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The Anatomy of a Kidney

Lying below the fibrous CAPSULE of the kidney is the CORTEX - the Latin word for tree bark. Depending on how the kidney is cut, the cortex may appear striated. This appearance is the result of the position of the small kidney filters, the GLOMERULI - a Latin word for small balls of yarn. These tend to line up along the blood vessels supplying them. The cortex also contains the convoluted tubules both proximal and distal. Each glomerulus filters into a PROXIMAL CONVOLUTED (OR ROLLED UP) TUBULE and this proximal (or nearest) tubule continues on as the LOOP OF HENLE. These loops constitute most of the MEDULLA (Latin for marrow) and they converge into striated areas called the PYRAMIDS.

All these features may be seen in the following diagrams and pictures. The next part is not hard to understand but it is rather tedious. The loop of Henle, or course, leads back to the cortex and there it becomes the DISTAL (farthest) CONVOLUTED tubule. So now we have both PROXIMAL and DISTAL CONVOLUTED tubules in the cortex. The next step is for the distal tubules to join a collecting duct. The collecting ducts run back through the pyramids and end up opening through a little PAPILLA (Latin for nipple).

This is the finished urine and here it drains into a MINOR CALIX. If we translate all this into English we find that the urine comes out like milk from a nipple and drains into a MINOR (Latin for less) CALYX which is Greek for the CUP OF A FLOWER!! (We might say it droppeth like the gentle rain from heaven.) The calices (plural for calix) are the first places that we see the tough white material that is so well demonstrated in the pig and the beef kidneys.

The small calices drain into bigger calices and then into the PELVIS of the kidney. Pelvis is Latin for basin but it is really funnel shaped and drains into the ureter and hence to the bladder. (Ureter is from the Greek and actually means a urinary passage!)

Check all this out below:

As all mammalian kidneys have much in common and if you want to do a hands-on study of the kidney it is a good idea to go to the butcher’s shop and see what you can pick up.  Judging from the kidneys illustrated below the one most like the human kidney is from the pig.  Unfortunately in our civilized cities the kidneys have already been trimmed and are encased in plastic.  They have most likely lost the renal artery and vein as well as the ureter.  The renal artery, vein and ureter will be discussed later but for now let us make use of what we have.  If you cut from the rounded side of the kidney to the pelvis and open it up like a bean you will understand the pig’s kidney on the left.  (Sorry, I wasn’t able to get a gorilla kidney.)








The cortex surrounds the kidney like bark. Note the well marked calices (all that white tissue).  A few red cells drifted into the calices when the kidney was cut but help to show their structure.  The pyramids are extremely prominent.  The pelvis has, of course, been cut through but the ureter and many blood vessels have been trimmed off.   
Pig Kidney  








The beef kidney was much larger than the pig kidney and is shown at about a third its size.  Again the cortex is prominent but the pyramids are not so well marked.  One may be seen at the upper right.  At the bottom right a papilla opens into a calyx.

Sometimes the human kidney is lobulated, but not to the extent of the beef kidney.


Beef Kidney


Now a word about the positions of the large blood vessels and the ureter:  If you will look back at the diagram of the kidney on this page the order of these structures is correct.  The renal vein is at the front, the renal artery next and the ureter is behind both.  This is the VAD vein-artery-duct position.

The artery, however, soon gives off a large branch that passes in front of the vein leading to some really good artists misplacing it.  The renal artery gives off many branches and they eventually give rise to the afferent arterioles which will be discussed very shortly.


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