Urine Formation Review
1.) Blood flows into the kidney until it reaches
a cluster of capillaries called a glomerulus that surrounds the starting point of each nephron, a cupped shaped hollow structure called Bowman’s Capsule.
2.) Water and other substances leave circulation
and enter into Bowman’s Capsule at a rate of about 180
L/day in healthy individuals. This mixed
fluid then enters the proximal tubule. Normally at this point, 65% of filtered Na+
and Cl- are reabsorbed with about 65% of
the water being reabsorbed as well. The majority of glucose is reabsorbed by
healthy individuals at this point. H+ is secreted back into the proximal tubule,
thus lowering the pH of the urine.
3.) The filtrate progresses into the descending Loop of Henle
where 20% of the water that was removed is added back to the filtrate.
4.) As the filtrate progresses into the ascending Loop of Henle,
significant amounts of electrolytes are reabsorbed back into the body, but this
area is impermeable to water. Therefore,
water is not reabsorbed producing dilute urine.
5.) This dilute urine is then moved to the collecting ducts where it is stored
until it is moved out of the kidney, and voided from the body.
6.) Urea is passively reabsorbed throughout most
of the tubule and about half remains in the filtered load; thus, the kidney’s
ability to secrete urea efficiently is directly related to the glomerular filtration rate (GFR).
