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RBF > Salt and water balance > Flashcards

Salt and water balance Flashcards

1
Q

Plasma oslmolarity

hypersomolarity
hyposomolarity

A

285-295 mOsm/L

Hyperosmolarity - too much cation, and too little water
Hyposmolarity - too little cation and too much water

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2
Q

Hypotonic vs hypertonic solution isotonic

A

Hypotonic - cell gets big - less solute in solution than cell so water moves into cell

Hypertonic - cell shrinks - more solutes outside cell so water moves out

Isotonic - no change in cell shape

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3
Q

Glomerulus

A
  • Afferent arterole brings blood in, then get water absorbed into bowmans space
  • then blood exits efferent arteriole

Free filtration of salt and water occurs here

-protein is also filtered here

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4
Q

Where is most of sodium and water reabsorption?

A

-in the proximal tubule

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5
Q

Loop of henle
-descending and ascneding limb
distal convuluted tutbule
collecting duct

A

-descending limb - water reabsorption
ascendign limb - sodium reabsoprtion
a tiny bit of sodium is absorbed in distal convuluted tubule and collecting duct
-water is absorbed in the collecting duct - ADH - secreted by pituiatyr, to try and get more water absorpiton

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6
Q

What does ADH do?

A
  • made in hypothalamus, secreted in pituitary
  • increased production if BP falls or osmolarity increases
  • increase water absorption from collecting tubule
  • increase BP and reduces osmolarity
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7
Q

Aldosterone

A
  • acts on distal convolute tubule and collecting ducts
  • increases sodium reabsorption and potassium excretion
  • stimulated by potassium and angiotensin 2

-binds to aldosterone receptor and alters the sodium potassium pump so get more sodium reabsorped into blood, and more potassium excreted

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8
Q

Renin- angiotensin system

A

juxtaglomerular apparatus senses a decrease in renal perfusion and secretes renin
-renin increases production of angiotensin and angiotensin 2

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9
Q

Angiotensin 2

A

Released when you want to increase blood pressure

  • vasoconstriction
  • adh release stimulated
  • sodium reabsorption in proximal tubule
  • thirst
  • lower GFR by contraction of mesangial cells, thus reducing the area of glomerular filtration
  • also increases GFR by constriction of efferent arteriole
  • stimulates release of aldosterone
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10
Q

Hypernatraemia

A
  • impaired thirst/level of consciousness
  • no access to fluid
  • burns, diarrhoea, blood loss
  • solute diuresis
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11
Q

Diabetes

A
  • person has polyuria and water loss - large amount of urine
  • reduction of ADH or reduced efficacy of ADH
  • dilute urine (<200mOsm/kg)
  • patient cant drink enough to keep up with losses
  • elevated plasma osmolality, hyper-natraemia, dehydration
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12
Q

Types of DI

A
  • central - from traumatic brain injury
  • Nephrogenic - problem with aquaporin channel in kidney
  • partial or complete resistance to ADH
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13
Q

Hyponatraemia

A
  • excessive sodium loss
  • excessive water retention
  • check urine osmolality - if it is greater than 100mosmol/kg - then very very dilute urine
  • consistent with polydispsia - water intoxication
  • also psychotropic drugs
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14
Q

pseudohyponatraemia

A
  • check plasma osmolarity
  • if this is normal then the person has pseudohyponatraemia
  • false reading
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15
Q

Hypovolaemic

A

Dehydrated

  • urine sodium less than 20mmol/L
  • sodium loss but relatively less water loss
  • diarrhoea, vomiting
  • bowel obstruction
  • skin losses - burns, sweating
  • urinary losses - diuertics, addisons disease ect.
  • patient is volume deplete
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16
Q

Hypervolaemic

A
  • fluid overload
  • sodium retention but more water retention
  • cirrhosis
  • nephrotic syndrome
  • heart failure
  • renal failure
17
Q

Euvolaemic

A

SIADH - syndrome of inappropriate adh

  • endocrinopathies - hydrothroyodi, low cortisol
  • diuretics, fluid replacement
18
Q

SIADH

A

-inappropriate ADH production in absence of normal stimuli such as low BP
-body acucmulates too much water, stored in cells though so patient doesnt appear to be overloaded
-urine Osmol - not low, usually greater than 150
Plasma osmolality - low

19
Q

Causes of siadh

A 
trauma including surgery
tumurs
chronic lung disease
head injury 
medications
20
Q

Symptoms of hyponatraemia

A
  • depends on how quicjly it has developed
  • slow - brain adaption, confused not quite self
  • rapid - cerebral odeema
  • confsuon, seizures, coma
21
Q

Brain adaptation

A
  • water gain causes cerebral oedema - much less of a problem if it develops slowly
  • over time brain cells adapt
  • resulting in correction of cerebral oedema

RBF (31 decks)

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