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ESA3 - Urinary System > Control of Blood Volume > Flashcards

Control of Blood Volume Flashcards

1
Q

What ion usually goes along with Na+ to maintain electroneutrality?

A

Cl-

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2
Q

Why not just add/remove water to or from the plasma to change its volume?

A

Because that would change the plasma osmolarity

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3
Q

Where in the nephron does the majority of sodium reabsorption occur?

A

Proximal tubule

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4
Q

Describe the fluid that leaves the proximal tubule in terms of its osmolarity

A

Isosmotic - because as ions are reabsorbed, water is also reabsorbed maintaining the osmolarity of the fluid in the PCT

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5
Q

Describe the permeability of the thin descending limb of the loop of henle

A

Very permeable to water, less to ions

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6
Q

What is proximal tubule Na+ reabsorption stimulated by?

A

RAAS

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7
Q

When renal artery BP increases, what causes reduction in sodium reabsoption in the proximal tubule?

A

Reduced number of Na-H antiporter and reduced Na-K-ATPase activity

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8
Q

Where is all the glucose and amino acids reabsorbed?

A

PCT

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9
Q

Where is the majority of sodium, chloride and potassium reabsorbed?

A

PCT

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10
Q

What are the two routes through which reabsorption can take place?

A

Transcellular - through a cell

Paracellular - via the intercellular space between cells

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11
Q

What is the main transporter in the PCT on the basolateral side of cells?

A

3Na-2K-ATPase

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12
Q

What does the basolateral side of cells face?

A

Faces the interstitium

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13
Q

What does the apical membrane face?

A

Lumen

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14
Q

Describe what the NaKATPase does in the tubule

A

Pumps out Na+ ions using active transport

This creates an electrochemical gradient which favours the movement of Na+ into the cell from the apical side

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15
Q

Where in the nephron are there NO aquaporins present?

A

Ascending limb of the loop of henle

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16
Q

Where are AQP1 channels present?

A

PCT and descending loop of henle

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17
Q

Where are AQP2, AQP3 and APQ4 channels present?

A

Collecting ducts

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18
Q

What channels are present in the proximal tubule that involve sodium?

A

1) Na-H antiporter
2) Na-Glucose symporter
3) Na-AA co-transporter
4) Na-Pi

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19
Q

What are the three regions of the proximal tubule and how are these divided?

A

S1, S2, S3

Pars convolute resides in cortex, divided into S1 and proximal part of S2

Pars recta resides in outer medulla - makes up distal part of S2 and S3

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20
Q

What is the S1 segment of the proximal tubule impermeable to and what is the significance of this?

A

Not permeable to urea and Cl-

Their concentration increases in S1 which creates a concentration gradient which is used in the S2 and S3 segments.

In S2 and S3, Cl- can be transported from the lumen of the tubule into the peritubular capillaries either paracellularly or transcellularly down their concentration gradient

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21
Q

How is glucose reabsorbed in the proximal tubule?

A

Transported across apical membrane against their concentration by co-transport - SGLUT transporters move glucose with 2 sodium ions. Then, glucose crosses the basolateral membrane via facilitated diffusion.

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22
Q

How are amino acids reabsorbed in the proximal tubule?

A

Na+/amino acid symporters are present on the apical side of cells in the S1 segment which reabsorbs all the amino acids

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23
Q

What does the Na+/H+ antiporter do in the PCT?

A

Moves Na+ ions in to the tubular cells and expels H+ into the tubule (maintains pH)

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24
Q

How is sodium reabsorbed in the S1 segment of the PCT?

A

1) Na-H exchange
2) Co-transport with glucose (SGLT2)
3) Co-transport with amino acids
4) Co-transport with phosphate

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25
Q

On which membrane is Na-K-ATPase located?

A

Basolateral

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26
Q

On which membrane is the SGLT transporter located?

A

Apical

27
Q

Which is the primary site of sodium reabsorption in the loop of henle?

A

Thick ascending limb

28
Q

How is sodium absorbed in the thick ascending limb?

A

Via NKCC2 on the apical membrane

29
Q

How does the NKCC2 transporter work?

A

Moves one sodium ion, one potassium ion and two chloride ions across the apical membrane

30
Q

How does the sodium potassium ATPase on the basolateral membrane establish an electrochemical gradient?

A

By pumping 3 sodium ions out of the cell and 2 potassium ions into the cell - creating a low intracellular concentration of sodium and also making the inside of the cell negatively charged (meaning sodium can move down its electrochemical gradient through transporters on the apical membrane)

31
Q

In the thick ascending limb, how are potassium ions transported back into the tubule?

A

Via ROMK channels (prevents toxic build up of potassium within the cell)

32
Q

In the thick ascending limb, how are chloride ions transported out of the cell into the tissue fluid?

A

Via CIC-KB channels

33
Q

How does water reabsorption occur in the thin descending limb?

A

Passively, via AQP1 channels

No sodium reabsorption

34
Q

What is Bartter syndrome?

A

Genetic condition caused by mutations in the genes that code for the NKCC2 transporter, apical potassium channel or basolateral chloride ion channel. This results in decreased NaCl reabsorption

Leads to hypokalaemia because more sodium being reabsorbed in the distal tubule leading to increased excretion of K+

Leads to hypovolaemia as decreased reabsorption of NaCl means less osmotic pressure

35
Q

What can be used to treat hypertension by inhibiting the NKCC2 transporter in the thick ascending limb?

A

Loop diuretics

36
Q

How do loop diuretics work?

A

Inhibit NKCC2 in the thick ascending limb
Increase excretion of NaCl in the urine
Reduces water absorption
Therefore reduces plasma volume

37
Q

Describe the histology of PCT cells

A
  • Brush border
  • Large outside diameter
  • Lots of mitochondria
38
Q

Where does sodium reabsorption occur in the nephron?

A

PCT, ascending loop of henle, DCT and collecting duct

39
Q

What happens when all the glucose transporters are saturated with glucose?

A

Glucose goes in the urine

40
Q

When are glucose transporters fully saturated?

A

At 11 mmol/L

41
Q

On which membrane is ROMK found in the thick ascending limb?

A

Apical membrane

42
Q

On which membrane is NKCC2 found in the thick ascending limb?

A

Apical membrane

43
Q

What drug inhibits the action of the Na-H exchanger in the PCT?

A

Amiloride

44
Q

What transporter is regulated by parathyroid hormone?

A

Sodium dependent phosphate transporter in the proximal tubule

45
Q

How is albumin reabsorbed in the proximal tubule?

A

Albumin taken in to tubular cells via receptor mediated endocytosis

Then lysosome breaks it down into its amino acids and the amino acids are transported into the capillary via passive amino acid transporters

46
Q

What happens to the K+ and Cl- after they are taken into the cell with sodium via NKCC2 in the thick ascending limb?

A

K+ diffuse via ROMK back into lumen

Cl- ions move into interstitium

47
Q

In the thick ascending limb, why is it vital that K+ diffuses back into the filtrate after entering tubular cells via NKCC2?

A

In order to maintain activity of NKCC2
Otherwise there would be a lower concentration of K+ in the lumen so K+ would want to move from the tubular cells into lumen rather than the other way around

48
Q

Why is the ascending limb known as the diluting segment?

A

Because the ascending limb reabsorbs NaCl but not water

Descending limb reabsorbs water but not NaCl

49
Q

Describe the osmolarity of the tubule fluid leaving the loop

A

Hypo-osmotic (more dilute) compared to plasma

50
Q

What is the role of the early DCT?

A

Absorption of ions, including Na+ , Cl- and Ca2+

51
Q

How does NaCl enter across the apical membrane in the early DCT?

A

Via electroneutral NCC transporter

52
Q

What drug acts on the NCC transporter in the DCT?

A

Thiazides

53
Q

What transporter does amiloride target?

A

ENaC in DCT

54
Q

How does NaCl enter and leave the tubular cell in the late DCT?

A

Enters via NCC and ENaC on the apical membrane

Leaves via NaKATPase on the basolateral membrane

55
Q

What diuretics is ENaC sensitive to?

A

Amiloride

56
Q

Is movement through ENaC electroneutral?

A

No, difference drives paracellular Cl- ion reuptake

57
Q

Describe the osmolarity of the fluid leaving the DCT

A

More hypo-osmotic - further dilution has occurred

58
Q

Where is a major site of calcium reabsorption?

A

DCT

59
Q

Describe calcium reabsorption in the DCT

A

There is apical calcium transport - then cytosolic calcium immediately binds to calbindin which shuttles calcium to the basolateral aspect of the DCT cell.

It is then transported out via NCX

60
Q

What are the two main types of cell found in the collecting duct?

A

Principal cells and intercalated cells

61
Q

How do principal cells of the CD reabsorb sodium?

A

Via ENaC

62
Q

What do intercalated cells do?

A

Secrete either H+ or HCO3- to alter blood pH

63
Q

What does spironolactone do?

A

Acts as an antagonist of aldosterone receptor in the collecting duct - reduces sodium reuptake

ESA3 - Urinary System (16 decks)

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