Lecture 3: Definition of Tubular Processes (Bolser)

Question 1

define filtration

Answer 1

process by which water and solutes in the blood leave the vascular system thru filtration barrier and enter Bowman’s capsule

Question 2

define secretion

Answer 2

process by which moving substances into the tubular lumen from the cytosol of epithelial cells that form the walls of the nephron

Question 3

define reabsorption

Answer 3

the process of moving substances from the lumen across the epithelial layer into the surrounding interstitium.

Question 4

define excretion

Answer 4

exit of the substance from the body

Question 5

tubular transport maximum (Tm)

Answer 5

the maximum amount of a substance that can be reabsorbed or secreted by tubules.

Question 6

what is the excretion rate formula? (it determines the amount excreted)

Answer 6

excretion rate (mg/min) = U x V
U = concentration in urine
V = urine flow rate

Question 7

what is the formula for filtered load? (it determines the amount filtered)

Answer 7

filtered load (mg/min) = P x GFR
P = concentration in plasma

Question 8

what is excretion equal to?

Answer 8

the filtration for a substance that is neither secreted nor reabsorbed. Inulin is the perfect example of this substance

Question 9

what substance is filtered and neither secreted nor reabsorbed?

Answer 9

inulin

Question 10

if a substance
amount excreted < amount filtered
then what happened to that substance?

Answer 10

then it has been reabsorbed

Question 11

what are examples of reabsorbed substances?

Answer 11

water, Na, Cl, HCO3, K, organic solutes (like sugars, amino acids, etc)

Question 12

what is the formula for the amount reabsorbed?

Answer 12

amount reabsorbed = amount filtered - amount excreted

Question 13

if a substance
amount excreted > amount filtered
then what happened to that substance?

Answer 13

then the substance has been secreted

Question 14

what is the formula for the amount secreted?

Answer 14

amount secreted = amount excreted - amount filtered

Question 15

what are examples of secreted substances?

Answer 15

K, H, NH3, organic acids and bases (like uric acid, PAH, drugs, etc)

Question 16

what is splay?

Answer 16

it is a manifestation of the fact that nephrons have a range of tubular maximum. some nephrons have lower tubular maximums than the average and they will start leaking substances into urine earlier than other nephrons.