Part 149

THE UROGENITAL SYSTEM

This system (Apparatus urogenitalis) includes two groups of organs, the urinary and the genital. The =urinary organs= elaborate and remove the chief excretory fluid, the urine. The =genital organs= serve for the formation, development, and expulsion of the products of the reproductive glands. In the higher vertebrates the two apparatus are independent except at the terminal part, which constitutes a urogenital tract, and includes the vulva in the female and the greater part of the urethra in the male.

THE URINARY ORGANS

The =urinary organs= (Organa uropoiëtica) are the kidneys, ureters, bladder, and urethra. The =kidneys= are the glands which secrete the urine; they are red-brown in color, and are situated against the dorsal wall of the abdomen, being in most animals almost symmetrically placed on either side of the spine. The =ureters= are tubes which convey the urine to the =bladder=. The latter is an ovoid or pyriform sac, situated on the pelvic floor when empty or nearly so; it is a reservoir for the urine. The urine accumulates in the bladder until that organ is full, and is then expelled through the =urethra=.

FIG. 374.—GENERAL DORSAL VIEW OF URINARY ORGANS OF HORSE.

1, Right kidney; 1′, left kidney; 2, 2′, adrenal bodies; 3, 3′, ureters; 4, urinary bladder; 4′, anterior end of bladder with cicatricial remnant of urachus; 4″, urethra; 5, aorta; 6, 6, renal arteries; 7, 7, external iliac arteries; 8, 8, internal iliac arteries; 9, 9, umbilical arteries. (After Leisering’s Atlas.) ]

THE URINARY ORGANS OF THE HORSE

THE KIDNEYS

Each kidney (Ren) presents two surfaces, two borders, and two extremities or poles, but they differ so much in form and position as to require a separate description of each in these respects.

The =right kidney= (Ren dexter) in outline resembles the heart on a playing card, or an equilateral triangle with the angles rounded off. It lies ventral to the upper parts of the last two or three ribs and the tip of the first lumbar transverse process. The =dorsal= (or superior) =surface= (Facies dorsalis) is strongly convex; it is related chiefly to the diaphragm, but also to a small extent posteriorly to the psoas muscles. In well hardened specimens, especially those from thin subjects, impressions of the last two ribs and the tip of the first lumbar transverse process are usually visible. The =ventral= (or inferior) =surface= (Facies ventralis) is in general slightly concave, and is related to the liver, pancreas, cæcum, and right adrenal; it either has no peritoneal covering, or only a narrow area externally is so covered. The =internal border= (Margo medialis) is convex and rounded; it is related to the right adrenal and the posterior vena cava. It presents about its middle a deep notch, the =hilus= (Hilus renalis); this is bounded by rounded margins, and leads into a space termed the =renal sinus= (Sinus renalis). The vessels and nerves reach the kidney at the hilus, and the sinus contains the pelvis or dilated origin of the ureter. The =external border= (Margo lateralis) is rounded, and is thinner than the internal one. It consists of two parts, anterior and posterior, which meet at an external angle; the anterior part fits into the renal impression of the liver. The duodenum curves around the external border. The =anterior extremity= (Extremitas cranialis), thick and rounded, lies in the renal impression of the liver. The =posterior extremity= (Extremitas caudalis) is thinner and narrower.

FIG. 375.—DIAGRAM OF POSITION AND DORSAL RELATIONS OF KIDNEYS OF HORSE.

Areas of direct relations are inclosed by continuous lines; parts of skeleton which overlie the kidneys but are not in contact with them are indicated by dotted lines. L.I-III, lumbar transverse processes. ]

FIG. 376.—KIDNEYS AND ADRENALS OF HORSE, DORSAL VIEW.

Hardened in situ. Impression of seventeenth rib on right kidney is indicated by small cross. ]

FIG. 377.—KIDNEYS AND ADRENALS OF HORSE, VENTRAL VIEW.

Hardened in situ. Left renal vein (not marked) is seen curving round posterior end of left adrenal. ]

The =left kidney= (Ren sinister) is bean-shaped. It is considerably longer and narrower than the right one, and is situated nearer the median plane and further back, so that the hilus of the left kidney is about opposite to the posterior extremity of the right one. It lies usually under the upper part of the last rib and the first two or three lumbar transverse processes. The =dorsal surface= is convex, and is related to the left crus of the diaphragm, the psoas muscles, and the base of the spleen. The =ventral surface= is convex and irregular; the greater part of it is covered by the peritoneum. It is in relation with the origin of the small colon, the terminal part of the duodenum, the left adrenal, and the left extremity of the pancreas. The =internal border= is longer, straighter, and thicker than that of the rightkidney. It is related to the posterior aorta, the adrenal, and the ureter. The =external border= is related chiefly to the base of the spleen. The =anterior extremity= extends almost to the saccus cæcus of the stomach; it is related to the left end of the pancreas, and the splenic vessels. The =posterior extremity= is usually larger than the anterior one.

The form of the left kidney is variable. In some cases its outline is similar to that of the right kidney, but its ventral surface is convex and is often marked by several furrows which diverge from the hilus. In well hardened specimens the three areas of the dorsal surface are often distinct. The psoas area is flat, parallel with the inner border, and widens behind. The diaphragmatic area is small and convex; it is crescentic and is confined to the anterior pole. The splenic area, convex and external, is often so extensive and distinct as really to constitute a third surface.

=Fixation.=—The kidneys are held in position chiefly by the pressure of adjacent organs and by the renal fascia. The latter is a special development of the subperitoneal tissue, which splits into two layers to inclose the kidney, together with the perirenal fat or capsula adiposa. On account of its relations with the liver, pancreas, and the base of the cæcum, the right kidney is much more strongly attached than the left one. It is, therefore, not surprising that the latter varies somewhat in position; its posterior pole may be found ventral to the third or fourth lumbar transverse process. The position of the right kidney seems to be very constant, excluding its movements during respiration.

FIG. 378.—FRONTAL (HORIZONTAL) SECTION OF KIDNEY OF HORSE.

The renal vein is removed. A large accessory renal artery entered the posterior pole. Sections of arteries in limiting layer between cortical and medullary substance are white in figure. ]

=Weight and Size.=—The right kidney is usually one or two ounces heavier than the left. The average weight of the right kidney is about 23 to 24 ounces (ca. 700 gm.); that of the left, about 22 to 23 ounces (ca. 670 gm.). The relation of the weight of both kidneys to the body-weight is about 1 ∶ 300–350.

Chauveau gives as an average 750 grams for the right kidney, and 710 grams for the left. Ellenberger and Baum (24 cases) give the right kidney as varying between 430 and 840 grams; and the left between 425 and 780; this is an average of 635 grams (about 22½ ounces) for the right kidney, and 602.5 grams (about 21½ ounces) for the left. They give the relation of the weight of both kidneys to the body-weight as 1 ∶ 255–344. In a Percheron mare weighing about 2000 pounds the right kidney weighed 4 pounds 3 ounces, and the left one 4 pounds. In a horse of medium size the right kidney is about six inches (ca. 15 cm.) in length, about the same in width, and about two inches (ca. 5 cm.) thick. The left kidney is about seven inches (ca. 18 cm.) long, four to five inches (ca. 10 to 12 cm.) wide, and two to two and a half inches (ca. 5 to 6 cm.) thick.

=Structure.=—The surface of the kidney is covered by a thin but strong =fibrous capsule= (Tunica fibrosa), which is in general easily stripped off the healthy kidney. It is continued along the hilus and lines the renal sinus. Sections through the kidney show it to consist of an external cortical substance and an internal medullary substance. The =cortical substance= (Substantia corticalis) is red brown in color and has a granular appearance. It is dotted over with minute dark points; these are the =renal= (or Malpighian) =corpuscles= (Corpuscula renis), each consisting of the dilated origin of a uriniferous tubule (Capsula glomeruli), with an invaginated tuft of capillaries (Glomerulus) inclosed by it. The =medullary substance= (Substantia medullaris) is more resistant and presents a distinct radial striation. Its central part is pale, but its periphery, the =intermediate zone=, is of a deep red color; in the latter are seen, at fairly regular intervals, sections of the relatively large arciform vessels, which are taken to represent the demarcation between the primitive lobes. Between the vessels the medulla is prolonged somewhat toward the periphery, forming the bases of the =renal= (or Malpighian) =pyramids=. These are not very pronounced in the kidney of the horse, especially as the gland is not papillated. Between the bases of the pyramids processes of the cortex dip in toward the sinus, forming the =renal columns=. The inner central part of the medulla forms a concave ridge or crest which projects into the pelvis of the kidney; the crest is marked by numerous small openings at which the renal tubules terminate.

FIG. 379.—TRANSVERSE SECTION OF RIGHT KIDNEY OF HORSE THROUGH THE HILUS.

Posterior portion of organ hardened in situ. Note curvature of dorsal surface. ]

Examination with a pocket lens shows that the cortex is imperfectly divided into =lobules= (Lobuli corticales). Each lobule consists of an axial =radiate part= (Pars radiata), surrounded by a =convoluted part= (Pars convoluta). The former (formerly termed pyramids of Ferrein) appear as ray-like prolongations from the bases of the pyramids (hence also termed medullary rays), and consist largely of narrow, straight or slightly flexuous, tubules (limbs of the loops of Henle). The convoluted part (formerly termed the labyrinth) is granular in appearance, and consists largely of the renal corpuscles and convoluted tubules.

The =pelvis= of the kidney (Pelvis renalis) is the dilated origin of the excretory duct. It lies in the sinus of the kidney, and it is funnel-shaped, but flattened dorso-ventrally. The =renal crest= (Papilla communis) projects into the outer part of the pelvis in the form of a horizontal ridge with a concave free edge. The tubules of the middle part of the medullary substance open on this crest into the pelvis. The tubules from each end of the kidney do not open into the pelvis proper (Recessus medius), but into two long, narrow diverticula (Recessus terminales), which proceed from it toward the poles of the kidney. The wall of the pelvis consists of three layers. The external =fibrous coat= or adventitia is continuous with the supporting tissue of the kidney. The =muscular coat= consists of longitudinal and circular fibers. The =mucous coat= does not cover the renal crest, nor is it continued into the diverticula of the pelvis. It has a yellowish tinge, and presents numerous folds. It contains glands (Glandulæ pelvis renalis) which secrete the thick mucus always found in the pelvis.