Question #301
Which of the following is true of the fluid formed at the glomerulus?
Urine is formed by a process of ultrafiltration at the glomerulus, followed by selective secretion and reabsorption in the tubules. The primary filtered product is approximately isosmotic with plasma and has a similar ionic composition. The retention of large negatively charged protein molecules provides a electrical drive for the movement of negatively charged ions, i.e. chloride, into the glomerular filtrate: the glomerular fluid chloride concentration is therefore higher than that in the plasma.
In healthy subjects the primary filtrate contains very little protein, though it is often detectable in trace amounts. The primary filtrate does contain glucose but all of this is usually reabsorbed before the fluid leaves the kidney.
Urea is actively reabsorbed as fluid moves along the tubules. The urea concentration in the primary filtrate is therefore higher than that in the final urine.