Tubular function

Question 1

Where does reabsorption take place in the nephron?

Answer 1

All epithelial cells lining nephron carry out reabsorption but primarily in Proximal convoluted tubule

Question 2

What are the types of movement from fluid to blood?

Answer 2

• paracellular (between cells)
• Transcellular (through cells)
• Reabsorption (filtrate to blood)
• Secretion (blood to filtrate)
• Excretion (Elimination through urine)

Question 3

What are the types of transcellular movement?

Answer 3

• Passive diffusion
• Facilitated diffusion (with grad using transporter)
• Primary active transport (against grad using transporter)
• Secondary active transport (One molecules with grad but transporter carries another molecule with it)

Question 4

Where is glucose reabsorbed?

Answer 4

Early in PCT

Question 5

What transporters are used to reabsorb glucose into blood?

Answer 5

1) SGLT2 97%
2) SGLT1 3%
both use secondary active transport, sodium travels with concentration gradient and glucose is carried across with it
3) GLUT2 and GLUT1 transport from cells of PCT to blood

Question 6

What factors affect the transport maximum of glucose and amino acids?

Answer 6

• Rate at which transporters can operate

- Na gradient substantial so doesn’t affect absorption

Question 7

In what condition is the transport maximum exceeded?

Answer 7

Diabetes

Question 8

What is the cause of glucosuria outside diabetes?

Answer 8

• Genetic dysfunction in reabsorption (Fanconi syndrome)

- Can be induced by action of SGLT2 inhibitors e.g. Gliflozin

Question 9

Where are Amino Acids reabsorbed?

Answer 9

Early in PCT

Question 10

What transporters are used for movement of AAs?

Answer 10

Secondary active transport using sodium and chlorine concentration gradients

Question 11

What can cause Aminoaciduria?

Answer 11

• congenital disorders of AA metabolism where too many AAs (can’t all be reabsorbed)
• Transport protein defects (Hartnup disease)

Question 12

Where is sodium reabsorbed?

Answer 12

PCT 70% 
Ascending Loop Henle 20%
DCT 5%
Collecting duct 3%
Excretion of 2%

Question 13

What transporters are used to move sodium in the PCT?

Answer 13

• sodium-glucose pump
• sodium-aminoacid pump
• sodium-hydrogen pump
• sodium potassium ATP pump (movement from PCT to blood)

Question 14

What transporters are used to move sodium in the ascending loop of henle?

Answer 14

• Na/K/Cl co-transporter

- Na/K ATP pump still used to move into blood

Question 15

What transporters are used for sodium movement in DCT?

Answer 15

• Na/Cl transporter
• facilitated diffusion of just sodium
• Na/K ATP pump still

Question 16

What transporters are used to move sodium in the Collecting duct?

Answer 16

• facilitated diffusion Sodium transporter

- Na/K ATP pump

Question 17

What are the limiting factors in reabsorption of sodium?

Answer 17

• in PCT and loop of henle limiting factor is gradient

- DCT and collecting duct (no gradient used) so aldosterone used as rate limitation

Question 18

What is the function of aldosterone in sodium reabsorption?

Answer 18

• aldosterone increases Na/K ATP pump expression so more sodium can be reabsorbed into blood
• by increasing aldosterone can stop any excretion of sodium

Question 19

Why is sodium important in treatment of hypertension and heart failure?

Answer 19

• If want to reduce blood pressure then reducing amount of sodium in blood will reduce the amount of water and so lowers pressure
• More excreted sodium means less sodium in blood
• heart therefore doesn’t have to work as hard

Question 20

What drugs are used to block Na/K ATP transporter?

Answer 20

Spironolactone

Question 21

What transporter do Thiazides act on?

Answer 21

Na/Cl transporter

Question 22

What transporter do loop diuretics act on?

Answer 22

Na/K/Cl transporter

Question 23

What transporter do SGLT2 inhibitors act on?

Answer 23

Na/Gluc transporter

Question 24

What ion is used in reabsorption of water?

Answer 24

Sodium

water follows movement of sodium

Question 25

What forms of movement are used in reabsorption of water?

Answer 25

Paracellular and transcellular

Question 26

Where is water reabsorbed?

Answer 26

PCT 65% Desc Loop Henle 15% ADH dependant reabsorption in DCT and Collecting duct

Question 27

What transporter molecule is used by ADH to affect water reabsorption?

Answer 27

AQP2 (aquaporins) | - inserted into ducts to increase movement of water back into blood

Question 28

Explain the counter-current multiplier mechanism?

Answer 28

- Loop of Henle filtrate is flowing down descending and up ascending - whereas the Vasa Recta blood next to the loop is flowing the opposite direction - Na actively pumped out of ascending loop Henle and passively into vasa recta - therefore the further along/ lower down the vasa recta the more sodium - due to high concentrations of sodium as vasa recta moves up the descending loop of henle lots of water is reabsorbed - this then means filtrate of descending limb is becoming more concentrated which drives the concentration gradient when its moves along to the ascending limb

Question 29

How does filtrate concentration change in the loop of henle?

Answer 29

Getting more and more concentrated in the descending loop and getting less and less concentrated in ascending loop (opposite for blood)

Question 30

Where is urea reabsorbed and secreted in the nephron?

Answer 30

- PCT 50% reabsorbed - Loop of Henle all of that 50% secreted back into filtrate - collecting duct 80% reabsorbed - excrete 20%

Question 31

By what process is urea reabsorbed in the PCT?

Answer 31

Passive diffusion

Question 32

Why is urea reabsorbed in the Collecting duct?

Answer 32

Contributes to loop and medullary interstitial hyperosmolarity needed for water reabsorption

Question 33

What is tubular secretion?

Answer 33

removal of substances from interstitium or blood to go into filtrate

Question 34

What substances are secreted in the nephron in order to control blood plasma

Answer 34

- Potassium - Hydrogen - Urea

Question 35

Give an example of toxins removed in the urine which therefore need to be secreted?

Answer 35

- Creatinine | - Uremic toxins

Question 36

What substances are secreted in the nephron?

Answer 36

- H, K and urea - metabolites and toxins - Drugs cleared

Question 37

What substances can be used to assess the kidney clearance?

Answer 37

- PAH - Cinnamoylglycine Often used to check how well a drug can be cleared