Perirenal fatA layer of fat surrounds and cushions the kidney. A sheep kidney often comes to the tray still partly buried in it.
Renal capsuleA thin but strong fibrous covering that holds the kidney's shape. On a healthy kidney it strips off easily.
Renal hilumThe dent in the middle of the kidney's inner border. The renal artery enters here; the renal vein and the ureter leave.
Renal veinIt returns blood from the kidney to the inferior vena cava.
Renal arteryIt branches straight from the aorta. It carries blood into the kidney to be filtered.
UreterIt begins at the renal pelvis and carries urine to the bladder.
Sheep kidney, cut 5
Renal cortexThe outer layer, under the capsule. The renal corpuscles, where blood is filtered, are all found here.
Renal medullaThe inner region, one broad mass in the sheep. Its stripes all run toward the renal crest.
Renal crestA common papilla formed by the fusion of the pyramids. The tubules of the medulla open on it into the renal pelvis.
Renal pelvisThe widened, funnel-shaped start of the ureter. In the sheep it cups the renal crest.
Renal sinusThe hilum opens into this space inside the kidney. It holds the renal pelvis, the vessels and fat.
Pig kidney, cut 4
Renal pyramidIn the pig the medulla is divided into separate pyramids. Each points in toward the sinus.
Renal papillaThe point of a pyramid. Its collecting ducts release urine into a minor calyx here.
Minor calyxEach minor calyx holds a papilla and catches the urine leaving it.
Major calyxThe pig's renal pelvis divides into two major calyces. One lies toward each end of the kidney. The minor calyces drain into them.
How this list was compiled: Every name and detail checked on 2026-09-30 against Septimus Sisson, The Anatomy of the Domestic Animals (2nd ed., 1914, public domain), the urinary organs of the horse, ox, sheep and pig: the sheep's smooth, bean-shaped kidney embedded in fat, its hilus and its renal crest or common papilla formed by the fusion of the pyramids; the pig's two major calyces, its minor calyces each holding a papilla, and its distinct pyramids; the fibrous capsule, perirenal fat, renal sinus and renal pelvis, https://archive.org/details/anatomyofdomesti00siss; against OpenStax Anatomy and Physiology 2e, section 25.3 Gross Anatomy of the Kidney (fibrous capsule, renal fat pad, hilum, cortex, medulla, pyramids, papillae, calyces, pelvis, ureter, renal artery and vein), https://openstax.org/books/anatomy-and-physiology-2e/pages/25-3-gross-anatomy-of-the-kidney; and against Wikipedia, Mammalian kidney, Kidney, Renal capsule and Renal sinus, text only. The list of structures in a dog kidney dissection from the University of Minnesota College of Veterinary Medicine (hilus, cortex, medulla, renal crest, renal sinus, renal pelvis, ureter), https://vanat.ahc.umn.edu/carnLabs/Lab17/Lab17.html, was read as a further check on the names. Licence: own work
The drawing: Drawn for this site on 2026-10-04 by script: three upright kidneys with the hilum facing right. The outline of a kidney cut lengthwise, the place of the sinus, the pyramids standing round it with their papillae in the calyces and the pelvis narrowing to the ureter are laid out after fig. 1127, Vertical section of kidney, and the outside shape with the vessels and ureter at the hilum after fig. 1122, The anterior surfaces of the kidneys, both in Henry Gray, Anatomy of the Human Body (20th ed., 1918), public domain, from Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Gray1127.png and https://commons.wikimedia.org/wiki/File:Gray1122.png). The sheep's single renal crest and the pig's two major calyces follow the text of Septimus Sisson, The Anatomy of the Domestic Animals (2nd ed., 1914), public domain. Own work, nothing traced. Licence: own work
How it works
Three line drawings of the kidney a class cuts: a sheep kidney as it comes to the tray, the same kidney sliced lengthwise, and a pig kidney sliced the same way. Learn the fifteen parts before lab day.
Read the full guide
Outside first, then the cut
Numbers 1 to 6 are what you see before cutting: the fat, the capsule that peels away, and the hilum with its artery, vein and ureter. Cut the kidney lengthwise into two flat halves and numbers 7 to 11 appear. A sheep kidney has one renal crest. A pig kidney, numbers 12 to 15, has separate pyramids and calyces, as a human kidney does.
The capsule strips off a healthy kidney easily. Peel it back to see the sheep kidney's smooth surface.
No separate pyramids in your sheep kidney? That is normal: they are fused into the renal crest.
Questions and answers
What are the parts of a sheep kidney?
Outside: perirenal fat, the renal capsule, and the hilum with the renal artery, renal vein and ureter. Cut open: the cortex, the medulla, one renal crest, the renal pelvis and the renal sinus.
How is a sheep kidney different from a human kidney?
A human kidney has several separate pyramids, each ending in a papilla that drains into a minor calyx. In the sheep the pyramids are fused into a single ridge, the renal crest, which opens into the renal pelvis.
Does a pig kidney have pyramids?
Yes. A pig kidney has distinct renal pyramids. Each papilla sits in a minor calyx, and the minor calyces join two major calyces that meet in the renal pelvis.
What is the renal hilum?
The notch in the middle of the kidney's inner border. The renal artery enters there, and the renal vein and the ureter leave.