Introduction

The urinary systems of dogs and cats consist of several key structures, including the kidneys, bladder, ureters, and urethra. Positioned on either side of the body, the kidneys reside in the back region, nestled between the ribs and the pelvis. As blood is filtered through the kidneys, it generates a liquid waste product called urine. The ureters function to transport this urine to the bladder, where it is temporarily stored before being expelled through the urethra, a tubular conduit leading to the outside of the body (1) . In the development stage, the metanephric blastema and ureteric bud converge to create the nephron and collecting duct (CD), which ultimately develop into the mammalian kidney. Each nephron encompasses essential structures such as Bowman's capsule and both ascending and descending loops of Henle, along with proximal tubules (PTs) (2) . The urinary system divides itself into two segments: the upper urinary tract, comprising the kidneys and ureters, and the lower urinary tract, which includes the bladder and urethra. Serving as a vital organ, the kidney performs multiple roles in filtering and removing waste, producing urine through this filtration process. Beyond waste management, the urinary system also plays a crucial role in maintaining balance in blood pressure, calcium levels, pH, ions, and water. Blood flows to the kidneys through the renal artery, with both organs situated within the abdominal cavity, typically receiving blood supply from paired renal arteries branching off from the abdominal aorta (3) . The kidney operates with a sophisticated system of filtration units, meticulously regulating the amounts of salts, water, and other small compounds in the filtrate. Urine is stored in the bladder until the urinary nerve system signals its release through the urethra during urination (4) .

Surrounding each kidney is a robust, fibrous renal capsule that provides structure and protection to the organ. The outer layer of the kidney is referred to as the renal cortex, where the functional units known as nephrons reside to carry out the blood filtration process. Located anterior to the renal medulla, this cortex houses structures called renal pyramids, which, with their funnel-like shape, contribute to urine production along with blood vessels in the medulla (5) . Within the kidney exists the funnel-shaped renal pelvis, which collects urine and channels it from the nephrons to the ureter and the bladder. The renal pelvis further includes the renal calyx, serving as the collection point for urine being transferred from the renal pyramids (6) . This study aims to provide a comprehensive comparative morphology of the kidneys in domestic dogs and cats.

Experimental Animals: Twenty healthy adult animals (ten local cats and ten local dogs), regardless of sex, were chosen for this study. The mean weight of local cats is (2 ± 0.4 kg). The mean weight of local cats is (2 ± 0.4 kg) In contrast, the average weight of the local canines was ( 20 ± 3 kg ) between the ages of 1 and 3 years. Kidney samples were collected from twenty normal cats and dogs (males and females), animals were obtained from Basra city. A physical checkup verified each dog's and cat's health.

Sampling Methods for Anatomical Study: Ten samples of local dogs were taken for anatomical study. Ten cats were caught using a special American-made Havahart 1045 trap designed to catch live animals without harming them. The Ethics Committee of the College of Veterinary Medicine, University of Basrah, approved all procedures used in this study in accordance with License No. 71/2024. These animals were anesthetized with ketamine 10% and xylazine 2% by intramuscular injection (7) . After that, the animals were sacrificed by bleeding in the carotid artery and emptying the blood using a catheter. Then, the samples were injected with a mixture of ammonia and latex at a ratio of two parts ammonia to three parts latex, to which carmine powder was added to give the mixture a red color (8) . After that, latex was injected through a catheter to show the blood supply to the kidneys. The abdomens of all animals were opened. Then, the viscera were removed carefully. A weight balance (WANT Balance Instrument) was used to weigh the kidneys after they had been properly removed from the animals and their fat had been cleaned. They were then submerged in formaldehyde (10% buffered formalin for 24-48hrs) for post fixation. A measuring tape was used to take measures of the kidneys' length, width, thickness, and weight after they were all collected. The width is measured at the kidney's extremities and midpoint, while the length is measured from the cranial extremity to the caudal extremity. Vernier caliber is used to quantify the thickness of the cortex and medulla; this measurement is finished before the fixation stage (9).

Photograph (1).Vernier Caliber

Photograph (2).a cat trap model Havahart1045

Measuring and Static Analysis

1.Weight (gm): each kidney's weight was measured using a sensitive balance (digital weight balance).

2.Volume (cubic centimeter) of kidneys' volume were measured using the water displacement method.

3. The relative weight of the kidneys to the body weight was massed.

Results

Anatomical Study of the Domestic Dog and cat:

According to the current study, the urinary system consists of the kidneys, renal pelvis, ureters, bladder, and urethra. (Fig. 1) A dog's kidney is bean-shaped, smooth, and contains a single renal papilla (Fig. 6). The left kidney is slightly more caudally, whereas the right kidney is located between T12-13 and L2-3. Normal kidneys are positioned close to the vertebral column and are similar in size and shape on both sides (Fig. 2,9). Cat kidneys can be oval or bean-shaped. Smooth, and contains a single renal papilla. In cats, the cranial portion of the kidney was larger than the caudal portion, whereas, in dogs, the cranial portion was smaller than the caudal portion (Fig. 3,4). In cats, the kidney's fibrous outer, inner, and peripheral layers are called the renal capsule, cortex, and medulla. A renal lobe comprises the medulla and the surrounding cortex, which is divided into numerous pyramidal structures (Fig. 7).

Figure (1).abdominal cavity in dog show the right kidney (RA).left kidney (LK).and liver yellow raw (L).stomach(S). urinary bladder (UB). Abdominal cavity (AC) vein cava(VC).

Figure (2).abdominal cavity in cat show the right kidney(RA), left kidney (LK), liver(L), urinary bladder(UB), Abdominal cavity(AC) and vein cava(VC)

Figure (3).Aorta (A), Right Renal Artery (RRA), Left Renal Artery (LRA), Right Ureter (RU), Left Ureter (LU), and Right Kidney (RK) are depicted in figure 3.in canines

Figure (4).show The vena cava (VC), right kidney (RK), left kidney (LK), right renal vein (RRV), and left renal vein (LRV).

Figure (5).show right kidney (RK),left kidney(LK) right renal artery(RRA) , aorta(A) vein cava(VC) right ureter (UR) left ureter (LU) left renal artery (LRA) in cat.

Figure (6).longitudinal section of kidney in dog. Cortex(C), medulla(M) renal pelvis (RP).

Figure (7).show kidney in cat Cortex(C),medulla(M)renal pelvis (RP).

There are two zones in the renal medulla (inner lighter and outer dark) and a reddish-brown renal cortex (Fig. 6). The lumbar area, which is lateral to the spine and against the back of the abdominal wall, contains the two kidneys, which are encapsulated organs. Figure 1 Two layers of fat provide extra protection, and the kidneys' soft tissue is supported by the fibrous renal capsule that covers them (Fig. 5). The renal pelvis was longitudinal in dogs, whereas in cats, it was transverse. While the dogs' cortex is larger than the cats', the cats' medulla is larger. Cats are red (Fig 6,7), while dogs are reddish-brown (Fig 1,2). The kidneys are supplied via the left and right renal arteries, which branch off the abdominal aorta. The right renal artery leaves the abdominal aorta before the left renal artery. The right renal artery is longer than the left. The renal arteries divide into dorsal and ventral branches when they enter the kidney. Other sources, however, assert that the renal arteries in cats and dogs divide into several branches. The renal arteries sprang from the abdominal aorta anatomically as a single artery left laterally (Fig. 3,4, and 5). It was also noted that the outer cortex of the kidney in cats has many clear veins compared to dogs (Fig. 8 and 9). The adrenal glands are located above the kidneys. The kidneys are paired retroperitoneal organs typically located between the transverse processes of the T12-L3 vertebrae. The left kidney is often slightly higher than the right (Fig .1, 2). The kidneys are covered in three layers on the outside. The renal fascia is the tightest layer of connective tissue at the top. The second layer, known as the perirenal fat capsule, aids in maintaining the kidneys' stability. The renal capsule (Fig. 8) is the third and deepest layer. The kidney's three interior parts are the medulla in the center, an outer cortex, and the renal pelvis in the area known as the kidney's hilum (Fig 6). A concave part of the bean shape is where blood vessels and nerves enter and depart, and the hilum is where the ureters exit the kidney (Fig 5). The kidney's internal structure includes the location of its ureter, vein, and renal artery (8) . An outer cortex, a medulla in the center, and a renal pelvis in the area known as the kidney's hilum comprise the kidney's internal structure. As the ureters exit the kidney, the hilum, the concave portion of the bean, is where blood vessels and nerves enter and exit the kidney (Fig. 7). The right kidney weighed 50.05±5.44 grams on average. The left kidney's average weight (53.97±7.42) The right kidney's average length was (5.18±1.87) ) cm. The left kidney's average length was 5.36±2.18. The dogs' mean total weight was 25.15 ±3.89. The width of the right kidney was 3.47±0.68 cm, whereas the width of the left kidney was 4.23±1.20 cm (Table 1). The left kidney weighed an average of 39.31±13.56 grams, whereas the right kidney weighed an average of31.749±11.47 grams. The right kidney was 4.49 ± 1.05 cm in length on average. The left kidney's mean (4.34±1.05) The average kidney width was 3.64±0.74 cm for the right kidney, 3.76±0.62 cm for the left kidney, and 3.3±0.74 cm for the cat's overall weight (Table 2).

Figure (8).longitudinal section of kidney in dog show renal vein (RV) renal artery (RA) ureter(U).

Figure (9).longitudinal section of kidney in cat hulis (H)

Discussion

Urine formation and secretion, as well as waste removal from the circulation, are the urinary system's functions, which help maintain the volume and composition of bodily fluids, even though its effects are widespread. A mammal's urinary system typically consists of the kidneys, ureters, bladder, and urethra. The kidneys are the main organs that filter blood and produce urine, while the other parts are only auxiliary structures used for urine storage and transportation. Our results showed some morphological-histological differences between domestic cats and dogs.

A Comprehensive Examination of Canine Urinary Anatomy: The urinary system comprises several components, including a bladder, a urethra, two kidneys, and two ureters. The kidneys are located on both sides of the spinal column in the lower abdominal cavity, positioned retroperitoneally. This study aligns with the research conducted by (10) , which also focused on a test subject. The current study reveals that a dog's kidney has a distinctive bean shape, characterized by a smooth surface and a single renal papilla. This observation aligns with the findings of (11) , who also described the kidneys of dogs in similar terms, emphasizing their bean-like form and smooth exterior with a solitary renal papilla. The results indicate a consensus among researchers. Notably, both kidneys exhibit this smooth, bean-shaped morphology and are enveloped by a delicate fibro-muscular capsule. This conclusion is further supported by the research of (4 , 12 - 15) , all of which corroborate these anatomical characteristics disagree with (16) . The left kidney is slightly further back in the abdomen, the right kidney lightly further back in the abdomen, and the right is positioned between the T12-13 and L2-3 vertebrae. Typically, healthy kidneys are found near the vertebral column, exhibiting comparable size and shape on both sides. This observation aligns with the findings of (17) , indicating that the right kidney tends to be located further towards the front compared to the left in dogs.

The renal medulla is characterized by two distinct zones: an outer layer that appears darker and an inner layer that is noticeably lighter. Surrounding this medulla is the renal cortex, which exhibits a reddish-brown hue. The findings of this study align with the observations made by (18) . Thus, the renal cortex stands out with its reddish-brown color, contrasting with the two-toned zones of the renal medulla-one dark and the other paler.The kidneys are sheltered by two protective layers of fat, which serve as an extra line of defense. Meanwhile, the fibrous renal capsule envelops these organs, supporting their sensitive tissues. (13) reported similar observations in ruminants, noting that this fatty layer can sometimes entirely obscure the kidneys. As a protective barrier, the fat cushions the body against the compressive pressures from neighboring organs. As explained by (4) , adipose tissue wraps around the slopes and sides of the kidneys. Consistent with the studies conducted by (4) and (19) , a clearly defined ureter can be seen prominently emerging from the center of the kidneys' unique renal pelvis.

The kidneys are supplied via the left and right renal arteries, which branch off the abdominal aorta. The right renal artery leaves the abdominal aorta before the left renal artery. The right renal artery is longer than the left. The renal arteries divide into dorsal and ventral branches when they enter the kidney. The result of the study is similar to  (20) .(21) .   According to the literature, the renal arteries emerged from the abdominal aorta on both sides. The dorsal and ventral branches of the renal arteries were separated (4) (17) . Two interlobar arteries were sent to the ventral surface from the dorsal branch, while one was sent to the dorsal surface from the ventral branch. (20 , 22).

The renal arteries in cats and dogs divide into several branches. The renal arteries sprang from the abdominal aorta anatomically as a single artery left laterally. The result of the study agrees with showed that the cat's right dorsal branch produced three to five segmental arteries, its right ventral branch four to six segmental arteries, its left dorsal branch three to six segmental arteries, and its left ventral branch three to four segmental arteries (20) . Perched atop each kidney are the adrenal glands, small but vital endocrine organs. The kidneys themselves, which are two in number, are situated in the retroperitoneal space, resting against the back wall of the abdominal cavity. These organs typically lie between the transverse processes of the T12 to L3 vertebrae. Notably, the left kidney is often positioned slightly higher than its right counterpart.

Three distinct layers on their exterior envelop the kidneys. The outermost layer the renal fascia, consists of tightly woven connective tissue that provides robust support at the uppermost section. Beneath this, the second layer is called the perirenal fat capsule, which plays a crucial role in ensuring the kidneys' stability within the abdominal cavity. The innermost layer, the renal capsule, closely encases the kidneys. Internally, the kidneys are structured into three primary components: the medulla, which is centrally located. The outer cortex that surrounds it; and the renal pelvis, situated in an area named the hilum of the kidney.

The right and left kidneys are positioned at the levels of the second or third lumbar vertebrae, along with the twelfth or thirteenth thoracic vertebrae, extending from the first to the third lumbar vertebrae (23) . At the same anatomical level, the aorta branches into the renal arteries on both the left and right sides. According to (15) , it was noted that the right renal artery is consistently longer than its left counterpart, while the left renal vein surpasses the right in length. This study indicates that the renal arteries emerge from both sides of the abdominal aorta, aligning with findings in existing literature (17 , 20) . According to (24) , the renal arteries emanate from the ventral surface of the aorta. In various animals, such as dogs (25) , cats (26) , and guinea pigs (27), these arteries divide into two or more distinct branches. While some studies (20 , 22) have indicated the presence of an additional third branch in certain specimens, (28) demonstrated that in cats, the dorsal and ventral branches further divide into four branches. In contrast, in dogs, they produce just two branches. The current study presents specific measurements of the kidneys, revealing that the average length of the right kidney is approximately 5.18 ± 1.87 cm, while the left kidney measures about 5.36 ± 2.18 cm. Furthermore, the width of the right kidney is recorded at 3.47 ± 0.68 cm, contrasted with the left kidney's width of 4.23 ± 1.20 cm. In terms of weight, the right kidney averages 50.05 ± 5.44 grams, and the left kidney weighs around 53.97 ± 7.42 grams. These findings diverge significantly from the results presented by (29) , which indicated the length of the right kidney to be 5.87 ± 0.97 cm and the left kidney 5.95 ± 0.98 cm. Additionally, the widths in (29) study were noted as 3.01 ± 0.42 cm for the right kidney and 3.40 ± 0.47 cm for the left kidney. The weights reported were considerably lower, with the right kidney at 38.64 ± 17 grams and the left at 38.86 ± 19.50 grams.

The current investigation reveals that the kidneys of cats may exhibit either an oval or bean-like configuration. This observation aligns with the findings of (30) , which indicated that the kidneys of squirrels presented a semi-bean shape. At the same time, e, which characterized those of mice. In both species, the kidneys displayed a smooth surface devoid of any lobulation or fissuring. These results are also consistent with the research conducted by (31) , which described the kidneys of mole rats as having a bean shape, a smooth texture, and a reddish-brown coloration.In felines, the kidneys possess distinct layers, including the fibrous outer layer known as the renal capsule, the inner region referred to as the cortex, and the central part called the medulla. The medulla forms each renal lobe and the encompassing cortex, which is segmented into multiple pyramidal structures. The findings presented align with previous studies conducted by (32) across all mammals and those by (33) focusing on desert rodents.

The kidneys receive their blood supply from the left and right renal arteries, which emerge from the abdominal aorta. Notably, the right renal artery branches off from the abdominal aorta prior to the left renal artery. This leads to a longer course for the right renal artery than its left counterpart. Upon entering the kidneys, the renal arteries bifurcate into dorsal and ventral branches. In cats and dogs, these renal arteries branch out into multiple subdivisions. Anatomically, the renal arteries originate as a singular artery from the abdominal aorta, which extends laterally. This observation aligns with the findings of previous studies (20) (22) (31) (32) The abdominal aorta is responsible for delivering blood flow, with each abdominal aorta is responsible for delivering blood flow, with each kidney generally receiving its blood supply from a distinct artery. Given that the left kidney is positioned further away from the median plane than the right, the right renal artery appears shorter than the left. Ultimately, the renal artery is divided into right and left branches.The current study presents detailed measurements regarding kidney dimensions, noting that the average length of the right kidney is 4.49 ± 1.05 cm, while the left kidney measures 4.34 ± 1.05 cm. Furthermore, the width of the right kidney is reported to be 3.64 ± 0.74 cm, and the left kidney has a width of 3.76 ± 0.62 cm. In terms of weight, the right kidney averages 31.749 ± 11.47 grams, contrasted with the left kidney, which weighs 39.31 ± 13.56 grams. These findings differ significantly from those reported by (29) , where the length of the right kidney was found to be 3.83 ± 0.46 cm and the left kidney 3.82 ± 0.32 cm. Additionally, the study by (29) recorded the width of the right kidney at 2.42 ± 0.22 cm and the left kidney at 2.48 ± 0.31 cm. Regarding weight, (29) reported the right kidney's average weight as 11.14 ± 3.31 grams and the left kidney's average weight as 12.05 ± 3.48 grams.

Conclusion

The present study observed that the kidneys of dogs were larger and heavier than those of cats, with a dark red-brown coloration. The kidneys of both dogs and cats were recorded as bean-shaped in dogs, while in cats, they were either bean-shaped or oval.

Conflicts of interest

The authors declare that there is no conflict of interest.

Ethical Clearance

This work is approved by The Research Ethical Committee.

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