Kidney: Glucose Reabsorption

Question 1

Site of Glucose reabsorption in kidney

Answer 1

all in early proximal tubule

Question 2

Describe mechanism of Glucose reabsorption

Answer 2

At luminal border:
* Glucose & Na+ bind to SGLT-2 (co-transport)
* Na+ diffuses along electrochemical gradient
* glucose co transported against concentration gradient

At basolateral border: glucose carries into ISF by facilitated diffusion through GLUT-2 (down chemical gradient)

Question 3

difference between SGLT-2 in early PCT & late PCT in glucose reabsorption

Answer 3

• Early PCT: reabsorbes 97% of filtered glucose
• Late PCT: reabsorbes 3% of filtered glucose

Rendering Urine Nearly free of glucose

Question 4

Glucose transport at luminal border is inhibited by

Answer 4

• Ouabain: blocks Na+K+ pump
• Phlorizin: competetive inhibition of SGLT-2

Question 5

Management of hyperglycemia cause by type 2 DM maintained by glucose reabsorption

Answer 5

SGLT-2 inhibitors (canagliflozin, dapagliflozin)

Question 6

transport maximum of glucose is determined by

Answer 6

number of glucose carriers in PCT

Question 7

TmG value in male & female

Answer 7

• Male: 375mg/ min
• Female 300mg/ min

Question 8

definition of renal threshold of glucose

Answer 8

plasma glucose level at which glucose begins to appear in urine,

Question 9

Value of Renal threshold of glucose in arterial & venous blood

Answer 9

• Arterial: 200mg/dl
• Venous: 180mg/dl

Question 10

Relationship between Plasma glucose level & filtered load of glucose

Answer 10

Linear direct relationship

Question 11

Describe relationship between plasma glucose & Glucose reabsorbed

Answer 11

at plasma glucose less than 200mg/dl:
* All filtered glucose is reabsorbed (many SGLT carriers)
* Filtration=reabsorptiom
* Reabsorption curve is (initially) Identical to Filtration curve

at plasma glucose more than 200mg/dl (200-300):
* curve shows splay/ bending
* some filtered glucose is not reabsorbed due to heterogenity of TmG of nephrons

at plasma glucose more than 300mg/dl:
* No increase in rate of reabsorption
* Carriers are fully saturated
* Maximal TmG

Question 12

Describe relationship between plasma glucose & Glucose excreted

Answer 12

Plasma concentration less than 200mg/dl:
* No excretion of urine

Plasma concentration more than 200mg/dl (200-300):
* some glucose excreted

Plasma concentration more than 300mg/dl:
* Excresion curve becomes parallel to filteration curve
* additional filtered glucose is excreted

Question 13

Enumerate causes of Glycosuria

Answer 13

• Diabetes mellitus
• Renal Glucosuria

Question 14

Explain how Diabetes mellitus causes glucosuria

Answer 14

high plasma glucose level exceeding renal threshold of glucose

Question 15

Explain pathology of renal glucosuria

Answer 15

• there is defect in glucose transport
• renal threshold decreases
• TmG decreases
• Increase excretion of glucose
• thus leading to Osmotic diuresis & loss of Electrolytes (K+ & Na+)