Week 4 - C - Week 3 - Sodium and Water Balance

Question 1

Does water follow sodium or does sodium follow water?

Answer 1

Water follows sodium everywhere

Question 2

What controls the sodium levels in the body?

Answer 2

Mineralocorticoid activity

Question 3

sodium retention in exchange for potassium and/or hydrogen ions What is this known as? When does sodium retention tend to occur?

Answer 3

Mineralocorticoid activity

When there is a drop in blood pressure

Question 4

What does the kidneys release in response to detecting a low blood pressure? how does this process aim to correct blood pressure? (what in the correction process releases aldosterone)

Answer 4

The kidney releases renin, which cause anhiotensinogen to be converted to angiotensin 1 which is converted to angiotensin 2 via ACE

Angiotensin 2 causes the release of aldosterone from the adrenal cortex which promotes sodium reabsorption in the kidney tubules

Question 5

What is the main mineralocorticoid?

Answer 5

Aldosterone

Question 6

What does too little mineralocrticoid activity do sodium and what happens to water?

Answer 6

Too little causes increased sodium loss causing increased water loss (decreases BP)

Question 7

What is diuresis?

Answer 7

Diuresis is increased production of urine

Question 8

What is arginine vasopressin another name for?

Answer 8

ADH = AVP anti-diuretic hromone - arginine vasopressin

Question 9

Where is ADH released from and what does it act on the kindey tubules to cause?

Answer 9

Released from the posterior pituitary and causes increased water reabsoprtion thus the antidiuretic effect

Question 10

Is concentrated urine due to high or low ADH levels?

Answer 10

High ADH levels

Question 11

When the the urine is described as having a high urine osmolality, is this concentrated or dilute urine?

Answer 11

Concentrated urine - high urine osmolality

Dilute urine - low urine osmolality

Question 12

If the plasma volume is increased (meaning there is uptake of sodium and water), if the H2O plasma volume continues to increase howver the sodium levels decrease, what is a syndrome that can be a cause of this?

Answer 12

The syndrome of inappropriate antidiuretic hormone (ADH) secretion (SIADH)

Question 13

In SIADH, what happens to the, osmolality of the serum (blood)? WHat happens to the urine osmolality?

Answer 13

Low serum osmolality due to other minerals being excreted in urine also

Urine osmolality is raised (>100mOsmol/kg, urine NA+ >20mmol/l)

Question 14

Condition where the hyponatremia results from an excess of water rather than a deficiency of sodium?

Answer 14

SIADH

Question 15

What is the best way to remember the causes of SIADH secretion? (3Cs)

Answer 15

Chest - pneumonia, TB, carcinoma

Cranial causes - head injury

Chlorpropamide (sulphonylurea) - no longer recommended for use

Question 16

Which type of lung cancer can cause SIADH?

Answer 16

Small cell lung cancers can produce ectopic ADH and large amounts can lead to SIADH

Question 17

Decreased [Na+] can be due to too much water or too little sodium

SIADH is a cause of the too much water

What disease cause too little sodium leading to a decreased [Na+]?

Answer 17

Addison’s disease

Question 18

What are other causes of a decreased serum sodium concentration?

Answer 18

Vomiting and diarrhoea

Excessive sweating

Question 19

Increased [Na] can be due to: too little water or to too much sodium

What disease can cause too little water?

Answer 19

Diabetes insipidus (problem with ADH secretion) (also a very little water intake)

Question 20

What is a cause of too much sodium leading to an increased sodium concentration in the blood? (these are rare)

Answer 20

Some IV medications are given as sodium salts

High intake of salty foods in infants

Question 21

A 24 year-old student presents with a six month history of malaise, tiredness, poor appetite and one stone weight loss. She has developed a craving for salty foods – crisps in particular. She has had a number of dizzy spells particularly while in warm places. She is thin. She has low BP which falls further on standing. You have the impression that she is tanned, and you find increased pigmentation in her mouth and hand creases. What is suspected diagnosis?

Answer 21

Addison’s disease

Question 22

What is the other name for primary adrenal insufficiency? What is it?

Answer 22

Addison’s disease

Caused when something attacks the outer part of the adrenal gland - the adrenal cortex stopping it from producing aldosterone and cortisol properly

Question 23

Due to the fact the body cannot produce enough steroid’s in addison’s disease, how does this cause the patient to be dehydrated?

Answer 23

Adrenal glands cannot produce aldosterone, leads to lack of reabsorption of sodium and water - therefore as sodium and water are lost through the urine patient is dehydrated

Question 24

The patient in Addison’s is hypotensive due to a decreased ECF therefore experiences dizziness , why is there excess ACTH in Addison’s>

Answer 24

Due to the decreased cortisol levels, the hypothalamus senses a decrease and increases corticotrophin-releasing homrone production, this causes an increase in ACTH levels to try and correct the low cortisol levels

Question 25

Why does the increased ACTH levels cause increased pigmentation of the skin?

Answer 25

The ACTH contains the sequence for the melanocyte stimulating hormone (MSH)

Eventually proteases breakdown the ACTH exposing the MSH which will lead to darkened patches of skin and easy tanning

Question 26

What will the potassium and sodium levels show on blood tests?

Answer 26

Sodium levels will be low

Potassium levels will be high

Question 27

In a patient presenting to hospital (usually for another illness), and they are found to have a low sodium, what should you check for? Volume status is usually unremarkable

Answer 27

Check for Addisons

Question 28

If Addison’s comes back negative, what is usually thought to be the cause? Does a non-osmotic stimulus override an osmotic stimulus in this condition?

Answer 28

SIADH - syndrome of inappropriate ADH secretion

a non-osmotic stimulus overrides an osmotic stimulus in this condition

Question 29

What are example’s of non-osmotic stimuli?

Answer 29

Hypovalaemia, hypotension, vomiting, diarrhoea and sweating

Question 30

A 29 year-old man is admitted to ITU following a cycling accident in which he sustained a severe head injury. During his ITU stay his urine output is in excess of 12 litres daily; his IV fluid requirement is correspondingly large. Serum sodium is 167 mmol/L (high) on admission to ITU and slowly falls as fluid replacement ‘catches up’. He is in addition commenced on desmopressin (exogenous ADH) which produces a sharper fall in sodium. Diagnoses?

Answer 30

Diabetes insipidus

Question 31

Why is it likely that the previous case shows diabtes insipidus?

Answer 31

Pituitary could potentially be damaged on injury, leading to posterior pituitary dysfunction decreasing ADH production which is causing the excess urine

Question 32

Why in diabetes insipidus is the patients sodium high?

Answer 32

Sodium levels are high as due to the increased water loss, the ECF is decreasing and therefore there is increased sodium reabsorption

Question 33

Does hypovalaemia imply water or sodium defecit?

Answer 33

Hypovolaemia implies water deficit.

If it is present when [Na] is low, then there must be an even bigger sodium deficit.

This is important: hypovolaemia in hyponatraemia → too little sodium.

Question 34

What is the usual clinical finding for hypervolaemia?

Answer 34

Oedema

Question 35

In heart failure, blood volume is usually decreased as it gathers in the feet/legs, what does this do to the compensatory mechanisms?

Answer 35

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Question 36

[Na] itself is helpful. If very low ( 155 mmol/L), then YES it is serious What symptoms can arise from low or high sodium meaning it is very serious?

Answer 36

altered consciousness, confusion, nausea

Question 37

How should I treat it?

Too little sodium →

Too much water →

Too little water →

Too much sodium →

Answer 37

Too little sodium → give sodium

Too much water → fluid restrict

Too little water → give water

Too much sodium → get rid of excess sodium e.g. diuretics (furosemide) to induce natriuresis, and then replace just the water