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3 Urinary Unit > 9 Control of Plasma Osmolarity > Flashcards

9 Control of Plasma Osmolarity Flashcards

1
Q

Between what range does urine osmolarity vary?

A

50-1200 mOsm/Kg

1200 (maximum possible)

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2
Q

What is the normal osmolarity of cells?

A

280-310 mOsm/Kg

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3
Q

Juxtamedullary nephrons make up 10-15% of the total nephrons in the kidneys. What is there function and how does their structure differ from the cortical nephron?

A

Responsible for making concentrated urine

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4
Q

How is the vertical concentration gradient in the kidney maintained?

A

Vasa recta and long loope of henle

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5
Q

Why are there no aquaporin channels in the ascending loop of henle?

A

Diluting action of filtrate

Removes solute without water

Increase osmolarity in interstitium

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6
Q

In which patients might there be a lack of vertical concentration gradient within the kidney?

A

Patients on prolonged loop diuretics

Transplant patients

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7
Q

At what point is the osmotic gradient within the loop of henle at its highest?

A

At deepest point of loop of henle

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8
Q

How is urea reabsorbed from the lumen of the tubule in the proximal convulted tubule?

A
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9
Q

Small changes in plasma concentration cause small hormonal changes. What happens as a result of these hormonal changes? Where does this hormonal regulation take place?

A
  1. Alter water uptake in kidney
  2. Stimulate thirst

Where?:

Late distal tubule

Collecting duct in nephron

Hormone= aldosterone

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10
Q

Outline the thirst response. (how is it sensed, where and how is it perceived?)

A
  • Perceived:
    • Peripherally eg drying of oral mucosa
  • Sensed:
    • Lateral pre-optic area of hypothalamus- responsive to raised plasma osmotic pressure/reduced ECF volume
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11
Q

Outline the thirst mechanism. (when is it active)

A

Thrist mechanism active when level of hyperosmotic dehydration surpasses protective capacity of kidneys

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12
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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13
Q

How do you alter plasma osmolarity?

A
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14
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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15
Q

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

A
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16
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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17
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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18
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
19
Q

How is a change in plasma osmolality detected in the body and what are the 2 pathways used to restore osmolarity?

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
  • (organum vasculosum of the lamina terminalis)*
20
Q

What is the plasma osmolarity feedback loop?

A

Always a little bit of ADH, never 0

21
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

22
Q

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

A
23
Q

What is diabetes insipidus? What are the 2 types of diabetes insipidus?

A
24
Q

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

A
25
Q

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

A
26
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
27
Q

How may someone with hyponatraemia present?

A
  • Can be confused, lethargic, muscle paralysis, blurred vision, muscle cramps
  • Serum conc lower than 135mmol
28
Q

How may someone with hypernatraemia present?

A
29
Q

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

A
  • Active secretion of NaCl
  • Urea recycling
  • Vasa recta maintaining gradient
30
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
31
Q

What are some causes of hypernatraemia?

A
32
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

33
Q

How does heart failure lead to hyponatremaia?

A

Too much water in ECF

34
Q

What are some causes of hypovolemic hyponatremia?

A
36
Q

When would nephrogenic diabetes insipidus present?

A
  • As baby
  • Salt restrict, give thiazide diuretics and monitor fluid balance
  • DONT GIVE NORMAL SALINE
37
Q

Fill in the following table with true or false.

A
42
Q

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

A

SALT

47
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
50
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
55
Q

Apart from fluid restriction, how can you treat hyponatremia?

A

Infusion of hypertonic saline and furosemide

56
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?
57
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

62
Q

How does the ENaC drive further reabsorption in the DCT?

A

Not electroneutral so drives paracellular transport of Cl-

63
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

3 Urinary Unit (23 decks)

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