Lecture 38: Renal Systems 3

Question 1

How is filtered load calculated and what does it measure?

Answer 1

Filtered load = GFR x plasma [S]
* Measures total amount of a substance filtered into Bowman’s space

Question 2

How do you determine whether a substance undergoes net secretion or reabsorption in the nephrons?

Answer 2

By comparing filtered load (100%) and excretion of a substance
- If excreted amount < filtered load, then reabsorption has occurred
- If excreted amount > filtered load, secretion has occurred

Question 3

What is the normal plasma [glucose] value?

Answer 3

1g/L

Question 4

How is the filtered load of glucose calculated and what is the normal value?

Answer 4

GFR x plasma [glucose]
= 0.125L/min x 1g/L
= 0.125g/min

Question 5

How much glucose is reabsorbed across kidney proximal tubule epithelia?

Answer 5

100%

Question 6

How is glucose transported across kidney proximal tubule epithelia?

Answer 6

1. SGLTs: apical, sodium-dependent
2. GLUTs: basolateral, sodium-independent - only dependent on glucose gradient

Question 7

How is glucose absorbed in the GI tract?

Answer 7

Only absorbed via SGLT1 and GLUT2

Question 8

How is glucose re-absorbed in the early proximal tubule and how much?

Answer 8

SGLT2 reabsorbs 90% of filtered glucose paired with GLUT2 on the basolateral side

Question 9

How is glucose re-absorbed in the late proximal tubule and how much?

Answer 9

SGLT1 reabsorbs 10% of filtered glucose paired with GLUT 1 on the basolateral side

Question 10

Compare the main glucose transporters in the kidney vs. the intenstine:

Answer 10

Kidney: SGLT2
Intestine: SGLT1

Question 11

Is filtered load saturable and why?

Answer 11

No as it’s freely filtered from plasma

Question 12

Describe whether glucose transport can be saturated or not:

Answer 12

Can be saturated if the plasma [glucose] increases, resulting in excretion of excess glucose in the urine

Question 13

At what concentration is the glucose capacity of transporters reached?

Answer 13

~400mg/min - they don’t work fast enough to reabsorb all the glucose

Question 14

What is glucose in the urine indicative of?

Answer 14

Diabetes mellitus

Question 15

What is the function of diuretics?

Answer 15

Increase urine: anti-hypertensive drugs

Question 15

What is a SGLT2 inhibitor (Jardiance) used for?

Answer 15

• Glucose gets excreted instead of reabsorbed
• Lowers blood glucose
• Diabetic drug
• Improves kidney and cardiovascular disease

Question 16

How is blood volume controlled?

Answer 16

1. Osmoreceptors in the brain - trigger vasopressin/ADH to be released
2. Baroreceptors in arteries and heart

Question 17

What cardiac medication is taken to treat hypertension?

Answer 17

Ca2+ antagonists and beta blockers

Question 18

What is the main organ responsible for excreting excess sodium?

Answer 18

Kidney

Question 19

Where is sodium reabsorbed in the nephron?

Answer 19

1. PCT (66%)
2. TAL (25%)
3. DCT (5%)
4. CD (3%)

Question 20

How much sodium is excreted?

Answer 20

0.5-1% of filtered load

Question 20

Describe sodium reabsorption in the thick ascending limb of henle (TAL):

Answer 20

• Semi-tight epithelia: permeable to sodium not water
• Trans (50%) and paracellular (50%)

Question 20

Describe sodium reabsorption in the proximal convoluted tubule (PCT):

Answer 20

• Leaky epithelia
• Trans- and paracellular
• Provides gradient for absorption of essential nutrients
• Isotonic reabsorption - equal amounts of sodium and water

Question 20

What transporter is present in the TAL for sodium reabsorption and what inhibits it?

Answer 20

NKCC2 for 2Cl- and K+
* Loop diuretics (furosemide) inhibit NKCC2, diuresis increases

Question 21

What transporters are present in the PCT for sodium reabsorption?

Answer 21

* SGLT1/2 for glucose * NHE3 for H+

Question 22

What do loop diuretics e.g. furosemide treat?

Answer 22

1. Hypertension to reduce loop volume 2. Edema in lungs and legs

Question 23

How does furosemide reduce blood volume?

Answer 23

25% Na+ and water reabsorption - inhibiting NKCC2 with furosemide controls 25% of water reabsorption

Question 23

What type of epithelia is in the thin descending loop of henle (tDLH)?

Answer 23

Leaky - water reabsorption

Question 24

Where is the final osmolarity of urine determined?

Answer 24

Collecting tubule but the counter-current system helps keep the interstitium hypertonic - further urea reabsorption

Question 24

Describe sodium reabsorption in the distal convoluted tubule (DCT):

Answer 24

* Tight epithelia * Transcellular

Question 25

What transporter is present in the DCT for sodium reabsorption and what inhibits it?

Answer 25

NCC for Cl- * Diuretics (thiazides) inhibit NCC to induce mild diuresis

Question 26

Describe sodium reabsorption in the cortical collecting tubule (CCT):

Answer 26

* Tight tight epithelia * Transcellular * Regulated by hormones (aldosterone)

Question 27

What transporter is present in the CCT for sodium reabsorption and what inhibits it?

Answer 27

ENaC * Diuretics (amiloride) inhibits ENaC- very mild diuresis