Lecture 10: Regulation of Na Balance and Extracellular Fluid Volume (Bolser) Flashcards Preview

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Flashcards in Lecture 10: Regulation of Na Balance and Extracellular Fluid Volume (Bolser) Deck (30):
1

what does Na balance determine?

the size of the ECF (extracellular fluid) and long term regulation of blood pressure

2

what determines filtered load of Na?

GFR (glomerular filtration rate)

3

what regulates Na excretion?

autoregulation of GFR buffers changes in Na excretion that might occur as a result of large changes in blood pressure

4

what is tubuloglomerular feedback?

it involves the macula densa - "the salt detectors."

when they notice that Na is increased, it triggers a DECREASE in GFR

5

what is glomerulotubular balance

in NORMAL conditions, the rate of proximal tubular Na reabsorption is adjusted to match the filtration rate by reabsorption of a relatively constant fraction of filtered Na.

It buffers the Na excretion when actue changes in GFR change the filtered load of Na.

6

mechanisms of glomerulotubular balance

1. an increase in the filtered load of organic acids cause a proportional increase in Na reabsorption

2. peritubular capillary starling forces - Increased GFR leads to less water leaving the glomerular capillaries and entering the peritubular capillaries resulting in an increase in peritubular capillary oncotic pressure and a decrease in peritubular capillary hydrostatic pressure. this favors fluid flow from interstitium into the capillaries (reabsorption).

3. loss of glomerulotubular balance during increased Na uptake. GFR increases but percentage of Na reabsorbed drops so the increased Na load is excreted.

7

what is most important about glomerulotubular balance?

even with wildly changing BP and transient increases in filtered load, starling forces are activated so that sudden changes in filtered load are compensated and the net effect is that 2/3 of Na are reabsorbed.

8

what allows Na loads to be excreted with a increase in BP?

hydrostatic pressure increases

fluid uptake into peritubular capillaries decreases

tubular Na reabsorption decreases

Na excretion increases

9

what allows Na loads to be excreted with an increase in extracellular fluid volume?

oncotic pressure decreases

fluid uptake into peritubular capillaries decreases

tubular Na reabsorption decreases

Na excretion increases

10

what effect does aldosterone have on the distal tubule and collecting duct

it acts on principal cells to increase Na lumen permeability to increase Na reabsorption

11

aldosterone does what 3 things to increase Na permeability

1. increases permeability of the luminal border of the cell to Na

2. increased quantity of Na, K-ATPase

3. increased amount of ATP to the ATPase to increase enzyme activity

12

what 4 things regulate aldosterone release?

1. low Na in diet + low Na plasma = increase aldosterone release

2. increase K in plasma = increase aldosterone release

3. increased plasma angiotensin II = increase aldosterone release

4. ACTH necessary for basal release

13

a decrease in plasma volume does what to Na excretion?

decreased plasma volume causes
|
increase renin secretion
|
increase plasma angiotensin
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increase aldosterone secretion
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increase plasma aldosterone
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increase tubular reabsorption of Na
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DECREASED Na excretion

14

what effect does an increase in plasma K have in K excretion?

increased plasma K
|
increase aldosterone secretion
|
increase plasma aldosterone
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increase tubular secretion of K
|
Increase K excretion

15

what is the main way K is secreted?

through principal cells in collecting ducts

16

what can cause increases in plasma potassium?

metabolic acidosis, trauma and/or dietary issues they trigger the following cascade:

increase K plasma
|
increase aldosterone secretion
|
increase plasma aldosterone
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increase tubular secretion of K
|
Increase K excretion

17

what controls the release of renin

1. afferent arteriole baroreceptors detect ECF volume

2. macula densa - detect decreases in NaCl tubules stimulates renin

3. increased renal sympathetic nerve activity increases renin release by decreasing renal blood flow

18

what is atrial natriuretic peptide (ANP)

it is a hormone released from atria in response to increased ECF volume.

19

in what ways does ANP increase Na excretion?

increasing GFR,

inhibiting Na reabsorption in collecting duct

inhibits renin and aldosterone secretion

20

when is the sympathetic nervous system important in regulating Na reabsorption?

when ECF (extracellular fluid) volume falls

21

what effect does the sympathetic nervous system have in increasing Na reabsorption?

it enhances the release of renin and influences peritubular capillary hydrostatic pressure through an increase in the filtration fraction. this promotes a greater proportion of the renal plasma being diverted into Bowman's capsule before it reaches the peritubular capillaries. this results in a decrease in peritubular capillary hydrostatic pressure which favors Na reabsorption.

22

what is the filtration fraction formula?

FF = GFR / RPF

23

what effect does an increase in GFR have on Na?

it INCREASES Na excretion

24

what are diuretics?

compounds that alter urine flow primarily by influencing Na reabsorption in various locations of the nephron

25

wht kind of diuretic is the strongest? what is an example of this type of diuretic?

loop diuretics

example of a loop diuretic is lasix (aka furosemide)

26

what do loop diuretics do?

cause Na to remain in diluting segments

27

what is the action of lasix?

inhibits Na reabsorption in thick ascending limb

as a result more Na is delivered to distal nephron and tubular fluid entering the cortex is not diluted. in the presence of ADH less water can be reabsorbed.

less Na is transported into the medullary interstitium, so the medullary concentration gradient is reduced, resulting in less water reabsorbed in the medullary collecting ducts

the end result is diuresis and natriuresis (Na excretion)

28

action of thiazides

1. inhibition of Na-Cl cotransporter in the distal tubule

this results in more Na and water being delivered to the colecting ducts and a diuresis and naturesis

29

what are some examples of potassium-sparing diuretics?

amiloride and spironolactone

30

action of potassium-sparing diuretics

Na channel blockers prevent Na from entering cells thereby reducing reabsorption and inducing diuresis and natriuresis

aldostereone receptor blockers prevent hte actions of aldosterone, resulting in same effects

both types of diuretic reduced the amount of K that is secreted by reducing the availability of intracellular Na.

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