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The fundamental elements of the urinary apparatus are the kidneys (french: les reins) - two glandular organs situated in the loins behind the peritoneum, each of which is provided with a duct - the ureter - for the passage of the secretion to a reservoir - the bladder - by which it is periodically expelled from the body through a tube of outlet - the urethra.

Physical characters of the kidneys

The kidney in its typical form is bean-shaped. It is elongated from above downwards, compressed between its parietal and abdominal surfaces, and presents at its anterior and internal aspect a cleft, the hilum, leading to a cavity, called the sinus, in which lie the renal vessels, nerves, and duct. The gland in the male averages about four and three-quarter inches in length, an | inch and an eighth, m thickness and weighs about five ounces. The dimensions of the female kidney differ little from those of the male, but its weight is from one-seventh to one-fifth less. In the child the organ is relatively large, but its permanent elation to the body weight is usually attained by the end of the tenth year of life.

It offers for description two surfaces, two extremities, and two borders. The anterior or visceral surface is convex, and looks obliquely forwards and outwards ; the posterior or parietal surface, less convex than the anterior, looks inwards and backwards ; the rounded upper extremity is usually somewhat larger than the lover, and is placed about half an inch nearer to the median sagittal plane of the body. The external border is narrow and convex. The internal border (or surface) ,looking forwards, inwards, and slightly downwards, is relatively broad, and is ssured vertically in the middle third of its length by the hilum. The hilum is a slit -like aperture bounded by two rounded lips of variable and jLiequal thickness. The posterior lip is nearer to the middle line than the anterior,, id between the two pass the renal vessels and nerves, the duct, and a quantity of :,t-bearing connective tissue. The sinus (fig. 609), occupied by the structures just kmed, is narrowest near its entrance, and about an inch in depth. Its fundus is perced by the renal vessels and nerves, and by the uriniferous tubules ; and gives attachment to the primary branches (calices) of the duct.

Investment and fixation

The entire organ is enveloped and supported by a lid of capsule of fat -bearing connective tissue derived from the parietal layer of subperitoneal fascia (fig. 608). The adipose element may be in large or small quantity. In the latter case the investment often appears as a transparent fascial pile, which in renal operations may be mistaken for peritoneum, or fascia transversalis ; or, if the fat be excessively developed, it may form a kind of hernial protrusion into the parietal incision. Should the sustentacular power of the fatty capsule become impaired from any cause, the phenomenon of movable or wandering kidney is established, the organ tending to shift its place as far and in such flection as the attachment of its vessels to the main trunk will permit. A partial Cjering of peritoneum is loosely adherent to its anterior surface.


Position and relations

The kidney is commonly said to lie in the lumbar region. It is, however, intersected by the horizontal and vertical planes which separate the hypochondriac, lumbar, epigastric, and umbilical regions from each other, and hence belongs to all these segments of the abdominal space. The vertical level may be said to correspond to the last thoracic and two upper lumbar vertebrae, the right lying in most cases from a third to half an inch lower than the left, but exceptions to this rule are not infrequent.

The posterior surface, with the corresponding portion of the atty capsule, rests against the posterior abdominal wall in front of the eleventh and twelfth ribs and the transverse processes of the first and second lumbar vertebrae ; he left kidney usually reaching as high as the upper border of the eleventh rib, he right only to its lower border. The only visceral relation posteriorly is on the left side, where the spleen slightly overlaps the kidney opposite the upper half of its outer border. The parietal relations on both sides are as follow :

  • the diaphragm;
  • the anterior lamella of the posterior aponeurosis of the transversalis (separating the organ from the quadratus lumborum);
  • the psoas;
  • the three fasciae - diaphragmatic, transversalis, and iliac -which line these muscles respectively;
  • and the last thoracic, the ilio-hypogastric, and the ilio-inguinal nerves, and the anterior divisions of the first and second lumbar vessels, all running obliquely downwards and outwards in front of the quadratus lumborum to pierce the transversalis beyond le outer border of the quadratus. Owing to the higher level of the left kidney, this diaphragmatic area of contact is larger than that of the right organ. This area moreover, may be increased on either side when the arcuate ligaments which give origin to a large portion of the posterior fibers are attached to the ti of the transverse process of the second lumbar vertebrae instead of that of the firs.

The pleura has an indirect but important relation to the kidney. The inferior, limit of the pleural sac extends almost horizontally outwards from the lower border of the twelfth thoracic vertebra, crossing the last rib near its neck, and the eleventh rib about two inches farther outwards. As a rule, the incision in renal operation may be carried safely to the lower border of the last rib ; but, should this bone is absent or very short, the eleventh rib may be mistaken for it, and the serous membrane would then be in danger. It is probable too that the pleura reaches to a lower point in those cases where the arcuate ligaments are attached to the second lumbar transverse process. The presence of a thirteenth rib would invoh, a contraction of the space available for the surgical exploration of the organ.

The upper extremity of each kidney is crowned by the suprarenal body, which encroaches also upon its anterior surface and inner border, and is fixed to it by connective tissue derived from the subperitoneal fascia.

The anterior or visceral surface is differently related on the two side

The right kidney is in contact in about its upper half with the renal impression the liver (page 1015), and below with the ascending colon and duodenum ; the hepatic area being covered with peritoneum, while the second stage of the duodenum and more externally the ascending colon are directly attached to the surface subperitoneal tissue ; but the two non-peritoneal areas vary considerably in the relative proportions, not only in different subjects, but in the same subject under different conditions of distension of the duodenum and the colon. The second stage of the duodenum is also more or less in relation with the right renal vessel The left kidney lies behind the stomach, the pancreas, the splenic vessels, t descending colon, and the colic vessels. Its anterior surface may be divided in three portions : an upper or gastric area, separated from the stomach by the peritoneum of the lesser sac ; a middle or pancreatic area, attached to the pancreas by subperitoneal connective tissue, and crossed also by the splenic vein where tt vessel lies behind the upper border of the gland, and by the splenic artery, which runs in a serpentine course immediately above the vein ; and an inferior or col ] area, the outer portion of which is covered by the splenic flexure and upper part of the descending colon ; the inner by a layer of peritoneum (of the greater sac) and the colic vessels.

The outer border of the kidney reaches a point about three and a half or four inches external to the lumbar spinous processes. On the right side, it is in contact with the liver in its upper half or two-thirds ; on the left, its upper third or half rests against the renal groove in the posterior portion of the visceral surface of the spleen. I The inner border of the right kidney lies close to the vena cava, especially above ; that of the left is divided from the aorta by an interval of an inch or more.

The position of the kidneys at the back of the abdominal cavity involves a certain amount of pressure upon the organs and their vessels and nerves by the weight of the viscera in front when the body is supine, and there is reason to believe that their secretory functions are consequently influenced by changes of posture to an extent that may be utilized in therapeutics.

The structures lying within the sinus are the renal artery and vein, the renal Lymphatics (vessels and glands), a plexus of nerves, the duct, and more or less connective and adipose tissue continuous with the fatty capsule. The renal artery s a branch of the aorta given off opposite the first lumbar vertebra and behind the pancreas. On reaching the hilum it breaks up into four or five branches, which generally lie directly in front of the duct, and behind the vein ; but irregular vessels nay pierce the gland above or below the hilum, and a branch of the artery not frequently passes immediately behind the duct (fig. 607). The left renal vein receives the spermatic or utero-ovarian vein, and is usually somewhat lower than the right. The shortness of the right renal vein should be remembered in the Operation of nephrectomy.


Structure of the kidneys


The kidney when removed from its fatty investment is seen as a yellowish-red organ covered by a thin but strong fibrous capsule (tunica propria), which is prolonged through the hilum into the sinus, where it becomes continuous with the sheaths of the renal vessels, and extends as far as the attachments of he subdivisions of the duct around the renal papilla. The whole capsule may )e easily peeled off from the healthy kidney, except at the bottom of the sinus where it is fixed by the vessels and duct ; and as the capsular vessels are of small size, the process of stripping is attended with little hemorrhage when practiced on the course of operations upon the living subject.

On section through the hilum the renal parenchyma is found to be made up )f two structural elements, the medulla and the cortex ; the former consisting of a variable number (eight to eighteen) of conical segments called pyramids of Malpighi, the apices of which project into the bottom of the sinus (fig. 609) and are surrounded by the primary segments (calices) of the duct, while their bases are turned towards the surface, but are separated from it and from each other by 'he cortex. The pyramids average in their axial diameter about three-quarters if an inch, and have a width at the base of about two-thirds of an inch. They J ire smooth and somewhat glistening in section, and marked with delicate striae which converge from base to apex, and indicate the course of the uriniferous tubules. The blunted apex, or papilla, single or in association with one or even wo of its fellows, is embraced by a calyx, and if examined with a hand lens will e seen to present forty or fifty minute apertures, the foramina papillaria, through which the secretion escapes into the duct.

The cortex may be divided into two portions : a peripheral layer, the cortex proper, which is a little less than half an inch in thickness, and extends from the capsule to the bases of the pyramids of Malpighi ; and processes called columnae tertini, which dip inwards between the Malpighian pyramids to reach the bottom i the sinus, where they are covered by the fibrous capsule and more or less adipose tissue. In section the cortex is somewhat granular in aspect, and in an ejected kidney is seen to be dotted with minute points corresponding to vascular glomeruli lying within the caecal origin of the uriniferous tubules (capsules of Bowman). Examined more closely, it displays a number of small pyramidal i groups of tubules, some belonging to the cortex proper, with their bases resting j upon the bases of the Malpighian pyramids, the apices directed towards, but not I reaching, the periphery ; others forming a part of the columnae Bertini, and ! disposed almost at right angles to the last. These cortical groups are called j pyramids of Ferrein, in contradistinction to the much larger medullary pyramids of Malpighi.

The kidney of a fetus differs from that of the adult in the lobular subdivision i of its surface, each lobule corresponding to the base of a pyramid of Malpighi capped by a thin layer of cortex. Such a condition is permanent in some of the ! lower animals ; but in man the superficial indications of morphological segmentation usually become obliterated during the progress of growth of the cortical tissue, ' and are seldom visible after the age of ten. j

Uriniferous tubes.

The secreting tubules commence by a number | of spherical capsules (capsules of Bowman), which lie in the cortex. From each capsule passes a tube with a narrow neck, which becomes wide and convoluted then, narrowing again, runs down into the subjacent Malpighian pyramid, form! a loop (looped tube of Henle), returns into the cortex, where it again become! dilated and contorted, and, after undergoing a final constriction, opens into straight collecting tube, the axial element of a pyramid of Ferrein. The collection : tubes run into the Malpighian pyramids, unite with each other to form a small number of larger tubes, which terminate by opening on to the papillary apex of the pyramid, and into the corresponding calyx of the duct. The tubes are lined wit | epithelium throughout, the cells being tesselated in the capsule, irregularly cubic ; in the convoluted tubes, flattened on the loops of Henle, and columnar in the cortical collecting tubes and in the straight tubes of the medulla. ;


Vessels of the kidneys

The kidney is very vascular. The larger arterial branches, : traced in section from the point at which they pierce the bottom of the sinus, will be found to run up between the pyramids of Malpighi to subdivide at that bases into cortico-medullary arches which lie between the cortex and medullar gigiving off arterioles in both directions, the cortical branches supplying afferent twigs to the glomeruli within the capsules of Bowman ; the medullary branches running inwards to form plexuses around the straight and looped tubules of the Malpighian pyramids. The efferent vessels of the Malpighian glomeruli form a capillary plexus around the uriniferous tubules and terminate in the renal veins. The surface of the kidney receives small collateral arteries which pass through the fatty capsule from the suprarenal, spermatic, and lumbar vessels. The superficial veins appear in the form of little stellate groups (stars of Verheyen), which are very distinct when the organ is congested. The renal lymphatics may be divided nto two sets, capsular and parenchymatous. They terminate in a series of glands lying with the renal vessels in the subperitoneal tissue, and their contents are ultimately conveyed into the receptaculum chyli.

Nerves of the kidneys

The nerves form a plexus accompanying the vessels, and are derived mainly from the sympathetic through the solar and aortic plexuses, the semilmiar ganglia, and the splanchnics. They communicate with the spermatic plexuses. Some filaments have also been traced from the pneumogastrics.


 

Varieties

The principal variations of the kidney are as follow :

1. In form. - Disproportionate increase of one or other diameter, producing the long, globular, and discoid types. ;

2. In size. - Inequality : one being small, the other compensatingly large.

3. In number. - The organ may be single, then usually occupying its ordinary position in one or other loin ; or, still more rarely, it may be triple, in which case' the additional gland is either lateral or median. '

4. In position. - One or both kidneys may be above or below the normal level, ^ in the latter and far more frequent case encroaching upon the iliac fossa, or even J entering the true pelvis in front of or behind the rectum ; or the displacement may ! be horizontal, the organ lying upon the vertebral column or even in the opposite loin. |

5. By fusion of the two kidneys ; the union involving the lower extremities only! (' horseshoe kidney '), or the whole length of their inner borders.

6. In mobility. - Undue mobility is usually, if not always, due to a laxity of that portion of the subperitoneal tissue which constitutes the fatty capsule ; but a peritoneal meso-nephron is said to have been seen in extremely rare cases of movable kidney.

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