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Functional development

At birth the kidneys have a multilobular appearance, due to the development of the ureter anlage in the metanephric blastema. Normally, towards the end of the fetal period, the lobes are considerably smoothed, but they still exist until after birth.

Completion of the smoothing follows during childhood by the increase in volume of the connective tissue and the increase in size of the nephrons without any change in their number.

With only few exceptions, adult kidneys no longer exhibit any lobulation.

Fig. 13 - Development of the smooth kidney surface

  1. Renal medulla
  2. Calix minor
  3. Renal cortex

Fig. 13

In humans renal lobulation is easily seen only in the embryonic and fetal periods, but can extend into childhood. At birth, however, it is strongly attenuated.

In adults, the cortical zones of the individual lobes, «A to E», fuse and the smoothing of their depressions leads to a smooth and uniform renal surface structure.

Since the renal architecture is finalized between the 5th and 15th weeks of intrauterine development; organogenesis of the kidneys lasts well beyond the embryonic phase until far into the fetal period.

Fig. 14 - Anatomy of the kidney at the end of its development

  1. Ureter
  2. Renal pelvis
  3. Vena renalis
  4. Arteria renalis
  5. Major calix
  6. Minor calix
  7. Cortex
  8. Capsula renis
  9. Medullary rays
  10. Papilla renalis
  11. Sinus renalis
  12. Columna renalis
  13. Medullary pyramid

Fig. 14

The renal parenchyma is divided into an outer cortical zone and an inner medullar zone.

In its interior the kidney has a hollow space, the renal sinus, into which the papillas intrude and where the trunks of the renal vessels are found.

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Illustration on the right show detail of the vascular supply of a renal lobe.

Fig. 15 - Vascular supply of the kidney
at the end of the development

Papilla renalis
Interlobar artery
Interlobar vein
Arcuate artery
Arcuate vein
Interlobular arteries and veins

Fig. 15

One sees the renal pyramid surrounded by the interlobar vessels as well as their continuations, the arcuate vessels.

From them originate the interlobular vessels that form the afferent arterioles, followed by a capillary network (not shown here).