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S and P- E and W > Sodium and Water > Flashcards

Sodium and Water Flashcards

1
Q

What causes of dehydration are there? (13)

A 
Vomiting
Diarrhoea
Alcohol
Diabetes mellitus
Diabetes insipidus
Bleeding
Brain injury to posterior pituitary
Post-operative
Sepsis
Anorexia 
Bruns
Earthquakes
Iatrogenic
Exercising
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2
Q

What is the normal difference between intracellular and extracellular osmolality?

A

It is normally the same

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3
Q

How do potassium and sodium levels compare between intracellularly and extracellularly?

A 
K+= High intracellularly and low extracellularly
Na+= Low intracellularly and high extracellularly
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4
Q

Why is regulation of salt more important than regulation of water?

A

If there is a difference in osmolality between the intracellular and extracellular compartment then cells will either pop or shrivel up

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5
Q

What is normal serum sodium concentration?

A

135-145mmol/L

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6
Q

Where is the majority of water in our bodies?

A

Majority is intracellular

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7
Q

What percentage of the body is water?

A

60%

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8
Q

What is the extracellular compartment divided into?

A

Intravascular- 20%

Interstitial- 80%

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9
Q

What is giving IV dextrose like?

A

Water

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10
Q

Describe what happens when you give dextrose IV?

A

The ‘water’ is given directly into the intravascular fluid compartment and this will equilibrate very quickly with interstitial fluid compartment causing an increase in ECF volume (interstitial and intravascular). Water doesn’t rely on active transport and moves down osmotic gradients so will follow glucose into intracellular compartment
End result- Increase in volume of all three compartments

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11
Q

What effect does giving dextrose have?

A

Increases ICF volume

Decrease serum Na+ concentration

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12
Q

Describe what happens when you give isotonic saline (0.9%)?

A

You give it into the intravascular fluid (IV) and because Na+ and water equilibrate very quickly between the interstitial and intravascular compartments you get equilibration across the ECF/ There’s not much change in serum Na+ concentration because you have given an isotonic solution which has a very similar Na+ concentration to normal ECF. Because the solution is isotonic, there’s no difference in concentration/osmotic gradient between the ICF and ECF.
End result: isotonic saline will expand the ECF

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13
Q

Describe what happens with hypertonic saline?

A

THe hypertonic solution will rapidly equilibrate across ECF causing a rise in ECF Na+ conc. Because it’s hypertonic it increases the concentration/osmotic gradient between ICF and ECF so fluid moves from ICF to ECF- results in decrease in ICF volume

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14
Q

Where is ADH synthesised?

A

Hypothalamus

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15
Q

Where is ADH secreted from?

A

Neurohypophysis

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16
Q

What are the actions of ADH?

A

Direct vasoconstrictor
NaCl reabsorption in thick ascending limb of loop of henle
Water retention in collecting ducts

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17
Q

What is the feedback system for ADH in the brain?

A

Hyperosmolar fluid reaches hypothalamus
Release of AVP
Reduced urinary volume and increased water reabsorption
Increase in intravascular fluid volume and normalises plasma osmolality

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18
Q

What is the main stimulus for ADH release?

A

Osmolality

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19
Q

What non-osmotic stimuli are there for ADH release?

A 
Stress
Hypoxia
Pain
Volume depletion
(All caused by surgery)
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20
Q

What does the glomerulus do?

A

Filters plasma

Relatively impermeable to large and negatively charged moleculew

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21
Q

What is the glomerulus freely permeable to?

A

Na+
K+
Water

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22
Q

Where are juxtaglomerular cells mainly found?

A

Along smooth muscle in afferent arteriole- releases renin into artery

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23
Q

Where are 70% of solutes and water reabsorbed rapidly?

A

Proximal tubule

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24
Q

What does the fact that fluid reabsorption is normally isosmotic mean?

A

Same amount of sodium and water is reabsorbed in PCT- solute conc at end of PCT is same as plasma solute concentration

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25
Q

What is the loop of Henle dependent on?

A

Active transport

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26
Q

What does the loop of Henle allow generation of that is required for concentration of urine?

A

Counter-current mechanism

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27
Q

How is reabsorption of salt mainly achieved?

A

By the Na+/K+/2Cl- triple transporter

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28
Q

How does vasopressin affect the triple transporter?

A

It increases expression

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29
Q

Where is urine maximally diluted?

A

Start of distal tubule

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30
Q

Where is most water reabsorbed?

A

Collecting duct

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31
Q

How does ADH act to increase water reabsorption?

A

It acts on V2 receptors to stimulate synthesis and assembly of AQP2 which allows water to move in from tubular lumen into cell. The water then moves via passive transporter out of cell into capillaries

32
Q

What is the main effect of aldosterone?

A

Acts on the distal tubule and collecting duct:
Promotes Na+ and water retention
Lowers plasma K+ concentration

33
Q

How does angiotensin II act?

A

It acts on adrenal cortex to stimulate aldosterone release

It also causes vasoconstriction and Na+ reabsorption

34
Q

What is the aldosterone feedback system?

A

Low blood pressure/low ECF as it reaches juxtaglomerular cells around afferent arteriole in kidneys. You get an increase in renin which drives the production of angiotensin then increases aldosterone etc

35
Q

What is ANP?

A

Atrial natriuretic peptide- Polypeptide released from cardiac myocytes in right atrium- it is released in response to stretch

36
Q

What are the actions of ANP?

A

Increases urinary excretion of Na+ and water
Inhibits Na+ reabsorption by collecting duct
Inhibits renin production and aldosterone secretion

37
Q

What are the effects of drinking too little on water balance (serum osmolality, ADH, thirst, urine, urine osmolality, ICF volume, ECF volume and serum Na+)?

A 
serum osmolality: Increases
ADH: Increases 
Thirst: Increases 
Urine: Oliguria and dark
Urine osmolality: Increases
ICF volume: decreases 
ECF volume: Unchanged
Serum Na+: Increased
38
Q

What are the effects of drinking too much on water balance (serum osmolality, ADH, thirst, urine, urine osmolality, ICF volume, ECF volume and serum Na+)?

A 
serum osmolality: Decreases
ADH: Decreases 
Thirst: Decreases 
Urine: Polyuria and pale
Urine osmolality: Decreases
ICF volume: Increases 
ECF volume: Unchanged
Serum Na+: Unchanged/decreased
39
Q

How can ICF be affected other than by drinking too much or too little?

A

Diabetes insipidus

40
Q

What causes diabetes insipidus?

A

Lack of ADH (cranial) or failure to respond to ADH (nephrogenic)- excessive urine output

41
Q

What is the urine like in DI?

A

Dilute despite elevated serum osmolality

42
Q

What is the diagnostic test for ADH?

A

Fluid deprivation

43
Q

What do you observe following fluid deprivation test?

A

Weight
Urine volume and osmolality
Serum osmolality and Na+ concentration

44
Q

How do you determine whether diabetes insipidus is central or nephrogenic?

A

DDAVP

45
Q

What is SIADH?

A

ADH secretion is inappropriate for given plasma osmolality

46
Q

What are the causes of SIADH?

A 
Intracerebral tumours/masses
Cerebrovascular accident
Tumour secreting ADH
Drugs/medication
Pneumonia
47
Q

What are the consequences of SIADH?

A

Low serum osmolality

High urine osmolality

48
Q

What is the treatment for SIADH?

A

Treat underlying cause
Fluid restriction
Tolvaptan (V2 receptor antagonist)

49
Q

How can you treat someone that has had too much to drink and subsequently increased ICF?

A

Fluid restriction

50
Q

What causes confusion?

A

High and low ICF

51
Q

What are the effects of hypervolaemia similar to?

A

Giving 0.9% saline- it increases the ECF volume and the Na+ conc stays the same because the extra fluid has the same composition as normal plasma

52
Q

What are the main consequences of hypervolaemia?

A

Expanded ECF
Plasma osmolality is normal
Plasma sodium is normal

53
Q

What happens if interstitial fluid space expands?

A

You are increasing space between cells which leads to pitting oedema
Pleural effusion- water between lining of lungs and pleural spaces

54
Q

What does increase in vascular volume cause in hypervolaemia?

A

High blood pressure

Elevated jugular venous pressure

55
Q

What causes isolated hypervolaemic states?

A 
Renal failure
Mineralocorticoid excess (due to increased salt and water retention)
56
Q

What occurs in fluid overload?

A

Increase in ECF volume but intravascular volume is decreased

57
Q

What important causes of fluid overload are there?

A

Heart failure
Cirrhosis
Low albumin

58
Q

How does heart failure cause decrease in blood volume?

A

Pump isn’t working properly

59
Q

How does liver failure and low albumin states cause decrease in blood volume?

A

The low albumin within the vessels means that there is less oncotic pressure drawing water back into vessels so more water will leave the vessels and enter the interstitial compartment rather than intravascular compartment

60
Q

What does low blood volume cause?

A

ADH secretion -> water retention

Aldosterone secretion -> salt retention

61
Q

What is ascites?

A

Fluid retention in the abdomen

62
Q

What is serum Na+ conc dependent on?

A

Intracellular fluid volume

63
Q

What are the consequences of liver failure causing hypervolaemia?

A

Low serum Na+
Low serum osmolality
Low urinary sodium

64
Q

What does hypovolaemia cause?

A

Reduction in ECF volume

65
Q

What are the causes of reduction in ECF?

A

Losses of intravascular fluid compartment (bleeding e.g. gastric ulcers)
Any fluid loss of salty water in particular diarrhoea and vomiting

66
Q

Who are particularly susceptible to ECF depletion?

A

Children due to diarrhoea and vomiting

67
Q

What are the losses like in diarrhoea and vomiting?

A

Initially isotonic losses (lose same amount of Na+ and water)
Non-osmotic ADH secretion (volume depletion rather than due to change in osmolality- water retention without equivalent Na+ retention- Dilutional hyponatraemia

68
Q

What are the clinical manifestations of reduction in ECF volume?

A 
Tachycardia
Low blood pressure
Postural hypotension
Decreased consciousness
Oliguria
Dry mucous membranes
Poor skin turgor
Cold peripheries
69
Q

What causes osmotic diuresis?

A

Active osmolite e.g. glucose or mannitol- freely filtered at glomerulus, increases osmotic potential of tubular fluid and decreases water reabsorption- increase in urine volume and decrease in ECF and ICF

70
Q

What common condition leads to osmotic diuresis?

A

Diabetes mellitus- high blood glucose concentration and high glucose filtrate conc

71
Q

What effect does osmotic diuresis have?

A

Reduce ECF and reduce ICF- increase in serum Na+ conc

72
Q

What is the commonest cause of mineralocorticoid deficiency?

A

Drugs e.g. renin inhibitors, ACE inhibitors and ARBs

Important to consider Addisons

73
Q

What are the consequences of mineralocorticoid deficiency?

A

Increased urinary sodium
Due to loss of aldosterone mediated Na+ reabsorption
Increase ICF and decrease ECF

74
Q

Apart from mineralocorticoid deficiency, what else can increase ICF and decrease ECF?

A

Diuretics

75
Q

What does furosemide do?

A

Inhibits triple transporter- loop diuretic

76
Q

Where do thiazide diuretics act?

A

On distal tubule and inhibit Na+/Cl- cotransporter

77
Q

How do you treat changes in water/Na+ homeostasis?

A 
Identify the compartment where the problem is :
If loss of fluid then give back fluid:
Low ICF- give water (5% dextrose)
Low ECF- give saline
If the compartment is overfilled:
High ICF- fluid restrict
High ECF- diuretics

S and P- E and W (3 decks)

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