CHAPTER V. PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. Situation, form, and size of the kidneys-Coats of the kidneys-Division of the substance of the kidneys-Pelvis, calices, and infundibula-Pyramids— Cortex-Columns of Bertin-Pyramidal substance-Pyramids of FerreinTubes of Beilini-Cortical substance-Malpighian bodies-Convoluted tubes-Narrow tubes of Henle-Intermediate tubes-Distribution of bloodvessels in the kidney-Vessels of the Malpighian bodies-Plexus around the convoluted tubes-Veins of the kidney-Stars of Verheyen-Lymphatics and nerves of the kidney-Summary of the physiological anatomy of the kidney. THE urine is generally regarded by physiologists as the type of the excrementitious fluids, it having no function to perform in the economy, but being simply retained in the bladder to be voided at convenient intervals. All the remarks, indeed, that have been made concerning excretion in general may be applied without reserve to the action of the kidneys; and there are few subjects in physiology of greater interest than the process of urinary excretion, with its relations to nutrition and disassimilation. In entering upon the study of the functions of the kidneys, it will be found useful to consider certain points in their anatomy. The kidneys are symmetrical organs, situated beneath the peritoneum in the lumbar region, invested by a proper fibrous coat, and always surrounded by more or less adipose tissue. They usually extend from the eleventh or twelfth rib downward to near the crest of the ilium; and the right is always a little lower than the left. In shape, the kidney is very aptly compared to a bean; and the concavity, the deep, central portion of which is called the hilum, looks inward toward the spinal column. The weight of each kidney is from four to six ounces, usually about half an ounce less in the female than in the male. The left kidney is nearly always a little heavier than the right. Outside of the proper coat of the kidney is a certain amount of fatty tissue enclosed in a loose fibrous structure. This is sometimes called the adipose capsule; but the proper coat consists of a close net-work of the ordinary white fibrous tissue, interlaced with numerous small fibres of the elastic variety. This coat is thin, smooth, and readily removed from the surface of the organ. At the hilum it is continued inward to line the pelvis of the kidney, covering the calices and blood-vessels. This coat, however, is not continued into the substance of the kidney. On making a longitudinal section of the kidney, it presents a cavity at the hilum, bounded internally by the dilated origin of the ureter. This is called the pelvis. It is lined by a smooth membrane, which is simply a continuation of the proper coat of the kidney, and which forms little cylinders, called calices, into which the apices of the pyramids are received. Some of the calices receive the apex of a single pyramid, while others are larger, and receive two or three. The calices unite into three short, funnel-shaped tubes, called infundibula, corresponding respectively to the superior, middle, and inferior portions of the kidney. These finally open into the common cavity, or pelvis. The substance of the kidney is composed of two distinctly-marked portions called the cortical, and the medullary, or pyramidal. The cortical substance is reddish and granular, rather softer than the pyramidal substance, and is about one-sixth of an inch in thickness. This occupies the exterior of the kidney, and sends little prolongations (columns of Bertin') 1 BERTIN, Mémoire pour servir à l'histoire des reins.-Mémoires de l'Académie Royale des Sciences, année, 1744, Paris, 1748, p. 77. between the pyramids. The surface of the kidney is marked by little polygonal divisions, giving it a lobulated appearance. This, however, is simply due to the arrangement of the superficial blood-vessels. The medullary substance is arranged in the form of pyramids, sometimes called the pyramids of Malpighi, from twelve to fifteen or eighteen in number, their bases presenting toward the cortical substance, and their apices being received into the calices at the pelvis. Ferrein subdivided the pyramids of Malpighi into smaller pyramids (the pyramids of Ferrein), each formed by about one hundred tubes radiating from the openings at the summit of the pyramids toward their bases.' The tubes composing these pyramids were supposed to pass into the cortical substance, forming corresponding pyramids of convoluted tubes, thus dividing this portion of the kidney into lobules, more or less distinct. The medullary substance is firm, of a darker red color than the cortical substance, and is marked by tolerably distinct striæ, which take a nearly straight course from the bases to the apices of the pyramids. As these striæ indicate the direction of the little tubes that constitute the greatest part of the medullary substance, this is sometimes called the tubular portion of the kidney. There are few subjects connected with the physiological anatomy of the organism that present greater interest than the minute anatomy of the kidney; and this is one of the organs which has been most closely and persistently studied by anatomists. Without referring in detail to the investigations of Malpighi,' whose name is attached to the corpuscles of the cortical substance, Bellini," who first studied the straight tubes, Ferrein,' who described the tubes of the corti 1 FERREIN, Sur la structure des viscères nommés glanduleux, et particulièrement sur celle des reins et du foie.—Mémoires de l'Académie Royale des Sciences, année, 1749, Paris, 1753, p. 499, et seq. MALPIGHIUS, Opera Omnia, Lond., 1686, tomus secundus, De Renibus. BELLINI, Exercitationes Anatomicæ duæ de Structura et Usu Renum ut et de Gustus Organo, Lugd. Batav., 1711. • Op. cit. cal substance, and other of the earlier anatomists, we will proceed to study the structure of the kidney as it appears at the present day from the researches of later anatomists, who have brought to bear upon their investigations more perfect methods of injection and the improved microscopes now in use. Among the authors whose researches have developed the views now held by the best anatomists, may be mentioned Henle,' Bowman,' Goodsir,' Müller, Gerlach,' Kölliker, Toynbee,' Huschke,' Isaacs,' with some quite recent German and French observers, who have lately advanced new and interesting views that have an important bearing upon the mechanism of the secretion of urine. The arrangement of the secreting portion of the kidneys classes them among the tubular glands, presenting a system of tubes, or canals, some of which are supposed simply to carry off the urine, while others separate the excrementitious constituents of this fluid from the blood. It is difficult to determine precisely where the secreting tubes merge into the excretory ducts, but it is the common idea that the cortical substance is the active portion, while the tubes of the pyramidal portion simply conduct away the excretion." 1 HENLE, Traité d'anatomie générale, Paris, 1843, tome ii., p. 503, et seq., and Zur Anatomie der Niere, Gottingen, 1862. * BOWMAN, On the Structure and Use of the Malpighian Bodies of the Kidney. -Philosophical Transactions, London, 1842, p. 57, et seq. 3 GOODSIR, London and Edinburgh Monthly Journal of Medical Science, London and Edinburgh, 1842, p. 474. 4 MUELLER, Manuel de physiologie, Paris, 1851, tome i., p. 369, et seq. 5 GERLACH, Beiträge zur Structurlehre der Niere.-MÜLLER'S Archiv, 1845, § 378, in CANSTATT'S Jahresbericht, Erlangen, 1846, S. 36. • KÖLLIKER, Ueber Flimmerbewegung in den Primordialnieren, Idem, S. 36. 7 TOYNBEE, On the Minute Structure of the Human Kidney.—Medico-Chirur gical Transactions, London, 1846, vol. xxix., p. 303, et seq. * HUSCHKE, Encyclopédie anatomique, Splanchnologie, Paris, 1845, tome v., p. 285, et seq. • ISAACS, Researches into the Structure and Physiology of the Kidney, and On the Function of the Malpighian Bodies of the Kidney.-Transactions of the New York Academy of Medicine, New York, 1857, vol. i., p. 377, et seq. 10 TODD AND BOWMAN, Physiological Anatomy and Physiology of Man, Phila Pyramidal Substance.-Each papilla, as it projects into the pelvis of the kidney, presents from ten to twenty-five little openings, measuring from to of an inch in diameter. The tubes leading from the pelvis immediately divide at very acute angles, generally dichotomatously, until a bundle of tubes arises, as it were, from each opening. These bundles constitute the pyramids of Ferrein. In their course, the tubes are slightly wavy and nearly parallel with each other. These are called the straight tubes of the kidney, or the tubes of Bellini. They extend from the apices of the pyramids to their bases, and pass then into the cortical substance. The pyramids contain, in addition to the straight tubes, a delicate fibrous matrix and numerous bloodvessels; which latter, for the most part, pass beyond the pyramids, to be finally distributed in the cortical substance. Recent researches have shown that some of the convoluted tubes dip down into the pyramids, returning to the cortical substance in the form of loops. This arrangement will be fully described in connection with the cortical portion. The tubes of the pyramidal substance are composed of a strong, structureless basement-membrane, lined with granular, nucleated cells. According to the researches of Bowman, the tubes measure from to of an inch in diameter at the apices, and near the bases of the pyramids their diameter is about of an inch.' The membrane of the tubes is dense and resisting, and portions of it with the epithelial lining removed can generally be seen in microscopical examinations, when the pyramidal substance has been simply lacerated with needles. This membrane is from 30000 to go of an inch in thickness.' The cells lining the straight tubes exist in a single layer delphia, 1857, p. 789. This is the idea advanced in nearly all works on physiology, when any opinion is expressed with regard to the relative activity of the cortical and the pyramidal portions of the kidney. 1 KÖLLIKER, Handbuch der Gewebelehre des Menschen, Leipzig, 1867, S. 488. TODD AND BOWMAN, op. cit., p. 793. KÖLLIKER, Microscopic Anatomy, London, 1860, p. 406. |