Reabsorption

Question 1

How much of the volume is reabsorbed?

Answer 1

99% of filtered liquid

Question 2

Driving force of reabsorption

Answer 2

-reabsorption happens from lumen to extracellular fluid
-has to go through two membranes (apical and basolateral)
-Ion that goes through first is sodium where anion follows then H2O and then other molecules
-Na+ is reabsorbed by active transport
-electrochemical gradient drives anion reabsorption
-water moves by osmosis, following solute reabsorption

Question 3

Mechanism of Na+ reabsorption

Answer 3

• from the lumen sodium will need to enter the cell first and then from the cell to extracellular fluid
  -Because sodium has high concentration in the lumen and low concentration in the cell it will diffuse passively through a sodium channel
  -Then concentration of sodium is low inside the cell and high outside so it will need a Na+/K+ pump to enter the extracellular fluid

Question 4

Glucose transport : Reabsorption

Answer 4

-in epithelium cells glucose is low outside and high inside, so to go inside it will need secondary active transport (Na+/glucose symporter)
-then will just need passive transport for glucose to enter extracellular fluid by glucose carrier

Question 5

Membrane Proteins

Answer 5

-membrane proteins have binding sites, meaning they can become saturated
-> so if the membrane protein can only take up 60 glucose molecules and there’s 100 molecules then the rest will eventually go to urine

Question 6

Renal Threshold and Transport maximum

Answer 6

-Transport maximum (Tm) is transport rate at max saturation (mg/min)
-Renal threshold is plasma concentration at which saturation occurs (mg/mL)

Question 7

Calculating renal threshold

Answer 7

GFR x [plasma] = Tm
ml/min x Renal threshold = mg/min

Question 8

Where is secretion regulated?

Answer 8

the distal tubule

Question 9

Secretion of organic anion

Answer 9

-moving from plasma to lumen
-using indirect active transport twice
-Na+/K+ pump to keep the concentration of sodium in extracellular fluid low
-dicarboxylate (anion) uses indirect active transport from Na+ stored energy to move from extracellular fluid to inside the cell.
-the basolateral organic anion transporter (OAT) transports organic anion to lumen using energy stored in the dicarboxylate gradient

Question 10

Excretion

Answer 10

-depends on urine flow
-> excretion = filtration - reabsorption + secretion

Question 11

Excretion rate

Answer 11

urine flow x urine [x]

Question 12

Clearance

Answer 12

excretion (amt/time) / plasma[x] (vol/time)
“volume of plasma cleared of substance (x) per time”

Question 13

Clearance of creatine or inulin

Answer 13

-neither reabsorbed nor secreted
-ex/ plasma [x]
ex: 4 inulin/ 4/100 = 100 mL/min
-it’s equal to GFR
-if filtration and excretion are the same, then there is no net reabsorption or secretion, and the clearance of a substance equals the GFR

Question 14

Clearance of glucose

Answer 14

clearance of glucose would be zero because glucose is not excreted.
-100% reabsorption

Question 15

Clearance of urea

Answer 15

-net reabsorption
-Clearance < GFR
-anytime clearance is less than GFR we get net reabsorption

Question 16

Clearance of penicillin

Answer 16

-net secretion
-any time you have clearance is greater than GFR= net secretion

Question 17

Micturition