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general increase in length which takes place during distension, the pylorus is moved a variable distance to the right beneath the quadrate lobe of the liver, and at the same time the long axis of the whole organ becomes much more oblique, running forwards, downwards, and to the right. Finally there is developed a special dilatation of the pyloric part, known as the antrum pyloricum, which in extreme distension is carried so far to the right that it may even reach to the hypochondrium.
Shape and Position of the Stomach as seen by X-Ray Examination.-Examination of the stomach by means of X-rays after a "bismuth meal" has given important information about the shape and position of the stomach in the living, and about the changes which occur as the stomach fills and empties.
These examinations corroborate, in great part, the conclusions which have been arrived at by the study of formalin specimens so far as the shape of the stomach, and its division into parts, is concerned. In regard, however, to the position and direction of the stomach, X-rays show that the stomach in the living, and especially in the erect attitude, is more vertical than it is after death, and when the body is examined in the horizontal position. In the upright position, in fact, the long axis of the organ appears to be nearly vertical. The general shape and position of the stomach in the vertical position, moderately distended, is shown in Fig. 923. From this it will be seen that not only is the body of the stomach nearly vertical, but that the greater curvature reaches down to the umbilicus, and may descend even beyond it. The pyloric part is directed upwards, as well as backwards, and the pylorus is not usually the lowest point of the stomach.
The other anatomical features of the stomach described above are well brought out. Thus the fundus is a hemispherical dome, lying to the left of the terminal portion of the oesophagus, and continuous in outline with the body of the stomach. It usually contains gas, and appears translucent to X-rays. The body is of uniform outline, and the pyloric part is marked off from it by the incisura angularis, on the lesser curvature. Further, the pyloric part shows division into pyloric antrum' and pyloric canal. The incisura angularis and sulcus intermedius are distinct.
The position of the stomach is greatly influenced by attitude and by the condition of the abdominal muscles. Contraction of the abdominal muscles can elevate the stomach from 5 to 13 cm., or 2 to 5 inches, and the change from the horizontal to the erect attitude alters the height of the inferior border from 2 to 10 cm. This sinking which occurs in the alteration from the horizontal to the erect attitude, accounts largely for the differences found between the stomach seen in the postmortem room or on the operating table and the stomach displayed by means of X-rays. Thus, if the stomach figured on p. 1167 be considered fixed at the cardiac end, and somewhat fixed at the pylorus, and the pyloric antrum and greater curvature should sink downwards, the shape, as seen from the front, would closely resemble the X-ray appearances found often in the living.
The empty stomach is a contracted tubular organ, except at the fundus, where it appears to be always dilated. When food is taken, when the individual is standing or sitting, it runs down to the point where the gastric walls are in contact with one another. The distal portion of the stomach dilates for some distance, or at least as far as the pyloric canal.
As the stomach becomes filled the whole of the body of the organ becomes dilated, but the fundus and cardiac portion more particularly so, and these two latter regions act as a storehouse.
There is no definite division of this portion from the remainder of the stomach by a permanent sphincter, but the peristaltic waves of contraction begin about the middle of the organ, and form a fleeting constriction between the two parts.
As peristalsis goes on, the tubular pyloric part relaxes somewhat. The waves of peristalsis here become so deep as to divide this portion into chambers. The food substances are forced through the pylorus by successive waves of peristalsis, and in the form, usually, of jets which impinge against the posterior aspect of the duodenal wall.
Should there be undigested masses, the pyloric valve relaxes to allow them also to pass into the duodenum.
STRUCTURE OF THE STOMACH.
The stomach wall is composed of four coats-namely, from without inwards: (1) Tunica serosa, (2) tunica muscularis, (3) tela submucosa, and (4) tunica mucosa (Fig. 924). Tunica Serosa.-The serous coat is formed of the peritoneum, the relations of which
to the stomach have already been described. It is closely attached to the subjacent muscular coat, except near the curvatures, where the connexion is more lax; and it confers on the stomach its smooth and glistening appearance.
Tunica Muscularis.-The muscular coat, which is composed of unstriped muscle, is thinnest in the fundus and body, much thicker in the pyloric portion, and very highly developed at the pylorus. It is made up of three incomplete layers-an external, stratum longitudinale; a middle, stratum circulare; and an internal of oblique muscular fibres, fibræ obliqua.
The stratum longitudinale consists of longitu dinal fibres, continuous with those of the oesophagus on the one hand, and those of the duodenum on the other (Fig. 926, A). They are most easily demonstrated on the lesser curvature, where they can be traced down from the right side of the œsophagus. Over the greater curvature and on the two surfaces they are present as an extremely thin and irregular sheet. Towards the pylorus the longi tudinal fibres grow much thicker, and also much tougher and more closely united, and they take part in the formation of the pyloric valve.
A specially condensed band of these can be often made out both on the front and back at the antrum pyloricum, the form of which is said to be due to their presence. These bands are known as the ligamenta pylori (pyloric ligaments).
FIG. 925.-MUSCULAR COAT OF THE STOMACH, seen from within after removal of the mucous and submucous layers. The anterior half of the stomach is shown, viewed from behind (Cunningham).
The stratum circulare is composed mainly of circular fibres, continuous with the more superficial of the circular fibres at the lower end of the oesophagus (Fig. 925). They begin as a set of U-shaped bundles which loop over the lesser curvature at the right of
Further to the right
the cardia, and pass downwards and to the left on both surfaces. these looped fibres are succeeded by circles which surround the organ completely. Traced towards the narrow end of the stomach, the circular bundles grow thicker, and at the pylorus they undergo a further in
crease, giving rise to the pyloric sphincter which surrounds the orifice as a thick muscular ring.
The fibre oblique, forming the inner layer, consist of fibres which are arranged on the fundus and adjacent parts of the stomach, in much the same manner as those of the middle layer are on the body and pyloric part of the organ (Fig. 926, C). They are continuous above with the deeper circular fibres of the inferior end of the oesophagus, and form U-shaped bundles which loop over the stomach immediately to the left of the cardia, and run very obliquely downwards and to the right for a considerable distance on both surfaces of the organ. These looped fibres, as they pass to the left, gradually become less oblique, and finally form circles which surround the wide end of the stomach completely, even as far as the summit of the fundus. The oblique fibres can be most readily shown by removing the circular fibres on either surface below the cardia. When traced towards the right, they will be found to terminate by turning down and joining the fibres of the circular layer.
Tela Submucosa. The submucous coat is a layer of strong but loose connective tissue, which lies between and unites the muscular and mucous coats (Fig. 924). It is more loosely attached to the muscular and more closely to the mucous coat, and it forms a bed in which the vessels and nerves break up before entering the mucous membrane.
Tunica Mucosa.-If examined in the fresh state soon after death, the mucous coat is of a reddish-gray colour and of moderate consistence. When examined some time after death, the colour turns to a darker gray, and the whole membrane becomes softer and more pulpy. It is thicker (over 2 mm.) and firmer in the pyloric than in the cardiac part, and is thinnest at the fundus, where it often shows signs of post-mortem digestion. When the stomach is empty all three outer coats, which are extensile, contract; whilst the inextensile mucous coat, as a result of its want of elasticity, is thrown into numerous prominent folds or ruga, which project into the interior and, as it were, occupy the cavity of the contracted organ. These are, in general, longitudinal in direction, with numerous cross branches, and they are largest and most numerous along the greater curvature. They disappear when the stomach is distended.
FIG. 926. THE THREE LAYERS OF THE MUSCULAR COAT OF THE STOMACH. A, External or longitudinal layer; B, Middle or circular layer; C, Internal or oblique layer. a, Longitudinal fibres of oesophagus; b, Superficial circular fibres of esophagus passing into circular fibres of stomach in B; c, Deep circular fibres of oesophagus passing into oblique fibres of stomach in C; d, Oblique fibres forming rings at the fundus; e, Submucosa.
When the surface of the mucous coat is examined in a fresh stomach, it is seen to
be marked out into a number of small, slightly elevated, polygonal areas, area gastrica, by numerous linear depressions; the mucous membrane is consequently said to be mamillated (Fig. 927, A). These little areas, which measure from 1 to 6 mm. in diameter, are beset with numerous small pits, foveola gastrica, about 2 mm. wide, which are the mouths of the gastric glands, and they are so closely placed that the amount of surface separating them is reduced (particularly in the pyloric portion, where the gland mouths are widest) to a series of elevated ridges, plice villosa, resembling villi on section. Although the gland mouths cannot be seen with the naked eye, a very slight magnification is sufficient to show them clearly; it is also possible to see the gland tubes leading off from the bottom of each (Fig. 927, B).
Minute Structure of the Mucous Coat.-In structure the mucous coat consists of an epithelial covering composed of long columnar cells, and of numerous tubular glands, glandule
gastric glands, with gland tubes at bottom
Depression between two
Mouth of gastric gland
FIG. 927.-MUCOUS MEMBRANE OF THE STOMACH. A, Natural size; B, Magnified 25 diameters. In A the rug and the mamillated surface are shown. In B the gland mouths (foveola gastrica), with the gland tubes leading off from some of them, and the ridges separating the mouths (plica villosa)
gastrica, which are prolonged outwards from this surface, and which are enclosed in a delicate connective tissue stroma, with some small lymph nodules, noduli lymphatici gastrici. The bases of the glands reach outwards to the lamina muscularis mucosa, a layer consisting of an external longitudinal and an internal circular layer of plain muscle fibres.
Glandulæ Gastricæ.-These consist of a duct terminating in one or more secreting tubules. The duct is lined with columnar epithelial cells, similar to those which cover the sur face of the mucous membrane. Three varieties of glands are found in different regions of the stomach, and are named from their position
(1) Cardiac Glands. - These glands are situated close to the sophageal opening. The duct ter minates in a single long tubule, which is lined with short columnar granular cells.
(2) Fundus Glands.-In these glands the duct terminates in one or more tubules, lined with polyhedral cells, termed the chief or cen tral cells. At intervals, between this layer of cells and the basement mem brane, are placed larger spheroidal cells, which stain more deeply as a rule, termed the parietal or oxyntic cells. These glands are found in the fundus and body of the stomach. (3) Pyloric glands are found in the pyloric portion of the stomach. These consist of a short duct, terminated in a group of short but tortuous gland tubules. These tubules are lined with short columnar or polyhedral cells, similar to the central cells of the fundus glands.
Blood-vessels. The arteries of the stomach are all derived ultimately from the cœliac artery The gastric artery arises from this trunk direct. Having reached the lesser curvature and given off an oesophageal branch, it divides into two large branches, which run, one on each side of the organ, along this curvature, and join below with two similarly-disposed arteries derived from the right gastric branch of the hepatic. From the two arches thus formed, four or five large branches pass to each surface of the stomach, and soon pierce the muscular coat. Along the greater curvature several smaller branches reach the stomach from the right and left gastro-epiploic arteries, which are branches respectively of the gastro-duodenal and the splenic, and run in the gastro-colic ligament close to its attachment to the stomach. Finally, four or five short gastric arteries, branches of the splenic, are distributed to the fundus of the stomach, which they reach by passing forwards between the layers of the gastro-lienal ligament. At first the arteries lie beneath the peritoneum; very soon, however, they pierce the muscular coat, which they supply, and, reaching the submucos break up to form a close network of vessels. From these arise numerous small branches, which enter the mucous membrane and form capillary plexuses around the glands as far as the surface. The veins begin in the capillary plexuses around the glands; uniting, they form a network in the submucosa, from which arise branches that pierce the muscular coat, and finally end in the following veins the right gastro-epiploic, which joins the superior mesenteric; the left gastroepiploic, and four or five veins corresponding to the short gastric arteries, which join the splenic; the coronary vein of the stomach, which runs along the lesser curvature from left to right, and joins
the portal vein. These veins contain numerous valves which, though competent to prevent the return of blood in the child, are rarely so in the adult.
The lymph vessels of the stomach arise in an extensive plexus in the mucous membrane around the gastric glands. They then join a plexus of vessels in the tela submucosa, from which some vessels pass at intervals to join another plexus of vessels, subserous in position; piercing the muscular coats obliquely in their course. The efferent vessels pass mainly from the subserous plexus, and are arranged in three main groups, which pass in different directions, and drain three different areas of the stomach wall.
One set of vessels is connected mainly with the whole of the lesser curvature, from fundus to pylorus, and the adjacent half or two-thirds of the anterior and posterior surfaces of the stomach. These vessels pass to the superior gastric glands, along the lesser curvature, and, in company with the left gastric artery, to the coeliac glands.
The second set of vessels drains an area which includes the greater curvature below the fundus, and the adjacent portions of the anterior and posterior surfaces of the stomach. These vessels pass with the right gastro-epiploic artery to some inferior gastric glands which lie below and behind the pylorus, and thence they pass with the hepatic artery to the coeliac glands.
The third set of vessels drains the region of the fundus. The vessels from this area pass in the gastro-lienal ligament to the spleen, where they are connected with some splenic glands, and pass onwards, along the superior border of the pancreas, to the coeliac glands also.
The superior and inferior gastric glands and the splenic glands are the first glands interposed in the course of the lymph vessels. The coeliac glands form the second set.
The nerves are derived from the two vagus nerves and from the caliac ganglia of the sympathetic. The vagi nerves pass through the diaphragm with the oesophagus, the left lying on its anterior, the right on its posterior aspect; in this way they reach the anterior and posterior surfaces of the stomach respectively. Here they unite with the sympathetic fibres from the cœliac plexus, which pass to the stomach with the branches of the coeliac artery. The nerve fibres, which are chiefly non-medullated, form two gangliated plexuses, those of the myenteric plexus and the submucous plexus, in the muscular and submucous coats respectively.
The development of the stomach is described with that of the intestines on pp. 47 and 1249.
The small intestine is the portion of the digestive tube which is placed between the stomach and the beginning of the large intestine. It commences at the pylorus, where it is continuous with the stomach, and ends at the valvula coli by joining the large intestine. It occupies the greater portion of the abdominal cavity below the liver and stomach (Fig. 913), and is found in the umbilical, hypogastric, and both lumbar regions; also, but to a less extent, in the other regions of the abdomen, and in the pelvic cavity.
In length, the small intestine usually measures over 20 feet. According to Treves, it is 22 ft. in the male, 23 in the female, whilst Jonnesco gives the average length at 24 ft. 7 ins., or 7 metres. In form it is cylindrical, with a diameter varying from nearly two inches (47 mm.) in the duodenum to a little over an inch (27 mm.) at the end of the ileum; there is thus a gradual diminution in its size from the pylorus to the valvula coli.
The small intestine is relatively longer in the child than in the adult; at birth it is to the total height of the child as 7 to 1, whilst in the adult the proportion is as 4 to 1. Notwithstanding Treves' results, it is generally held that the small gut is relatively longer in the male than the
While the former figures, 20 to 22 feet, represent the entire length of the intestine in its most extended form, after death, when muscular tonus has disappeared, it is probable that during life the length is not so great. The muscular coats, both longitudinal and circular, are more or less contracted, and probably the total length during life may be estimated as 15 to 17 feet.
In formalin-hardened bodies the small bowel rarely measures more than 12 or 13 feet in length. Similarly its diameter is often reduced in places to or inch (12.5 to 187 mm.), although the greater part of the gut may retain its usual width: these narrow parts have apparently been fixed in a state of contraction.
The small intestine is divided more or less arbitrarily into three parts (Fig. 873) -namely, the duodenum, constituting the first eleven inches, distinctly marked off from the rest by its fixation and the absence of a mesentery; the intestinum jejunum ("empty intestine") which comprises the upper two-fifths, and the intestinum ileum ("twisted intestine") the lower three-fifths of the remainder. The jejunum and ileum pass imperceptibly into one another, and the line of division drawn between them is entirely artificial; however, if typical parts of the two-namely, the beginning of the jejunum and the end of the ileum-are selected, they differ so