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When seen in sections of the frozen body (Fig. 908), the oesophagus usually appears either as a flattened tube with a transverse slit-like cavity, or as an oval or rounded canal with a more or less stellate lumen. The former condition is more common in the neck, owing to the pressure of the trachea, and the latter in the thorax.
When exposed in the ordinary postmortem examination soon after death, it has rather the appearance of a solid muscular rod or band than of a hollow tube.
The esophagus presents three distinct constrictions, one situated at its beginning, another at the point where it is crossed by the left bronchus, and the third where it passes through the diaphragm. The two upper constrictions are of the same size, and will admit without injury an instrument with a maximum diameter of (20 mm.). At each of these points the tube is flattened from before backwards.
The oesophagus varies in length in different individuals, from 8 to 14 inches (20 to 35 cm.). The distance from the upper incisors to the beginning of the oesophagus averages about 6 inches (15 cm.).
During life the cervical portion is said, under ordinary circumstances, to be closed and flattened from before backwards by outside pressure, whilst the thoracic portion may be open owing to the negative pressure in the thorax. The passage into the stomach is also said to be open (Mickulicz), but this is doubtful.
The size at the two constrictions, when the tube is fully distended, is 23 mm. transversely, and 17 mm. antero-posteriorly. The other parts vary in diameter between 26 and 30 mm. (Jonnesco).
In its first curvature to the left the divergence is greatest opposite the third thoracic vertebra. The second inclination to the left begins about the seventh thoracic vertebra, and continues to the end of the esophagus, being considerably increased as the diaphragm is approached.
Relations of the Esophagus.-The relations (Fig. 908) differ so widely in the neck and thorax that they must be described separately for each of those regions.
In the Neck.-Anteriorly lies the trachea -to the posterior membranous wall of which the esophagus is loosely connected by areolar tissue and in the groove at each side, between the trachea and oesophagus, the recurrent nerve ascends to the
larynx (Fig. 908, A). Posteriorly lie the FIG. 908.-TRACINGS FROM FROZEN SECTIONS TO
vertebral column and the longus colli
SHOW THE RELATIONS OF THE ESOPHAGUS at the levels of the 1st, 3rd, 5th, 8th, and 9th thoracic vertebræ, respectively.
Aorta; C. Common carotid artery; D, Diaphragm;
L.B, Left bronchus; L.C, Left subclavian artery;
to the deviation of the tube to the left in the inferior part of the neck, its relation to the carotid sheath and thyreoid gland is much more intimate on the left than on the right side.
In the Thorax.-The oesophagus passes successively through the superior and posterior mediastina, in the former lying close to the vertebral column, but in the latter advancing somewhat into the thoracic cavity and coming into contact with the back of the pericardium. The trachea still lies anterior to it as far as the fifth thoracic vertebra, where the trachea bifurcates. Immediately below that the œsophagus is crossed by the left bronchus (Fig. 908, C), and in the rest of its thoracic course it lies in the closest relation to the back of the pericardium. Posteriorly, in the upper part of the thorax, it rests on the longus colli muscles and the vertebral column; but below the bifurcation of the trachea, as already explained, it advances into the cavity of the posterior mediastinum, and is soon separated from the vertebral column by the vena azygos, the thoracic duct, the upper five aortic intercostal arteries of the right side, and in its lower part by the thoracic aorta as well.
On its left side, in the upper part of the thorax, lie the left pleura and the left subclavian artery, with the thoracic duct in a plane posterior to the artery; in the middle region, the aorta, and lower down the left pleura again, for a little way, before the esophagus pierces the diaphragm. On the right side the tube comes into relation with the arch of the vena azygos, whilst the right pleura clothes it both below and above that level.
The two vagus nerves, after forming the anterior and posterior pulmonary plexuses descend to the oesophagus, where they form, by uniting with one another and with the branches of the sympathetic, the anterior and posterior œsophageal plexuses. Lower down the left nerve winds round to the anterior, whilst the right turns to the posterior surface of the oesophagus, and in this relation they pass with the tube through the diaphragm to reach the stomach.
The diaphragmatic portion, about half an inch in length (1 to 1.5 cm.), corresponds to the portion of the tube which lies in the esophageal orifice (or canal) of the diaphragm. The plane of this orifice is very oblique or almost vertical, and its abdominal opening looks forwardand to the left, and but little downwards. Above and in front, where it is bounded either by the posterior edge of the central tendon or by a few decussating fibres of the muscular portion of the diaphragm, which meet behind the tendon, the œsophageal orifice has practically no length. and consequently the oesophagus here passes into the abdominal cavity immediately after leaving the thorax. At the sides and behind, on the other hand, the decussating bands from the tw crura, which embrace the orifice, are so arranged that they turn a flat surface (not an edge towards the opening, and thus, behind and at the sides, the orifice or canal is of some length and on these aspects there is a portion of the tube in contact with the diaphragm for a distance of 1 to 1 cm. But this contact takes place not around a horizontal line, but in a very oblique plane corresponding to that of the orifice.
The oesophagus, in passing through the orifice, is connected to its boundaries by a considerable amount of strong connective tissue, but it is extremely difficult, or impossible, to demonstrate any direct naked-eye connexion between the œsophageal muscular fibres and those of the diaphrag
The anterior or right boundary of the œsophageal orifice, formed of fibres derived from both crura of the diaphragm, is strongly developed and prominent, and usually lies in the œsophages. groove, on the back of the left lobe of the liver, which groove is rarely due to the pressure of the cesophagus alone.
The pars abdominalis of the oesophagus is very short, for immediately after piercing the diaphragm the tube expands into the stomach. However, when the empty stomach is draw forcibly downwards, a portion of the front and left side of the tube, about half an inch in lengt (1 to 15 cm.), is seen, to which the above term is applied. This part is covered with peritoneum, derived from the great sac in front and on the left, whilst its right and posterior surfaces are uncovered. It is generally described as lying against the œsophageal groove and the left triangular ligament of the liver in front, but it never actually comes in contact with the latter of these structures, which is attached to the upper surface of the left lobe of the liver by one edge, and to the diaphragm, over an inch in front of the oesophagus, by the other. As regards the former, the œsophageal groove of the liver is generally occupied by the prominent right margin of the œsophageal orifice of the diaphragm and occasionally by the oesophagus as well. Possibly tha margin is so strongly developed and so prominent in order that it may bear the pressure of the liver off the gullet, which otherwise might be interfered with in its dilatation during the passage of food When the stomach is fully distended the abdominal part of the oesophagus almost disappears being absorbed into the stomach in its distension.
The portion of the oesophagus which adjoins the stomach is sometimes described as consisting of two parts, namely, the ampulla phrenica and the antrum cardiacum. The former is
fusiform expansion of the tube, of variable length and girth, which lies within the thorax immediately above the point where the gullet is grasped between the two muscular margins of the œsophageal opening and the diaphragm. It lies in the lowest part of the posterior mediastinum where this is bounded anteriorly by the back of the diaphragm.
The antrum cardiacum is another name for the abdominal portion of the oesophagus. It is funnel-shaped, and expands towards the stomach.
Relation of the Aorta to the Esophagus.-The arch of the aorta, passing back to reach the vertebral column, crosses to the left side of the oesophagus; consequently the descending thoracic aorta lies at first to its left; lower down, however, as the aorta passes on to the anterior aspect of the vertebral column, and the gullet inclines forwards and to the left, the aorta comes to lie posteriorly, and then, as the diaphragm is approached, it lies not only posteriorly, but also somewhat to the right of the oesophagus (Figs. 907 and 908).
Relation of the Thoracic Duct to the Esophagus.-The thoracic duct, lying to the right of the aorta below, is not directly related to the esophagus (Fig. 908, E); but higher up (Fig. 908, D and E) it lies posterior to it. About the level of the aortic arch the duct passes to the left, and above this (Fig. 908, B and A) will be found on the left side of the oesophagus, and on a plane somewhat posterior to it.
Relation of the Pleural Sacs to the Esophagus.-Above the level of the arches of the aorta and of the vena azygos, between which the oesophagus descends, the pleuræ, though not lying in immediate contact with the oesophagus, are separated from it only by a little connective tissue, and on the left side also, behind the subclavian artery, by the thoracic duct (Fig. 908, B). Here, in thin bodies, the left pleura is very close to the oesophagus, and the thoracic duct, lying on its left side, may occasionally be seen through the pleural membrane. Below the arch of the azygos vein the right pleura clothes the right side of the oesophagus-and very often even a considerable portion of its posterior surface too, thus forming a deep recess behind it almost as low down as the opening in the diaphragm. On the left side, below the level of the aortic arch, the left pleura comes in contact with the gullet, only for a short distance, just above the diaphragm (Fig. 908, E).
Variations.-The chief anomalies found in the oesophagus are: (1) Annular or tubular constrictions; (2) diverticula, of which the most interesting-known as "pressure pouches "—are usually situated on the posterior wall close to its junction with the pharynx, and these sometimes require surgical interference; (3) doubling in part of its course; and (4) communications between the trachea and oesophagus.
Structure of the Esophagus (Fig. 911).—The œsophageal wall is composed of three proper coats (1) tunica muscularis, (2) tela submucosa, and (3) tunica mucosa. addition, it is surrounded by an outer covering of areolar tissue (4) tunica adventitia, by which it is loosely connected to the various structures related to it in its course. This loose covering permits of its free movement and of its increase in size, or of its diminution, during the act of swallowing.
The tunica muscularis is composed of two layers an outer of longitudinal, and an inner of circular fibres. The longitudinal layer is highly developed, and, unlike the condition usually found in the digestive tube, it is as stout as, or in places stouter than, the circular layer. Its fibres form along the greater length of the tube an even covering outside the circular layer, and below they are continued into the longitudinal fibres of the stomach. Above, near the superior end of the cesophagus, the longitudinal fibres of each side, separating at the back, pass round towards the anterior aspect and form two longitudinal bands (Fig. 909), which run up on the front of the tube, and are attached by a tendinous band to the superior part of the posterior surface of the cricoid cartilage (Fig. 909).
The circular muscular fibres, though not forming such a thick layer as the longitudinal fibres, are nevertheless well developed. Below, they are continued into both the circular and oblique fibres of the stomach. Above, they pass into the inferior fibres of the inferior constrictor of the pharynx.
At the superior end of the oesophagus the muscular fibres are entirely of the striated variety. Soon unstriped fibres begin to appear in increasing numbers, and in the inferior half or two-thirds only unstriped muscle is found.
The longitudinal fibres for about the superior fifth of the tube are entirely striped; in the second fifth striped and unstriped are mixed; whilst in the inferior three-fifths unstriped fibres alone are present. The circular fibres are entirely striated for the first inch; after this unstriped fibres appear; and in the inferior two-thirds, only unstriped muscle fibres
The longitudinal fibres are often joined by slips of unstriped muscle, or elastic fibres, which spring from various sources, including the left pleura (m. pleuro-œsophageus, constant, Cunningham), the bronchi (m. broncho-oesophageus), back of trachea, pericardium, aorta, etc. These slips assist in fixing the oesophagus to the surrounding structures in its passage through the thorax, and have been aptly compared to the tendrils of a climbing plant (Treitz). The tela submucosa, composed of areolar tissue, is of very considerable thickness, in
order to allow of the expansion of the tube during swallowing. It connects the mucous
membrane loosely to the muscular coat, and admits of the former being thrown into folds
when empty. In this
coat are contained the
mucous glands(glandule oesophagea) which open into the cavity of the oesophagus (Fig. 911). The tunica mucosa is of a grayish-pink colour, much paler than that of the pharynı. and of a firm and resis tant texture. It is covered with a thick stratified, squamous ep thelium, on the surface of which the openings of numerous glands are found. Inferiorly, its junction with the gastric mucous membrane is indicated by a distinct, irregularly dentated or crenated line, which runs transversely round the tube. In carefully pre
served specimens the smooth mucous membrane of the oesophagus above this line contrasts strongly with the mamillated gastric mucous membrane below.
Owing to the inelasticity of this coat, and the fact that it is but loosely connected to
the muscular coat by the submucosa, it is thrown into a series of longitudinal folds when the oesophagus is empty and contracted; hence the stellate lumen often seen in sections of the gullet.
Glands. Numerous racemose mucous glands, the glandulæ œsophageæ, large enough to be seen distinctly with the naked eye, are found in the submucosa. They are pretty evenly distributed over the whole tube, and do not appear to be more numerous towards either end. In addition to these, other glands, resembling closely those of the cardiac end of the stomach, are found in the mucous membrane of certain portions of the œsophagus. They are entirely confined to the mucosa, and do not extend beyond the lamina muscularis mucosa. These glands are specially numerous at both the upper and lower ends of the tube.
Vessels and Nerves. Its arteries consist of numerous small branches derived, in the neck, from the inferior thyreoid, in the thorax, from the bronchial arteries and thoracic aorta, and in the abdomen, from the left gastric artery, and also from the left inferior phrenic.
The veins form a plexus on the exterior of the oesophagus, from which branches pass, in the lower part of the tube, to the coronary vein of the stomach, and, higher up, to the azygos, and thyreoid veins. There is thus established on the lower part of the oesophagus a free communication between the portal and systemic veins.
The lymph vessels pass to the inferior set of deep cervical glands in the neck, and to the posterior mediastinal glands, many of which, of large size, are seen around the tube, in the thorax. The nerves are derived from the recurrent, and from the cervical sympathetic in the neck, from the vagus and sympathetic nerves in the thorax.
THE ABDOMINAL CAVITY.
As the remaining parts of the digestive system lie within the abdomen it will be necessary to describe that cavity, and to refer briefly to its lining membranethe peritoneum-before passing on to the consideration of the viscera which are contained within it.
The abdomen is that portion of the trunk which lies below the diaphragm. It consists of a wall, composed in part of bones, muscles, tendons, fascia, etc., enclosing a large cavity, in which lie the greater part of the digestive, urinary, and generative systems of organs, as well as blood-vessels, nerves, and other structures. The greater part of the wall of the cavity, and the surfaces of the viscera, are clothed by a continuous smooth membrane, the peritoneum. The cavity is completely filled by the organs mentioned. They lie in contact with one another, and when they are in situ the so-called cavity is merely a potential space between the peritoneal surfaces of adjacent viscera. When air is admitted, as, for instance, by opening the abdominal wall in any place, the viscera fall away from one another and a space is formed, in place of the capillary interval which exists under normal conditions between them. In the following description, the term abdomen or abdominal cavity is used to indicate the region enclosed by the muscular and bony walls, and the term peritoneal cavity the potential space inside the peritoneal membrane between the viscera.
Shape. In general shape the cavity is of a somewhat oval form, with the long axis directed vertically. The superior end is wider than the inferior. It is strongly flattened from before backwards, and is encroached upon in the median plane posteriorly by the projection forwards of the vertebral column.
On transverse section, it will be noticed that the front of the vertebral column lies at no great distance from the back of the anterior abdominal wall (usually 2 to 3 inches), while on each side of the vertebral column there is a deep recess, occupied by the kidneys and portions of the intestine.
The abdominal cavity is divisible into the abdominal cavity proper and the pelvis minor. Vertical section of the trunk shows that the pelvis minor (O.T. true pelvis) lies below and behind the abdominal cavity, of which it forms a funnel-shaped termination. The long axis of the funnel is directed downwards and backwards. As the walls of these two regions are markedly different, the boundaries will be considered separately.
Boundaries of the Abdomen Proper.-The cavity is limited above by the concave vault of the diaphragm, which is dome-shaped and presents a right and a left cupola