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GERR > Tubular function > Flashcards

Tubular function Flashcards

1
Q

Where does reabsorption take place in the nephron?

A

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

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2
Q

What are the types of movement from fluid to blood?

A
  • paracellular (between cells)
  • Transcellular (through cells)
  • Reabsorption (filtrate to blood)
  • Secretion (blood to filtrate)
  • Excretion (Elimination through urine)
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3
Q

What are the types of transcellular movement?

A
  • 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)
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4
Q

Where is glucose reabsorbed?

A

Early in PCT

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5
Q

What transporters are used to reabsorb glucose into blood?

A

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

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6
Q

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

A
  • Rate at which transporters can operate

- Na gradient substantial so doesn’t affect absorption

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7
Q

In what condition is the transport maximum exceeded?

A

Diabetes

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8
Q

What is the cause of glucosuria outside diabetes?

A
  • Genetic dysfunction in reabsorption (Fanconi syndrome)

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

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9
Q

Where are Amino Acids reabsorbed?

A

Early in PCT

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10
Q

What transporters are used for movement of AAs?

A

Secondary active transport using sodium and chlorine concentration gradients

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11
Q

What can cause Aminoaciduria?

A
  • congenital disorders of AA metabolism where too many AAs (can’t all be reabsorbed)
  • Transport protein defects (Hartnup disease)
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12
Q

Where is sodium reabsorbed?

A 
PCT 70% 
Ascending Loop Henle 20%
DCT 5%
Collecting duct 3%
Excretion of 2%
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13
Q

What transporters are used to move sodium in the PCT?

A
  • sodium-glucose pump
  • sodium-aminoacid pump
  • sodium-hydrogen pump
  • sodium potassium ATP pump (movement from PCT to blood)
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14
Q

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

A
  • Na/K/Cl co-transporter

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

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15
Q

What transporters are used for sodium movement in DCT?

A
  • Na/Cl transporter
  • facilitated diffusion of just sodium
  • Na/K ATP pump still
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16
Q

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

A
  • facilitated diffusion Sodium transporter

- Na/K ATP pump

17
Q

What are the limiting factors in reabsorption of sodium?

A
  • in PCT and loop of henle limiting factor is gradient

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

18
Q

What is the function of aldosterone in sodium reabsorption?

A
  • aldosterone increases Na/K ATP pump expression so more sodium can be reabsorbed into blood
  • by increasing aldosterone can stop any excretion of sodium
19
Q

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

A
  • 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
20
Q

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

A

Spironolactone

21
Q

What transporter do Thiazides act on?

A

Na/Cl transporter

22
Q

What transporter do loop diuretics act on?

A

Na/K/Cl transporter

23
Q

What transporter do SGLT2 inhibitors act on?

A

Na/Gluc transporter

24
Q

What ion is used in reabsorption of water?

A

Sodium

water follows movement of sodium

25
Q

What forms of movement are used in reabsorption of water?

A

Paracellular and transcellular

26
Q

Where is water reabsorbed?

A

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

27
Q

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

A

AQP2 (aquaporins)

- inserted into ducts to increase movement of water back into blood

28
Q

Explain the counter-current multiplier mechanism?

A
  • 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
29
Q

How does filtrate concentration change in the loop of henle?

A

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

30
Q

Where is urea reabsorbed and secreted in the nephron?

A
  • PCT 50% reabsorbed
  • Loop of Henle all of that 50% secreted back into filtrate
  • collecting duct 80% reabsorbed
  • excrete 20%
31
Q

By what process is urea reabsorbed in the PCT?

A

Passive diffusion

32
Q

Why is urea reabsorbed in the Collecting duct?

A

Contributes to loop and medullary interstitial hyperosmolarity needed for water reabsorption

33
Q

What is tubular secretion?

A

removal of substances from interstitium or blood to go into filtrate

34
Q

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

A
  • Potassium
  • Hydrogen
  • Urea
35
Q

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

A
  • Creatinine

- Uremic toxins

36
Q

What substances are secreted in the nephron?

A
  • H, K and urea
  • metabolites and toxins
  • Drugs cleared
37
Q

What substances can be used to assess the kidney clearance?

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

GERR (49 decks)

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