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The circulation within the liver is, therefore, arranged differently from that of other glands, and in order to understand properly the structure of the liver, it is necessary t give some account of the relations which it presents to the blood vessels which pass to and
The vena portæ and the arteria hepatica propria pass up to the liver between the twe layers of the hepato-duodenal ligament, anterior to the foramen epiploicum. Here they are accompanied by the bile-duct, which lies to the right, whilst the artery is placed to the left, and the portal vein posterior to both. In this order they enter the porta hepatis, and there become rearranged, so that the vein lies behind, the artery in the middle, and the duct in front. Each breaks up into two chief branches-a right and a left-and several smaller ones, which enter the liver substance, surrounded by a prolongation of the connective tissue coat of the liver (O.T. Glisson's capsule). Within the organ the three vessels run and divide together, so that every branch of the portal vein is accompanied by a corresponding (but much smaller) branch of the hepatic artery and of the hepatic duct: and the three, surrounded by a prolongation of the fibrous capsule,
FIG. 943.-DIAGRAM illustrating the arrangement of the blood-vessels (on left) and of the hepatic cells an bile-ducts (on right) within a lobule of the liver. The first diagram shows the interlobular veins running aror.ad the outside of the lobule, and sending their capillaries into the lobule to join the centra: vein. In the second diagram the bile capillaries are seen, with the hepatic cells between them, radiating to the periphery of the lobule, where they join the interlobular bile-ducts.
and accompanied by branches of the hepatic nerves and lymph vessels, run in specia. tunnels of the liver substance, which are known as portal canals (Fig. 941, B).
The hepatic artery has but a small part to play in the hepatic circulation within the liver, and it is distributed in the following way. Reaching the porta hepatis of the liver it breaks up into branches which accompany the branches of the bile-ducts and of the portal vein into the interior, and it supplies minute branches, known as the vaginal and capsular branches, to the fibrous tissue which accompanies these vessels, and which also invests the surface of the liver. The terminal branches of the artery end in the branches from the portal vein which go to the liver lobules.
The portal vein within the liver divides, like an artery, into numerous branches, which pass in all directions in company with small branches of the bile-ducts.
Finally, the small terminal branches form an elaborate meshwork, whose vessels anastomose freely with one another, around the periphery of the liver lobules, and are known as interlobular vessels. From this meshwork small capillary-like channels pass into the interior of each lobule between columns of liver cells, towards a channel placed in the centre of the lobule, called the central vein. From the central veins the blood is carried into larger channels or sublobular veins, which pass to the hepatic veins, and so to the inferior vena cava.
The hepatic veins, formed by the union of the sublobular vessels, gradually unite with one another, and run towards the inferior vena cava. Their mode of termination is variable, but presents the following general arrangement :-The left lobe is drained by a vessel which joins the superior part of the inferior vena cava. The right lobe is drained by one or two vessels which join the superior part of the inferior vena cava, and by a series of small vessels, 4 to 12 in number, which pass from the inferior portion of the right lobe to the inferior vena cava. The caudate lobe and central portion of the liver are drained by
Ivessels which mostly pass to the inferior part of the inferior vena cava. The hepatic veins and their branches are not accompanied by branches of the bile-ducts, and are surrounded by a very small amount of connective tissue.
The lymph vessels of the liver are arranged in a superficial and a deep set :-1. The superficial set lies beneath the peritoneum on both (a) the visceral and (b) the parietal surfaces of the organ. (a) The vessels from the visceral surface pass chiefly to the hepatic glands, which lie between the layers of the lesser omentum; but some of them, from the posterior surface on the right lobe, join the lumbar glands, and others, from the posterior surface on the left lobe, go to the cœliac glands. (b) The vessels from the inferior surface pass in various directions. Those from the adjacent parts of the right and left lobes pass up in the falciform ligament, and pierce the diaphragm to reach the anterior mediastinal glands, and end finally in the right lymphatic duct. Those from the anterior part of this surface pass down to the inferior aspect, and join the hepatic glands in the lesser omentum. The lymph vessels from the back of the right lobe pierce the diaphragm between the layers of the coronary ligament, and join some glands in the thorax around the upper end of the inferior cava; others run in the right triangular ligament, and either pierce the diaphragm and end in the anterior mediastinal glands, or, turning down, join the cœliac group.
2. The deep lymph vessels accompany either (a) the portal or (b) the hepatic veins. (a) The former set pass out through the porta hepatis and join the hepatic glands, the efferent vessels of which join the coeliac glands. (b) Those which accompany the hepatic veins pierce the diaphragm with the vena cava, and having formed connexions with the group of glands at its superior end, within the thorax, turn down and join the beginning of the thoracic duct.
The nerves, which are chiefly of the non-medullated variety, are derived from the left vagus and the coeliac plexus of the sympathetic. The branches of the former pass from the front of the stomach up between the layers of the lesser omentum to the liver. Those of the latter pass from the coeliac plexus along the hepatic artery-forming the hepatic plexus-to the porta hepatis, where they enter the liver with the blood-vessels. They are distributed chiefly to the walls of the vessels and of the bile-ducts.
THE GALL-BLADDER AND BILE-PASSAGES.
Under this heading we have to consider the hepatic ducts, the gall-bladder, the cystic duct, and the bile-duct.
The excretory ducts of the liver (Fig. 943) begin within the hepatic cells as minute channels. Thence they run between the hepatic cells (Fig. 943), and are known as the ductus biliferi.
Outside the lobules these join (Fig. 943) the ductus interlobulares which, by uniting, form larger and larger ducts, and finally end in two, or more, chief branches, a larger from the right, and a smaller from the left lobe, which unite immediately after leaving the liver to form the ductus hepaticus.
As a rule, five or six ducts leave the liver at the porta hepatis; they generally unite into right and left main ducts; sometimes they all converge towards, and unite at the beginning of the hepatic duct. It is interesting to note that the ducts from the caudate lobes and process join the left branch of the main duct.
Ductus Hepaticus.-The hepatic duct is formed within the porta hepatis by the union of right and left chief ducts (Fig. 944), and passes downwards, with an irregular course, and, just beyond the porta hepatis, is joined by the cystic duct (Fig. 944) to form the ductus choledochus or bile-duct (O.T. common bile-duct). In length the hepatic duct usually measures about 1 to 14 inch (25 to 31 mm.), and in breadth, when flattened out, nearly inch (6 mm.), or about as much as a goose quill. It lies, practically altogether, within the porta hepatis.
Vesica Fellea (Gall-bladder). The gall-bladder, with the cystic duct, may be looked upon as a diverticulum of the bile-duct, enlarged at its extremity to form a reservoir for the bile. It is pear-shaped, and lies obliquely on the inferior surface of the liver (Fig. 944). The wide end, or fundus, usually reaches the anterior border of the liver-where there is sometimes a notch to receive it—and comes in contact with the anterior abdominal wall (Fig. 944). The corpus (body) runs backwards, upwards, and to the left, lying in the fossa for the gall-bladder, and near the porta hepatis passes rather abruptly into the narrow neck. The collum (neck) is curved medially towards the porta hepatis, in the form of the italic letter s, and when distended it presents on its surface a spiral constriction which is continued into the beginning of the cystic duct, and is due to a series of crescentic folds placed somewhat spirally round the interior of its cavity, forming the valvula spiralis (Heisteri). Having arrived near the porta hepatis, much reduced in size, it passes into the cystic duct. As a rule the gall-bladder is covered by the peritoneum of the inferior surface
of the liver, except on its antero-superior aspect, which is united to the fossa for the gall-bladder by areolar tissue. Sometimes, but rarely, this surface also is covered,
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FIG. 944.-STRUCTURES BETWEEN THE LAYERS OF THE LESSER OMENTUM.
In some cases the fundus of the gall-bladder does not reach the anterior border of the liver or the abdominal wall. In others it may be moved considerably to the right. of the vertical lateral plane-possibly as a result of distension of the stomach and colon-or as a result of tightlacing, it may be moved to the left, and may then lie near the median plane and far below the ribs (Fig. 918, p. 1167).
Its total absence, as well as the presence of two distinct gall-bladders, and several other irregularities in form, have been recorded.
Its size is usually about 3 inches (75 mm.) in length, and 1 to 14 inches (25 to 31 mm.) in diameter. Its capacity varies between 1 and 1 fluid ounces.
Structure of Gall-bladder. The wall of the gall-bladder is composed of an outer coat of peritoneum, the tunica serosa, usually incomplete; a middle coat of unstriped muscle intermixed with fibrous tissue, the tunica muscularis; and an inner coat of mucous membrane, the tunica mucosa, which is covered with columnar epithelium, and is raised into a number of small ridges, the plica tunica mucosa, which confer on it a reticulated appearance. The mucous membrane is always deeply stained with bile when the gallbladder is opened after death.
The cystic artery which supplies it with blood arises from the hepatic artery itself, or its right division, and divides into two branches, which run on the sides of the gall-bladder. The veins join the vena porta, and the nerves come from the sympathetic plexus on the hepatic artery.
Ductus Cysticus.-The cystic duct, about half the diameter of the hepatic duct (3 mm.), but usually slightly longer (14 to 1 inches: 31 to 37 mm.), begins at the neck of the gall-bladder, and running an irregular course backwards and medially joins the hepatic duct at the mouth of the porta hepatis, to form the bile-duct. The spiral constriction found in the neck of the gall-bladder is continued into the beginning of this duct. Sometimes the cystic duct joins the right hepatic duct instead of the hepatic duct proper.
Ductus Choledochus. The bile-duct (O.T. common bile-duct) begins at the mouth of the porta hepatis, where it is formed by the union of the hepatic and cystic ducts. From this it passes downwards, anterior to the foramen epiploicum, lying between the two layers of the lig. hepato-duodenale, with the portal vein behind
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and the hepatic artery to its left. It next descends behind and to the left of the superior part of the duodenum (Fig. 944), and then between the pancreas and descending part of the i duodenum. Finally, it meets the pancreatic duct, and the two, running together, pierce the medial wall of the descending part of the duodenum very obliquely, and open by a common orifice on the papilla duodenalis about 3 or 4 inches (87 to 10 cm.) beyond the pylorus (see p. 1185).
The length of the bile-duct is about 3 inches (75 mm.), and its diameter, which is very variable, is generally about inch (6 to 7 mm.).
Structure of the Excretory Ducts.-With the exception of the peritoneal coat, which is absent, the hepatic, cystic, and bile-ducts agree with the gall-bladder in general structure. The tunica mucosa contains a large number of mucous-producing glands, the glandulæ mucosæ biliosæ.
-Bile-duct Pancreatic duct
FIG. 945.-DIAGRAM SHOWING THE
A.D.S., Accessory pancreatic duct (of Santorini); C, Circular muscular fibres; L, Longitudinal muscular fibres; M, Mucous coat.
The bile and pancreatic ducts, in piercing the wall of the duodenum, run obliquely through its coats for about or an inch (12 to 18 mm.), and, as a rule, do not unite until they have almost reached the opening on the duodenal papilla (Fig. 945). This orifice is very much smaller than either duct, and the short and relatively wide common cavity which precedes it is sometimes known as the "ampulla of Vater." Occasionally the cystic and hepatic ducts open into the duodenum separately.
The pancreas is an elongated glandular mass which lies transversely on the posterior abdominal wall, with its right end resting in the concavity of the duodenum (Fig. 946), and its left end touching the spleen. It secretes a digestive fluid the pancreatic juice-which is conveyed to the duodenum by the pancreatic duct, and which constitutes one of the chief agents in intestinal digestion.
The absence of a true capsule, and the distinct lobulation of the gland, give the pancreas a very characteristic appearance (Fig. 948).
Position. The greater part of the gland lies in the epigastrium, but the tail and adjacent part of the body extend into the left hypochondrium.
The head is placed opposite the second and upper part of the third lumbar vertebra, whilst the body runs to the left, about the level of the first lumbar vertebra. It should be added, that very often the inferior portion of the head projects some distance below the subcostal plane, and thus lies in the umbilical region.
In shape the pancreas, when hardened in situ, is very irregular (Fig. 946), its right end being flattened and hook-like, whilst the rest of the organ is prismatic and three-sided. It may, perhaps, in general form be best compared to the letter J placed thus, particularly if the stem and hook of the letter are thickened.
The gland is divisible into a head (caput) with a processus uncinatus, a body (corpus), and a tail (cauda). The head corresponds to the hook of the, and runs downwards and to the left along the descending and transverse portions of the duodenum. The stem of the represents the body of the gland, and the thin left extremity of the body forms the tail. The narrow part connecting the head and body is the neck (Symington).
When removed from the body without previous hardening, the pancreas loses its true form, and becomes drawn out into a slender, elongated, tongue-shaped mass, with a wider end turned towards the duodenum, and a narrow end corresponding to the tail.
Its total length, when fixed in situ, is about 5 or 6 inches (125 to 15 cm.); after removal, if not previously hardened, it is easily extended to a length of 8 inches (20 cm.). Its weight is usually about 3 ounces (87 grammes).
Relations. The general position and relations of the pancreas may be briefly
expressed as follows:-The head (Fig. 946) lies in the concavity of the duodenum, with the vena cava inferior and abdominal aorta behind it; the body crosses the
FIG. 946.-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 inferior vena cava was left behind. The stomach bed is well shown. (From a body hardened by chromic acid injections.) left kidney and supra-renal gland; and the tail touches the inferior part of the spleen. The greater part of the organ lies behind the stomach, which must be. detached from the gastro-colic ligament, and turned upwards, in order to expose it. In describing the detailed relations, each part of the organ will require to be considered separately.
Caput Pancreatis.-The head of the pancreas is the large flattened and somewhat disc-shaped portion of the gland which lies in the concavity of the duodenum, extending along its second and third portions almost as far as the duodenal-jejunal flexure. Above,
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