Terminology

Some terms that you'll need to know to understand just what minimal change disease is...


 Kidney - Almost every human being has two kidneys.  They are small, bean-shaped organs (about the size of a fist) that are located on either side of the spine and below the rib cage.  Kidneys are responsible for constantly cleaning all of our blood and getting rid of the waste by producing urine. It is made up of about a million tiny filters that our blood flows through called nephrons.



Nephron - A nephron (NEF-ron) is a tiny filter within the kidney.  There are approximately a million nephrons in each kidney.  Each nephron works through a two different filter processes, the glomerulus and the tubule.






Glomerulus - The glomerulus (glom-AIR-you-lus) is the first filter in the kidney.  It works kind of like a pasta strainer.  A large, circular area called Bowman's capsule that allows blood to enter and has specifically sized holes in it that allow waste particles to pass through the holes into the tubules but keep blood cells and protein molecules in the body's circulation.  The glomerulus is actually composed of three different layers of filters: fenestrated endothelium, a basement membrane and epithelial cells called podocytes.


The three layers of the glomerulus:


1. Fenestrated endothelium -The innermost cells of the glomerulus.  Endothelial cells of the capillary (which carries the blood into Bowman's capsule) that are fenestrated or have holes in them to allow waste products to pass through.  These holes in the fenestrated endothelium do not allow red blood cells or large particles of protein to pass through, however, they are the largest holes and some particles that are important to the body are able to pass through this first layer.


2. Basement membrane - This second and center layer of the filter is an area made of collagen fibers and other proteins that are fused together but leave small holes to allow waste products to pass through. The space between the fibers and proteins of the basement membrane are smaller than the fenestrated endothelium and they are able to recapture particles of protein and put them back into circulation.

3. Podocytes (with foot processes) -These epithelial cells that surround the outside of Bowman's capsule have foot processes or small projections of the cell itself that are very close together.  In a normally functioning glomerulus, these podocytes are all separated from one another and aligned perfectly to form tiny slits that allow waste products to squeeze through but recapture all proteins.  The podocytes are the smallest and final layer of the filter.  In minimal change disease, the podocyte is the part of the cell that is malformed. 

The three layers of the glomerulus: 

fenestrated endothelium, basement membrane, and podocytes.  

Light (standard) microscope -A typical microscope that magnifies cells to 100 times their normal size.

Electron microscope -A powerful microscope that magnifies cells to 1 million times their normal size.



References:

http://www.nlm.nih.gov/medlineplus/ency/article/000496.htm

http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/

 http://courses.washington.edu/conj/bess/filtration/filtration.htm