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13 - Urinary > 4 - Plasma Osmolality > Flashcards

4 - Plasma Osmolality Flashcards

1
Q

What is normal osmolarity in the body?

A

- 280-310 mOsm/kg

  • 290 in interstitial fluid
  • 291 in blood plasma due to plasma proteins ==> oncotic pressure
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2
Q

How do you alter plasma osmolarity?

A
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3
Q

What is urine osmolarity?

A
  • Varies from 50-1200 mOsm/kg
  • Normal is 500-700
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4
Q

If there is an osmolarity change in the blood what does this mean the body has an issue with?

A

Water balance not Na reabsorption

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5
Q

What nephrons are responsible for concentrating urine and how do they do this?

A

- Juxta medullary long LOH generates gradient

- Vasa recta from efferent arteriole running paralell with Loop of Henle and blood running countercurrent maintains gradient

- Counter current multiplier system

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6
Q

What are the three processes involved in the counter-current multiplier system?

A
  • Active secretion of NaCl
  • Urea recycling
  • Vasa recta maintaining gradient
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7
Q

What is the difference in transport between the ascending and descending limb?

A
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8
Q

When may you see this concentration gradient between the loop of henle and the medullary interstitium and what are the consequences of this?

A
  • Newly transplanted kidney or long term loop diuretics as they block NKCC2 so no gradient can be established
  • Lots of dilute urine made
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9
Q

How can urea be used to help reabsorb more water?

A
  • Uptake in the PCT, 50% filtered is taken back

- Under ADH influence, urea reabsorbed from medullary CD

  • Urea increases osmotic gradient in the interstitium so more water reabsorbed
  • Urea then just taken back up into loop and cycles round
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10
Q

How do we supply blood to the medulla of the kidney without washing away the osmotic gradient needed to reabsorb water?

A

- Vasa recta with very slow flow

  • No active transport just passive absorption through endothelial cells

- Flow opposite direction to tubular fluid flow

  • Equilibriates at each level
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11
Q

How is a change in plasma osmolality detected in the body and what action is taken to resore the normal osmolality?

A

- Osmoreceptors in hypothalamus in OVLT

  • Cells in supraoptic nucleus containing baroreceptors sit close to OVLT so if low pressure means low volume and means high osmolarity so ADH secreted
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12
Q

What is the plasma osmolarity feedback loop?

A

Always a little bit of ADH, never 0

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13
Q

How does the effectiveness of ADH change with changes in plasma volume?

A

Changes in B.P (plasma volume) have an effect on response to changes in osmolarity

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14
Q

What happens once you have corrected a high plasma osmolality by taking a large drink?

A
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15
Q

What is diabetes insipidus and how can it cause issues with plasma osmolarity?

A
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16
Q

What is SIADH and how can it cause issues with plasma osmolarity?

A
17
Q

If you had a low plasma osmolarity what might you crave?

A

SALT

18
Q

What will happen to the osmolality of urine when plasma osmolality increases/decreases?

A
19
Q

What effect does ADH have on the receptors in the collecting duct?

A
  • Always AQP on basolateral membrane but not apical
  • When ADH present, AQP from vesicles are added to apical membrane
20
Q

How may someone with hyponatraemia present?

A
  • Can be confused, lethargic, muscle paralysis, blurred vision, muscle cramps (google quiz)
  • Serum conc lower than 135mmol
21
Q

How may someone with hypernatraemia present?

A
22
Q

If someone presented with the following blood parameters what may you think the diagnosis is and how may you treat it?

  • Serum osmolality 259 (decreased)
  • Urine osmolality 522 (decreased)
  • Urine Na 81 (increased)
A

- SIADH, kidneys are uneccessarily diluting urine

- Fluid restrict

  • Wean off any meds like valproate that cause inappropriate ADH release
23
Q

What are some causes of hyponatraemia?

A
  • Severe diarrhoea and vomiting (losing water too so no osmolality change)
  • Diuretics/Renal failure
  • Peritonitis
  • Burns
  • Na/Water imbalance
  • Anything that changes ADH secretion
24
Q

What are some causes of hypernatraemia?

A
25
Q

What are some conditions that can change ADH secretion from the hypothalamus?

A
  • SIADH
  • Heart failure
  • Liver/Kidney disease
  • Tumours e.g small cell lung
  • Meds e.g diuretics, PPIs, ACE inhibitors
26
Q

Why do we need to be careful when treating someone with hyponatraemia?

A

If we rapidly correct Na levels then rapid rise of Na pulls water from neurones, especially in brainstem, so neurones shrink, leading to

CENTRAL PONTINE MYELINOLYSIS

27
Q

If a patient presents with hyponatraemia what should you next calculate?

A

Work of osmolality - could be normal if glucose and urea are abnormal

28
Q

How does heart failure lead to hyponatremaia?

A

Too much water in ECF

29
Q

What are some causes of hypovolemic hyponatremia?

A
30
Q

Apart from fluid restriction, how can you treat hyponatremia?

A

Infusion of hypertonic saline and furosemide

31
Q

If a patient has abnormal serum sodium what are three things you need to establish?

A
  • Patient’s volume status?
  • How much sodium being lost in urine?
  • Is patient symptomatic?
32
Q

A 30 year old woman has been feeling light headed and nauseated for the past two days, she has not eaten or drunk much due to this and her B.P is 90/50, how do the macula densa cells respond?

A

Stimulate JGA to release renin

33
Q

When would nephrogenic diabetes insipidus present?

A
  • As baby
  • Salt restrict, give thiazide diuretics and monitor fluid balance
  • DONT GIVE NORMAL SALINE
34
Q

Fill in the following table with true or false.

A
35
Q

What causes solute and solvent to move from the interstitium to the capillary in the kidneys?

A
  • Hydrostatic pressure from the interstitium
  • Oncotic pressure in the peritubular blood
36
Q

What happens to the concentration of tubular fluid as it flows through the Loop of Henle?

A
  • In ascending limb gets more concentrated
  • In descending gets less
37
Q

How does the ENaC drive further reabsorption in the DCT?

A

Not electroneutral so drives paracellular transport of Cl-

38
Q

A 36 year old man is suspected to have primary hypersaldosteronism, what would you expect his U and E’s to be?

A
  • Increased Na, decrease K+
  • Normal urea
  • Decreased renin due to hypertension

Conn’s syndrome

13 - Urinary (24 decks)

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