The juxtaglomerular apparatus

By Supriyadi Pro -
Tigerstedt and Bergman, in 1898, found that extracts of rabbit kidney raised the blood pressure of anaesthetized rabbits and they gave the name renin to the pressor substance involved. Between 1925 and 1932 the three types of cells that are found in relation to the vascular pole of the glomerulus were described and the name ‘juxtaglomerular apparatus’ was applied to the complex by Goormaghtigh.

The association between the two discoveries and the final localization of renin in the granules of the epithelioid cells of the juxtaglomerular apparatus makes a fascinating story of research which has been reviewed by Cook (1971) and F aarup (1971).

The role played by the renin-angiotensin system in the functioning of the kidney has grown, from being merely the production of the most potent pressor substance known, to being a system which is probably deeply involved in the regulation of the glomerular filtration rate and the renal circulation in general.

The juxtaglomerular apparatus consists of the afferent and efferent arterioles of the glomerulus, a group of lacis cells which fills in the angle between them and a modification of part of the wall of the distal tubule of the same nephron known as the macula densa (Fig. 1.21).

Picture: A diagram of the juxtaglomerular apparatus
Fig. 1.21: A diagram of the juxtaglomerular apparatus. From Moffat (1975), by permission of Cambridge University Press.

The distal tubule may run alongside the afferent and efferent arterioles or it may cross them at right angles, but in all cases the main area of contact is between the macula densa and the lacis cells. There is also always an area of contact between the macula densa and the efferent arteriole, but contact with the afferent arteriole seems to be variable in extent.

Barajas (l970) studied the fine structure of the juxtaglomerular apparatus in serial sections of rat kidneys and found that contact with the afferent arteriole is relatively small, or even absent, and suggested that the variability was due to the plasticity of the lacis cells Which can be deformed as a result of (presumably) changes in the perfusion pressure.

Faarup (1971), on the other hand, found the afferent arteriole to be in contact with the macula densa to as great an extent as the efferent arteriole. There is often a distinct similarity between the different cell types, some of them showing many of the principal characteristics of others-for example, the lacis cells may contain granules and myofilaments, which are similar to those of the cells of the afferent arteriole.

The idea that the cell group which comprises the juxtaglomerular apparatus forms a functional unit is strengthened by recent freeze-fracture studies (Boll et al. 1975) which show the presence of gap junctions between lacis, epithelioid and mesangial cells, suggesting that there is metabolic and electrical coupling between the cells.

Read the full article: The Anatomy of the Renal Circulation

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