There are about a million nephrons in each kidney, and each nephron is about 30mm long. So that’s roughly 30km of nephron per kidney. If the string in the kidney purse is 15m long, that would mean 2000 times as long as can be pulled out of the purse in a lecture theatre.
This model can be used to impress on students the overall length of nephrons to the students, and how important that length is for effective filtering of the blood. The model also helps them understand that if we have something the size of a kidney purse, the nephrons themselves must be microscopic to fit in there, which is why it’s important for the students to study the histology, to understand what’s going on in those very small structures.
Click to enlarge the image of the Kidney Purse:
The string is wound onto on a reel inside a reel case, that can be tucked inside the kidney purse.
The reel is made from aluminium circles joined to a spindle made from a hollow rod of aluminium. Large-gauge screws are used to join the circles to the spindle.
The reel case is a section of PVC plumbing pipe, in this example 38mm diameter, sealed at both ends with duct tape. The inner surface of the duct tape is covered over so it doesn’t stick and two washers of felt help the reel move freely within the case.
The string is brightly coloured builder’s twine and runs from a small hole in the reel spindle and out of a large, smooth hole in the side of the reel case. About 15 meters of string were used in this example.
Click to enlarge images:
One end of the reel case has a hole though which a screwdriver can be inserted to wind the string onto the reel. An electric screwdriver of some kind is actually better than hand-winding the reel since the more even winding action means the string is less likely to snag when being pulled out.
The leather purse was designed to fit around the reel case without being too tight. A zip is inserted into the long curve and a small gap is left at the hilum, through which the string can run. The end of the string is finished with a fold of leather to simulate the start of the ureter. Dacron wadding is used to pad out the inside of the purse, around the reel case.
Click to enlarge images:
Background grid for the pattern is 100mm x 100mm.
Keywords: Teaching, Anatomy, Kidney, Urinary system, Science, Biology
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