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Its relations are as follows:-It forms the inferior boundary of the foramen epiploicum, and, above that foramen, it is in relation to the caudate process of the liver, while the quadrate lobe of the liver hangs downwards over it and to the right. The hepatic artery is in contact for a short distance with the superior border. Below, it rests on the head and neck of the pancreas. The portal vein, gastro-duodenal artery, and the bile-duct lie in contact with it on the left

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FIG. 932.-THE VISCERA AND VESSELS ON THE POSTERIOR ABDOMINAL WALL.

The stomach, liver, and most of the intestines have been removed. The peritoneum has been preserved on the right kidney, and the fossa for the caudate lobe. When the liver was taken out, the vena cava was left behind. The stomach bed is well shown. (From a body hardened by injection of chromic acid.)

side, and behind them the duodenum comes into contact with the right aspect of the inferior vena cava. The superior pancreatico-duodenal and the right gastro-epiploic vessels pass forwards below its inferior margin.

Its peritoneal relations are similar to those of the pyloric end of the stomach for about an inch. It is therefore at first invested by peritoneum on the right and left aspects, and the peritoneum passes upwards from its superior border as the right portion of the lesser omentum, forming the hepato-duodenal ligament, while from its inferior border the descending folds of the

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peritoneum pass downwards. The peritoneum is reflected from off the left surface on to the pancreas and abdominal wall, and forms a fold known as the right gastro-pancreatic fold, while the peritoneal covering of the right side is continued onwards along the whole of this part of the duodenum.

Pars Descendens.-The descending part (O.T. second portion) begins at the neck of the gall-bladder, passes down behind the transverse colon, and ends at the right side of the third or fourth lumbar vertebra. In length it measures 3 or 4 inches (8.7 to 10 cm.).

Its relations are as follows:-It lies on the right of the vertebral column and the inferior vena cava, from the first to the third or fourth lumbar vertebra, and is anterior to the pelvis

Top of omental bursa

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Corresponds to uncovered area of stomach
Gastro-splenic ligament (cut)

Phrenico-colic ligament

Left end of transverse mesocolon
Left colic flexure
Transverse mesocolon (cut)
Root of mesentery (cut)

FIG. 933. THE PERITONEAL RELATIONS OF THE DUODENUM, PANCREAS, SPLEEN, KIDNEYS, ETC. From a body hardened by injections of formalin. When the liver, stomach and intestines were removed the lines of the peritoneal reflections were carefully preserved. The peritoneum is coloured blue. of the right kidney, the right renal vessels, and ureter, and also, to a varying extent, the front of the right kidney itself; while, below the level of those structures, it rests upon the psoas major

muscle.

The lateral aspect is in contact with the sloping inferior surfaces of the liver in its superior part, and with the right flexure of the colon below.

Peritoneal Relations.-The anterior aspect is covered by peritoneum, except about its middle, where the root of the transverse mesocolon crosses the duodenum. Not infrequently, the transverse colon has no mesentery, but is itself in direct contact with the wall of the duodenum. In other cases, the colon is in contact with the peritoneal surface of the duodenum, below the line of reflection of the transverse mesocolon.

The head of the pancreas is in contact with its concave left margin, and occasionally overlaps it anteriorly and posteriorly; and along the margin of the pancreas, both anteriorly and pos teriorly, are branches of the superior and inferior pancreatico-duodenal vessels, the veins often forming a dense network on the posterior aspect.

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Pars Infer he third or fo sverse in 933.

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The bile-duct, after passing down behind the superior part of the duodenum, descends between the head of the pancreas and the descending part, nearly as far as its middle; there it is joined by the pancreatic duct, and the two, piercing the wall of the duodenum obliquely, open by a common orifice on its inner aspect, about 3 to 4 inches (87 to 10 cm.) beyond the pylorus.

Pars Inferior. The inferior part (O.T. third portion) begins at the right side of the third or fourth lumbar vertebra. It is described in two parts, pars horizontalis, transverse in direction, and pars ascendens; and it shows that arrangement in Fig. 933.

The pars horizontalis runs more or less transversely to the left across the inferior vena cava (Fig. 933) for one or two inches, and the pars ascendens passes very obliquely, or even vertically, upwards in front of the aorta and left psoas major muscle. Finally, having reached the inferior surface of the pancreas, it bends forwards, and passes into the jejunum.

Anteriorly, it is crossed (about the junction of its two divisions) by the superior mesenteric vessels, and also by the root of the mesentery (Fig. 933). On each side of this it is covered by coils of small intestine. Posteriorly, the pars horizontalis lies across the vena cava inferior; the pars ascendens lies on the aorta, the left renal vein and occasionally also the artery, and the left psoas major muscle, all of which separate it from the vertebral column. Above, it is closely applied in its whole extent to the head of the pancreas. The left side of the pars ascendens, which is free, lies in contact with some coils of the small intestine.

Peritoneal Relations.-The inferior part of the duodenum is covered by peritoneum on its anterior surface throughout, except where it is crossed by the superior mesenteric vessels and the root of the mesentery, which contains these vessels (Fig. 933). In addition, its ascending part is also clothed by this membrane on its left side.

The attachment of the root of the mesentery begins, above, quite close to the duodeno-jejunal flexure, on the front of the duodenum; thence it runs down on the anterior aspect of the ascending part, and finally leaves the duodenum about the union of the two divisions of its third portion.

Duodenal Fossæ.-In the neighbourhood of the pars ascendens are found three well-known fossæ of the peritoneum which are of some surgical interest; they are the superior and inferior duodenal and the paraduodenal fossa (Fig. 934). Other rarer forms are occasionally present.

When the ascending part of the duodenum is drawn over to the right, and the angle between its left side and the posterior abdominal wall is examined, one or two triangular folds of peritoneum will generally be found crossing over that angle from the duodenum to the abdominal wall. Each fold has one edge attached to the duodenum, another to the parietal peritoneum at the left of the duodenum, whilst the third is free, and bounds the opening of a small pouch which lies behind the fold, the recessus duodeno-jejunalis. Of these folds, the upper is termed the plica duodeno-jejunalis, and it is situated near the termination of the duodenum, with its apex directed up and its free margin down. It sometimes contains between its two layers the termination of the inferior mesenteric vein. Behind it lies a prolongation from the recessus duodeno-jejunalis termed the superior duodenal fossa. Its opening looks downwards, and will usually admit the tip of a finger (Fig. 934). The second, known as the plica duodeno-mesocolica, is placed lower down, at the side of the same part of the duodenum. Its free border is directed upwards, as is the mouth of the inferior duodenal fossa, which lies behind it. This latter is larger and more constant than the superior duodenal fossa, and is present in 75 per cent. of bodies, whilst the superior is present in 50 per cent. (Jonnesco).

FIG. 934. THE DUODENAL FOSSE AND FOLDS.

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transverse colon and mesocolon have been thrown up, and the mesentery has been turned to the right and cut. The paraduodenal fossa (of Landzert) is situated to the medial side of the inferior mesenteric vein, between it and the terminal part of the duodenum. It is not shown in the illustration.

Paraduodenal Fossa (fossa of Landzert). This fossa, which is seen best in the

Duodenum

Superior duodenal fossa

Inferior duodenal fossa

Transverse mesocolon

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Inferior mesenteric vein Left colic artery

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infant, is placed some distance to the left of the ascending part of the duodenum. It is produced by the inferior mesenteric vein raising up a fold of peritoneum, as it runs medially along the side of the fossa, and then above it (see Fig. 934, where the vein, but not the fossa, is shown). It is limited below by a special fold (the mesenterico-mesocolic fold). According to Moynihan, this is the only fossa to the left of the duodenum capable of developing into the sac of a hernia; and when this occurs, the inferior mesenteric vein always lies in the anterior margin of the orifice of the sac (accompanied for some distance by the ascending branch of the left colic artery).

Hood-like
plica circularis

Duodenal papilla Common opening of bile and pancreatic duct Plica longitudinalis duodeni

Peritoneal Relations of the Duodenum.-Whilst the relations of the peritoneum to the second and third portions of the duodenum are usually described as in the foregoing account, it should perhaps be pointed out, that it is not really the front, but the right half of the circumference of the descending portion which has a serous coat. Similarly, it is the inferior and anterior half of the circumference of the horizontal portion of the inferior part which is clothed by peritoneum, whilst considerably more than half of the circumference of its ascending

portion is covered; for the peritoneum forms a fold running in behind this portion, in addition to covering its left side and half its anterior aspect.

FIG. 935.-THE PAPILLA DUODENI IN THE INTERIOR OF THE DUODENUM.

Interior of Duodenum.-No plicæ circulares are found in the duodenum for an inch or two beyond the pylorus. They then begin; at first as low, scattered, and irregular folds; further down, they gradually become larger, more regular and more numerous; and by the time the middle of the descending part is reached they have attained a considerable development. In the inferior part of the duodenum the folds are large, prominent, and closely set.

On the inner aspect of the descending portion, about its middle-namely, 3 or 4 inches (8.7 to 10 cm.) beyond the pylorus-is seen a prominent papilla, on 'which the bile and pancreatic ducts open by a common orifice (Fig. 935). This is known as the papilla duodeni (Santorini).

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The papilla duodeni is placed beneath, and protected by, a prominent, hood-like plica circularis, which is situated immediately above it. From its lower margin a firm ridge of the mucous membrane, the plica longitudinalis duodeni, descends for a considerable distance, and acts as a frenum, which fixes the papilla and directs its apex somewhat downwards (Fig. 935) The papilla is prominent, and nipple or dome-shaped, and at its summit is placed the small orifice, which will usually admit the point of a pencil; the whole bears a close resemblance to the nozzle of a perfume-spray.

Nearly an inch higher up, and invariably on the ventral side of the papilla (sometimes as much as a to inch distant), is seen a second and smaller papilla, the caruncula minor of Santorini, at the point of which is placed the very small orifice of the accessory pancreatic duct. This second papilla seems to be constantly present, although sometimes so small that it may easily escape detection unless carefully sought for. When well developed, it may have a hood-like plica circularis and a little frenulum, like those of the bile papilla.

Structure of the Duodenum.-The tunica serosa, which is incomplete, has already been described in detail, in connexion with each part of the duodenum.

The tunica muscularis is well developed, and is pierced by the bile and pancreatic ducts, but otherwise calls for no special description.

The tela submucosa differs from that of the rest of the small intestine, in that it contains, especially in the superior half of the duodenum, the glandulæ duodenales [Brunneri]. These are small acino-tubular glands, closely resembling the pyloric glands of the stomach; they lie in the submucous coat, and send their ducts through the muscularis mucosa to open on the surface between the glandulæ intestinales, or sometimes into these glands themselves (Fig. 929). They can be exposed by the removal of the peritoneal and muscular coats, and also some of the submucosa, when they appear as little round or flattened masses of a reddish-gray colour, varying in size from th to 11th of an inch in diameter (5 to 20 mm.). They form an almost continuous layer as far as the opening of the bile duct; beyond this they diminish progressively, and completely disappear near the duodeno-jejunal flexure.

The tunica mucosa, which is thicker in the duodenum than in any other part of the small intestine, is covered throughout with broad, short villi.

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Various Forms of Duodenum.-Three different types of duodenum have been described— (1) The annular, in which the curves separating the various parts are open, and the two extremities come fairly close to one another. (2) The U-shaped, in which the horizontal part of the inferior part is very long, and the ascending part is nearly vertical; and (3) the V-shaped duodenum, in which the horizontal portion of the inferior part is very short or absent.

Vessels and Nerves.-The duodenum receives its blood from the superior and inferior pancreatico-duodenal arteries, branches of the gastro-duodenal and superior mesenteric arteries respectively. The blood is returned by the corresponding veins, the superior of which opens into the superior mesenteric, and the inferior into the beginning of the portal vein.

The lymph vessels of the duodenum follow for the most part the course of the blood-vessels. From the anterior surface, lymph vessels pass along the course of the inferior pancreaticoduodenal artery, and communicate with lymph glands found along the course of that vessel. Thence they pass to the inferior coeliac glands, beside the origin of the superior mesenteric artery. The vessels from the posterior aspect accompany the superior pancreatico-duodenal artery, communicate with the inferior gastric glands, and terminate in the coeliac glands.

The nerves come from the cœliac plexus of the sympathetic.

Flexura Duodenojejunalis.—When the ascending part of the duodenum reaches the inferior surface of the pancreas, at a point opposite the left side of the first or second lumbar vertebra, it turns abruptly forwards, downwards, and to the left, and passes into the jejunum. This abrupt bend is known as the duodeno-jejunal flexure. Unlike the rest of the duodenum, which is subject to considerable variations in position in different individuals, the duodeno-jejunal flexure is fixed by a thin band of unstriped muscle, which is attached above to the strong connective tissue around the cœliac artery, as well as to the left crus of the diaphragm. This band passes posterior to the pancreas, and inferiorly it joins the muscular coat of the duodenum at the flexure. It is known as the m. suspensorius "duodeni (O.T. muscle of Treitz).

The duodeno-jejunal flexure is occasionally directed to the right, and it lies at a variable distance from the root of the transverse mesocolon. When the attachment of the transverse mesocolon is low, the duodeno-jejunal flexure is in contact with it.

Duodenal Pouches or Diverticula.-Occasional diverticula are found passing from the duodenal wall in different directions. Such diverticula may be hernial protrusions of the mucous and submucous coats through the muscular wall, termed false diverticula, or they may be "true" diverticula, in which all the coats are represented.

They are usually situated on the aspect of the duodenum which is in contact with the pancreas, and frequently in the neighbourhood of the orifice of the bile duct.

Some of these appear to be due to the pressure from the interior of the duodenum, while others, and the majority of the true diverticula, are rather congenital in origin, and are possibly associated with the diverticula which give rise to the liver and pancreas.

HEPAR.

The liver is the large glandular organ which secretes the fluid called bile (fel). It occupies the superior and mainly, the right portion of the abdominal cavity, and lies immediately below the diaphragm.

Its secretion is conveyed away from it by the hepatic ducts and the bile-duct to the duodenum. With the bile duct there is connected a pear-shaped diverticulum, the gall-bladder (vesica fellea), which lies in contact with the liver, and which serves apparently for the temporary storage of bile.

In addition to secreting bile, the liver plays an important part in the metabolism of both the carbohydrate and nitrogenous materials absorbed from the intestine which are conveyed to it by the portal vein, and it also has to do with the production and the destruction of some of the blood-cells.

Physical Characters. The liver is a large irregularly shaped mass, of a reddish-brown colour, soft and pliant to the touch, somewhat readily lacerated, and highly vascular.

It is of uniform consistence throughout, and little of its internal structure can be made out by naked-eye examination. If, however, a torn surface is examined, the liver tissue is seen to be somewhat granular. Under the investing peritoneum the surface is somewhat mottled.

This mottled or granular appearance is due to the lobules (lobuli hepatis) of

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