Transport of Ions and Water (B2: W4) Flashcards Preview

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Flashcards in Transport of Ions and Water (B2: W4) Deck (37):
1

Define the different movements that occure in the tubule

  • Filtration - movement of water or solute from the capillaries into the tubular space
  • Secretion - things moving into the tubule
    • Usually from peritubular capillaries
    • Or ammonium from epithelial cells
  • Reabsorption - from tubule to peritubular space
  • Excretion - what gets out in the urine

2

What are the routes by which molecules pass in and out of the tubule?

  • Transcellular - moves through two membranes
    • Apical membrane (luminal)
    • Laminal membrane 
  • Paracellular - between tight junctions

3

What kind of transporters are used in the tubule?

  • Active transport 
    • Primary - use ATP
    • Secondary (coupled) - use concentration gradient
      • Symport
      • Antiport
  • Passive transport
    • Simple diffusion
    • Uniport facilitated diffusion

4

How is sodium moved out of the tubular lumen in the PCT?

Glu/Amino acid symporter

H antiporter

5

How is sodium moved out of the tubular lumen in the thick ascending limb of loop of Henle?

K symporter

Cl symporter

Loop diuretics affect this - block transport

6

How is sodium moved out of the tubular lumen in the DCT?

Cl symporter

 

7

How is sodium moved out of tubular lumen in collecting duct?

Ion channel

Aldosterone enhances conductance

8

How is sodium moved into peritubular space?

Na/K ATPase

9

What perentage of sodium is excreted from the original filtered load of 100%?

Fractional excretion = 0.5%

67% of Na is reabsorbed in PCT

10

How is chloride moved up its electrochemical gradient from the tubular lumen?

  • In PCT: antiporter stored energy
  • In ascending loop: K+ symporter
  • In DCT: Na+ symporter

11

How is a concentration gradient for passive Cl reabsorption created?

  • Na is reabsorbed into the body
    • Water follows
    • Causes a negative potetial increase
  • Concentration of luminal Cl increases
    • Now it wants to diffuse out 

12

How does the concentration of sodium change along the proximal tubule?

Na concentration doesn't change

Water goes with it

Concentration stays the same as a result

13

How does the concentration of chloride change along the proximal tubule?

Cl increases slightly and then plateaus

As water and sodium leave, chloride gets concentrated 

Enough to support passive reabsorption of Cl

14

How does the concentration of inulin change along the proximal tubule?

Concentration of inulin continues to increase

It is stuck in the tubule and cannot be reabsorbed into body

As water is removed, it becomes more concentrated

15

What is the significance of potassium homeostasis?

Need a balance between what is consumed and what is excreted

  • Keep a relatively low extracellular concentration
  • Important to get it into cells from extracellular space

16

How do hydrogen and potassium behave in the case of metabolic acidosis?

  • pH outside of the cells decreases
    • H+ is high
  • H+ moves into cells
  • Shifts K+ out of cells

17

How do hydrogen and potassium behave in the case of metabolic alkalosis?

  • pH outside of the cells increases
    • Decrease in H+
  • H+ moves out of cell
  • K+ moves into cell

18

How do hydrogen and potassium behave in the case of hypokalemia?

  • K+ concentration outside of cells decreases
  • K+ moves out of cell
  • H+ moves into cell
    • Extracellular pH increases

19

How do hydrogen and potassium behave in the case of hyperkalemia?

  • Extracellular K+ increases
  • K+ moves into cell
  • H+ moves out of cell
    • Extracellular pH decreases

20

What direction is potassium shifted in response to consuming a meal?

Insulin works to shift K into cells

Indirectly stimulates Na-H antiporter

21

What effect do ß agonists have on potassium concentration?

ß agonists shift K into cells

Directly stimulate Na-K ATPase pump

22

What effect does aldosterone have on potassium concentration?

Moves K into cells

Stimulates pump

23

What effect does exercise have on potassium concentration?

Moves K out of cells

24

How does most potassium leave the tubular lumen?

Through intercellular channels

25

How is potassium handled in the distal tubule and collecting ducts?

Potassium is secreted by principal cells 

26

How much potassium is excreted from the initial filtered load of 100%?

Fractional excretion = 10-20%

  • Potassium concentration outside of cells is really low
  • Need to excrete a greater percentage
  • Collecting duct is sensitive to aldosterone
    • Causes secretion

27

What two physiolgoical factors affect potassium secretion?

  1. Intracellular potassium
  2. Aldosterone

28

How does aldosterone regulate potassium secretion?

  • Aldosterone increases Na conductance
    • Na moves out of collecting duct
    • Causes depolarization
  • Potassium moves in as sodium rushes out

29

What are the two mechanisms for release of aldosterone from the adrenal gland?

  1. Blood pressure pathway that we know (angiotensin II)
  2. An increase in potassium directly stimulates aldosterone release from the adrenal gland

30

How does a blocked aldosterone system affect the plasma concentration of potassium?

​Blocked aldosterone: increase in potassium intake increases plasma concentration of potassium

  • As serum potassium concentration goes up, aldosterone goes up
  • The amount of potassium consumed does not normally affect potassium concentration

31

How does potassium consumption affect potassium excretion?

The more potassium consumed, the more excreted 

32

Which are the potassium losing diuretics versus the potassium sparing diuretics?

  • Potassium-losing
    • Furosemide
    • Thiazide
  • Potassium-sparing
    • Amiloride

33

Why is furosemide a potassium-losing diuretic?

Blocks transporter in DCT

  • Na and water are not reabsorbed, excess remains in tubule
  • Flow is increased
  • Membrane is depolarized
    • Enhances K secretion 

NaCl excretion increases, K excretion increases

Thiazide works the same way

34

Why is amiloride a potassium-sparing diuretic?

Works on aldosterone sensitive conductance

  • Blocks K conductance
  • Membrane hyperpolarizes
    • No driving force for K to be secreted

Flow increases, NaCl excretion increases, K is spared

35

What is Bartter's syndrome (type I)?

Mutation of Na/K/Cl transporter in thick ascending limb

  • Acts like a loop diuretic
  • Potassium levels decrease
    • Alkalosis
    • Polydipsia (thirst)
    • Polyuria
    • Normal-low blood pressue

36

What is Gitelman's syndrome?

Mutation of Na/Cl transporter in distal tubule

  • Acts like a thiazide diuretic
  • K decreases
    • Low potassium
    • Alkalosis
    • Polydipsia
    • Polyuria
    • Normal-low blood pressure

37

What is Liddle's syndrome (pseudohyperaldostronemia)?

Incrased number and open time of principal cell sodium channels

  • Like a K sparing diruetic
  • K concentration stays the same
    • Low potassium levels
    • Alkalosis
    • Hypertension