Water Balance Flashcards

1
Q

Describe the distribution of water in the body

A

60% body weight is water
40% water is intracellular fluid
20% water is extracellular fluid

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2
Q

Describe the distribution of extracellular fluid

A

1/4 is plasma

3/4 is interstitial fluid

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3
Q

Why must osmolarity be kept constant?

A

To maintain cellular specialisation

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4
Q

What is the role of the kidneys in water balance/

A

To ensure that the water intake and output is equal

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5
Q

What is osmotic clearance?

A

The volume of plasma that would contain all the combined solutes excreted in urine

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6
Q

How is osmotic clearance calculated?

A

Urine osmolarity/plasma osmolarity x urine volume

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7
Q

What is free water clearance?

A

The rate of solute free excretion

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8
Q

How is free water clearance calculated?

A

Urine volume - osmotic clearance

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9
Q

If urine is isotonic, what is free water clearance?

A

Zero

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10
Q

If urine is hypotonic, what is free water clearance?

A

Positive

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11
Q

If urine is hypertonic, what is free water clearance?

A

Negative

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12
Q

What stimulates ADH secretion?

A
Increasing osmolarity
Decreasing plasma volume
Nausea
Hypoglycaemia
Hypoxia
Angiotensin II 
Stress
Pain
Temperature
Hypercapnia
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13
Q

What inputs regulate thirst?

A

Osmoreceptors in hypothalamus detect plasma osmolarity
Hypovolaemia
Angiotensin
Oropharyngeal sensory receptors

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14
Q

Describe the role of oropharyngeal sensory receptors

A

It immediately removes thirst sensations as it takes time to decrease osmolarity

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15
Q

What drinks would heighten the satiety of oropharyngeal sensory receptors?

A

Cold, carbonated drinks

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16
Q

What is the action of ADH?

A

Translocation of aquaporins in the collecting duct to increase water and urea reabsorption

17
Q

What is diabetes insipidus?

A

Lack of ADH secretion

18
Q

What are the symptoms of diabetes insipidus if there is no access to water?

A

Hypernatraemia

19
Q

What are the symptoms of diabetes insipidus is there is access to water?

A

Polyuria and polydipsia

20
Q

What is the syndrome of inappropriate ADH secretion?

A

Excessive ADH secretion

21
Q

What are the symptoms of syndrome of inappropriate ADH secretion?

A

Lack of dehydration if no access to water

Hyponatraemia if access to water

22
Q

What are the renal symptoms of diabetes mellitus?

A

Polydipsia and polyuria