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Physiology > Regulation of Na, osmolarity and ECFV > Flashcards

Regulation of Na, osmolarity and ECFV Flashcards

1
Q

Unregulated fluid loss occurs due to

A
  • sweat
  • stool
  • respiratory
    (insensible)
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2
Q

Regulated fluid loss occurs due to

A

Renal

  • urine can vary from 50-1200 mOsm
  • measured as specific gravity (1.002-1.050)
  • obligate urine volume to eliminate waste products
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3
Q

Fluid intake

A

Thirst

- stimulus generates desire for and allow the intake of water

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4
Q

Electrolyte loss

A

Occurs with accompanying water loss

  • unregulated: sweat, stool
  • regulated: renal
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5
Q

Electrolyte intake

A

Cravings or hunger

- depends on availability

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6
Q

Why is the electrolyte balance across cell membranes essential?

A
  • partitioning water between intra and extracellular fluid spaces
  • keeping cells from shrinking/swelling
  • allows for electrical charge related actions
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7
Q

In a person after drinking 1 liter of water:

A 
Little change in 
- plasma mOsm
- urine electrolyte conc. 
Big change in
- urine mOsm
- urine production
*primarily regulated by ADH in the distal segments of the nephron*
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8
Q

What happens when there is excess water in the body?

A

Body fluid osmolarity is reduced, kidney excretes urine with a low osmolarity

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9
Q

What happens when there is a deficit of water in the body?

A

Extracellular fluid osmolarity is high, kidney excretes urine with a high concentration

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10
Q

Kidney can excrete a large volume of dilute urine or a small volume of concentrated urine without major changes in ______

A

Rates of excretion of solutes (Na and K)

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11
Q

____ of sodium and water excretion is regulated reabsorption

A

10%

- one can be regulated independently of the other

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12
Q

Formation of dilute urine

A

Decrease reabsorption of water

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13
Q

How do you decrease reabsorption of water?

A

Decrease ADH release, which decreases water permeability of the distal tubule, cortical and medullary duct

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14
Q

In the proximal tubule, water and solutes are reabsorbed ______

A

At the same pace (iso-osmotic)

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15
Q

Water reabsorption in the thin descending loop

A

Passive due to interstitial concentration gradient

  • unregulated
  • could get renal medullary washout due to overconsumption of water
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16
Q

When the renal medulla is no longer hypertonic, the kidney can no longer ______

A

Concentrate urine

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17
Q

Remaining urine after the thick ascending loop becomes more ____ without _____

A

Dilute; any increase in volume

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18
Q

The ability to form concentrated urine is dependent on what 2 things?

A
  • ADH: production in the CNS and appropriate tubular response
  • renal medullary hypertonicity
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19
Q

Continuous reabsorption of electrolytes adds to _____

A

Increasing renal medullary hypertonicity

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20
Q

What are the 2 basic requirements for forming concentrated urine?

A
  • high level of ADH

- hihg osmolarity of renal medullary interstitial fluid

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21
Q

How does increased reabsorption of water occur?

A

Increase ADH release

  • increases water permeability of distal tubule, cortical and medullary collecting ducts
  • increases urea permeability of medullary collecting duct, which increases medullary tonicity
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22
Q

Countercurrent multiplier mechanism

A

Process by which renal medullary interstitial fluid becomes hyperosmotic
- depends on arrangement of loops of Henle and vasa recta

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23
Q

Factors contributing to renal medullary hypertonicity

A
  • active transport of solutes from thick ascending limb into medullary interstitium without reabsorption of water
  • active transport of Na from medullary collecting ducts into interstitium (increased with aldosterone)
  • facilitated diffusion of urea from medullary collecting ducts into interstitium (ADH)
  • diffusion of small amounts of water into medullary interstitium, which is rapidly removed
  • counter-current multiplier mechanism
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24
Q

Loop of Henle is only able to establish a ______ gradient

A

200 mOsm, before back diffusion of electrolytes results in equilibration

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25
Q

Why are juxtamedullary nephrons most susceptible to NSAID toxicity?

A

O2 tension decreases the deeper you go into the renal medulla, but the tubular epithelial cells are the most metabolically active as we progress to dehydration

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26
Q

What is a major reason for high medullary osmolarity?

A

Active transport of sodium and co transport of potassium, chloride, etc from thick ascending loop into the interstitum

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27
Q

Parallel current flow transfer is dependent on

A
  • diffusion constant
  • time/flow ratio
  • -> less transfer than counter current flow
  • -> once equilibrium is achieved there is no further exchange
28
Q

Counter current flow is dependent on

A
  • diffusion constant (same)
  • time/flow ratio
  • -> overall greater transfer than parallel flow (utilizes whole contact area)
  • -> never reaches equilibrium, will always have a gradient directing flow
29
Q

What helps preserve a high medullary interstitial fluid osmolarity?

A

The fact that the large amounts of water reabsorbed from the cortical collecting tubule is being reabsorbed into the cortex, instead of the medulla

30
Q

What causes urea to diffuse out of the tubule into the renal interstital fluid?

A

High concentration of urea in the tubular fluid of the inner medullary collecting duct
- diffusion facilitated by urea transporters that are activated by ADH

31
Q

Rate of urea excretion is determined by what 3 things?

A
  • concentration of urea in the plasma
  • glomerular filtration rate
  • renal tubular urea reabsorption
32
Q

Where does secretion of urea occur?

A

Thin loop of Henle, from the medullary interstitium

- also facilitated by urea transporter

33
Q

What are 2 features of medullary blood flow that prevent the increase in solute concentration from being absorbed and washed away?

A
  • renal medullary blood flow is only <5% of total renal flow

- vasa recta serves as countercurrent exchangers, minimizing washout of solutes from medullary interstitium

34
Q

Due to hypertonicity of renal medulla, the concentration gradient favors _____

A

Electrolyte movement into the capillary as blood flows out

35
Q

The faster the blood flows, the less time there is to equilibrate which leads to _____

A

Renal medullary washout

36
Q

Does the vasa recta create the medullary hyperosmolarity?

A

No, but it prevents it from being dissipated

37
Q

There is an obligatory ____ required to eliminate metabolic waste products

A

Water load

38
Q

What is the obligatory urine volume dependent on?

A
  • solute load that needs to be eliminated

- max concentrating ability of the kidney

39
Q

_____ the amount of solute and you have to _____ the amount of volume needed to excrete the solute

A

Increase; increase

40
Q

What controls ADH secretion?

A
  • Na
  • osmoreceptor cells stimulate secretion of ADH in response to increases in osmolarity
  • projections from baroreceptors in aortic and carotid sinuses in response to decreased blood volume/pressure
  • neurons that project to thirst centers stimulate drinking
41
Q

Alpha-2-agonist

A

Common class of sedative, causes increased urination due to blocking of ADH

42
Q

Osmolarity has a ______ impact on ADH secretion and thirst stimulation than pressure/volume

A

Greater

- 2-3% increase mOsm = 10-12% decrease ECF in effecting increase ADH

43
Q

Isotonic volume depletion has ______ than hypotonic volume depletion

A

Less impact

44
Q

Blood loss results in loss of fluid and Na ____

A

Equally

- no change in osmolarity

45
Q

How to correct dehydration in a horse undergoing an endurance race?

A
  • sweat is isotonic, so effect of the osmole receptor neurons is not triggered
  • give oral electrolytes to increase osmolarity of the ECF and stimulate the thirst response
46
Q

Why does water follow Na when aldosterone stimulates Na reabsorption?

A

Reabsorption of Na increases plasma Na concentration

47
Q

Blocking the ADH system can result in large changes in _______

A

Osmolarity, as Na intake changes

48
Q

Impairments of urine concentrating ability can cause large changes in _____

A

Osmolarity

49
Q

Loss of solute gradient in renal medulla, causes failure of the counter-current exchange mechanism is the cause of what?

A

Renal medullary washout, or tubular failure to extract electrolytes

50
Q

Diabetes insipidus

A

Lack of production or response to, ADH

  • patient will take in large amounts of water and salt in an effort to maintain blood volume
  • will lead to renal medullary washout, impairing ability to conserve water
51
Q

ECF volume regulation: local renal mechanisms

A
  • changes in GFR
  • changes in tubular reabsorption
  • changes in tubular secretion
  • changes in hormones (local)
52
Q

ECF volume regulation: systemic mechanisms

A
  • changes in hormones (systemic)
  • changes in sympathetic activity
  • changes in blood pressure
  • changes in blood composition
53
Q

ECF volume is mainly determined by _____

A

Intake and output of water and electrolytes (esp. Na)

54
Q

____ of the water we take in is excreted as urine

A

30-50%

55
Q

If total GFR were to drop by 50%, the remaining nephrons will

A

Have to double their GFR to compensate

56
Q

Angiotensin summary

A
  • stimulates aldosterone
  • constricts efferent arterioles
  • directly increases sodium reabsorption
  • increases systemic bp (vasoconstrictor)
57
Q

Angiotensin helps regulate what 3 things by regulating sodium retention?

A
  • blood pressure
  • blood volume
  • extracellular fluid volume
58
Q

Aldosterone summary

A
  • stimulate Na reabsorption
  • H2O tends to follow
  • complete lack of results in relying only on pressure natriuresis, requires close management
59
Q

ADH summary

A
  • promotes water retention
  • excess ADH does not result in great increases in blood volume
  • complete lack of results in relying only on pressure diuresis, requires close management
60
Q

ANP summary

A
  • excretion of more water and sodium
  • increased levels directly inhibits reabsorption of sodium and water by the renal tubules, especially in the collecting ducts
  • also inhibits renin secretion and angiotensin formation, reducing renal tubular reabsorption
61
Q

Sympathetic input plays a role in ____

A

Moderate to severe dehydration or loss of blood volume due to hemorrhage
- pressure receptors in large blood vessels activate sympathetic nervous system when blood volume decreases

62
Q

Pressure natriuresis and diuresis are important regulators of

A

Over consumption and have an impact over a very wide range of intakes and will be effective even without autoregulation

63
Q

The balance between ECF and blood volume is controlled by what?

A

Starlings forces

64
Q

Causes of edema formation

A
  • increased hydrostatic pressure
  • decreased colloidal pressure
  • increased capillary permeability due to inflammation/prostaglandins or endotoxemia
  • lymphatic drainage due to trauma
65
Q

Glomerulonephritis is a common cause of __________

A

Hypoalbuminemia

Physiology (33 decks)

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