DISEASES OF THE KIDNEYS.
THE kidneys are deeply seated in the lumbar region, lying one on each side of the vertebral column, behind the peritoneum. They measure about 4 inches in length, 2i- inches in breadth, and 11 inch or more in thickness. The left is usually longer and narrower than the right. The weight of each kidney is usually stated to be about 41 ounces in the male, and somewhat less in the female.
It is exceedingly difficult to reach any certain results by per cussion as to the size, or even as to the presence, of the kidneys. Auscultatory percussion is much more valuable for this purpose than is simple percussion. Palpation is used with the patient lying on his back. Any considerable enlargement or displacement of the kidney can be made out in this way.
Each kidney is enclosed in a connective-tissue capsule, the blood vessels of which are continuous with those of the cortex. In healthy kidneys, when the capsules are stripped off the surfaces of the kidneys are left smooth except at the points where the blood-vessels are broken off. If, however, there has existed a nephritis which has involved the stroma of the kidney, when the capsule is stripped off the surface is left torn and roughened.
The kidneys are composed of two portions—the cortical, which performs the excreting functions of the kidney, and the pyramidal, which conveys the urine to the calyces. Their component parts are : the uriniferous tubes, blood-vessels, glomeruli, lymphatics, and stroma.
Each uriniferous tube begins in a glomerulus at some point in the cortex of the kidney. The tube is at first of large size, is arranged in convolutions, and is lined with large epithelial cells which are closely joined together, have a thin and fragile limiting membrane and a cell body which is easily changed by preservative fluids. As the tube approaches the pyramidal portion of the kidney its course becomes straighter and its calibre smaller, it runs down into the pyramid for a considerable distance, then turns upon itself, forming a loop (Hen] e's loop), and goes back into the cortex. The loop portion
of the tubes is lined with flattened cells having an oval, bulging nucleus. After the tube has again reached the cortex it becomes larger, runs in a straight line nearly up to the surface of the kidney, and is lined with large epithelial cells of which the limiting mem branes are more distinct and the cell bodies more resistant than is the case in the convoluted tubes. Now the tube again becomes luted for a short distance, then runs a straight course down through the cortex into the pyramid. In the pyramid it joins one of the large collecting tubes and so finally reaches its outlet into a calyx. The tubes in the pyramids are lined with large epithelial cells, having a very distinct limiting cell membrane and very resistant cell bodies.
The renal arteries are large in proportion to the size of the kid neys. Each artery divides into four or five branches which pass in at the hilus, penetrate the substance of the organ between the enter the cortex between the pyramids, subdividing, until they reach the bases of the pyramids where they form arches. From these are given off small arteries which run straight up into the cortex, and from these arteries are given off the little branches to the glomeruli.
The efferent veins from the glomeruli are continuous with a system of capillaries surrounding the cortex tubes which empty into veins running parallel with the straight arteries in the cortex. There are also many veins and venous capillaries in the pyramids. All empty into the large renal vein which joins the inferior vena cava.
The glomeruli are formed of a: capsule and an enclosed tuft of small blood-vessels. The capsule is continuous with the basement substance of a uriniferous tube, and is lined with a continuous layer of flat endothelial cells. The tuft is composed of vessels of capillary size, but with rather thick walls. Their endothelial lining does not seem to be continuous as it is in most capillaries. Their outer sur faces are covered with a continuous layer of fiat, nucleated cells.