Compensatory hypertrophy of the kidney readily develops when one kidney is lost or congenitally defective. In the case of congenital absence of one kidney the other will be found homogeneously enlarged, and weighing nearly the same as the two normal kidneys together. The different regions of the kidney bear the same relations to each other, each being enlarged in its due proportion. The function of the kidneys is also completely carried out by the single one.

It has been determined by experiments in animals that compensatory hypertrophy develops after excision of one kidney in full-grown animals, although it is more complete when the operation is done in the newborn. It is remarkable how soon after such excision complete restoration of the renal functions occurs, the secretion of urea having reached its normal in one case about two days after the operation, and the animals having remained from the first apparently unaffected in health.

In the hypertrophied kidney there is new-formation of tissue. There is not, however, a numerical increase in the lobules of the kidney, the glomeruli not being increased in number, although slightly in size. As the capsules are the expanded ends of the tubules, the latter also are not increased in number. They are not even increased greatly in diameter, and the hypertrophy seems to consist chiefly in an elongation and increased convolution of the tubules, with great new-formation of epithelium.

Besides this form of compensatory hypertrophy, there may be an enlargement of both kidneys in diabetes insipidus, and perhaps also in diabetes mellitus.

Literature

Rosenstein, Virch. Arch., liii., 1871; Gudden, ibid., lxvi.,1876; Grawitz and Israel, ibid., lxxvii., 1879; Beumer, ibid., Ixxii., 1878; Coats, Proceedings Med. Soc. of London, vii., 1884.