Morpho-histological investigation of kidney of bactrian camel (Camelus bactrianus)

Abstract

Morphological characteristics of the kidneys in the two-humped camels were investigated using the anatomical and histological methods. The 2 kidneys in the camel contributed about 0.6% of the body weight. The ratio of thickness of the renal medulla to the cortex was 4:1, which indicated that Henle’s loops in camel’s kidneys were very long. In cortex, there were more juxtamedullary nephrons and mid-cortical nephrons which had longer Henle’s loops. Proximal convoluted tubules were far longer than the distal ones. In the outer medullary zone, the vasa recta were grouped obviously into specific vascular bundles which alternated with the bundles of Henle’s loops and collecting tubules. The inner medullary zone was thicker than the outer one. Specialised fornices were formed by projecting of either side of the pelvis and extended between renal pyramids to medullary outer zone where second pyramids clearly occurred. The characteristics above showed that kidneys in bactrian camels possessed a strong reabsorption and hence promoting the production of high concentrated urine.

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Journal of Camel Practice and Research December 2009 / 1
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The two-humped camel has high ability that can
endure thirst and produce high concentrated urine.
Experiments have demonstrated that the camel is not
in danger even it loses body fluid up to the 30% of the
total body reserves. There are very few references
available regarding the water metabolism in two-
humped camel body, and more inferential
explanations (Shui, 1990) within the references rather
than objective evidences. In recent years, there have
been some studies on physiology and biochemistry of
water metabolism and its regulatory factors in camel.
Because the two-humped camel has higher blood flow
through the kidneys and more osmotic pressure which
ensures the reabsorption of water and retains alkaline
reserves, these are the important functions that could
ensure the regulation of the blood acid-base balance
in the shortage of water, maintain blood volume, and
ensure the normal water metabolism in body (Xiang et
al, 1997). Antidiuretic hormone and aldosterone were
the important factors which regulate the water
metabolism and urinary output in two-humped camel
(He et al, 1999). There is difference between the arterial
supply to the two-humped camel’s kidney and other
animals (Chen and Liu, 2000). In case of water
shortage, camel can excrete high concentrated urine to
reduce the water loss and can drink salty water which
contains fairly high salt concentration (Zhao, 1995).
This paper describes morphological and histological
features of the two-humped camel’s kidney.
Materials and Methods
Ten adult healthy male and female two-humped
camels from pasturing area of Inner Mongolia Ala
Shan You Qi, one of the aridest areas in China, were
used in this study.
All protocols were approved by the Chinese
Committee for Animal Use for Research and Education.
The individuals were anaesthetised with an
intraperitoneal injection of sodium pentobarbital and
killed by cervical blood-letting. Their kidneys were
weighed and 10 integral kidneys were fixed in the 10%
of formaldehyde solution for morphological
observations and the relevant data were measured bya
sliding caliper. Another 10 fresh kidneys were used
for histological observations. Many slides were
papered from the upper, middle and deeper sections
of cortex, and the medulla from the centre of the kidney,
and then were fixed in the 10% of formaldehyde
solution. The size of these pieces was 8mm×4mm×
1mm. Paraffinised sections were then stained with H
Galley Proof-4
Vol 16 No 2, p 1-6
MORPHO-HISTOLOGICAL INVESTIGATION OF
KIDNEY OF BACTRIAN CAMEL (Camelus bactrianus)
Chun-sheng Xu1,2, Hui-jun Bao1, Feng-Hua Qi2, Yi Liu1, Jun-hui Qin1,
Jameel Ahmed Gandahi1, Qiu-sheng Chen1
1College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, 210095
2Shihezi University, Shihezi 832003, PR China
ABSTRACT
Morphological characteristics of the kidneys in the two-humped camels were investigated using the
anatomical and histological methods. The 2 kidneys in the camel contributed about 0.6% of the body
weight. The ratio of thickness of the renal medulla to the cortex was 4:1, which indicated that Henle’s loops
in camel’s kidneys were very long. In cortex, there were more juxtamedullary nephrons and mid-cortical
nephrons which had longer Henle’s loops. Proximal convoluted tubules were far longer than the distal ones.
In the outer medullary zone, the vasa recta were grouped obviously into specific vascular bundles which
alternated with the bundles of Henle’s loops and collecting tubules. The inner medullary zone was thicker
than the outer one. Specialised fornices were formed by projecting of either side of the pelvis and extended
between renal pyramids to medullary outer zone where second pyramids clearly occurred. The characteristics
above showed that kidneys in bactrian camels possessed a strong reabsorption and hence promoting the
production of high concentrated urine.
Key words: Bactrian camel, high concentrated urine, histology, kidney, morphology
Please Checked by
Figs 1,2,3,4,5,6,7
Tables 1,2,3,4,5,6.7
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2 / December 2009 Journal of Camel Practice and Research
& E. Olympus microscope was used to observe and
photograph the slides, and the data were measured by
micrometer ruler.
Results
Morphological observations
The left and right kidneys of the two-humped
camel appeared fabiform-like, with smooth surface (Fig
1). The average size of left kidney was 19 cm×14 cm×9
cm, and the right one 18 cm×14 cm×8 cm. The total
weight of two kidneys was 3.0 kg, accounting for 0.6%
of its body weight. In a cross section of the fixed kidney
specimen, the boundary between the cortex and the
medulla was obvious. The cortical colour was light
while the medullary colour was bright. The junction
of the cortex and medulla was serrated, and the
average thickness of the cortex was 4 times that of the
medulla. The medulla was further divided into light
colour medulla interna and bright colour medulla
externa. The thickness of medulla interna was two
times to the medulla externa. The medulla was
composed of 11 or 12 renal pyramids. The pyramidal
nipples merged mutually to form crystal across renal
pelvis. A distinct secondary renal pyramid was formed
in the side-bottom of the adjacent renal pyramid. The
bases of these pyramids were towards the cortex while
the apices were towards the medulla interna. The
secondary renal pyramid in the kidney lateral edge
was particularly obvious (Fig 2). The renal pelvis was
the intumescent segment of the cranial part of the
ureter which was located in the renal sinus.
Eliminating the renal parenchyma, about 10 or 11
protuberant mucous folds could be seen. The folds
were radiated from the dorso-ventral side of the renal
pelvis, and stretched to the medulla externa among the
renal pyramids. The correspondent dorso-ventrum of
renal pelvis protruded into the boundary of the
medulla interna and the medulla externa, connected
to each other and formed fornix structure. This is the
secondary renal pyramids located at the convex
surface of the fornix structure. The renal sinus was
filled with adipose tissue, and the ureter, renal artery
branches and renal vein tributaries passed through it.
The ureter debouched behind the 1/3 of renal pelvis.
Before it entered into renal hilus, the renal artery had
been divided into two dorsal and ventral branches. The
tributaries of the renal vein merged and left away from
the renal hilus.
Histological observations
The renal capsule was composed of dense
connective tissue. In its deep stratum, lamellar smooth
muscle fibres could be seen distinctly. The cortex was
composed of cortical labyrinth and medullary rays. The
cross-section quantity of the proximal convoluted
tubule in cortical labyrinth was more far than the distal
convoluted tubule (20:1) (Fig 3). The brush border of
the proximal convoluted tubule was well developed.
The renal corpuscles were distributed in the central
cortex section and cortico-medullary junction, but
below the capsule in the range of 1000 to 1500 µm, no
renal corpuscles found (Fig 4). The quantity of the
juxtamedullary nephrons and the intermediate
nephrons was much more than that of the superficial
nephrons. In cortex, the density of the renal corpuscle
was 115/mm2, so it was sparser. There were
differences between the size of the renal corpuscles of
superficial nephrons and the juxtamedullary ones. The
diameter of the former was 200 to 220 µm (external
diameter of Bowman’s capsule) and 190 to 210 µm
(diameter of glomerulus), and the latter was 260 to 280
µm and 250 to 270 µm, respectively. Medullary rays
broadened out gradually from the capsule to the
cortico-medullary junction, containing the parallel
uriniferous tubule and plenty of capillaries. In cortex,
the blood capillaries kept tightly close to the renal
tubules and the distribution was very rich among them,
and it occupied the most of renal interstitium.
The medulla could be differentiated into medulla
externa and medulla interna. The vasa rectae in the
medulla externa was well grown. Under the cortical
labyrinth, it extended and formed wide vasa rectae
bundles. The latter were arranged alternatively with
the uriniferous tubule bundles of the cortical medullary
rays. The width of the vascular bundle was nearly
equal to that of the uriniferous tubule bundle. Inside
the vascular bundle, the thin segment of the renal
tubule was not seen (Fig 5).
The dissepiment of vasa rectae was very thin.
From the superficial layer of the medulla externa
(medulla side of arcuate artery), the change of the
simple cuboidal epithelium lining the descending limb
into simple squamous epithelium lining the thin
segment of the descending limb of Henle’s loop was
clear (Fig 6).
In a cross section of the medulla interna,
collecting ducts, thin segments of the descending limbs,
pars rectae as well as many blood capillaries among
them could be observed (Fig 7). Sometimes, the small
funiculose vessels could also be seen. The wall of the
collecting tubule is built of regular simple cuboidal
epithelium. Its cell cytoplasm was bright and the
boundary was clear. The tubal wall of pars recta was
formed of low simple cuboidal epithelium, the
cytoplasm was addicted to eosin and the boundary
was unsharpened.

Journal of Camel Practice and Research December 2009 / 3
In the papillary segment of the medulla interna,
the interstitial tissue became increasing; the papillary
duct was obvious, with epithelium increasing in height
and changed into the simple columnar type. The cells
were bright and the boundaries were clear. There was
much thinner segment of Henle’s loop and blood
capillaries between papillary ducts (Fig 8).
Discussions
Animals (such as Meriones unguiculata,
Macropus, African wild donkey, desert goat and sheep
etc.) which inhabit the arid or environments with
water shortage for a long time, or were accustomed to
drink salty water or eat high salty food, have the ability
of excreting high concentrated urine. However, animals
(such as Sus scrofa domestica, Wildebeest and
bedfordiae etc.) which inhabit the moist climate or the
regions with adequate water supply, generally, excrete
more diluted urine. These properties must be relevant
with the thickness of kidney medulla. The proportion
of thickness of the medulla and cortex was 5:1 in
Meriones unguiculata, Macropus, African wild
donkey, and it was 3:1 in desert goat and sheep, where,
the medullary portion was broad. However the
proportion of the thickness of medulla and cortex was
1:5 in Sus scrofa domestica and bedfordiae and 1:1 in
Wildebeest. The medullas of these animals were
relatively narrow (Mbassa, 1988). The proportion of
Fig 1. External morphology of the camel kidney. Formalin
fixed. Left kidney (L). Right kidney (R). Renal artery
(). Renal vein ().
Fig 2. Frontal plane of the kidney. Formalin fixed. Cranial
(Cr). Caudal (Ca). Dorsal half (D). Ventral half (V).
Cortex (C). Medulla (M). Secondery pyramid (). Renal
pelvic projection (). Fornix (). Pelvic (). Renal
sinus ().
Fig 3. Cortical labyrinth. Corpuscula renis (). H&E. Bar
=2.5 µm Fig 4. Proximal convoluted tubule (Pt). Distal convoluted
tubule (Dt). H&E. Bar = 0.25 µm

4 / December 2009 Journal of Camel Practice and Research
thickness of the medulla and cortex was directly
proportional to the relative length of Henle’s loop, the
larger the proportion, the longer the Henle’s loop; and
vice versa. Long Henle’s loop was helpful for
establishing higher osmotic pressure gradient in the
medulla, then forming high urinary concentration, and
also it could reduce the loss of water in urine. The
proportion of thickness of the medulla to cortex was
4:1 in the two-humped camel. This could be speculated
that the Henle’s loop was longer in the former.
Moreover, this confirms that the medulla of the two-
humped camel have morphological basis to form high
osmotic pressure gradient.
The distribution of renal corpuscles could not
be observed till a distance of 1000 to 1500 µm beneath
the renal capsule of two-humped camel in present
study. Nephrons in the central and deep cortices were
distributed widely, but in the medulla interna and
renal papilla we could see plenty of thin segment
sections. This indicated that short loop nephrons of
the two-humped camel were very few, the majorities
were juxtamedullary nephrons and long loop middle
nephrons, and its thin segment was long too. Animals
which come from the arid region (such as meriones
unguiculata and small meriones unguiculata etc.) had
more juxtamedullary nephrons and middle nephrons,
Henle’s loop and its thin segment was longer, and
normally they excrete highly concentrated urine
(Valtin, 1977).
The surface of proximal convoluted tubule had
Fig 5. Cortex. Capsule (). Cortical labyrinth (). H&E. Bar
=2.5 µm. Fig 6. Outer zone of medulla (longitudinal section). Vascular
bundle of vasa rectae (). Uriniferous tubule bundle
(). H&E. Bar =2.5µm.
Fig 7. Outer zone of medulla (cross section).Vascular bundle
of vasa rectae (). Uriniferous tubule bundle ().
H&E. Bar =2.5µm.
Fig 8. Inner zone of medulla. Thin segment (arrows).
Collecting tubule (Ct). H&E. Bar =1µm. These Figures
above had been checked.

Journal of Camel Practice and Research December 2009 / 5
brush border which increased the absorptive surface
area largely. About 70-80% of moisture in the original
urine was reabsorbed again here. Beliveau and
Bruneter (1984) guessed that animals inhabiting the
arid area should have longer proximal convoluted
tubule, and it was shorter comparatively in animals
inhabiting abundant water source. However, there was
no enough morphological evidence to support this
view. In the present study, the most of renal tubule
sections in the renal cortex were proximal convoluted
tubule with well grown brush borders, and distal
convoluted tubules were seldom. This demonstrated
that proximal convoluted tubule of two-humped camel
was long enough, so it has more power than other
animals to absorb original urine.
The renal vein of the camel is unique and is
different from other domestic animals, it could be
related to with high concentrated urine production
(Saber, 1987). In the present study, in was observed
that the blood supply of two-humped camel kidneys,
was abundant, and the relationship between the
uriniferous tubules and blood vessels is very close. It
might be helpful to promote the movement of
substance contained in urine between uriniferous
tubule and blood vessel. Stephenson et al (1976)
emphasised that the uriniferous tubules and blood
vessels were integrated functionally, instead of treating
them as 2 isolated sections. After exit of the efferent
glomerular arterioles of the juxtamedullary nephrons
from the renal corpuscle, it formed straight arterioles
and descended into the medulla in different depths,
and returned into interlobular veins or arcuate veins.
Therefore, it would form a lot of “U” shape blood vessel
loops in the medulla. In some of animal’s kidney
which could produce highly concentrated urine, the
vasa rectae assembled and formed special blood vessel
bundles out of the medulla externa. These blood vessel
bundles were arranged alternatively with the
uriniferous tubule bundles formed by the straight
segments of the Henle’s loop and collecting ducts.
Kaissling et al (1975) believed that the short loop
nephron, mixed with thin segment of vasa rectae was
a typical structure of small desert animal kidneys.
Moreover, they pointed out that macrofauna living in
arid environment with few water supply lacks this
kind of structure. In the present study, we observed that
the arrangement of the vasa rectae in the two-humped
camel’s kidney was very special, which assembled and
formed obvious vascular bundles in the medulla, and
arranged alternately with the uriniferous tubule
bundles. In the medulla externa, this kind of vascular
bundles was particularly broad. Being different from
small-sized desert animals, and in contrary to the
standpoint of Kaissling et al (1975), the distribution of
the thin segment could not be seen in the vasa rectae
of the two-humped camel’s kidney. The alternative
arrangement mode of rectiserial Henle’s loop and
uriniferous tubule was the important factor for
reabsorbing the moisture in original urine and
exchanging the other substance, and then producing
high concentrated urine (Jones and O’Morchoe, 1983).
However; in two-humped camel kidney, the
medulla interna was well grown. The renal pelvis gave
off mucous prominences from the ventro-dorso and
stretched to the medulla externa, and formed distinct
secondary pyramid. This demonstrated that the renal
pelvis of the two-humped camel belongs to the model-
II renal pelvis, and is responsible for the ability of
producing high concentrated urine. The appearance
of the advanced medulla interna, renal pelvis
projections and secondary pyramids was helpful to
produce the highest concentration gradient in the
medulla, and then concentrated urine in desert rodent
(Barret et al, 1978).
The kidney weight and its ratio to the body
weight were different in different species. The kidney
weight of rabbits, pigs, humans, horses and oxen was
18-24g, 400-500g, 300g, 900-1500g and 1200-1400g,
respectively. The percentage of the kidney’s weight to
the body weight was 0.6%-0.7%, 0.5%-0.6%, 0.4%,
0.29%-0.39% and 0.2%, respectively (Tian, 1993 and
Cheng, 1994). Generally, the bigger the animal's
physique, the smaller the ratio, and vice versa. There
was an inverse proportion between the physique and
the percentage. However, the physique of the two-
humped camel was bigger and its percentage was
nearly the biggest (0.6%). It points to the ability of
kidney of two-humped camel in handling urine.
Acknowledgement
This research was funded by the grant (No.
39500109) from the National Science Foundation of PR
China.
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