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Normal Histology
Glomeruli
- Interstitium -
Tubules - Vessels
Vessels
The main renal artery arises from the aorta and it is divided, usually, into the anterior and posterior branches and sometimes also into an inferior division. This artery is divided to form the segmental arteries, usually four or five, although there are many variants. These arteries irrigate different segments of the kidney and they are end arteries: there is not significant collateral circulation between the territories supplied by them. The segmental arteries divide within the renal sinus to form the interlobar arteries which enter the kidney crossing the space between the calyces and adjacent cortical parenchyma, they continue by the space between pyramids (medulla) and the septa or columns of Bertin (the cortical tissue that surrounds pyramids).
The interlobar arteries divide, dichotomously, to originate the arcuate arteries that are located between cortex and medulla, tending to surround one half of a pyramid. This arrangement creates two sets of arcuate arteries between adjacent pyramids with each of the sets running between the septa of Bertin and the medullary tissue in the pyramids. Each one of these sets supplies a part of the septum proximate to it. This vascular pattern reinforces the concept that septa of Bertin are derived by the process of lobar fusion, whereby the cortical cap of the pyramid in each lobe fuses with its neighbour during fetal development (Heptinstall's Pathology of the Kidney, 5º Edition. 1998; pp.17-18).
The arcuate arteries converge near the centers of the basal surfaces of the pyramids, but do not anastomose (end arteries).
The arcuates give off branches: the interlobular or cortical radial arteries, which are arranged radially over the basal surface of the pyramids, perpendicular to the renal surface. Few interlobular arteries reach the surface of the kidney where anastomose with capsular branches of suprarenal and gonadal arteries.
The interlobular arteries give off lateral branches at regular intervals: the afferent arterioles. Some afferent arterioles can form directly of the arcuate, or even directly of interlobars.
There are not arteries penetrating in the renal medulla.
The veins are originated in the cortex and follow parallel to the interlobular, arcuate, interlobar, and segmental arteries until forming the main renal vein.
Figure 1. The arcuate arteries (green arrow) run by the interstitial space between the cortex and medulla, and they are accompanied by lymphatic vessels, nerves and veins (asterisk) (H&E, X100).
Figure 1b. Arteries have internal and external elastic lamina; with immunofluorescence the elastic lamina is autofluorescent and is better evidenced (Direct immunofluorescence for IgG, X400).
Figure 2. The cortical radial or interlobular arteries (asterisk) are branches of the arcuate and originate the afferent arterioles. Usually they have, depending of the thickness of their wall, several layers of muscular cells. The structures marked with the green arrows are arterioles. (H&E, X300).
Figure 3. In arteries there is an elastic lamina located between the intima and the muscular layer. This elastic lamina can be easily seen in the greatest arteries and it is more difficult to identify, with routine satins, in the smaller arteries. In this image the elastic lamina is well evidenced (arrows); it is undulated when the artery has relaxed its wall, as it happens in habitually processed tissues. (Gomori’s trichrome, X300).
The efferent arterioles form the peritubular capillary plexus shortly after they are formed or after running variable distances into medullary rays. The medulla receives blood exclusively from the efferent arterioles of juxtamedullary glomeruli. The blood passes from the peritubular capillaries to the interlobular veins.
Figure 4. The arterioles are usually seen in relation to its respective glomerulus. Normally, they have one to three layers of smooth muscular cells. In this image we see an arteriole with a sinuous course (green arrows) and its glomerulus (asterisk) (H&E, X400).
Figure 5. Glomerular arteriole (green arrow). When we only see one of the two arteries in the glomerular hilium is very difficult or impossible to differentiate, with the routine stains, if it is afferent or efferent arteriole (H&E, X400).
The renal arteries and arterioles have the same histologic structure that arteries or arterioles elsewhere in the body. They are formed by endothelium, subendothelial connective tissue or intima, internal elastic lamella (difficult to identify in the small arteries), muscular media, and adventitia that fuses with the interstitial tissue.
Afferent arterioles are the main resistance vessel in the kidney and regulate blood flow by contraction or relaxation of the layers of smooth muscle.
Bibliography
Venkatachalam MA, Kriz W. Anatomy. In: Jennete JC, Olson JL, Schwartz MM, Silva FG (editors) Heptinstall's Pathology of the Kidney, 5º Edition. Lippincott-Raven, Philadelphia, 1998; pp.3-66.
Kern WF, Silva FG, Laszik ZG, Bane BL, Nadasdy T, Pitha JV.. Atlas of Renal Pathology. W. B. Saunders Company, Philadelphia, 1999; pp.1-6.
Histology: Glomeruli - Interstitium - Tubules
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