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Flashcards in K Regulation Deck (56):
1

What is renal secretion?

moving a substance from the blood into the lumen of a nephron

2

What is the mechanism through which secretion of substances takes place?

Active pumps on the basolateral side of the nephron tubule cell, establishing a gradient (high inside cell)

3

Apical part of a lumen cell = ? Basolateral = ?

Apical = The part that faces the tubule lumen

Basolateral = the part that faces the interstitium

4

Secretion of organic cations through the tubule cell is different from secretion of organic anions. Why?

Since the electrical force on the ion from the negative membrane potential favors movement of the cation into the cell, from the interstitial fluid.

5

What is the significance of the fact that many molecules in the blood use the same transporter to be secreted into the lumen of the nephron?

secretion of one substance might be decreased in the presence of one of its competitions for the carrier protein

6

Why is it that a substance that is secreted may not always stay in the tubular lumen? (2)

There can be back leak through the "tight" junctions

pH of urine can affect charge, and thus solubility of substance

7

What happens with ASA when the urine is highly acidic (as in acidemia)?

Since ASA is an organic acid, low pH will protonate it, and cause it to leak back in

8

How can you treat overdose on ASA via the renal tubules?

Give lots of bicarb

9

Organic cations are also called what?

Organic bases

10

If the dissociated state of an organic base predominates, what will predominate: excretion or reabsorption?

Excretion

11

Acidification of urine increases or decreases reabsorption of organic bases?

decreases

12

What are atropine, morphine and cimetidine--organic acids or bases?

Organic bases

13

Excretion = ?

Secretion + filtration

14

Why is PAH used to demonstrate renal plasma flow?

For the most part, it mostly cannot reabsorbed, only filtered and secreted

15

What is the point at which the renal nephrons secrete the maximum amount of a substance?

Transport maximum

16

What is the equation for renal plasma flow?

[(Upah)(V) / Ppah ]/ (1-hematocrit)

17

Why isn't PAH perfect?

Some is absorbed from the nephron

18

How do you calculate the filtration fraction?

GFR/ ERFP

19

What is the filtration fraction?

The percent of the plasma delivered to the kidneys that is filtered

20

Why is K so important to homeostasis?

Establishes membrane potentials (like in the heart)

21

Is K bound to plasma proteins? What is the consequence of this?

No, thus it is freely filtered at the glomerulus

22

Where does most K reabsorption take place? How regulated is this?

Ascending loop of Henle

Essentially unregulated

23

What/where are the regulated parts of K reabsorption?

Distal tubule and collecting duct

24

What happens to the tubules in hyperkalemia?

High K+ stimulates the Na/K+ATPase pump on basolateral surface. This transports K+ into the tubule cell. K+ can then flow down its electrochemical gradient through open K+ channels in the luminal membrane.

25

What is the chemical that stimulates K secretion (besides K itself)?

Aldosterone

26

What happens to the renal tubule in hypokalemia?

the Na+/K+ATPase pump is inhibited. The collecting duct intercalated cells have a K+ resorption pump on their luminal membrane and this pump is continually active.

27

True or false: The collecting duct intercalated cells have a K+ resorption pump on their luminal membrane and this pump is continually active. Only the Na/K pump on the basolateral surface of tubule cells are regulated

True

28

What is the main effect of aldosterone on K reuptake/secretion?

increase the number of active epithelial sodium channels (ENaCs) in the collecting ducts, increasing the reabsorption of Na+ and increase the secretion of K+.

29

What is the effect of ANP on ENaC? What is the effect on plasma [K]?

Inhibited, leading to increased [K]

30

In what cells are the Na/K pumps regulated within a nephron?

Principle cells

31

What are the two ways discussed in lecture that increases aldosterone production?

1. Increased plasma [K]
2. Activation of renin-angiotensin system

32

What are the five effects of aldosterone?

1. Increase the amount of Na/K-ATPase in the basolateral membrane
2. Increase expression of EnaC in apical membrane
3. Elevate SGK1 to further 1 and 2
4. Stimulates CAP1 to activate ENaC
5. Increases K channels

33

What is the effect of ouabain?

inhibits Na/K pump

34

What is the effect of a diuretic? What does this do to K secretion?

inhibits the reabsorption of water at some point in the nephron, causing water and K to be secreted

35

What is the effect of loop diuretics?

Block the Na/K/Cl pumps in the thick ascending loop of Henle on the luminal side. This leads to a decrease in water reabsorption, because there is a lower gradient of solutes

36

What lab value (discussed in this lecture specifically) should be closely monitored with patients on diuretics?

[K]

37

What is the MOA of thiazide diuretics?

inhibit NaCl reabsorption in the early distal tubule, thus inhibiting water following

38

What causes the increase in K secretion to increased flow?

Cilia bending causes cascade to be activated, Ca activation, and K channels recruited

39

What are the potassium sparing diuretics? How do they work?

Aldosterone inhibitors, which will decrease Na and water reabsorption

40

What is a complication of using aldosterone inhibitors?

Hyperkalemia

41

What is the effect of metabolic alkalosis on the Na/K ATPase on the basolateral membrane of principal cells of the late distal convoluted tubule and collecting ducts? What happens to the intracellular [K]?

Increases x2

42

What are the three loop diuretics?

Furosemide
Ethacrynic acid
Bumetaide

43

Which side of the principal cells is the Na/K ATPase on: the basolateral or the luminal side?

Basolateral

44

Why does the reabsorption of other positive ions decrease in response to the presence of loop diuretics?

The drug lowers the positive Electrochemical gradient in the lumen

45

What is the major source of K loss in the nephrons: the inactivation of the pump or the increase flow, leading to increased K excretion

Increased flow

46

What causes the increased K excretion seen in metabolic alkalosis?

Increases the Na/K ATPase action in the distal tubule, increasing K intake into the cell from the ECF, and thus causing it to flow into the lumen

47

Chronic metabolic alkalosis + decreased ECF results in a significant increase in K excretion. Why?

Increases aldosterone d/t lower BP. This activates the Na/K pump

48

What is the effect of acidosis on [K]? How?

Sometimes causes hyperkalemia.

Caused by an intake of H into cells, leading to outflow of K to maintain electric neutrality

49

What is the effect of aldosterone on K secretion? How?

Increases via increasing the Na/K pump action

50

What controls secretion of aldosterone?

plasma [K]

51

What is Conn syndrome, and how does it relate to K secretion?

Causes excess aldosterone, thus increases K secretion

52

What is Addison's disease, and how can it cause Hyperkalemia?

Inhibition of aldosterone, leading to less function of the Na/K pump

53

What is the effect of beta blockers on K?

May cause hyperkalemia

54

What is the effect of catecholamines on plasma [K]?

Hypokalemia

55

What is the main cell type that is involved in K regulation?

Principle cells of the distal tubule

56

What are the three ways that an increased plasma [K] will increase K secretion?

1. Increases Na/K ATPase activity
2. Increased gradient potential
3. Increased aldosterone synthesis