Question

Blood Flow through Kidneys =       1,600 Liters/24 hours

Filtrate removed from blood =        180     Liters/24hours

Urine formed =         1.5       Liters/24hours

Table showing concentration of certain solutes in body fluids

Solute in water	Afferent Arteriole	Efferent Arteriole	Capsule	Collecting duct	Renal Vein
Urea	30	30	30	2000	25
Uric Acid	4	4	4	50	3.3
Inorg. Salts	720	720	720	1500	719
Protein	7,000	8,000	0	0*	7,050
a.a.'s	50	50	50	0*	49
Glucose	100	100	100	0*	98

            (All concentrations in mg/100ml)                                                         * in healthy kidney,

1a. Draw a simplified cartoon a nephron including structures at top of each column and any other structures you wish – be sure to label the structures! (you can skip the renal vein!).

1b Now look at how concentration of urea and protein change in various locations of the kidney – for each of these locations you need to contrast the concentrations and explain (hint: think about using the terms filtration/filtrate, reabsorption, and secretion…) what is happening to cause the changes you see in the table.

a. Compare and contrast urea/protein in the efferent arteriole:

b. Compare and contrast urea/protein in the capsule

c. Compare and contrast urea/protein in the collecting duct

d. Compare and contrast urea/protein in the renal vein

1c Concentration of amino acids and glucose in the renal vein is lower than in the incoming blood (for example in the afferent arteriole) – what is happening to these molecules in the kidney that is decreasing their concentration? (hint: notice they are not found in the urine!)

Answer 1

1a. Draw a simplified cartoon a nephron including structures at top of each column and any other structures you wish

1b Now look at how concentration of urea and protein change in various locations of the kidney – for each of these locations you need to contrast the concentrations and explain (hint: think about using the terms filtration/filtrate, reabsorption, and secretion…) what is happening to cause the changes you see in the table.

a. Compare and contrast urea/protein in the efferent arteriole:

The blood already passed through the glomerulus, proteins were not filtered from the blood. Urea levels should decrease because these molecules were actually filtered from blood and entered the capsule.

b. Compare and contrast urea/protein in the capsule

The levels of proteins here are zero because they are not being filtered from the blood, but urea levels are maintained as they passed into the capsule to follow the path of being filtrated from blood.

c. Compare and contrast urea/protein in the collecting duct

This duct here has no proteins because since the capsule step they were not filtrated from blood, but now the urea levels are greatly increased because the secretion already passed through the loop of Henle that already reabsorbed water and some other molecules.

d. Compare and contrast urea/protein in the renal vein

The renal vein is there to retrieve the water and some nutrients that might be lost during excretion. The efferent arteriole keeps going into the loop of Henle and transforms into the renal vein, that's why this vein still has high protein levels (not filtered in the glomerulus) and lower urea levels (filtered in the glomerulus).

1c Concentration of amino acids and glucose in the renal vein is lower than in the incoming blood

The molecules seem to disappear, because they are neither in the retrieved mix by the renal vein, nor in the produced urine. The molecules are staying in the cells that form this tissues. Glucose and amino acids are up taken by the cells to fulfill their normal metabolism and functions, that is why we can note such variation here.