The excretory duct of the kidney is a musculo-mucous canal, expanded and irregularly branched above, narrow and of fairly uniform dimensions in the rest of its course.
At its origin in the sinus renalis it appears in the form of a number of short tubes, usually eight or nine, called calices, each of which embraces the papillary extremity of a pyramid of Malpighi two or three lines above its apex, or occasionally two papillae may be connected with a single calyx. The calices average about a third to half an inch in length, and open directly or by means of intermediate tubes (infundibula) into two short passages, the superior and inferior pelves, which in turn combine after a longer or shorter course to form the common pelvis. The inferior and larger pelvis has a diameter of about two- fifths of an inch; the superior is about one-third less. The common pelvis varies greatly in different subjects. It usually appears as a more or less funnel-shaped portion of the canal, wider above (about three-fifths of an inch), where it lies between the two lips of the hilum; narrow below, where it arches downwards and inwards to become continuous with the relatively uniform portion of the duct known as the ureter proper. In some cases, however, it can scarcely be said to exist as a dilatation.
Under ordinary circumstances it is flattened from before backwards, its anterior and posterior walls being in contact, and its channel represented by a fissure. It is in relation behind with the posterior lip of the hilum, from which it is separated by more or less adipose tissue continuous with the fatty capsule, and occasionally by an irregular branch of the renal artery. The renal vein and artery imbedded in fat lie in front, and anterior to these structures are situated the descending portion of the duodenum on the right side, and the pancreas on the left.
The ureter extends from the termination of the pelvis to the bladder, running in a kind of lymph-space between the laminae of the subperitoneal tissue. It is a tube of about a sixth of an inch in diameter when distended, and is fairly uniform in size, except about two inches below the kidney where a slight constriction is usually found (Bruce Clark). Its length is variously stated, but the average in the male adult may be taken as about twelve inches. The excessive estimates sometimes given depend upon the untrustworthy indications afforded by admeasurement after the removal of the structure from the body.
Course and relations
The tubes lie about three inches apart at their commencement, but this distance gradually lessens to about two inches as they descend towards the sacro-iliac joint. In the true pelvis they at first diverge, but finally on nearing the base of the bladder run forwards and inwards to pierce the wall of the viscus, and at their termination are separated by a distance of about an inch and a quarter. The course of each tube may be conveniently divide into three stages, abdominal, pelvic, and vesical. The abdominal portion, running downwards and slightly inwards, is in a relation, posteriorly, with the psoas and its fascia, and the genito-crural nerve, and with the common iliac artery near its bifurcation. Anteriorly, it is covered by peritoneum and intestines, and is crossed by the colic and spermatic vessels. Internally, it is opposed on the right side to the inferior vena cava, on the left to the aorta; the vein being almost in contact with the right ureter, while the artery is separated from the left tube by an interval that gradually diminishes from one inch above to half an inch opposite the bifurcation of the vessel.
The pelvic portion runs in front of the sacro-iliac synchondrosis then upon the obturator internus and its fascia behind and below the psoas, finally leaving the pelvic wall to join the bladder. In this position, in the male it is crossed superiorly and internally by the vas deferens, and lies under cover of the free extremity of the vesicula seminalis, separated from its fellow by a distance of an inch and a half.
In the female it runs parallel with, and four to six lines from the cervix uteri, behind the uterine artery, through the uterine plexus of veins, and beneath the root of the broad ligament; finally crossing the upper third of the vagina to reach the vesico-vaginal interspace and pierce the bladder opposite the middle of the vagina. A calculus in the lower end of the tube might be detected by a vaginal examination. The vesical portion, about half an inch in length, runs obliquely downwards and inwards through the coats of the bladder, and opens on to the mucous surface at a distance of about three-quarters of an inch to an inch from its fellow, and from the internal urinary meatus.
The wall of the ureter is about a twenty-fifth of an inch in thickness, and consists of a mucous membrane, a muscular coat, and an external connective tissue investment. The mucous membrane is longitudinally plicated, and is lined with a multiple layer of transitional epithelium, continuous with that of the papillae above, and with that of the bladder below. Mucous follicles are said to exist in the pelvis renalis. The muscularis is about one-fiftieth of an inch in thickness, and consists of two layers, an external composed of annular fibers, an internal of fibers longitudinally disposed. After the tube has entered the bladder the circular fibers appear as a kind of sphincter around its vesical orifice; while the longitudinal fibers spread out to form with those of the opposite side a triangular expanse with its apex at the internal urinary meatus and its base corresponding to a line drawn between the two ureteric orifices.
Vessels and nerves
The arteries of the ureter come from the renal, spermatic, internal iliac, and vesical; the veins terminate in the corresponding trunks; and the lymphatics pass to the pelvic and lumbar glands and into the receptaculum chyli. The nerves are supplied by the spermatic, renal, and hypogastric plexuses.
The most important variation consists in the partial or complete duplication of the tube owing to the late union or to the non-union of the superior and inferior infundibula or pelves. In rare cases the calices form three pelves which may in like manner remain separate in part or in the whole of their course to the bladder.