Effect of luminal flow on doming of mpkCCD cells in a 3D perfusable kidney cortical collecting duct model.

The cortical collecting duct (CCD) of the mammalian kidney plays a major role in the maintenance of total body electrolyte, acid/base, and fluid homeostasis by tubular reabsorption and excretion. The mammalian CCD is heterogeneous, composed of Na+-absorbing principal cells (PCs) and acid-base-transporting intercalated cells (ICs). Perturbations in luminal flow rate alter hydrodynamic forces to which these cells in the cylindrical tubules are exposed. However, most studies of tubular ion transport have been performed in cell monolayers grown on or epithelial sheets affixed to a flat support, since analysis of transepithelial transport in native tubules by in vitro microperfusion requires considerable expertise. Here, we report on the generation and characterization of an in vitro, perfusable three-dimensional kidney CCD model (3D CCD), in which immortalized mouse PC-like mpkCCD cells are seeded within a cylindrical channel embedded within an engineered extracellular matrix and subjected to luminal fluid flow. We find that a tight epithelial barrier composed of differentiated and polarized PCs forms within 1 wk. Immunofluorescence microscopy reveals the apical epithelial Na+ channel ENaC and basolateral Na+/K+-ATPase. On cessation of luminal flow, benzamil-inhibitable cell doming is observed within these 3D CCDs consistent with the presence of ENaC-mediated Na+ absorption. Our 3D CCD provides a geometrically and microphysiologically relevant platform for studying the development and physiology of renal tubule segments.

Solute and water transport along an inner medullary collecting duct undergoing peristaltic contractions.

The mechanism by which solutes accumulate in the inner medulla of the mammalian kidney has remained incompletely understood. That persistent mystery has led to hypotheses based on the peristaltic contractions of the pelvic wall smooth muscles. It has been demonstrated the peristaltic contractions propel fluid down the collecting duct in boluses. In antidiuresis, boluses are sufficiently short that collecting ducts may be collapsed most of the time. In this study, we investigated the mechanism by which about half of the bolus volume is reabsorbed into the collecting duct cells despite the short contact time. To accomplish this, we developed a dynamic mathematical model of solute and water transport along a collecting duct of a rat papilla undergoing peristaltic contractions. The model predicts that, given preexisting axial concentration gradients along the loops of Henle, ∼40% of the bolus volume is reabsorbed as the bolus flows down the inner medullary collecting duct. Additionally, simulation results suggest that while the contraction-induced luminal hydrostatic pressure facilitates water extraction from the bolus, that pressure is not necessary to concentrate the bolus. Also, neither the negative interstitial pressure generated during the relaxation phase nor the concentrating effect of hyaluronic acid has a significant effect on bolus concentration. Taken together, these findings indicate that the high collecting duct apical water permeability allows a substantial amount of water to be extracted from the bolus, despite its short transit time. However, the potential role of the peristaltic waves in the urine-concentrating mechanism remains to be revealed.

Prolonged prenatal hypoxia selectively disrupts collecting duct patterning and postnatal function in male mouse offspring.

KEY POINTS: In the present study, we investigated whether hypoxia during late pregnancy impairs kidney development in mouse offspring, and also whether this has long-lasting consequences affecting kidney function in adulthood. Hypoxia disrupted growth of the kidney, particularly the collecting duct network, in juvenile male offspring. By mid-late adulthood, these mice developed early signs of kidney disease, notably a compromised response to water deprivation. Female offspring showed no obvious signs of impaired kidney development and did not develop kidney disease, suggesting an underlying protection mechanism from the hypoxia insult. These results help us better understand the long-lasting impact of gestational hypoxia on kidney development and the increased risk of chronic kidney disease. ABSTRACT: Prenatal hypoxia is a common perturbation to arise during pregnancy, and can lead to adverse health outcomes in later life. The long-lasting impact of prenatal hypoxia on postnatal kidney development and maturation of the renal tubules, particularly the collecting duct system, is relatively unknown. In the present study, we used a model of moderate chronic maternal hypoxia throughout late gestation (12% O2 exposure from embryonic day 14.5 until birth). Histological analyses revealed marked changes in the tubular architecture of male hypoxia-exposed neonates as early as postnatal day 7, with disrupted medullary development and altered expression of Ctnnb1 and Crabp2 (encoding a retinoic acid binding protein). Kidneys of the RARElacZ line offspring exposed to hypoxia showed reduced ß-galactosidase activity, indicating reduced retinoic acid-directed transcriptional activation. Wild-type male mice exposed to hypoxia had an early decline in urine concentrating capacity, evident at 4 months of age. At 12 months of age, hypoxia-exposed male mice displayed a compromised response to a water deprivation challenge, which was was correlated with an altered cellular composition of the collecting duct and diminished expression of aquaporin 2. There were no differences in the tubular structures or urine concentrating capacity between the control and hypoxia-exposed female offspring at any age. The findings of the present study suggest that prenatal hypoxia selectively disrupts collecting duct patterning through altered Wnt/ß-catenin and retinoic acid signalling and this results in impaired function in male mouse offspring in later life.

Histomorphometric comparison of the human, swine, and ovine collecting systems.

The ovine kidney has been recently determined to be a better model than the swine kidney for the study of collecting system healing after partial nephrectomy. However, there is no histological study comparing the collecting systems of these species. To compare human, swine, and ovine collecting systems using histomorphometry. The collecting systems of 10 kidneys from each species (human, swine, and ovine) were processed for histomorphometry. The thickness of the three layers (mucosal connective tissue, submucosal muscular, and adventitial connective tissue) were measured. The densities of smooth muscle fibers, elastic system fibers, and cells were also measured. Additionally, blood vessel density in the adventitial connective tissue was measured. Analysis of the collecting systems from the three species presented several differences. The adventitial connective tissue from the swine samples was thicker, with more blood vessels and smooth muscle fibers, compared with that from the human and ovine samples. Swine also had higher density of elastic fibers on the submucosal muscular layer. Ovine and human collecting systems shared several similar features, such as blood vessel and elastic fiber density in all layers and the density of cellular and muscular fibers in the submucosal muscular and adventitial connective tissue layers. The collecting system of the ovine kidney is more similar to that of the human kidney compared with that of the swine kidney. This may explain the differences between the healing mechanisms in swine and those in humans and sheep after partial nephrectomy. Anat Rec, 299:967-972, 2016. © 2016 Wiley Periodicals, Inc.

Anatomical Relationship Between the Kidney Collecting System and the Intrarenal Arteries in the Sheep: Contribution for a New Urological Model.

Previous studies have demonstrated that the pig collecting system heals after partial nephrectomy without closure. Recently, a study in sheep showed that partial nephrectomy without closure of the collecting system resulted in urinary leakage and urinoma. The aim of this study was to present detailed anatomical findings on the intrarenal anatomy of the sheep. Forty two kidneys were used to produce tridimensional endocasts of the collecting system together with the intrarenal arteries. A renal pelvis which displayed 11-19 (mean of 16) renal recesses was present. There were no calices present. The renal artery was singular in each kidney and gave two primary branches one to the dorsal surface and one to ventral surface. Dorsal and ventral branches of the renal artery were classified based on the relationship between their branching pattern and the collecting system as: type I (cranial and caudal segmental arteries), type II (cranial, middle and caudal segmental arteries) or type III (cranial, cranial middle, caudal middle, and caudal segmental arteries). Type I was the most common branching pattern for the dorsal and ventral branches of the renal artery. The arterial supply of the caudal pole of the sheep kidney supports its use as an experimental model due to the similarity to the human kidney. However, the lack of a retropelvic artery discourages the use of the cranial pole in experiments in which the arteries are an important aspect to be considered.

Morphological and molecular investigations of the holocephalan elephant fish nephron: the existence of a countercurrent-like configuration and two separate diluting segments in the distal tubule.

In marine cartilaginous fish, reabsorption of filtered urea by the kidney is essential for retaining a large amount of urea in their body. However, the mechanism for urea reabsorption is poorly understood due to the complexity of the kidney. To address this problem, we focused on elephant fish (Callorhinchus milii) for which a genome database is available, and conducted molecular mapping of membrane transporters along the different segments of the nephron. Basically, the nephron architecture of elephant fish was similar to that described for elasmobranch nephrons, but some unique features were observed. The late distal tubule (LDT), which corresponded to the fourth loop of the nephron, ran straight near the renal corpuscle, while it was convoluted around the tip of the loop. The ascending and descending limbs of the straight portion were closely apposed to each other and were arranged in a countercurrent fashion. The convoluted portion of LDT was tightly packed and enveloped by the larger convolution of the second loop that originated from the same renal corpuscle. In situ hybridization analysis demonstrated that co-localization of Na(+),K(+),2Cl(-) cotransporter 2 and Na(+)/K(+)-ATPase α1 subunit was observed in the early distal tubule and the posterior part of LDT, indicating the existence of two separate diluting segments. The diluting segments most likely facilitate NaCl absorption and thereby water reabsorption to elevate urea concentration in the filtrate, and subsequently contribute to efficient urea reabsorption in the final segment of the nephron, the collecting tubule, where urea transporter-1 was intensely localized.

Renal development: a complex process dependent on inductive interaction.

Renal development begins in-utero and continues throughout childhood. Almost one-third of all developmental anomalies include structural or functional abnormalities of the urinary tract. There are three main phases of in-utero renal development: Pronephros, Mesonephros and Metanephros. Within three weeks of gestation, paired pronephri appear. A series of tubules called nephrotomes fuse with the pronephric duct. The pronephros elongates and induces the nearby mesoderm, forming the mesonephric (Woffian) duct. The metanephros is the precursor of the mature kidney that originates from the ureteric bud and the metanephric mesoderm (blastema) by 5 weeks of gestation. The interaction between these two components is a reciprocal process, resulting in the formation of a mature kidney. The ureteric bud forms the major and minor calyces, and the collecting tubules while the metanephrogenic blastema develops into the renal tubules and glomeruli. In humans, all of the nephrons are formed by 32 to 36 weeks of gestation. Simultaneously, the lower urinary tract develops from the vesico urethral canal, ureteric bud and mesonephric duct. In utero, ureters deliver urine from the kidney to the bladder, thereby creating amniotic fluid. Transcription factors, extracellular matrix glycoproteins, signaling molecules and receptors are the key players in normal renal development. Many medications (e.g., aminoglycosides, cyclooxygenase inhibitors, substances that affect the renin-angiotensin aldosterone system) also impact renal development by altering the expression of growth factors, matrix regulators or receptors. Thus, tight regulation and coordinated processes are crucial for normal renal development.

Three-dimensional reconstruction of the rat nephron.

This study gives a three-dimensional (3D) structural analysis of rat nephrons and their connections to collecting ducts. Approximately 4,500 2.5-µm-thick serial sections from the renal surface to the papillary tip were obtained from each of 3 kidneys of Wistar rats. Digital images were recorded and aligned into three image stacks and traced from image to image. Short-loop nephrons (SLNs), long-loop nephrons (LLNs), and collecting ducts (CDs) were reconstructed in 3D. We identified a well-defined boundary between the outer stripe and the inner stripe of the outer medulla corresponding to the transition of descending thick limbs to descending thin limbs and between the inner stripe and the inner medulla, i.e., the transition of ascending thin limbs into ascending thick limbs of LLNs. In all nephrons, a mosaic pattern of proximal tubule (PT) cells and descending thin limb (DTL) cells was observed at the transition between the PT and the DTL. The course of the LLNs revealed tortuous proximal "straight" tubules and winding of the DTLs within the outer half of the inner stripe. The localization of loop bends of SLNs in the inner stripe of the outer medulla and the bends of LLNs in the inner medulla reflected the localization of their glomeruli; i.e., the deeper the glomerulus, the deeper the bend. Each CD drained approximately three to six nephrons with a different pattern than previously established in mice. This information will provide a basis for evaluation of structural changes within nephrons as a result of physiological or pharmaceutical intervention.

Flexible ureterorenoscopy for lower pole stones: influence of the collecting system's anatomy.

BACKGROUND: The impact of renal anatomy on the success rate of flexible ureterorenoscopy (fURS) for lower pole stones is less clear than it is on shock wave lithotripsy, for which it is a recognized influence factor. We analyzed safety and efficiency of fURS using modern endoscopes for lower pole stones dependent on the collecting system's configuration. PATIENTS AND METHODS: We retrospectively evaluated a consecutive sample of 111 fURS for lower pole stones at our tertiary care center between January 2010 and September 2012 from our prospectively kept database. All procedures were performed with modern flexible ureterorenoscopes, nitinol baskets, holmium laser lithotripsy, and ureteral access sheaths whenever needed. The infundibular length (IL) and width (IW) and infundibulopelvic angle (IPA) were measured and the data were stratified for stone-free status and complications classified by the Clavien-Dindo scale. Univariate and multifactorial statistical analyses were performed. Correlation of operation time (OR-time) with anatomical parameters was conducted. RESULTS: Ninety-eight (88.3%) of the 111 patients were stone free after a single fURS. On multifactorial analysis, the stone size and IL had significant influence on the stone-free rate (SFR) (p<0.01), whereas IW did not. An acute IPA (<30°) also had significant influence (p=0.01). The incidence of complications and OR-time were not influenced by the pelvicaliceal anatomy. CONCLUSIONS: fURS is a safe and efficient treatment option for lower pole kidney stones. A long infundibulum and a very acute IPA (<30°) negatively affect the SFR. However, with second look procedures, a complete stone clearance is achievable even in case of unfavorable anatomic conditions. A narrow infundibulum has no negative effect while using modern endoscopes. The complication rate is not affected by the collecting system's anatomy.

Architecture of vasa recta in the renal inner medulla of the desert rodent Dipodomys merriami: potential impact on the urine concentrating mechanism.

We hypothesize that the inner medulla of the kangaroo rat Dipodomys merriami, a desert rodent that concentrates its urine to over 6,000 mosmol/kg H(2)O, provides unique examples of architectural features necessary for production of highly concentrated urine. To investigate this architecture, inner medullary vascular segments in the outer inner medulla were assessed with immunofluorescence and digital reconstructions from tissue sections. Descending vasa recta (DVR) expressing the urea transporter UT-B and the water channel aquaporin 1 lie at the periphery of groups of collecting ducts (CDs) that coalesce in their descent through the inner medulla. Ascending vasa recta (AVR) lie inside and outside groups of CDs. DVR peel away from vascular bundles at a uniform rate as they descend the inner medulla, and feed into networks of AVR that are associated with organized clusters of CDs. These AVR form interstitial nodal spaces, with each space composed of a single CD, two AVR, and one or more ascending thin limbs or prebend segments, an architecture that may lead to solute compartmentation and fluid fluxes essential to the urine concentrating mechanism. Although we have identified several apparent differences, the tubulovascular architecture of the kangaroo rat inner medulla is remarkably similar to that of the Munich Wistar rat at the level of our analyses. More detailed studies are required for identifying interspecies functional differences.

Anatomical relationship between the collecting system and the intrarenal arteries in the rabbit: contribution for an experimental model.

Intrarenal anatomy was studied in detail to evaluate how useful rabbits could be as a urologic model. Only one renal artery was observed, which was divided into dorsal and ventral branches in all cases. Three segmental arteries (cranial, mesorenal and caudal) was the most frequent branching pattern found in both the dorsal and ventral division. There was an important artery related to the ureteropelvic junction in both dorsal and ventral surfaces in all specimens. The cranial pole was supplied by both dorsal and ventral divisions of the renal artery in 23 of 41 casts (56%). Although the cranial pole of the rabbit kidney could be useful as a model because of the resemblances with human kidney, the different relationship between the intrarenal arteries and the kidney collecting system in other regions of the kidney must be taken into consideration by the urologists, when using rabbit kidney in urological research.

Anatomic variations in vascular and collecting systems of kidneys from deceased donors.

INTRODUCTION: Nephroureterectomy for transplantation has increased owing to the greater number of deceased donors. Anatomic variations may complicate the procedure or, if unrecognized, compromise the viability of kidneys for transplantation. METHODS: We reviewed 254 surgical descriptions of nephroureterectomy specimens from January 2008 to December 2009. All organs collected according by standard techniques were evaluated for age, cause of death, renal function, frequency of injury during the procedure, as well as variations in the vascular and collecting systems. RESULTS: The mean donor age was 42 years (range, 2-74). The mean serum creatinine was 1.2 mg/dL (range, 1.0-7.0). The causes of death were cerebrovascular cause (stroke; n = 130), traumatic brain injury (n = 81) or other cause (n = 43). Among the anatomic variations: 8.6% (n = 22) were right arterial anatomical variations: 19 cases with 2 arteries and 3 cases with 3 arteries. In 25 cases (9.8%) the identified variation was the left artery: 2 arteries (n = 23), 3 arteries (n = 1) and 4 arteries (n = 1). We observed 9.8% on right side and 1.5% on left side venous anatomic variations, including 24 cases with 2 veins on the right side and 4 cases with 2 veins on the left side. Three cases of a retroaortic left renal vein and 1 case of a retro necklace vein (anterior and posterior to the aorta). Two cases of ureteral duplication were noted on the left and 1 on the right kidney. There were 3 horseshoe and 1 pelvic kidney. In 7.5% of cases, an injury to the graft included ureteral (n = 3), arterial (n = 10), or venous (n = 6). CONCLUSION: The most common anatomic variation was arterial (17.8%). Duplication of the renal vein was more frequent on the right. The high incidences of anatomic variations require more attention in the dissection of the renal hilum to avoid an injury that may compromise the graft.

Molecular physiology of the medullary collecting duct.

The mammalian kidney is responsible for a multitude of homeostatic functions, which are mediated by both structural and functional diversity along the renal tubule. In this article, we focus on the major functions of the terminal portion of the renal tubule, the medullary collecting duct system. The role of the medullary collecting ducts in determining the composition of the final urine through controlled water, sodium, chloride, potassium and urea reabsorption, ammonia transport, and acid-base homeostasis is discussed. The molecular identity of the major channels and transporters that contribute to medullary collecting duct function are described in detail, including; aquaporins, urea transporters, the epithelial sodium channel (ENaC), the Na,K-ATPase, H-ATPase, Rh glycoproteins, and sodium bicarbonate transporters. Knowledge gained from studies in knockout mice is also discussed.

A proposed new classification for the renal collecting system of cattle.

OBJECTIVE: To evaluate the intrarenal anatomy of kidneys obtained from cattle and to propose a new classification for the renal collecting system of cattle. SAMPLE POPULATION: 37 kidneys from 20 adult male mixed-breed cattle. PROCEDURES: Intrarenal anatomy was evaluated by the use of 3-D endocasts made of the kidneys. The number of renal lobes and minor renal calyces in each kidney and each renal region (cranial pole, caudal pole, and hilus) was quantified. RESULTS: The renal pelvis was evident in all casts and was classified into 2 types (nondilated [28/37 {75.7%}] or dilated [9/37 {24.3%}]). All casts had a major renal calyx associated with the cranial pole and the caudal pole. The number of minor renal calices per kidney ranged from 13 to 64 (mean, 22.7). There was a significant correlation between the number of renal lobes and the number of minor renal calices for the entire kidney, the cranial pole region, and the hilus region; however, there was not a similar significant correlation for the caudal pole region. Major and minor renal calices were extremely narrow, compared with major and minor renal calices in pigs and humans. CONCLUSIONS AND CLINICAL RELEVANCE: The renal collecting system of cattle, with a renal pelvis and 2 major renal calices connected to several minor renal calices by an infundibulum, differed substantially from the renal collecting system of pigs and humans. From a morphological standpoint, the kidneys of cattle were not suitable for use as a model in endourologic research and training.

The pelvic kidney of male Ambystoma maculatum (Amphibia, urodela, ambystomatidae) with special reference to the sexual collecting ducts.

This study details the gross and microscopic anatomy of the pelvic kidney in male Ambystoma maculatum. The nephron of male Ambystoma maculatum is divided into six distinct regions leading sequentially away from a renal corpuscle: (1) neck segment, which communicates with the coelomic cavity via a ventrally positioned pleuroperitoneal funnel, (2) proximal tubule, (3) intermediate segment, (4) distal tubule, (5) collecting tubule, and (6) collecting duct. The proximal tubule is divided into a vacuolated proximal region and a distal lysosomic region. The basal plasma membrane is modified into intertwining microvillus lamellae. The epithelium of the distal tubule varies little along its length and is demarcated by columns of mitochondria with their long axes oriented perpendicular to the basal lamina. The distal tubule possesses highly interdigitating microvillus lamellae from the lateral membranes and pronounced foot processes of the basal membrane that are not intertwined, but perpendicular to the basal lamina. The collecting tubule is lined by an epithelium with dark and light cells. Light cells are similar to those observed in the distal tuble except with less mitochondria and microvillus lamellae of the lateral and basal plasma membrane. Dark cells possess dark euchromatic nuclei and are filled with numerous small mitochondria. The epithelium of the neck segment, pleuroperitoneal funnel, and intermediate segment is composed entirely of ciliated cells with cilia protruding from only the central portion of the apical plasma membrane. The collecting duct is lined by a highly secretory epithelium that produces numerous membrane bound granules that stain positively for neutral carbohydrates and proteins. Apically positioned ciliated cells are intercalated between secretory cells. The collecting ducts anastomose caudally and unite with the Wolffian duct via a common collecting duct. The Wolffian duct is secretory, but not to the extent of the collecting duct, synthesizes neutral carbohydrates and proteins, and is also lined by apical ciliated cells intercalated between secretory cells. Although functional aspects associated with the morphological variation along the length of the proximal portions of the nephron have been investigated, the role of a highly secretory collecting duct has not. Historical data that implicated secretory activity concordant with mating activity, and similarity of structure and chemistry to sexual segments of the kidneys in other vertebrates, lead us to believe that the collecting duct functions as a secondary sexual organ in Ambystoma maculatum.

Maximum urine concentrating capability in a mathematical model of the inner medulla of the rat kidney.

In a mathematical model of the urine concentrating mechanism of the inner medulla of the rat kidney, a nonlinear optimization technique was used to estimate parameter sets that maximize the urine-to-plasma osmolality ratio (U/P) while maintaining the urine flow rate within a plausible physiologic range. The model, which used a central core formulation, represented loops of Henle turning at all levels of the inner medulla and a composite collecting duct (CD). The parameters varied were: water flow and urea concentration in tubular fluid entering the descending thin limbs and the composite CD at the outer-inner medullary boundary; scaling factors for the number of loops of Henle and CDs as a function of medullary depth; location and increase rate of the urea permeability profile along the CD; and a scaling factor for the maximum rate of NaCl transport from the CD. The optimization algorithm sought to maximize a quantity E that equaled U/P minus a penalty function for insufficient urine flow. Maxima of E were sought by changing parameter values in the direction in parameter space in which E increased. The algorithm attained a maximum E that increased urine osmolality and inner medullary concentrating capability by 37.5% and 80.2%, respectively, above base-case values; the corresponding urine flow rate and the concentrations of NaCl and urea were all within or near reported experimental ranges. Our results predict that urine osmolality is particularly sensitive to three parameters: the urea concentration in tubular fluid entering the CD at the outer-inner medullary boundary, the location and increase rate of the urea permeability profile along the CD, and the rate of decrease of the CD population (and thus of CD surface area) along the cortico-medullary axis.

The dog kidney as experimental model in endourology: anatomic contribution.

Abstract A systematic study of the morphometry and the collecting system of the canine kidney is presented and compared with previous findings in humans. Renal measurements (kidney length, width, and thickness) were recorded. In addition, 110 three-dimensional endocasts of the kidney collecting system were produced and studied. Anatomic details, important to research and surgical training in endourology, were observed and recorded in canine kidneys. Dogs whose height was more than 70 cm at the withers presented similar kidney measurements to those found in the adult human. The collecting system consisted only of a renal pelvis with a variable number of recesses around its perimeter. The dog kidney is not a good model for experimental studies that consider the morphology of the collecting system. Kidneys from dogs taller than 70 cm, however, might be useful as a model in experimental studies in which renal volume is an important aspect, such as shockwave lithotripsy and endourology.

Pig kidney: anatomical relationships between the renal venous arrangement and the kidney collecting system.

PURPOSE: We present a systematic study of the anatomical relationship between the intrarenal veins and the kidney collecting system in pigs. MATERIALS AND METHODS: The intrarenal anatomy (collecting system and veins) was studied in 61, 3-dimensional endocasts of the kidney collecting system together with the intrarenal veins. RESULTS: There are free anastomoses between the intrarenal veins. The interlobar veins unite to produce large venous trunks, which form the renal vein. In our study we observed 2 trunks (cranial and caudal) in 54 of the 61 cases (88.53%) and 3 trunks (cranial, middle and caudal) in 7 (11.47%). Only the ventral surfaces of the cranial and caudal poles were drained by large veins, while the dorsal surfaces emptied by anastomoses into the ventral interlobar veins. There were large veins in a close relationship to the ventral surface (90.16%) and to the dorsal surface (3.28%) of the ureteropelvic junction. In 33 of the 61 cases (54.10%) there was 1 or 2 small dorsal veins. CONCLUSIONS: Although some results of intrarenal venous arrangement in pigs could not be completely transposed to humans, many similarities of pig and human kidneys support its use as the best animal model for urological procedures.