Sodium & Water Balance

Question 1

What happens to ADH secretion when there is an increased plasma osmolarity

Answer 1

Increases

Question 2

What happens to ADH secretion when there is an decreased plasma osmolarity

Answer 2

Decreases

Question 3

Describe the effect of ADH on the kidneys and the urine & plasma osmolarity

Answer 3

The distal convoluted tubule (DCT) and connecting tubule (CNT) cells present more aquaporins =>

More water is reabsorbed in the kidneys =>

Small volume of concentrated (high osmolarity) urine =>

Decreased plasma osmolarity

Question 4

What does high vs low osmolarity urine mean

Answer 4

High osmolarity
- concentrated urine
- low water to electrolytes etc ratio

Low osmolarity
- dilute urine
- high water to electrolytes etc ratio

Question 5

What is ADH aka

Answer 5

Arginine vasopressin (AVP)

Question 6

What is meant by mineralocortocid activity

Answer 6

Effects of steroids on Na+ balance

Question 7

What is the main steroid that show mineralocorticoid activity

Answer 7

Aldosterone
(Others include cortisol)

Question 8

What does a low vs high mineralocorticoid activity mean with regards to sodium

Answer 8

Low activity - Sodium loss
High activity - Sodium reabsorption

I.e. Aldosterone increases sodium (& hence water) reabsorption

Question 9

What stimulates aldosterone secretion

Answer 9

High K & angiotensin II (i.e. low bp)

Question 10

Where is water vs sodium present in the human body

Answer 10

Water - ICF & ECF (whole body)
Sodium - ECF alone (due to Na/K transporter)

Question 11

Does water follow sodium or sodium follow water?

Answer 11

Water follows sodium

Question 12

List signs of hyponatraemia, what effect does it have on…
- HR, BP, urine,
- skin, mucous membranes, eyes
- CNS

Answer 12

• increased HR, decreased postural BP, low urine output
• decreased skin turner, dry mucous membrane, sunken eyes
• decreased consciousness

Question 13

List signs of hypernatraemia

Answer 13

• Coughing, SOB, pulmonary oedema & effusion
• Ascites
• Ankle/ leg oedema
• Tiredness

Question 14

What are the two causes of hyponatraemia

Answer 14

• Too little sodium
• Too much water

Question 15

What are the two causes of hypernatraemia

Answer 15

• Too much sodium
• Too little water

Question 16

If a patient had hypernatraemia, would you expect more clinical evidence of change if it was due to too much sodium or too little water

Answer 16

Too much sodium

• sodium is confined to ECF
• water is distributed across all body compartments

Question 17

Hyponatraemia due to low sodium causes

Answer 17

• ↑ Na+ loss - not very common but can be fatal
  
  • Adrenal/kidney
  • Gut
  • Skin
• ↓ Na+ intake - very rare

Question 18

Hyponatraemia due to excess water causes

Answer 18

• ↓ H2O excretion e.g. SIADH - most common
• ↑ H2O intake (compulsive water drinking) - very rare

Question 19

Hypernatraemia due to excess sodium causes

Answer 19

• ↑ Na+ intake - very rare
• ↓ Na+ loss - not very common

Question 20

Hypernatraemia due to loss of water causes

Answer 20

• ↑ H2O loss e.g. diabetes insipidus - not very common but may come across
• ↓ H2O intake e.g. very young or very old - quite common

Question 21

Hyponatraemia treatment

Answer 21

• If due to too little sodium - give sodium IV as saline or orally
• If due to too much water - remove water through fluid restriction

Question 22

Hypernatraemia treatment

Answer 22

• If due to too little water - give water as IV dextrose
• If due to too much sodium - remove sodium through diuretics

Question 23

If it is a problem when sodium itself (too much or little) it can be very serious, what symptoms would you expect with abnormal Na

Answer 23

• Altered consciousness, confusion
• N & V
• fitting etc
• LIFE THREATENING!

Question 24

In health, ADH is released upon stimulation by osmotic stimuli. How is this different in disease

Answer 24

ADH is released in response to non-osmotic stimuli e.g.
Hypovolaemia/hypotension/pain/N&V

Question 25

What is SIADH

Answer 25

Syndrome of inappropriate ADH
This means ADH is released inappropriately to the osmolarity

Question 26

Why is SIADH often an incidental finding when doing the U&Es of a sick person?

Answer 26

• The secretion of ADH in response to a non-osmotic stimulus causes water retention
• This often occurs slowly and the retained water is distributed over all body compartments so patient’s volume status clinically may be unremarkable
• It is therefore often an incidental finding when U+Es done and Na+ found to be low

Question 27

SIADH investigations & management

Answer 27

Once you find low Na in the U&E’s of a sick individual you want to first exclude adrenal insufficiency & other sources of sodium loss

Only then you can diagnose water excess as the cause & diagnose/ treat for SIADH

Treatment - remove water through fluid restriction

Question 28

What does oedema signify

Answer 28

Plasma volume depletion due to altered starling forces @ capillary level => fluid leaks excessively into interstitium

Question 29

What is the body’s reaction to oedema

Answer 29

It reacts as if the patient is dehydrated =>
Secretes ADH & aldosterone =>
Water increases => oedema increases =>
Viscous cycle

Question 30

What is the sodium levels of a patient with oedema

Answer 30

Too much sodium (as well as too much water)

Question 31

Oedema treatment

Answer 31

Loop diuretics

Question 32

State the three IV fluid types & where they end up (plasma vs interstitial vs intracellular)

Answer 32

Dextrose - Plasma, interstitial & intracellular fluid
Saline - Plasma & interstitial fluid
Plasma/ blood - plasma only