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Biomedical subjects

G Gabella

Publications and source records attributed to G Gabella.

At least 73 records · Page 4Linked to original sources
PubMed1985

Structure of the musculature of the chicken small intestine.

The small intestine of the chicken was studied by light and electron microscopy. The musculature, measuring about 180 microns in thickness in the distended intestine, consists of four layers (outer longitudinal, outer circular, inner circular and inner longitudinal) which are directly apposed to one another. There is no layer of connective tissue equivalent to the submucosa of mammalian intestine, and the intestinal glands lie close to the inner longitudinal muscle. Mucosal folds are not formed during isotonic contraction of the intestine. The muscle cells of the chicken small intestine are characterized by large, numerous and sharply outlined dense bodies, by the presence of an extremely thin basal lamina, by prominent dense bands at the cell surface but relatively few intermediate junctions. There are many areas of direct apposition between cell membranes of adjacent cells and little collagen between the muscle cells. The four muscle layers have each distinctive structural features. Gap junctions between muscle cells occur only in the outer circular layer. The outer circular and outer longitudinal layers are closely apposed and numerous junctions of the adherens type link cells of the two layers. Intramuscular blood capillaries are rare and are found virtually only in the outer circular layer; their endothelial cells are joined by tight junctions. In the outer circular layer (but not in the other layers) there are two further cell types, fibroblasts and interstitial cells, which can be clearly distinguished from one another. The latter cells are intimately related to nerve bundles and are connected by gap junctions to some muscle cells.

Animals↗
PubMed1985

Chicken gizzard. The muscle, the tendon and their attachment.

The fine structure and the organization of muscle and connective tissue in the middle portion of the chicken gizzard (muscular stomach) has been studied by light and electron microscopy. The musculature is divided into long, well-defined bundles arranged circularly and concentrically and extending between the two tendons (tendinous aponeurosis). The muscle bundles are inserted onto the inner surface of the tendon at an angle of about 45 degrees. In addition to muscle cells (which are ultrastructurally similar to those of the small intestine) the musculature contains fibroblasts and interstitial cells and a small number of nerve bundles and capillaries. The gizzard tendons are very compact, made of parallel fascicles of collagen fibrils with interposed stellate tendon cells; ultrastructurally they are very similar to the tendon of skeletal muscles of this and other species. Their collagen fibrils range in size from 30 to 160 nm. The muscle cells that approach the tendon develop longitudinal invaginations of the cell membrane and then break into finger-like terminal processes heavily encrusted with dense bands. The membrane of the invaginations and the terminal processes are surrounded by a basal lamina material which embeds a conspicuous web of small collagen fibrils. The boundary between tendon and muscle is sharp, without interpenetration of the two tissues. A novel type of cell is found at the interface of muscle and tendon (junctional cells), filled with intermediate filaments and some rough endoplasmic reticulum and displaying a trace of a basal lamina.

Animals↗
PubMed1984

Transverse bands in smooth muscle cells.

In several preparations of intestinal musculature of mammals and other vertebrates, the smooth muscle cells showed distinct transverse striations. Their distribution was irregular, but they were often in register in adjacent cells. They were studied by light and electron microscopy, and it was concluded that they represent areas where the muscle cells had been crumpled, probably during or after fixation, especially in muscles that are curved and arranged in concentric arrays. A characteristic disruption in the arrangement of myofilaments was observed. These striations were not seen in control preparations of the guinea-pig taenia coli; however, when the taenia was wound around a rod after partial or complete fixation, transverse striations became apparent in the concave part of the coiled-up strip of muscle. The longitudinal compression of the muscle cells, which were made somewhat rigid by the fixation, is the most likely explanation of the transverse bands.

Animals↗
PubMed1984

Hypertrophic smooth muscle. V. Collagen and other extracellular materials. Vascularization.

In adult guinea-pigs, oral to a partial obstruction to the flow of ingesta in the ileum there is a marked increase in the diameter of the intestine and a hypertrophy of the muscle coat. The features of the intramuscular blood vessels and of the extracellular materials were studied by electron microscopy. There is a small increase in the amount of intercellular space measured morphometrically. The basal lamina surrounding the hypertrophic muscle cells is more prominent than in controls. In the intercellular space between muscle cells, in addition to collagen fibrils, there is abundant amorphous material of medium electron density and streak-like, electron-dense material often similar to thickened basal laminae. The total amount of stroma (intercellular materials) present in a unit length of intestine is greatly increased in hypertrophy; a role of the muscle cells in the production of new collagen and other extracellular elements is suggested by the present observations. Many new intramuscular blood vessels (mainly capillaries, some of which are fenestrated) are formed during hypertrophy of the intestinal wall, so that the circular muscle layer remains as well vascularized in the hypertrophic intestine as in the controls. Blood vessels are not formed within the longitudinal muscle layer.

Animals↗
PubMed1984

Size of neurons and glial cells in the enteric ganglia of mice, guinea-pigs, rabbits and sheep.

A quantitative light microscopic study has been carried out on the myenteric and submucosal ganglia of the stomach, duodenum, ileum, proximal colon and rectum of the guinea-pig; the enteric ganglia of the ileum were studied also in the mouse, rabbit and sheep. The area of the profiles of nerve cells, of nerve cell nuclei and of glial nuclei, and the proportion of the area of ganglia occupied by neuropil were measured, and the relative numbers of neurons and glial cells were estimated. The myenteric ganglia were found to be firmly anchored to the stroma of the muscle coat; their shape and the shape of their component cells varied with contraction and distension of the musculature. The range of neuronal sizes in the myenteric ganglia was extremely wide. In the guinea-pig, the myenteric neurons were on average largest in the stomach and duodenum and smallest in the ileum, with intermediate values in the colon and rectum; the submucosal neurons showed little variation in average size along the length of the gut. The average size of ganglion neurons in the ileum was greatest in the sheep and smallest in the mouse, and had intermediate values in the guinea-pig and rabbit. The percentage volume of neuropil in the myenteric ganglia was 51% in the mouse, 65% in the guinea-pig, 70% in the rabbit, and 74% in the sheep. The number of glial cells relative to the number of neurons was also ranked in the same order. In all the species examined the submucosal ganglia, when compared with the corresponding myenteric ganglia, had a smaller percentage volume of neuropil, a much smaller number of glial cells and (except in the mouse ileum) neurons of smaller average size. In all the ganglia there was a positive correlation between size of neurons and size of glial cells. The results are discussed in the light of possible relations between body size (and length of the intestine), numerical density of ganglion neurons, average size of neurons, amount of musculature, average distance between neurons, and amount of neuropil.

Animals↗
PubMed1984

Size of neurons and glial cells in the intramural ganglia of the hypertrophic intestine of the guinea-pig.

A quantitative light microscopic study has been carried out on the myenteric and submucosal ganglia of the guinea-pig ileum, after inducing hypertrophy of the wall with an experimental stenosis. The area of the profiles of nerve cells, of nerve cell nuclei and of glial nuclei, and the percentage area of the neuropil were measured, and the relative numbers of neurons and glial cells were estimated. The average size of neurons in both plexuses was greatly increased over the control values. Nearly half of the neuronal profiles measured over 500 microns2 in sectional area (less than 3% in the controls), and less than 1% measured less than 150 microns2 (21% in controls). The average size of glial nuclei (and presumably that of the glial cells too) was increased in the hypertrophic ganglia. The number of glial cells (relative to the number of neurons) was unchanged or slightly decreased in the hypertrophic myenteric ganglia; in contrast, it was markedly increased in the submucosal ganglia. In both ganglia the hypertrophy was accompanied by a decrease in the percentage volume of neuropil.

Animals↗
PubMed1984

Catecholamine-containing cells in the nerve plexus of the guinea pig gallbladder.

A population of catecholamine-containing cells, broadly belonging to the class of small intensely fluorescent (SIF) cells, was observed in the ganglionated plexus and around blood vessels of the guinea pig gallbladder. Their morphological features were studied by fluorescence and electron microscopy. Some cells were closely associated with ganglion neurons within the ganglionated plexus. Others were clustered into small groups located along blood vessels. Counts carried out on the whole gallbladder showed that these cells varied greatly in number between individuals and that they were most numerous shortly after birth (on average 230 cells). In the adult, their average number was about 30.

Animals↗
PubMed1984

Structure and innervation of the musculature at the gastroduodenal junction of the guinea-pig.

The musculature of the pylorus of the guinea-pig consists of a conspicuous ring of circular musculature. On one side, this tissue is apposed to the circular muscle layer of the duodenum, a complete septum of connective tissue intervening between the two muscles. On the other side, it is in continuity with the circular musculature of the gastric antrum. Bundles of longitudinal muscle, running close to the submucosa of the antrum, form a loop and contribute to the circular musculature of the pylorus. The subserosal longitudinal muscle of the antrum continues into the pylorus and the duodenum. The density of innervation, i.e. number of bundles, number of axons and percentage of varicosities per unit sectional area or per number of muscle cell profiles (estimated on large photographic montages of transversely sectioned muscles) is higher in the pylorus than in the duodenum, and is lowest in the antrum. In the duodenum nerve bundles occur in both the circular and the longitudinal muscle layer; the majority of axons and varicosities are situated between the bulk of the circular muscle and a layer of special muscle cells adjacent to the submucosa.

Animals↗
PubMed1983

Embryonic development of the smooth and striated musculatures of the chicken iris.

Both smooth muscle and striated muscle are present in the iris of the chick embryo. The two types of musculature form mixed clusters which include undifferentiated cells and many nerve fibres, but they are structurally quite distinct and have different origins. The smooth musculature originates around the 10th day from a laminar invagination (iridial lamella) of the posterior epithelium, and is therefore an ectodermal derivative. The striated musculature appears slightly later than the smooth musculature and originates from undifferentiated cells which are regarded as mesenchymal. After the 15th day in ovo the smooth musculature stops growing; its cells become confined to an area very near the pupillary margin and many develop pigment granules in the sarcoplasm. Many smooth muscle cells seem to undergo regressive changes; however, cells with the typical appearance of visceral muscle cells are still present in the iris of 3-month-old chickens. High density of innervation and vascularization, wide range of striated muscle fibre diameters, presence of lipid vacuoles and of large clusters of mitochondria in the striated fibres, occurrence of peripheral couplings of the sarcoplasmic reticulum, and presence of numerous fibroblast processes in the interstices between fibres, characterize the sphincter pupillae of the mature iris.

Age Factors↗
PubMed1983

The taenia of the rabbit colon, an elastic visceral muscle.

The longitudinal musculature (taeniae) of the rabbit proximal colon was studied by phase contrast and electron microscopy. The taenia coli of the rabbit has several structural features which are not found in other visceral muscles of this or other species, and which, on the other hand, are common in certain vascular muscles. Among the characteristics of taenia coli are: highly corrugated muscle cell profiles (even when the muscle is fixed in a resting condition), very high surface-to-volume ratio (1 micron m2/0.5 micron m3), large percentage volume of the extracellular space (about 40%), absence of intramuscular septa, and very large number of elastic fibres, which run mainly longitudinally in broad meshworks parallel to the serosal surface. Several points of contact between elastic fibres and muscle cell membrane occur at all levels along the length of the cells, often involving 11-nm microfibrils; these contacts, and others involving collagen fibrils, are regarded as cell-to-stroma junctions. The taenia coli is virtually devoid of intramuscular blood vessels, including capillaries. The possibility that the lack of capillaries is related to the abundance of elastic material is discussed.

Animals↗
PubMed1983

Asymmetric distribution of dense bands in muscle cells of mammalian arterioles.

Arterioles from viscera of mice, rats, guinea pigs, rabbits, sheep, and pigs were examined by electron microscopy. In all the organs and species investigated the muscle cells of the tunica media are arranged in tight helices and make several full turns. The myofilaments also are arranged approximately circumferentially, although there is often a little divergence between bundles of myofilaments in different areas of the same cell. The dense bands are conspicuous and anchor the myofilaments to the cell membrane; they are markedly larger and more numerous on the regions of the cell membrane facing the adventitia than on those facing the intima. This asymmetrical distribution is interpreted as essential to an efficient mechanism for constriction of the lumen.

Animals↗
PubMed1983

The collagen fibrils in the collapsed and the chronically stretched intestinal wall.

A partial and progressive obstruction of the ileum (stenosis) was produced by surgery in adult rats and guinea pigs. Oral to the stenosis the accumulation of ingesta imposed a condition of chronic stretch on the intestinal wall: the lumen was much distended and the wall increased in thickness, mainly by hypertrophy of the mucosa and muscle coat. The submucosa too increased in volume and its collagen fibrils showed marked ultrastructural changes: in the rat the collagen fibrils (which were of rather uniform diameter in the control submucosa, mean 87 nm) varied greatly in size and formed two distinct populations: large fibrils (similar to those of controls) and small fibrils (4-5 nm in diameter). The latter were probably newly formed fibrils and their number increased in the more advanced stages of hypertrophy. The small fibrils were usually gathered into groups of 15-60 but were found throughout the entire thickness of the collagen bundles. Aboral to the stenosis the intestine was collapsed. In the submucosa there was a widening of the range of fibril sizes, a small increase in the average size and the occurrence of very large and irregular fibrils. Similar changes occurred in the guinea pig; however, the size of the control collagen fibrils (57 nm) was smaller than in the rat, and in the condition of chronic stretch small and large fibrils could not be clearly separated into distinct populations.

Animals↗
PubMed1983

Innervation of the gall bladder and biliary pathways in the guinea-pig.

The innervation of the gall bladder and the biliary pathways was studied in guinea-pigs by means of histochemical methods for catecholamines and for acetylcholinesterase on whole mount preparations, on cryostat sections and on sections of plastic-embedded tissues. The gall bladder contains on average 367 neurons in a ganglionated plexus which lies at the outer surface of the muscle coat. The overall appearance of this plexus is rather similar to that of the submucosal plexus of the duodenum. From the gall bladder the plexus extends into the cystic duct, the hepatic duct and the common bile duct, but from the middle portion of the common bile duct downwards, it is positioned at or near the inner surface of the muscle coat. Concurrently with the marked increase in muscle thickness in the lower parts of the common bile duct, another ganglionated plexus appears, which is truly intramuscular. The latter plexus is highly developed, lies usually between longitudinal and circular muscle and resembles in appearance the myenteric plexus of the duodenum, with which it is in continuity. Throughout the biliary system, the extent of the ganglionated plexus is roughly related to the extent of the musculature. An exchange of adrenergic fibres between the ganglionated plexus and perivascular nerves is observed in the gall bladder. Another nerve plexus, without ganglia but rich in adrenergic and acetylcholinesterase-positive fibres, lies between the mucosa and the muscle coat. Very few nerve fibres run into the musculature of the gall bladder. On the other hand, in the thick musculature of the lower portion of the common bile duct, several intramuscular nerve fibres are found.

Acetylcholinesterase↗
PubMed1983

The musculature of the gall bladder and biliary pathways in the guinea-pig.

A study of the gall bladder and the biliary pathways was carried out in the guinea-pig by light and electron microscopy. The musculature of the distended gall bladder measures only about 220 microns in thickness and consists of muscle bundles running in various directions. The muscle cells are loosely packed and are much smaller than the muscle cells of the intestinal muscularis externa. They resemble, in structure and arrangement, the cells of the muscularis mucosae of the intestine. In the cystic duct, the hepatic duct and the upper third of the bile duct, the musculature is similar to that of the gall bladder but is sparser and mixed with abundant connective tissue (fibromuscular layer). In the middle and lower portions of the bile duct there is a progressive increase in the amount of musculature. While the outer diameter of the organ remains constant (about 1.3 mm), the amount of muscle in a transverse section of the duct increases more than ten times along the length of the duct. Here the muscle cells are large and densely packed and closely resemble those of the duodenal muscularis externa. The bile duct forms with the duodenum an angle of about 30 degrees and it opens into a large cavity within the duodenal wall, the ampulla, which has a complex muscular system of its own. The ampulla is drained into the duodenal lumen through a duct within the papilla, around which lies a ring of circular musculature. The pancreatic duct opens independently into the duodenum about 6 cm aboral to the bile duct.

Animals↗
PubMed1982

On the ultrastructure of the enteric nerve ganglia.

This brief article reviews some aspects of the ultrastructure of the enteric ganglia which have been brought to light by electron microscopy. The ganglion neurons are surrounded by a vast neuropil in which axons, dendrites and glial cells with their processes are tightly packed together. Blood vessels and connective tissue do not penetrate into the ganglia but lie outside them. The exclusion of connective tissue from the ganglia takes place during embryonic development and is complete soon after birth. By ultrastructural criteria it has proven difficult to classify neuronal cell types, in spite of the differences in their functional specializations and their projections. The glial cells are rich in gliofilaments and have processes which are firmly anchored to the surface of the ganglion. Glial cells outnumber ganglion neurons and probably confer structural stability to the ganglia and at the same time allow substantial changes in the shape of the ganglia and in the arrangements of its elements to occur when the adjacent muscle layers contract. Numerous specialized contacts are found between vesicle-containing nerve endings and glial cell bodies or glial processes. The question of how freely substances diffuse inside a ganglion, along the narrow spaces between processes and cell bodies, remains to be answered. Since parts of the surface of many neurons are directly covered by the basal lamina of the ganglion and by connective tissue, certain substances of the interstitial space may have direct access to the nerve cells. Investigations on the intraganglionic nerve endings have provided several classifications of axonal types, mainly based on the appearance of their vesicles. However, these classifications are tentative and are in many respects still uncertain. The great majority of endings originate from intrinsic neurons and synaptic specializations are commonly encountered.

Animals↗
PubMed1981

Gap junctions of the muscles of the small and large intestine.

The distribution of gap junctions (nexuses) in various parts of the small and large intestines of the guinea-pig was studied using the freeze-fracture technique and in thin sections. The percentage area of smooth muscle cell surface occupied by gap junctions varies from 0.50% in the circular muscle of the duodenum to zero in the longitudinal muscle of the ileum. In the circular muscle of the jejunum and ileum the area occupied by nexuses is 0.22% (or about 11 micrometers 2 per cell). The sizes of junctions range from less than 0.01 micrometer 2 to 0.20 micrometer 2, with two-thirds of them being smaller than 0.05 micrometer 2. In the colon, gap junctions are rare, very small and confined to the circular muscle layer. Even the smallest aggregates of intramembrane particles correspond to areas of close apposition between the membranes of adjacent cells; it is therefore justified to interpret them as being gap junctions. Some gap junctions are formed between a smooth muscle cell and an interstitial cell. Gap junctions are not found in the longitudinal muscle of the small intestine; this is in sharp contrast to the abundance of gap junctions in the adjacent circular layer. In the small intestine of cats and rabbits, gap junctions are abundant in the circular muscle layer, whereas they are very small in size and very few in number in the longitudinal muscle layer.

Animals↗