasmic matrix and cytoplasmic granules.

According to the author, the coexistence of ET-1 and histamine in mast cell granules was closely related to the strong vasoconstrictor effect on venous sphincters of canine liver. The strong correlation between the density of mast cells in tissues and the efficacy of tissue extracts to prevent blood coagulation, it was supposed long ago that mast cells contained the potent anticoagulant heparin.

According to [ 65 ] heparin is the only large glycosaminoglycan and its amount in the cell is about 20 pg. Activated mast cells, releasing heparin proteoglycans, inhibit the proliferation of smooth muscle cells in the tunica media of human arterial wall, while histamine stimulates it [ 10 ]. It was demonstrated by [ 9 ] the inhibitory effect of heparin on human myometrium proliferation, suggesting that it could induce the differentiation of uterine smooth muscle cells and to influence tissue remodelling and reconstruction in different physiological and pathophysiological events.

Glycosaminoglycan-positive, including heparin-positive mast cells were observed by us [ 16 ] in the walls of extra and intrarenal blood vessels in pigs Fig. To determine the amount of heparin-containing mast cells, they were initially stained with 0.

Positive reaction was detected both in mast cells in the connective tissue stroma among smooth muscle cell clusters, as well as within packs, in close vicinity to smooth muscle cells Fig. These data, compared to previously cited repots allowed assuming that heparin-containing mast cells regulated the growth of smooth muscle cells not only in the vascular wall, but also in the external anal sphincter in dogs [ 16 , 66 ]. Heparin contained- berberin positive mast cells arrows.

IAS- internal anal sphincter. GA- apocrine glands. Male 4 years dog. Courtesy by Dr I. Toluidine blue staining of the same area - 8A. Nitric oxide NO is a molecular free-radical gas, an important mediator with a variety of functions [ 67 ].

As this family of enzymes incorporates molecular oxygen, NOS are classified as dioxygenases with similar features with cytochrome P reductase. Cofactors needed for NO synthesis include flavin adenine dinucleotide FAD , flavin mononucleotide, nicotinamide adenine dinucleotide phosphate NADPH , haemoglobin and tetrahydrobiopterin. NOS-coding genes are localised in different chromosomes. The structure of enzymes is common, i. Apart regulating the mast cell phenotype and function [ 70 ], NO is also produced by mast cells.

Muscle cells are excitable; they respond to a stimulus. They are contractile, meaning they can shorten and generate a pulling force. When attached between two movable objects, in other words, bones, contractions of the muscles cause the bones to move. Some muscle movement is voluntary, which means it is under conscious control. For example, a person decides to open a book and read a chapter on anatomy.

Other movements are involuntary, meaning they are not under conscious control, such as the contraction of your pupil in bright light. Muscle tissue is classified into three types according to structure and function: skeletal, cardiac, and smooth Table 1.

Skeletal muscle is attached to bones and its contraction makes possible locomotion, facial expressions, posture, and other voluntary movements of the body. Forty percent of your body mass is made up of skeletal muscle. Skeletal muscles generate heat as a byproduct of their contraction and thus participate in thermal homeostasis.

Shivering is an involuntary contraction of skeletal muscles in response to perceived lower than normal body temperature. The muscle cell, or myocyte , develops from myoblasts derived from the mesoderm.

Myocytes and their numbers remain relatively constant throughout life. Skeletal muscle tissue is arranged in bundles surrounded by connective tissue. Under the light microscope, muscle cells appear striated with many nuclei squeezed along the membranes.

The striation is due to the regular alternation of the contractile proteins actin and myosin, along with the structural proteins that couple the contractile proteins to connective tissues.

The cells are multinucleated as a result of the fusion of the many myoblasts that fuse to form each long muscle fiber. Cardiac muscle forms the contractile walls of the heart. The cells of cardiac muscle, known as cardiomyocytes, also appear striated under the microscope. Unlike skeletal muscle fibers, cardiomyocytes are single cells typically with a single centrally located nucleus.

A principal characteristic of cardiomyocytes is that they contract on their own intrinsic rhythms without any external stimulation. Cardiomyocyte attach to one another with specialized cell junctions called intercalated discs. Intercalated discs have both anchoring junctions and gap junctions. Attached cells form long, branching cardiac muscle fibers that are, essentially, a mechanical and electrochemical syncytium allowing the cells to synchronize their actions.

The cardiac muscle pumps blood through the body and is under involuntary control. The attachment junctions hold adjacent cells together across the dynamic pressures changes of the cardiac cycle. Smooth muscle tissue contraction is responsible for involuntary movements in the internal organs.

It forms the contractile component of the digestive, urinary, and reproductive systems as well as the airways and arteries. Each cell is spindle shaped with a single nucleus and no visible striations Figure 1. Figure 1. Muscle Tissue. Watch this video to learn more about muscle tissue.

In looking through a microscope how could you distinguish skeletal muscle tissue from smooth muscle?