I was going through my university lecture on kidney structure and function, and am slightly confused because of a statement made by the lecturer. In the lecture he states that (I am paraphrasing what he said for copyright reasons); ''If 180L of blood plasma is filtered through the glomerular capillaries per day, and if 42 L is the total blood volume in the human body, so it is clear that the kidneys filter the blood plasma a total of 5 times per day (approx.). So the high GFR value of 180L/day is fundamental when it comes to the removal of soluble metabolic waste products like urea (every urea molecule lasts around 4 to 5 hours within the blood before it is removed).''
- Is the total blood volume 42 L, I thought it was around 4 to 5 L and of that approximately 3 L is plasma? Is my lecturer confusing blood volume with the total amount of fluid within the body, which I believe is equal to 42 L?
- If my assumption of there being 3 L of plasma comprising the total blood supply in the average human body, is it correct that the kidneys filter the blood plasma approximately 60 times per day instead of 5 times as he suggests?
- If the blood plasma is filtered around 60 times per day, does that mean that each molecule of urea lasts in the blood for approximately 24/60= 0.4 hours = 24 minutes, in contrast to the 4 to 5 hours he suggests in the lecture?
Any help would be truly appreciated!