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tissue, which completely surrounds each tubule and blood-vessel, and binds it to its I neighbours. It has been found possible to obtain an accurate idea of the arrangement of this connective tissue by submitting thin sections of the kidney to the action of certain digestive fluids. When this is done the tubules and blood-vessels are removed, and the connective tissue stroma is left behind. The connective tissue thus revealed is seen to form a continuous network, the spaces in which faithfully reproduce the outlines and the arrangement of the kidney tubules. The network of the stroma is continuous with the capsule of the kidney.
Vessels of the Kidney. The renal artery comes directly from the aorta, and is very large in proportion to the size of the organ to which it conveys blood. Its main branches, as they approach the kidney to enter the hilum, lie between the tributaries of the renal vein in front and the ureter behind. Within the sinus of the kidney the branches of the renal artery become arranged in a dorsal and a ventral group, the dorsal vessels lying behind, the ventral ones in front of the subdivisions of the ureter. ventral group of vessels supplies the part of the kidney which forms the anterior and lateral walls of the sinus; the distribution of the dorsal group is for the most part restricted to the portion of the kidney which lies behind, and to the medial side of the sinus.
Entering the substance of the kidney in the manner described above (p. 1265), the larger arteries lie in the intervals between the pyramids, and are called the arteriæ interlobares renis or interlobar arteries. These vessels dividing, form a series of incomplete arterial arches, the arteriæ arciformes, which pass across the bases of the pyramids. Although we speak of arterial arches, it must be understood that no anastomosis between the branches of the interlobar arteries actually takes place, but that each artery which enters the wall of the kidney sinus has an isolated distribution and possesses the characters of an "end artery.' Each arterial arch gives off a number of vessels which pass through the convoluted part of the cortex towards the surface of the kidney. These are known as the arteriæ interlobulares, and lie at very regular intervals. From them a number of short branches arise, termed vasa afferentia, each of which proceeds to the dilated extremity, or capsule, of a uriniferous tubule. Here the vas afferens breaks up into a much convoluted capillary mass, called a glomerulus, which is contained within the invagination of the capsule. The little vein which issues from the glomerulus, or vas efferens, instead of running directly into a larger vein, breaks up, after the manner of an artery, into capillaries which supply the tubules of the convoluted and radiate parts of the kidney cortex. Hence almost all the blood which supplies the tubules of the cortical part of the kidney passes in the first instance through the glomeruli. The tubules of the bases of the pyramids also receive their blood-supply through vasa efferentia derived from the glomeruli which lie near. The little vessels passing from these glomeruli break up into bundles of fine arteries, which give the bases of the pyramids their coarsely striated appearance. They are known as arteriolæ rectæ, and, like the arteriæ interlobulares, are very conspicuous in injected preparations of the kidney.
The fibrous capsule of the kidney receives minute branches from the interlobular arteries, some of which, piercing the capsule, communicate by capillaries with the vessels of the tunica adiposa.
Veins corresponding to the interlobular arteries and arteriola recta collect the blood from the capillaries surrounding the tubules, and unite to form a series of complete arches. across the bases of the pyramids. From these venous arcades vessels arise, which traverse the intervals between the pyramids and reach the sinus of the kidney, where they unite to form the dorsal and ventral tributaries of the renal vein. Some small veins in the superficial part of the cortex communicate through the fibrous capsule with minute veins in the capsula adiposa. Issuing from the kidney sinus, the veins run a direct course to end in the inferior vena cava.
Nerves of the Kidney. The nerves of the kidney accompany the branches of the artery, and are derived from the renal plexus. Their minute branches form regular net-like plexuses on the walls of the fine arteries and kidney tubules, and the presence of nerve terminations occurring among the epithelial cells lining the tubules has within recent years been demonstrated.
From clinical evidence it would appear that the nerve fibres which supply the kidney are portions of the tenth, eleventh, and twelfth thoracic nerves.
Variations. A marked difference in the size of the two kidneys is sometimes observed, a small kidney on one side of the body being usually compensated for by a large kidney on the opposite side. Cases of complete absence of one or other kidney are recorded.
A few cases are on record in which an extra kidney was found on the right or left side.
Traces of the superficial lobulation of the kidney, present in the foetus and young child, are often retained in the adult.
Horse-shoe kidney is not an infrequent abnormality. In these cases the two kidneys are united at their inferior ends, across the median plane, by a connecting piece of kidney substance. The amount of fusion between the two kidneys varies much; it is sometimes very complete, while in other cases it is but slight, the connexion being chiefly composed of fibrous tissue.
In very rare cases the kidney appears to be almost entirely surrounded by peritoneum and to be attached to the abdominal wall by a kind of mesentery, enclosing the vessels and nerves passing to the hilus. The condition is believed to be congenital.
Not very infrequently one or both kidneys are found at a much lower level than usual, and occupying a position in the iliac fossa or the pelvic cavity. This condition, when congenital, is associated with an arrest in the normal change in position, relative to surrounding structures, which the kidney experiences during development. In such cases the kidney does not receive its blood-supply from usually placed renal arteries, but from vessels which arise from the lower end of the aorta, or from the iliac, or the middle sacral artery. These congenitally abnormally situated kidneys do not usually possess the typical outline of the normal organ, but vary much in shape, and the hilum is often directed downwards or backwards, and not medially In some mammalian animals, such as the bear, the ox, the porpoise, etc., the kidneys are composed of a number of completely isolated lobes, each of which corresponds to one papilla, its pyramids and surrounding cortex; while in others, such as the horse, the fusion of the lobes is more complete even than in the human kidney, and a single mass represents the united papilla.
THE DUCT OF THE KIDNEY.
The duct of the kidney is called the ureter, and begins above in a thin-walled funnel-shaped expansion called the pelvis renalis, which is placed partly within and partly outside the sinus of the kidney. Towards the level of the inferior end of the kidney the part of the pelvis which lies outside the sinus diminishes in calibre, and forms a tube-like duct, the ureter, which conveys the urine to the bladder.
Pelvis of the Kidney. Within the sinus of the kidney the pelvis lies among the larger renal vessels. It is formed by the junction of two, or more rarely three, thin-walled tubes, the calyces majores, each of which has a number of branches. These latter, called calyces renales minores, are short, and increase in diameter they approach the sinus wall, to which they are attached. Their wide, somewhat funnel-like ends enclose the renal papillæ, and receive the urine, which enters them through the foramina papillaria. The calyces are usually about eight in number. one calyx sometimes surrounding two or even three papillæ. The portion of the pelvis that lies outside the kidney has in front of it, in addition to the renal vessels, on the right side, the descending part of the duodenum, and on the left side, a part of the pancreas and sometimes the duodeno-jejunal flexure (Fig. 979).
Ureter. The ureter is the vessel which carries the urine from the pelvis of the kidney to the bladder. It is a pale-coloured thick-walled duct with a small lumen While in situ it has a total length of about ten inches, and lies throughout its whole course in the subperitoneal tissue, behind the peritoneum, to which it is closely connected. In its superior part the ureter lies in the abdominal cavity, and in its inferior part in the pelvis minor (Figs. 983 and 988).
The normal ureter, in the flaccid condition, measures after its removal from the body eleven to fourteen inches.
The pars abdominalis, or abdominal portion of the ureter, about five or five and a half inches in length, is directed downwards and slightly medially, and lies upon the psoas major muscle. Certain structures are related to the ureters in a similar manner on each side of the body; for instance, the abdominal portion of each ureter is crossed very obliquely, on its anterior aspect, by the internal spermatic vessels and behind each ureter the genito-femoral nerve passes downwards and laterally (Fig. 983). Other structures are related to the duct of the right or left sid alone; on the right side, the descending part of the duodenum lies in front of the upper part of the ureter, and the line of attachment of the mesentery crosses it lowes down, just before the ureter enters the cavity of the pelvis minor. On the left side the line of attachment of the mesentery of the pelvic colon crosses the ureter. Crossing the common iliac, or the external iliac artery, the ureter enters the pelvis minor. The left ureter usually crosses the common iliac artery, and the right
ureter, in most cases, lies across the external iliac; but this arrangement is by no means constant. The course and position occupied by the abdominal portion of the ureter is well seen in Fig. 983.
In X-ray photographs, the shadow cast by the abdominal portion of the ureter when the latter has been rendered opaque, is seen to fall immediately in front of the tips of the transverse processes of the lower lumbar vertebra.
The pars pelvina or pelvis minor portion of the ureter is about four and a half or five inches in length; it passes downwards on the side wall of the pelvis, immediately behind the peritoneum, describing a curve which is convex backwards and laterally (Fig. 988). The most convex portion of this curve lies close to the deepest part of the greater sciatic notch (Fig. 988). As it descends upon the side wall of the pelvis the ureter forms the posterior boundary of the triangular district known as the obturator triangle. The lower limit of this triangle is formed by the ductus deferens, and the upper and anterior boundary by the external iliac vessels and the pelvic brim (Fig. 988).
In its course within the pelvis minor the ureter lies in front of the hypogastric artery, and crosses the medial aspect of the obturator nerve and vessels and of the obliterated umbilical artery. About the level of the ischial spine, the
Basal part of
ureter is crossed from Columna renalis of cortex
before backwards by the
ductus deferens, and
from this point onwards FIG. 987.-LONGITUDINAL SECTION OF THE KIDNEY, OPENING Up the Kidney it is not so intimately re
lated to the peritoneum. The pelvis of the kidney and some of its calyces have been laid open as they It now bends some
what medially and forwards, to reach the posterior angle of the bladder, and comes into relationship with the upper end of the vesicula seminalis, in front of which it lies. The ductus deferens having crossed the ureter also turns medially, and as it does so it lies at a higher level and on a posterior plane to the ureter. The inferior end of the ureter is surrounded by a dense plexus of veins which brings the vesical plexus into communication with the hypogastric vein. The great nerve cord which connects the hypogastric plexus with the pelvic plexus, also comes into relationship with the lower part of the pelvic portion of the ureter, in the region where the latter is crossed by the ductus deferens (Fig. 988).
When the right and left ureters reach the bladder they are a little more than two inches apart. They pierce the bladder wall very obliquely, and are embedded within its muscular tissue for nearly three-quarters of an inch of their length. Finally, they open into the bladder by two small slit-like apertures which are of a valvular nature, and prevent a backward passage of fluid from the bladder. It is probable, however, that an exaggerated idea of the valvular nature of the openings of the ureters into the bladder is obtained by an examination of the parts in the dead subject. When the bladder is empty the openings of
the ureters are placed about one inch apart, but when that viscus is distended they are often two inches, or more, distant from one another. As the ureter pierces the bladder wall the muscular fibres of the bladder and ureter remain quite distinct, and so the ureter, remaining a thick-walled tubular structure, appears to pass through a gap in the muscular wall of the bladder. The mucous coat alone of the ureter becomes continuous with that of the bladder.
The canal of the ureter is not uniform throughout, but is somewhat constricted in certain places, corresponding to the regions where the ureter is most sharply curved or changes its direction. These more constricted parts of the tube are described as occurring one in the middle of the abdominal portion, one at the
FIG. 988.-MEDIAN SECTION OF AN ADULT MALE PELVIS.
The coils of the small intestine and of the colon which lay within the pelvis have been lifted out in order to give a view of the side wall of the pelvic cavity.
junction of the abdominal and pelvic portions, and one in the pelvic part of the ureter. Also just before the ureter joins the pelvis of the kidney and just as it reaches the bladder wall its lumen is usually somewhat constricted.
In the female, the ureter, near its termination, passes beneath the lower part of the broad ligament of the uterus, and lies to the lateral side of the cervix uteri and the upper part of the lateral wall of the vagina. It is accompanied in the inferior part of its course by the uterine artery, which crosses it on its anterior aspect not far from its termination (Fig. 1002). Higher up it lies in the peritoneal ridge which forms the posterior boundary of the fossa ovarica, a posterior subdivision of the obturator fossa (Fig. 1002).
The wall of the ureter, which is thick and of a whitish colour, is composed of mucous, muscular, and fibrous coats. The tunica mucosa or mucous coat possesses an epithelium composed of many layers of cells, those nearest the surface being of
large size. When the canal is empty the mucous coat is thrown into numerous longitudinal folds, and so its lumen exhibits a stellate outline in transverse section. The submucous tissue varies much in thickness in different parts of the ureter, and contains some elastic fibres. The unstriated muscle fibres which compose the tunica muscularis or muscular coat are collected into bundles which are separated by a considerable amount of connective tissue, and are arranged, some longitudinally, some circularly. In the upper part of the ureter a relatively large amount of connective tissue is present deep to and among the bundles of muscle fibres, which are arranged in three distinct strata-an inner longitudinal, an intermediate circular, and an outer longitudinal. In the middle part of the vessel the same layers may be recognised, but the circularly disposed bundles of fibres are more numerous than higher up. In the lower part of the ureter the connective tissue is relatively scanty and the inner longitudinal fibres lie close to the lining epithelium; in this region also the longitudinal folds of the mucous coat become fewer and less marked. A short distance above the point where it reaches the bladder, the wall of the ureter becomes much thickened by the addition of a number of coarse bundles of longitudinally arranged muscle fibres, which are applied to the outer surface of the muscular coat. These muscle fibres form the so-called "sheath of the ureter," and are continued on the superficial aspect of the vessel as it passes through the bladder wall. In the portion of the ureter which traverses the wall of the bladder (pars intramuralis) nearly all the fibres of the muscular coat are disposed longitudinally, i.e., in a direction parallel to that of the vessel. The muscle fibres lie close beneath the epithelium, and end just where the mucous coats of the bladder and ureter become continuous. The tunica adventitia or outer fibrous coat of the ureter varies in thickness at different levels, and in its lower part blends with the connective tissue which lies among the muscle fibres forming the sheath of the ureter just mentioned.
The mucous membrane of the calyces and of the pelvis of the kidney possesses an epithelium resembling that of the ureter. Where each renal papilla projects into one of the calyces a deep circular recess, or fornix, is formed between the wall of the calyx and the sloping side of the papilla; at the bottom of this recess the epithelium of the calyx becomes continuous with that covering the papilla. At the foramina papillaria the epithelium joins that of the kidney tubules. muscular fibres in the wall of the calyces and of the pelvis are collected into loosely arranged bundles separated by wide intervals occupied by fibrous connective tissue. As in the ureter, the outermost and innermost fibres run in a longitudinal, the intermediate ones in a circular direction. The circularly arranged fibres alone form a distinct layer.
Vessels and Nerves of the Ureter.-The abdominal part of the ureter receives its blood-supply from the renal and internal spermatic arteries; the pelvic portion is supplied by the superior vesical and middle hæmorrhoidal vessels.
The nerves of the ureter reach it through the renal, the spermatic, and the hypogastric, plexuses.
Variations. The ureter is sometimes represented by two tubes in its upper portion. In rarer cases it is double throughout the greater part of its extent, or even in its whole length from the pelvis of the kidney to the bladder. In such cases there may be two openings into the bladder. Asymmetry as regards such abnormalities is very common. Most usually
Variations in the form of the pelvis of the kidney are of frequent occurrence. the pelvis divides into two large subdivisions, one of which passes in the direction of the upper, the other in that of the lower pole of the kidney. In some cases these branches come off directly from the ureter without the intervention of a pelvis, or a marked subdivision may lead to the formation of two pelves.
The vesica urinaria or urinary bladder is a hollow muscular organ situated in the anterior part of the pelvic cavity, above and behind the symphysis pubis. It lies in front of the rectum, from which it is separated in the male by the seminal vesicles and the terminal portions of the ductus deferentes, and in the female by the vagina and uterus. The ureters, which convey the fluid secreted by the kidneys, open into the base of the bladder about half an inch from the median plane.