Sodium and Water Balance

Question 1

How is serum sodium concentration measured?

Answer 1

[Na⁺] = mmol Na⁺/1L H₂O

Question 2

What is the reference interval for serum sodium concentration?

Answer 2

135-145mmol/l

Question 3

Generally, hyponatraemia becauses more serious when sodium levels fall below what level?

Answer 3

<120 mmol/l

Question 4

A low serum sodium concentration can be caused by which two things?

Answer 4

1. Low sodium concentration
2. High water concentration

Question 5

What symptoms may be experienced with hyponatraemia?

Answer 5

1. Altered conciousness
2. Confusion
3. Nausea
4. Vomiting
5. Fitting

Question 6

In which two compartments is water present within the body?

Answer 6

1. Extracellular fluid (ECF)
2. Intracellular fluid (ICF)

Question 7

The _____cellular fluid volume is much greater than the _____cellular fluid volume

Answer 7

The intracellular fluid volume is much greater than the extracellular fluid volume

Question 8

Which fluid compartment contains the vast majority of sodium?

Answer 8

ECF

Question 9

Why is it that the ECF has a far higher sodium content?

Answer 9

Na⁺/K⁺ pump activity

Question 10

Why is it possible to gain or lose a lot of water without suffering from clinical signs?

Answer 10

Gain or loss is spread across a large volume (ICF + ECF)

Effects are therefore “diluted”

Question 11

Loss of sodium will lead to a loss of what?

Answer 11

Water

Question 12

How is it possible for the kidneys to regulate water volume in the body?

Answer 12

By either retaining or excreting sodium, water is conserved or lost respectively

Question 13

How does a low sodium concentration impact the intracellular fluid?

Answer 13

It doesn’t

The ECF is reduced but the ICF remains relatively constant

Question 14

How does an increased H₂O concentration impact the ECF and ICF?

Answer 14

They both increase

Question 15

How is dehydration and hyponatraemia treated?

Answer 15

Administer sodium

1. IV saline in an emergency
2. Oral sodium can also be used

Question 16

How is oedema and hyponatraemia treated?

Answer 16

Fluid restriction

Question 17

The RAAS pathway acts to _________ blood pressure

Answer 17

The RAAS pathway acts to increase blood pressure

Question 18

Which two key endogenous steroids have mineralocorticoid activity?

Answer 18

1. Aldosterone
2. Cortisol

Question 19

Increased mineralocorticoid activity leads to what?

Answer 19

1. Sodium retention
2. Increased blood pressure

Question 20

Where does ADH act and what is the result of its action?

Answer 20

Renal tubules

Water reabsorption

Question 21

What is the name given to the concentrating mechanism within the kidneys which occurs as a result of ADH?

Answer 21

Countercurrent multiplication

Question 22

What properties of the descending limb of Henle allow for countercurrent multiplication?

Answer 22

1. Highly permeable to water
2. Impermeable to NaCl

Question 23

What properties of the ascending limb of Henle allow for countercurrent multiplication?

Answer 23

1. Active excrusion of NaCl into ECF
2. Impermeable to water

Question 24

How is water lost from the descending limb of Henle?

Answer 24

In response to NaCl being pumped into the interstitial fluid from the ascending limb of Henle

Question 25

Sodium is pumped out from the ascending limb of Henle until what osmolar difference exists between the ascending limb of Henle and descending limb of Henle/interstitial fluid?

Answer 25

200mos/litre

Question 26

Countercurrent multiplication continues until he fluid in the descending limb of Henle reaches a maximally hypertonic value of what?

Answer 26

1200mos/litre

Question 27

Name 3 non-osmotic stimuli for ADH release?

Answer 27

1. Hypovolaemia/hypotension 2. Pain 3. Nausea and vomiting

Question 28

What are some pathological reasons for an increased sodium loss?

Answer 28

1. Adrenal/kidney causes 2. Poor absorption in gut 3. Skin (e.g. burns)

Question 29

What are some pathological reasons for an increased water concentration?

Answer 29

1. Decreased excretion (e.g. SIADH) 2. Increased intake (compulsive water drinking)

Question 30

Sodium levels may be considered very high at which level?

Answer 30

\>160mmol/L

Question 31

How does an increased sodium concentration impact the ICF?

Answer 31

It doesn't It only affects (increases) the ECF

Question 32

For which pathological reasons may there be increased water loss and subsequent rise is sodium levels?

Answer 32

1. H₂O loss e.g. DI 2. Decreased H₂O intake

Question 33

In which situation is increased sodium most common?

Answer 33

Diabetic ketoacidosis (especially when associated with **vomiting**)

Question 34

How is hypernatraemia treated in the even of little water?

Answer 34

Give water

Question 35

How is hypernatraemia treated in the event of too much sodium?

Answer 35

Loop diuretic

Question 36

Why does Addison's disease lead to hyponatraemia?

Answer 36

Adrenal insufficiency Not enough steroids are made and sodium cannot be retained Sodium and water are lost

Question 37

Why are loop diuretics used to treat patients with oedema?

Answer 37

There is excess water and sodium Loop diuretics cause loss of both