The major vessels

By Supriyadi Pro -
The renal arteries and their branches  - As befits the very large volume of blood flowing through them, the main renal vessels are short, wide and pass straight from the aorta to the kidney and from the kidney to the inferior vena cava. As the renal artery is traced towards the kidney it gives off one or more branches to the suprarenal (which may come from the apical segmental artery) and other branches to the capsule, the perinephric tissues and the upper part of the ureter.

The capsular branches are particularly important-they usually leave the renal artery within the hilum and emerge to supply the capsule on both surfaces of the kidney. They anastomose with a superior capsular artery (usually from the suprarenal branch of the renal artery) and an inferior capsular artery (commonly from the testicular or ovarian artery).

The whole network of capsular arteries anastomoses not only with a number of retroperitoneal vessels, particularly the lumbar arteries, but also with the perforating vessels which emerge from the surface of the kidney. In this way, a potential collateral circulation to the renal substance exists and radiological demonstration of enlarged capsular vessels may be a valuable sign of obstructive disease of the renal artery. The appearance and diagnostic significance of this have been reviewed by Meyers et al. (1967).

 Near the hilum, the renal artery usually divides into anterior and posterior divisions which themselves divide further to give rise to segmental arteries, usually five in number. These were first studied systematically by Graves (1954) and subsequently by a number of other authors who have given more elaborate classifications of the segmental blood supply. Graves’s description, however, holds good for the majority of kidneys (Fig. 1.1).

Picture: Diagram to illustrate the most common arrangement of the renal segments
Fig. 1.1: Diagram to illustrate the most common arrangement of the renal segments

He named the segments as follows: Apical, which extends onto both back and front of the kidney; Upper (anterior); Middle (anterior); Lower, which includes both back and front of the lower pole; and Posterior. The posterior primary division of the renal artery usually gives rise to the posterior segmental artery and sometimes to the apical artery; the anterior division provides the others. Angiographic appearances of the segmenetal arteries have been described by Boijsen (1959), who adopted a slightly different claSsification.

The segmental arteries of the kidney are virtually end-arteries since, apart from the capsular anastomoses described above and some anastomoses in the pelvic area to be described later, each represents the sole blood supply to its own individual segment. They do not form any anastomoses between themselves in the kidney substance, a fact which was recognized by John Hunter who wrote: ‘The veins in the spleen and kidnies anastomose in very large trunks, while the arteries do not at all.

ABERRANT RENAL ARTERIES
These are present in about 25 per cent of cases and normally take the form of an extra branch of the aorta that runs parallel to the main renal artery, most commonly below it. It may enter the hilum but if it is sufliciently far from the renal artery it enters the substance of the kidney directly by piercing the cortex.

Such aberrant arteries are of importance not only as an obstacle to renal transplantation, but also because they are not usually additional to the normal complement of vessels, but represent precocious segmental branches, so that if one of them becomes obstructed for any reason the corresponding segment of the kidney will be deprived of its main blood supply.

Read the full article: The Anatomy of the Renal Circulation

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