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Endocrinology > Diabetes Insipidus > Flashcards

Diabetes Insipidus Flashcards

1
Q

Describe distribution of fluid in body?

A

1/3 extracellular

  • 1/4 of which is intravascular
  • 3/4 of which is interstitial

2/3 intracellular

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2
Q

What is interstitial fluid?

A

The fluid that bathes the cells

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3
Q

Name some anions and cations?

A

Cations: POSITIVE
Na+, Ca2+, K+

Anions: NEGATIVE
Cl-, HCO3-

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4
Q

What is osmolality?

A

A measure of the concentration of all the chemical particles in the fluid within the blood

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5
Q

In a healthy person describe what happens on ingestion of water?

A
  1. Ingestion of water
  2. Decrease in plasma osmolality (concentration)
  3. Increased cellular hydration
  4. Decreased secretion of vasopressin (ADH) leading to increased water excretion in kidney
  5. Also reduced thirst so reduced water intake
  6. Decreased total body water
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6
Q

In a healthy person describe what happens during lack of water?

A
  1. Lack of ingestion of water
  2. Increased plasma osmolality (concentration)
  3. Decreased cellular hydration
  4. Increased secretion of vasopressin leading to water retention in kidney
  5. Increased thirst so increased water intake
  6. Increased total body water
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7
Q

What are other names of vasopressin?

A 
Anti-diuretic hormone (ADH)
Arginine vasopressin (AVP)
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8
Q

What does vasopressin do?

A

Constriction of blood vessels

Retention of water by kidneys, due to increased water reabsorption in the collecting ducts

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9
Q

What controls vasopressin release?

A

Osmoreceptors in hypothalamus detect day to day changes in osmolality

Baroreceptors in brainstem and great vessels detect extreme pressure changes that occur in emergency situations

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10
Q

Difference between osmolarity and osmolality?

A

Osmolality: concentration of chemical particles in blood, taking account of lipids and proteins

Osmolarity: does not take into account lipids and proteins

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11
Q

How does vasopressin cause retention of water in kidney?

A

It opens up the channels in the collecting ducts, allowing water to flow from the tube to the blood

Your urine is therefore less water and more concentrated

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12
Q

Two types of diabetes insipidus, what are they?

A

Cranial DI: hyposecretion of vasopressin

Nephrogenic DI: insensitivity to vasopressin

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13
Q

Where is vasopressin produced and secreted?

A

Produced in hypothalamus

Secreted from posterior pituitary gland

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14
Q

Causes of cranial DI?

A

Anything that disrupts the hypothalamus

Tumour
Trauma
Surgery
Sarcoidosis
Idiopathic
Genetic
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15
Q

Cranial DI is caused by damage to hypothalamus AND posterior pituitary. True or false?

A

False!

Damage to p. pituitary alone does not cause DI because the vasopressin made in the hypothalamus can still leak out

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16
Q

Causes of Nephrogenic DI?

A

Calcium and potassium imbalance
Drugs
Kidney damage
Genetic

17
Q

Clinical features of DI?

A

Polyuria and resultant polydipsia

18
Q

What happens if DI patients lose their thirst mechanism, i.e. they are unable to sense they are thirsty?

A

They will quickly become dehydrated

DI patients rely on their thirst mechanism to keep hydrated, because they lose so much water they need to keep topped up

19
Q

Investigation of DI?

A

Urine volume: to confirm polyuria

Water deprivation test + desmopressin

Blood sugar: confirm its not DM

U+E: to confirm the polyuria is being caused by DI and not something else

MRI: hypothalamus to confirm cranial DI

20
Q

Differential diagnosis of polyuria?

A 
Diabetes mellitus
Diabetes insipidus
UTI
Kidney disorder
Hypokalaemia
Hypercalcaemia
Thyroid and pituitary dysfunction
Neurological
21
Q

Management of cranial DI?

A

Treat underlying cause

Desmopressin (synthetic vasopressin) is very effective as it replaces the lack of vasopressin

22
Q

In what ways can desmopressin be administered?

A

Nasally
Orally
Intramuscularly

23
Q

Management of Nephrogenic DI?

A

Treat the underlying cause

Avoid any drugs causing it
Free access to water

Very high desmopressin can sometimes help

24
Q

Describe the waterdeprivation and desmopressin test.

A

Patient is deprived of water until they’ve lost 5% body weight

Urine osmolality is measured (in DI it will be low (less than 300) since so much water being lost)

Person is then given desmopressin

If they have cranial DI urine osmolality will shoot up to over 800

If they have nephrogenic it will stay low

Endocrinology (19 decks)

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