J. Anat. (1979), 129, 1, pp. 45-50 45With 1 figurePrinted in Great Britain

Morphometric observations on the kidney of the camel,Camelus dromedarius

M. A. ABDALLA and 0. ABDALLA

Department of Anatomy, Faculty of Veterinary Science, University ofKhartoum, P.O. Box 32, Khartoum North, Sudan

(Accepted 12 June 1978)

INTRODUCTION

Sperber (1944) was one of the first to note that certain features of renal anatomyin different mammals vary with the aridity of the habitat. According to the counter-current theory developed since then, the efficiency of urine concentration and dilu-tion in the mammalian kidney can be inferred from the structure of the renal medullaand the length of the loop of Henle (Vimtrup & Schmidt-Nielsen, 1952; Lamdin,1959; Schmidt-Nielsen & O'Dell, 1961; Berliner & Bennett, 1967; Marsh, 1971).Evidence in favour of the countercurrent theory was first brought together by Hargi-tay & Kuhn (1951) and Wirz (1954). The theory has been tested and confirmed inmammals from widely different habitats (Schmidt-Nielsen, 1958, 1964; Gottschalk& Mylle, 1959; Pfeiffer, Nungesser, Iverson & Wallerius, 1960; Wirz & Dirix, 1973).The kidney of the camel is known to play a vital role in water conservation through

the production of a highly concentrated urine (Schmidt-Nielsen, 1964). However,those anatomical features which should be present in a kidney capable of producinghighly concentrated urine have not been deliberately looked for in the camel. Theavailable information on the camal kidney is mainly concerned with general morphol-ogy and topography (Chauveau, 1891; Lesbre, 1906; Leese, 1927; Droandi, 1936;Tayeb, 1948; Joseph, 1969; Abdalla, 1973).

This paper reports some measurements made on the kidney of the one-humpedcamel in an attempt to correlate structure and urine-concentrating capacity.

MATERIALS AND METHODS

Ten pairs of kidneys were collected from adult animals of both sexes at Tamboulcamel slaughterhouse.For macroscopic morphometry the volume of each kidney was determined by

water displacement (Scherle, 1970). This was confirmed by calculating the volumeof each kidney from its length, width and thickness. Each kidney was cut into slicesabout 1 cm thick across its long axis. The volumetric proportions of the cortex,medulla and renal pelvis were determined by the point-counting method (Dunnill,1968). A transparent grid with points arranged in a hexagonal lattice was super-imposed on the slices in turn. The hexagonal arrangement of points was preferredto the quadratic lattice (Weibel, 1963 a). The points were 0 5 cm apart. The relativethickness of the medulla was calculated as follows: relative thickness = mean thick-ness of the medulla x 10 . cube root of kidney volume, where kidney volume is theproduct of the dimensions of the kidney (Sperber, 1944).For microscopic analysis, five kidneys from five animals were used. Five blocks

0021-8782/79/2828-6190 $02.00 © 1979 Anat. Soc. G.B. & I.

M. A. ABDALLA AND 0. ABDALLA

of tissue were taken from different parts of the cortex of each kidney following astandard method of sampling (Weibel, 1963b). The blocks of cortical tissue werethen fixed in buffered neutral formalin and paraffin sections were cut at 7,am. Thesections were stained with haematoxylin and eosin. One section from each block wasselected as being the best technically (Weibel, 1963a). In such sections the volu-metric proportions of the glomeruli, tubules, and interstitial tissue with its bloodvessels were estimated by the recently developed dual purpose Zeiss integrating eye-piece. In each case 20 adjacent fields were analysed, covering almost the wholesection (using a x 16 objective and a x 1 2-5 eyepiece). The surface area of the tubulesin the cortex was estimated by the linear intercept method (Tomkeieff, 1945; Hennig,1956), using the same Zeiss eyepiece. The diameter of the glomeruli was measuredwith a graticule. The method of Weibel & Gomez (1962) was used to estimate thenumber of glomeruli in each kidney.The statistical analysis of the data obtained in this study was restricted to the

calculation of the arithmetic mean and standard deviation, as suggested by Weibel(1963 a).

RESULTS

Analysis ofgross slicesThe average volume of a kidney in the sample of adult camels studied was 858 ±

10 cm3 (mean + standard deviation). The volumetric proportions of the main com-ponents of the kidney are shown in Table 1.The renal cortex occupied about 50 % by volume of the kidney. The ratio of the

volume of cortex to medulla was 1-3:1, whereas the medullary/cortical thicknessratio was about 4:1. Measurements of the medulla were made from the cortico-medullary junction to the edge of the renal crest. The long axis of the medulla wasabout 16 cm. On the other hand the relative thickness of the medulla, which is anindicator of the length of the loops of Henle, was about 7-89. The renal crest itselfwas well developed (Fig. 1), and measured about 4 cm across its long axis.The volumetric proportion of the renal pelvis included all the tissues other than

cortex and medulla.

Table 1. The percentage and absolute volumes of the main components of the kidneyobtainedfrom the analyses of the gross slices

(The values are the arithmetic means and standard deviations of the populations studied.)

Component Percentage volume Absolute volume (cm3)

Cortex 51-37+ 2-03 440 75 + 5 2Medulla 38-78 + 2-09 332-73 +40Pelvis 9 77+1-10 83-82 + 2-6

Measurements on histological sectionsThe measurements made on sections of the cortex are shown in Table 2. The

absolute volume of the cortical tubules could be of functional significance. It wasfound to be about 335 5 cm3 in each kidney. The total glomerular volume wasabout 51-13 cm3. The rest of the cortical volume was occupied by interstitial tissueincluding blood vessels.

Sections of the medulla taken near the edge of the renal crest (inner medulla)

46

Morphometry of the camel's kidney

\b .. .

4.\ A

-' .--. 4 7. ½

Fig. 1. Longitudinal section of the right kidney of the camel. Note the well developed renal crestand medullary pyramids separated by branches of the renal pelvis. The kidney was fixedthrough the renal artery with 5% formalin. x i.

Table 2. Histological analysis of the renal cortex(The values pertain to each kidney and represent the arithmetic means and standard deviations.)

Percentage volume of cortex occupied by Number of Diameter of Total surface area____________ _ - - glomeruli glomerulus of tubules of cortex

Tubules Glomeruli Interstitial (x 106) (AgM) (m2)tissue

76-12+2-8 11-6+1-5 12-26+1-6 3-6±0-12 245+10 9-46+1-7

showed that the greater part of any given field was apparently occupied by thinsegments of the loops of Henle and collecting ducts.

DISCUSSION

Previous studies on the mammalian kidney have indicated that the ability toconcentrate urine is related to three main structural features. The first, and ap-parently the most important, is the relative thickness of the medulla. This is an indexof both the length of the loops of Henle, which act as a countercurrent multipliersystem, and of the length of the vasa recta, which act as a countercurrent exchangesystem. Schmidt-Nielsen & O'Dell (1961) found that the relative medullary thicknessin various mammalian species varied directly with the ability to produce hypertonicurine. The minimum value was found in beavers (1 3), the maximum in the water

47

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M. A. ABDALLA AND 0. ABDALLA

conserving African rodent Psammomys obessus. In this study the relative medullarythickness of the kidney of the camel was about 7-89. This value is very near to thatof the kangaroo rat (8 5) as reported by Schmidt-Nielsen & O'Dell (1961). Further-more, sections taken from the inner medulla of the kidney of the camel showed that,in addition to vasa recta, this part was occupied mainly by thin segments of loopsof Henle and collecting tubules. This indicated that there were many nephrons withlong loops - a requisite for the production of hypertonic urine (Schmidt-Nielsen,1964). However, Tisher (1971) and Tisher, Schrier & McNeil (1972) have shown thatrhesus and macaque monkeys produce concentrated urine in the absence of a welldeveloped inner medulla with long loops of Henle.The kangaroo rat produces highly concentrated urine, and Sperber (1944) found

that it had a medullary to cortical thickness ratio of 5: 1. In the camel in the presentinvestigation this ratio was about 4: 1. At the other end of the scale, Pfeiffer et al.(1960) stated that the ratio was about unity in Aplodontia (a primitive rodent whichproduces dilute urine).As suggested by Dunnill & Halley (1973), the ratio of the volume of cortex to

medulla may be of greater functional significance. They found that in man it rangedfrom 1-68 in the newly born to 2-59 in the adult. In the adult camel the value wasonly 1-3. Age differences have not been investigated here, but Lewis & Alving (1938)have shown that in man the ability of the kidney to concentrate urine decreases withage.The second feature concerns the architecture of the renal pelvis and its relation to

the medulla. In this connexion Pfeiffer (1968) reported that urea could be recycledfrom the pelvic urine in species in which the renal pelvis is thrown into folds called' specialized fornices'. The presence of these folds affords a close association betweenthe pelvic urine and the medullary tissue, thereby facilitating the recycling of ureawith consequent building up of the osmotic concentration in the medulla. In aprevious study (Abdalla, 1973) the renal pelvis of the camel was found to formnumerous 'specialized fornices' which were closely related to the renal pyramids.Therefore, in accordance with the theory advanced by Pfeiffer (1968), the ability ofthe kidney of the camel to produce concentrated urine is due in part at least to thespecial morphology of the renal pelvis and medulla.The third feature concerns the cortical tubules. Darmady, Offer, Prince & Fay

(1963) stated that the proximal tubule is responsible for the reabsorption of 7ths ofthe water entering the glomerulus. In the kidney of the camel the cortical tubulesoccupied about 76-12 + 2 8 00 by volume of the cortex, with an absolute volume ofabout 335-5 cm3 and a mean surface area of about 9 46 + 1-7 M2. In the human kidneythe cortical tubular surface area varies from 0-8 m2 at birth to a mean value of8-7 + 2-3 m2 in those over the age of 16 years (Dunnill & Halley, 1973).The number of glomeruli in the kidney does not seem to have a direct influence on

the ability to produce concentrated urine. The values for the various mammalianspecies have been listed by Smith (1951). In the kangaroo rat there are 18840glomeruli in each kidney. Munkacsi (1964) estimated the number to be about160000 in the kidney of the African jerboa. The latter species also produces highlyhypertonic urine. In the camel the mean glomerular number in one kidney was about3.6 + 0.12 x 106. This compares well with a value of about 3 9 x 106 for the ox (Smith,1951); and yet the ox is not noted for the production of hypertonic urine!

In view of the previous investigations on renal anatomy and physiology, and thepresent findings, it is concluded that the anatomical requisites for the production of

48

Morphometry of the camel's kidneyconcentrated urine are to be found in the kidney of the camel. However, the urine-concentrating role of antidiuretic hormones, well established in some other mammals,remains to be investigated in the camel.

SUMMARY

Morphometric analysis of the kidney of the camel was carried out on gross slicesand histological sections using standard morphometric methods. The renal cortexoccupied about 50 % by volume of the kidney, and the ratio of the thickness of themedulla to that of the cortex was about 4: 1. The relative thickness of the medullawas about 7-89. This parameter is an indicator of the lengths of the loops of Henleand vasa recta, and, according to the countercurrent theory, is consequently anindicator of the ability of the kidney to concentrate urine. In each kidney thevolume and surface area of the cortical tubules and the number of glomeruli weredetermined and compared with these parameters in some other mammals. Inaddition the architectures of the renal pelvis and medulla and their significance inrelation to the excretion of hypertonic urine were discussed. It was concluded thatthe kidney of the camel possesses the anatomical requisites for the production ofhypertonic urine.

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