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lateral side of the quadratus lumborum muscle. The lateral border is narrowest above, and widest just below its middle point, corresponding to the greater thickness of the kidney at this level.

In many ways it would be more satisfactory to apply the term facies muscularis or muscular surface collectively to the areas above described as "posterior surface" and "lateral border"; in like manner the term facies visceralis, or visceral surface, might be suitably applied to the so-called anterior surface of the organ. The edge separating the visceral from the muscular surface is the actual lateral edge or border of the kidney.

Anterior Relations and the Anterior Surface of the Kidney. The anterior relations of the kidneys not only differ on the two sides of the body, but also many

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Hypogastric artery

Common iliac artery
Internal spermatic artery

Inferior mesenteric artery ty

FIG. 983.-DISSECTION TO SHOW THE RELATIONSHIPS OF THE KIDNEYS AND OF THE URETERS

TO THE MUSCLES OF THE POSTERIOR ABDOMINAL WALL.

of the structures related to the anterior surface of each kidney undergo frequent changes in position during life. Hence it is not possible to give more than a general account of the anterior relationships of the kidneys.

Right Kidney.-A small area on the superior part of the anterior surface of the right kidney is in relation to the corresponding suprarenal gland (Fig. 983). The rest of the superior part of the anterior surface is in contact with the visceral surface of the liver, which is often hollowed out to form a fossa for the kidney. The suprarenal gland is bound to the kidney by connective tissue, while the part of the kidney in relation to the liver is, like the liver itself, covered by peritoneum, and thus the two organs, although closely applied, are really separated by a part of the general peritoneal cavity. Immediately anterior to the inferior end of the right kidney are usually found two parts of the alimentary canal-namely, the descending part of the duodenum and the right flexure of the colon, or the

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commencement of the transverse colon. The part of the kidney related to the duodenum lies to the medial side of the area which touches the colon, but the exact amount of the kidney in contact with each of these two parts of intestine varies much in different subjects. Frequently the colon and the kidney are both covered by peritoneum where they are in contact, but the duodenum is bound down to the kidney by connective tissue. In addition to the structures mentioned, some portion of the ileum, or of the jejunum, is often found in contact with a small part of the right kidney near its inferior end.

In some cases the peritoneal membrane does not cover the whole of the surface in contact with the liver, and then the superior part of the hepatic area of the kidney is, like the anterior aspect of the suprarenal gland, bound by connective tissue to the "uncovered" area on the posterior aspect of the liver.

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Hepatic area.

Duodenal area

Colic area

Crista iliaca.

Ureter

Ureter

Gastric area

-Splenic area

Pancreatic

area

-Jejunal area
Colic area

Crista iliaca

FIG. 984.-ANTERIOR ASPECT OF THE KIDNEYS AND GREAT VESSELS. The drawing was made, before removal of the organs, from a specimen in which the viscera had been hardened in situ. The dotted lines mark out the areas which were in contact with the various other abdominal viscera.

Left Kidney. The extreme superior and medial part of the anterior aspect of the left kidney is united by connective tissue to the lower part of the left suprarenal gland, and the area immediately below this is in contact with the stomach and the pancreas. The pancreas, like the suprarenal gland, is bound down to the kidney by connective tissue, but the stomach is separated from the area with which it is in apposition by a portion of the omental bursa. The area in actual contact with the stomach is a small somewhat triangular district situated above the level at which the pancreas is related to the kidney. The superior and lateral part of the anterior aspect of the kidney is related to the spleen, the two organs being separated by a portion of the general peritoneal cavity, except along the area where spleen and kidney are connected by the lieno-renal ligament. The anterior surface of the inferior end of the left kidney is related, towards the medial side, to a part of the jejunum, and, towards the lateral side, to the left flexure of the colon or to a part of the descending portion of the colon. In most cases, however, the colon lies against the posterior abdominal wall to the lateral side rather than on the anterior surface of the left kidney.

The right and left colic arteries, or their branches, as they pass laterally to reach the colon, are often related to the anterior aspects of the corresponding kidneys. The splenic vessels pass laterally in front of the left kidney (Fig. 979).

Cortical substance of kidney

The anterior surface of a kidney which has been hardened in situ is, like the posterior surface, not uniformly rounded, but marked by a series of impressions corresponding to the different structures which lie in contact with it. In the case of each kidney, the most prominent region on the anterior surface lies below the level of the middle of the kidney, and corresponds to the thickest part of the organ. From this prominence on the anterior surface a series of more or less flattened planes slope away towards the borders of the kidney. These flattened areas are the impressions formed by the viscera which lie on the anterior surface of the

kidney.

In the case of the
right kidney, three
impressions can usu-
ally be distinguished
on the anterior sur-
face. One occupies
the whole of the
upper part of the
organ, and is known
as the impressio he-
patica; another
stretches from the
most prominent point
to the inferior end of
the kidney, and is
related to the colon;
while the third ex-
tends along the
medial margin, below
the hilum, and is in

contact with the
second part of the
duodenum (Fig. 979).

The relative sizes of these three areas or impressions vary much in different specimens.
On the left kidney, also, three more or less defined, flattened impressions slope
towards the borders of the organ from the most prominent part of the anterior
surface. One of these, on the superior and lateral part of the kidney, is the splenic
impression; another, extending downwards to the lower end of the kidney, is for
the jejunum, or for the jejunum and colon; the third, above and in the region of the
hilum, is called the impressio gastrica, and corresponds to the position of the over-
lying stomach. Only a small portion of this impression is in direct contact with
the stomach, since the pancreas and a part of the suprarenal gland intervene
between the stomach and the kidney (Fig. 979).

Basal part of pyramid

Branch of renal... artery

Radiate part ["medullary rays "] of cortex

FIG. 985.-LONGITUDINAL SECTION THROUGH THE KIDNEY.

The vessels and fat have been removed to give a view of the wall of the kidney sinus. The points where the vessels enter the kidney substance are seen as holes in the sinus wall.

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It is common to find the left kidney thicker and less flattened antero-posteriorly than the right, the impressions, or "facets," upon its surface being at the same time better marked. With this probably is to be associated the fact that floating kidney is more rarely met with on the left than on the right side of the body.

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Extremities of the Kidney.—The kidney, fixed and hardened in situ, is usually more pointed at its inferior than at its superior end. The latter is wider from side to side, and often somewhat flattened from before backwards. The superior end of the kidney is bent somewhat forwards and rests upon the diaphragm, which separates it from the inferior part of the pleural cavity.

Sinus Renalis.-The sinus of the kidney (Fig. 985), into which the hilum opens, is a narrow space, having its long axis corresponding to that of the kidney. The thick walls of the sinus cavity are formed by the substance of the kidney, and are lined by a part of the fibrous kidney capsule which enters the sinus over the lips of the hilum. The floor of the sinus is not even, but presents a series of small projecting conical elevations called papillæ renales, which vary from six to fifteen in number. Radiating from each papilla are a number of somewhat raised bars, or ridges, of kidney substance, separated by depressed areas. The blood-vessels and nerves enter and leave the kidney by piercing the wall of the sinus where it is formed by these little depressed areas (Fig. 985). The rounded summit of each renal papilla is pierced by a number of minute openings called foramina papillaria, which are the terminal apertures of the secreting tubules of which the kidney is mainly composed. These openings all lie close together, and give rise to the so-called area I cribrosa upon the apex of the renal papilla. The urine secreted by the kidney escapes through the foramina papillaria into the subdivisions (or calyces) of the ureter or kidney duct.

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Kidney in Section.-Sections through the kidney (Fig. 985) show that it is composed to a large extent of a number of conical masses, known as pyramides renales or pyramids. These together constitute the substantia medullaris or medulla of the kidney, and are arranged with their bases directed towards the surface, and their apices projecting into the renal sinus, where they form the papillæ renales already mentioned. The pyramids are more numerous than the papillæ, two or three usually ending in each papilla in the middle part of the kidney, and sometimes as many as six or more in each papilla near the superior and inferior ends of the organ. The bases of the pyramids do not reach the surface of the kidney, but are separated from it by a thin layer of kidney substance called the cortex, or substantia corticalis of the kidney. The cortical substance not only covers over the bases of the pyramids, but also sends in prolongations, called columnæ renales or renal columns, between the pyramids, towards the sinus. The medullary part of the kidney exhibits in section a striated appearance, while the cortical part is more granular and usually different in colour. The outer part of each pyramid is called the basis pyramidis, and appears in section to be composed of alternate dark and light streaks, while the inner, or papillary part, is often of a lighter colour, and more uniformly and faintly striated.

In sections of the kidney the larger blood-vessels are seen, after they have entered the kidney substance, to lie between the pyramids; and some of their main branches are visible passing across the bases of the pyramids.

In the fœtus and young child, and sometimes, though much less distinctly, in the adult, the surface of the kidney is marked by a number of grooves dividing it into polygonal areas. These represent the lobes, lobi renales or reniculi, of which the kidney is originally composed, and each corresponds to one papilla with its pyramids and surrounding cortical substance.

cortex.

An examination, with an ordinary pocket lens, of a section through the kidney shows that the lighter striæ of the bases of the pyramids are continued into the As they pass through the cortex towards the surface of the kidney the striæ become less distinct, and appear, when cut longitudinally, as separate raylike prolongations carried outward from the bases of the pyramids. These parts of the cortex, which seem, in this way, to be continuations of the medulla, are called "medullary rays" and constitute the pars radiata; the portions which intervene between them form what is known as the pars convoluta or "labyrinth." The appearance presented by the cortex of the kidney in section varies much according to the plane in which the section has been taken. If the section passes through and lies parallel to the axis of a pyramid, the radiate part met

Pars convoluta

Pars radiata

with will appear as isolated streaks directed from the base of the pyramid towards the surface of the kidney, and separated from one another by narrow strips, or intervals, of the convoluted part. On the other hand, in sections made at right angles to the axis of a pyramid, or cutting this axis obliquely, the convoluted portion of the cortex presents the appearance of a continuous net, the meshes of which are occupied Corpuscle of by the radiate parts, and these latter now exhibit a circular or oval outline. In a similar manner Interlobular sections through the bases of the pyramids differ much in the appearances they afford according to the plane in which they are cut.

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Pars
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Kidney Tubules.-The glandular substance of the kidney is composed of a vast number of minute tubules, called tubuli renales or uriniferous tubules, all of which have an exceedingly complicated course. The wall of each tubule consists throughout of a basement membrane and of an epithelial lining, but the lumen of the tubule and the character of the epithelium vary much in its different parts. Every tubule begins in a thinwalled spherical dilatation, known as capsula glomeruli (O.T. Bowman's capsule), in which a complicated loop of capillary blood-vessels is contained. The tuft of capillaries is covered by a reflection of the delicate wall of the capsule, and is, as it were, invaginated into the capsule (Fig. 986). The capsules with their enclosed capillaries are called the corpuscula renis or kidney corpuscles, and are all placed

artery
Corpuscu-
lum renis
(glomerulus)
Arciform

arteries

FIG. 986.-DIAGRAMMATIC REPRESENTATION OF THE STRUCTURES FORMING A KIDNEY LOBE.

in the convoluted portion of the kidney cortex, where they may be recognised as minute red points just visible to the unaided eye and best marked when the renal vessels are congested. The part of the tubule leading from the capsule-first convoluted tubule-is very tortuous, and lies within the convoluted part of the cortex. Passing from the convoluted part, the tubule enters a radiate part, in which its course becomes less complicated, and here it receives the name of spiral tubule. From the radiate part the tubule enters the basal portion of the pyramid, and, diminishing in diameter, it pursues a straight course towards the apex of the pyramid, forming the so-called descending limb of Henle's loop. Within the apical portion of the pyramid the tubule suddenly bends upon itself, forming the loop of Henle, and reversing its direction, it passes back again through the base of the pyramid into the radiate part of the cortex as the ascending limb of Henle's loop. This ascending limb exhibits a slight spiral twisting. Leaving the radiate part, the tubule once more enters the convoluted part of the cortex, where its outline becomes so uneven that the name irregular tubule is applied to it. While still within the convoluted part, its contour having acquired a more uniform appearance, the tubule receives the name of second convoluted tubule; this latter finally ends in a short junctional tubule, which passes back into a radiate part of the cortex and joins a collecting tube. Each collecting tube receives numerous kidney tubules, and pursues a straight course through the radiate part of the cortex and the pyramid. Finally, several collecting tubes, uniting together, form an excretory tube, which opens on the summit of a renal papilla into a calyx of the ureter by one of the foramina papillaria already described. In microscopic sections the various portions of the kidney tubule may be distinguished by the position which they occupy and by the character of the lining epithelium.

Connective Tissue of the Kidney. The tubules and the blood-vessels forming the substance of the kidney are all united together by a very small amount of connective

Capsule

Collecting
tube

Loop of
Henle

Efferent

glomerular

vessel

Afferent -glomerular vessel

Glomerulus

In the middle part of the figure the course of one of the kidney
tubules is indicated, and in the lateral parts the disposition
of the larger arteries. A, Cortex; B, Basal portion;
and C, Papillary portion of pyramid.
The diagram at the right-hand side of the lower part of the
figure illustrates the connexions of the structures com-
posing a renal corpuscle.

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