The Kidneys


Rarely both kidneys may be absent, but the fetus is incapable of living. Absence of one kidney is more common and is not incompatible with life. The left organ is usually wanting and the right undergoes compensatory hypertrophy so as to perform its extra work.

Atrophy of a kidney is not infrequent, it being represented by a small body composed of connective tissue with very little glandular structure. A third kidney has been seen in a few cases. The lobulation of the kidneys during fetal life usually disappears by the tenth year, but it may persist till late life.

Horseshoe kidney is the result of the fusion of the two kidneys at either their upper or lower ends. The band of union may be purely fibrous or of renal tissue. The ureters, from two to four, arise from an anterior pelvis. The vessels are usually more numerous than normal and are generally anomalous.

One of the kidneys, usually the right, may become much displaced downward and hang from a much stretched peritoneal covering. Is the "floating kidney" and can give rise to many symptoms. The left may be displaced con-genitally. The relaxation of the support of the right kidney may be due to disease or displacement of the liver, to tight lacing, or to a dragging exerted by the stomach or transverse colon. The perirenal fat decreases, the peritoneal covering stretches, and the kidney is easily moved. The nerves and vessels and the ureters are put in a state of tension and severe symptoms arise. If the pedicle becomes twisted the circulation may suffer and by obstruction to the ureter urine collect and give rise to a hydronephrosis.

Circulatory Disturbances

Anemia of the kidneys is present in general anemia; or it may be due to gradual obstruction of the arteries, either by disease or by pressure from without. If the obstruction has been sudden, necrosis is usually present. The organ is small and light in color. If the anemia continues, there is interference with the secretion of urine and atrophy may ensue. Fatty degeneration appears first in the glomeruli but soon involves the parenchyma.

Acute hyperemia is generally a stage of acute inflammation in infectious conditions. Numerous irritating bodies that are excreted through the kidneys may give rise to the hyperemia. Such are certain poisons, as cantharides, carbolic acid, toxins of infectious conditions, as scarlet fever, those present in cases of extensive superficial burns. The kidneys are slightly enlarged, dark red in color, and soft. The capsule strips easily and on section much blood escapes. In the cortex are seen numerous minute red spots, the Malpighian bodies, and the congestion exists throughout. The epithelium usually shows some cloudy swelling. The urine may contain a few erythrocytes, a trace of albumin, and cylindroids.

Passive hyperemia may be due to cardiac or pulmonary disease, to thrombosis of the inferior vena cava or of the renal veins, or to pressure upon these veins from without. Sometimes there may be an acute passive stasis, the organ becomes much distended and death may result. Ordinarily the kidney is enlarged, dark in color, and soft, with a capsule that strips readily. The stellate veins are prominent, blood drips from the cut surface, the Malpighian bodies are enlarged and the bases of the pyramids are markedly congested. If the hyperemia is of long standing there is always more or less hyperplasia of the connective tissue. So much so that the organ, although enlarged, may be hard and dark in color, owing to the deposition of pigment; is known as cyanotic induration. The capsule is usually somewhat adherent and the surface of the organ irregular. The epithelial cells show some fatty degeneration and atrophy. 29

The amount of urine is diminished and contains varying numbers of red and white blood-corpuscles, some albumin, and a few hyaline or granular tube casts.

Hemorrhage in the form of punctate collections may occur in severe acute or passive hyperemia. The blood will be found within the interstitial tissues, in the tubules, or in Bowman's capsule; it may escape by actual rupture or by dia-pedesis. Large hemorrhages usually occur only as a result of trauma, but may be due to infarction. The urine will contain blood either as free corpuscles or as the so-called blood-cast.


The kidney may show most marked sclerotic changes, such as are found elsewhere in the body. All the vessels are not uniformly involved, so there are irregular appearances. The vessels" become gradually occluded by a thickening of the walls with a decrease in the lumen. The areas supplied by such vessels undergo atrophy, degeneration, and frequently become infiltrated with lime salts. Fibrous connective tissue forms to some extent, and as this contracts it compresses the urinary tubules. Excretion continues, the tubules dilate, and small retention cysts form both on the surface and in the kidney tissue. The kidney is smaller than normal, red or grayish-red, firm, and its surface shows depressed areas representing the atrophic portions, at which points the capsule may strip with difficulty. The cortex is diminished in thickness.

Microscopically the alterations in the blood-vessels are seen and the glomeruli in many instances are surrounded by greatly thickened capsules which may contract until the capillary tufts have been reduced to small fibrous masses. If there is much connective tissue present it indicates that there has been a chronic inflammation of the organ, an interstitial nephritis. This is not uncommon, as the same etiologic factors will bring about both the arteriosclerotic and the interstitial changes. Is caused by syphilis, chronic lead poisoning, gout, and old age.

In this form the urine is practically unchanged.

Infarcts of the kidney are common, as the arteries have practically no anastomoses with each other. In the anemic infarct the appearance varies according to the age of the lesion. When recent, there is a pale, circumscribed elevation on the surface of the kidney, surrounded by a narrow zone of hemorrhage. If old and connective-tissue formation has occurred, there is a depressed area. On section it is seen that the involved portion is conical in shape with the apex directed toward the hilum. The epithelium becomes cloudy and soon degenerates. This area becomes transformed into scar tissue in the course of time. In hemorrhagic infarcts the process is the same except that the area has become filled with blood which gives it its dark appearance.

Thrombosis of the larger renal veins may give rise to congestion and edema with degeneration and necrosis of the area involved.

Embolism is not uncommon, and on account of the lack of anastomoses of the renal arteries usually results in infarction. Embolism may be single or multiple, and if bacteria are present suppurative processes are present in addition to the already mentioned lesions.


Parenchymatous degeneration or cloudy swelling is a condition in which the secreting epithelium is involved. It occurs in diphtheria, scarlet fever, and in most of the infectious diseases.

If the conditions that bring about this change persist, the cloudy swelling is very apt to pass over into the acute parenchymatous nephritis. In cloudy swelling the kidney is larger than normal, somewhat softer, and yellowish or pale gray. The cut surface shows the Malpighian bodies as small red dots and the pyramids are often markedly congested. The cells in the tubules are swollen and cloudy on account of the presence of numerous minute granules, and the nuclei are hidden. The kidney may return to the normal or else acute Bright's disease or fatty degeneration may ensue.

Fatty degeneration may follow cloudy swelling or arise as a consequence of various diseases, as pernicious anemia or tuberculosis. As fat is never normally present in renal epithelium, its occurrence is always pathologic and is indicative of a degenerative process. It is due to the lack of nutrition, and at times is added a toxic effect of some substance in the circulating blood.

The kidney is about the normal size or smaller, is soft, the cortex is not thinned, and the organ is uniformly yellowish unless there is much congestion present. The fat may be diffusely present, or, what is quite common, occur in streaks along the collecting tubules of the pyramids. It is also seen as minute yellow points. The cells contain granules or oil drops of varying size.

Amyloid degeneration of the kidney follows the same causes as bring it about in the liver and spleen, such as the long-continued suppuration in bone diseases, in tuberculosis, and in syphilis. The kidney is usually much enlarged, harder than normal, and grayish or slightly yellowish in color. If the process is not general the organ will appear mottled, areas of fatty degeneration being present. This degeneration begins, as a rule, in the capillaries of the glomeruli, from which it extends to the neighboring connective tissue, but not to the epithelium. If the degeneration has not been extensive fatty changes are uncommon, as the blood-supply may still be sufficient for the nutrition of the epithelium. Microscopically the glomeruli are seen to consist of a homogeneous and translucent mass in which the capillaries cannot be distinguished. The capsule of Bowman may also be involved. As the circulation is interfered with the organ becomes anemic, and fatty degeneration of the epithelium occurs. The amyloid areas give a mahogany brown color on the addition of Lugol's iodin solution. The urine is diminished and contains albumin and hyaline casts occasionally.

Glycogen is found in the epithelium in the loops of Henle in cases of diabetes. The cells, instead of being granular, are homogeneous and give the dark brown color with iodin if the tissue has not been put in watery fluids. Glycogen differs from amyloid in being soluble in water.

Calcification may take place in old degenerated areas in the connective tissue or in the necrotic epithelial cells. Under this heading come the so-called "calcareous infarcts," in which various salts are deposited, particularly in the straight collecting tubules. They may be composed of urates, and the presence of such infarcts has been thought to indicate that a newborn child has breathed.