Renal calices

The renal calices are integral structures of the renal collecting system, responsible for collecting urine from the renal papillae and channeling it into the renal pelvis. Their anatomical arrangement shows significant variation among domestic species, reflecting differences in kidney morphology and urine drainage strategies.

1. General Overview of Renal Calices

Renal calices (singular: calyx) are cup-shaped structures surrounding the renal papillae—the tips of the renal pyramids where urine is excreted into the collecting system. Calices can be classified as:

• Minor calices, which receive urine directly from the papillae.

• Major calices, which are formed by the convergence of several minor calices and drain into the renal pelvis.

However, the presence and organization of these calices differ markedly across domestic species.

2. Species-Specific Differences

a. Dog and Cat (Carnivores)

• The kidneys are typically unipyramidal, meaning a single renal crest receives filtrate from all collecting ducts.

• No true renal calices are present.

• Urine drains directly from the renal crest into the renal pelvis, which then continues into the ureter.

• The renal pelvis is well developed and may show recesses in the cat that mimic calices but do not correspond to individual papillae.

b. Pig

• The pig kidney is multipyramidal and multilobar, with distinct renal papillae and true renal calices.

• Each papilla is surrounded by a minor calyx.

• Minor calices join to form major calices, which empty into a large renal pelvis.

• This arrangement resembles the human renal system and allows clear visualization of the calices in radiographic imaging.

c. Cattle (Ruminants)

• Cattle have a multipyramidal kidney with numerous lobes, each containing its own cortex and medulla.

• Each renal papilla is individually enveloped by a minor calyx.

• There is no renal pelvis in bovines; instead, major calices converge to form the origin of the ureter.

• This complex and segmented system is significant in diagnostic imaging and postmortem examination.

d. Horse

• The horse kidney is unipyramidal, similar to the dog.

• The renal pelvis is divided into two terminal branches: a major cranial and a caudal branch.

• Unlike dogs, horses possess a unique structure called terminal recesses, which receive urine from the terminal parts of the collecting ducts but do not form distinct calices.

• These terminal recesses are often confused with calices but lack papillary structures.