Anatomy and functions of the glomerulus

 

The glomerulus is a tiny ball of capillaries (very small blood vessels) inside Bowman's capsule, through which the urine is filtered.

The glomerular filtration rate (GFR) is the amount that is filtered. Usually, this is about 100ml per minute - only an expresso cupful, but this adds up to 150 litres per day! This is produced by the 2 million nephrons in the average healthy pair of kidneys in a young adult. 99% of this filtrate is re-absorbed, leaving one or two litres of urine to be passed each day.

The filter keeps blood cells and all large proteins (albumin, for example) in the blood and out of the urine.

With the natural aging process the GFR decreases very slowly. Usually this is not noticed and it is not a problem. If the rate slows down markedly, as in a diseased kidney, symptoms and signs of kidney disease result.