Water and Electrolyte Balance

Question 1

How much water is required daily to balance insensible losses?

Answer 1

1 Litre

Question 2

What is the daily RNI for sodium?

Answer 2

70mmol / 1.6g

Question 3

Despite the RNI for sodium what is the usually intake range?

Answer 3

90-440mmol / 2-10g

Question 4

What do high intakes of sodium lead to?

Answer 4

Hypertension

Question 5

The WHO also recommends how much potassium to reduce blood pressure and cardiovascular risk of stroke and CHD?

Answer 5

90mmol / 3.5g

Question 6

In healthy people the total body water constitutes what % of lean body weight in men and women?

Answer 6

Men 50-60% Women 45-50%

Question 7

In a healthy 70kg male what would his approximate body water content be in litres?

Answer 7

42L

Question 8

Body water is contained in what three major compartments?

Answer 8

Intracellular fluid, extracellular fluid and plasma

Question 9

What % of lean body weight is ICF?

Answer 9

35% / 28L

Question 10

What % of lean body weight is ECF?

Answer 10

12% / 9.4L

Question 11

What % of lean body weight is plasma?

Answer 11

4-5% / 4.6L

Question 12

What other areas of the body contain water?

Answer 12

Bones, dense connective tissue and epithelial secretions such as digestive secretions and cerebrospinal fluid

Question 13

Intracellular fluid and interstitial fluid is separated by what?

Answer 13

The cell membrane

Question 14

The interstitial fluid and plasma are separated by what?

Answer 14

The capillary wall

Question 15

In the absence of solute, how do water molecules move across the semi-permeable membrane?

Answer 15

Randomly and in equal numbers

Question 16

If solute is added what happens to the water?

Answer 16

It stays in the high-solute compartment

Question 17

The ability to hold water in a compartment can be measured as?

Answer 17

Osmotic pressure

Question 18

Osmotic pressure is defined as?

Answer 18

The primary determinant of the distribution of water between the three major compartments

Question 19

The concentrations of major solutes in the compartments is different each having one solute that is primarily?

Answer 19

Limited to the compartment to determine its osmotic pressure

Question 20

Intracellular fluid contains mainly which solute?

Answer 20

Potassium K+

Question 21

Most of the cell’s magnesium Mg2+ is bound and therefore osmotically?

Answer 21

Inactive

Question 22

In the extracellular compartment what solute predominates in the interstitial fluid?

Answer 22

Sodium Na+

Question 23

Proteins are found in which compartment of extracellular fluid?

Answer 23

Plasma

Question 24

The capillary wall is relatively impermeable to?

Answer 24

Plasma proteins

Question 25

The cell membrane is relatively impermeable to?

Answer 25

Na+ and K+

Question 26

Which pump restricts Na+ to ECF and K+ to ICF?

Answer 26

Sodium Potassium Pump

Question 27

Na+ moves freely across ? to achieve similar concentrations in interstitium and plasma

Answer 27

Capillary Walls

Question 28

What crosses the cell membrane and capillary wall and is osmotically inactive?

Answer 28

Urea - therefore retention of urea in renal failure does not alter the distribution of total body water

Question 29

What stores are the primary determinant of ECF volume?

Answer 29

Na+ stores

Question 30

ECF volume and tissue perfusion are maintained by appropriate alterations in ? secretion

Answer 30

Na+ secretion

Question 31

If Na+ intake is increased, where will the extra Na+ be initially added to?

Answer 31

ECF

Question 32

When the increased Na+ intake is initially added to ECF what happens next?

Answer 32

Increased ECF osmolality causes H2O to move out of cells, leading to ECF volume expansion

Question 33

How is balance restored in the ECF when Na+ is too high?

Answer 33

Excess Na+ is excreted in the urine

Question 34

1 litre of water given intravenously as 5% glucose is distributed how between the compartments?

Answer 34

Equally

Question 35

1 litre Saline (0.9% salt/99.1% H2O) given intravenously, remains in which compartment?

Answer 35

Extracellular

Question 36

Which is the correct treatment for extracellular water depletion?

Answer 36

0.9% Saline - as the Na+ keeps the water in this compartment

Question 37

The extracellular volume is determined by the concentration of sodium balance exerted by?

Answer 37

Kidneys

Question 38

Renal Na+ secretion varies directly with?

Answer 38

The effective circulating volume

Question 39

In a 70kg man what fraction of ECF is plasma?

Answer 39

1/3rd (4.6L)

Question 40

The plasma in the ECF of a 70kg male has what % lying in the venous side and what % in the arterial circulation?

Answer 40

85% (3.9L) venous side and 15% (0.7L) arterial circulation

Question 41

The fullness of the arterial vascular compartment (effective arterial blood volume) is the primary determinant of?

Answer 41

Renal Na+ and H2O excretion - which is the effective circulatory volume for body fluid homeostasis

Question 42

The fullness of the arterial compartment depends on the relationship between?

Answer 42

cardiac output and peripheral arterial resistance

Question 43

A diminished effective arterial blood volume is initiated by?

Answer 43

a fall in cardiac output or a fall in peripheral arterial resistance

Question 44

Changes in what ... contribute towards the main adaptive response to fluctuations in the effective circulating volume?

Answer 44

Tubular reabsorption

Question 45

Tubular reabsorption is X - dependant?

Answer 45

Flow-dependant

Question 46

Neurohormonal regulation of Na+ reabsorption occurs mainly in which areas of the kidney?

Answer 46

Proximal tubules and collecting ducts

Question 47

Neurohormonal regulation of ECF volume is mediated by?

Answer 47

Volume receptors rather than alterations in sodium concentration

Question 48

Which hormones control the day-to-day variations in Na+ excretion through their ability to diminish and augment Na+ reabsorption in the collecting ducts?

Answer 48

Aldosterone and Atrial Natriuretic Peptide (ANP)

Question 49

If there is a salt load, what is the chain of events that happens in the body to lead to an increase in Na+ excretion and homeostatic fluid rebalance?

Answer 49

1. Salt load leads to increase in circulatory and extracellular volume 2. Renal perfusion pressure and atrial and arterial filling pressure increases 3. Increase in renal perfusion pressure reduces the secretion of Renin, subsequently angiotensin 2 and aldosterone 4. Increase in atrial and arterial filling pressure increases release of ANP (atrial natriuretic peptide) 5. These factors combine to reduce Na+ reabsorption in the collecting duct promoting excretion of excess Na+

Question 50

If there is salt depletion in those with low salt intake or diarrhoea/vomiting what is the series of events that happens in the body to try and achieve homeostatic fluid rebalance?

Answer 50

1. Decrease in effective volume enhances the activity of the renin-angiotensin-aldosterone system 2. Also decreases secretion of ANP 3. Net effect is enhanced Na+ reabsorption in the collecting ducts 5. Reduced Na+ excretion increasing ECFV towards norm

Question 51

Marked hypovolaemia causes a decrease in GFR and proximal and ascending limb Na+ reabsorption leading to?

Answer 51

Na+ retention

Question 52

Body water homeostasis is affected by?

Answer 52

Thirst and kidneys diluting and concentrating function

Question 53

Thirst and kidney function is controlled by what receptor initially and in which gland?

Answer 53

Osmoreceptors / Hypothalamus

Question 54

Which hormone plays a central role in urinary concentration?

Answer 54

ADH

Question 55

The presence of ADH promotes?

Answer 55

Water reabsorption in the collecting ducts down the favourable osmotic gradient between the tubular fluid and the more concentrated intersitium

Question 56

Hyponatraemia is defined by which mmol/L Na+?

Answer 56

<135mmol/L

Question 57

What could be the cause of hyponatraemia with hypovolaemia extrarenally?

Answer 57

Vomiting, diarrhoea, haemorrhage, burns, pancreatitis

Question 58

What could be the cause of hyponatraemia with hypovolaemia in the kidneys?

Answer 58

Osmotic diuresis (e.g hyperglycaemia), diuretics

Question 59

Most people have a dietary potassium intake of?

Answer 59

80-150mmol daily depending on fruit and veg intake

Question 60

Most of the body's potassium is within which fluid compartment?

Answer 60

Intracellular

Question 61

A number of drugs affect K+ homeostasis by affecting the release of which hormone?

Answer 61

Aldosterone - these drugs include NSAIDs, heparin

Question 62

Diuretics affect K+ homeostasis by directly affecting?

Answer 62

Renal potassium handling

Question 63

What % of potassium intake is secreted in the GI tract?

Answer 63

10%

Question 64

How much K+ does vomit contain?

Answer 64

5-10mmol/L

Question 65

K+ is secreted by the colon and diarrhoea contains how much?

Answer 65

10-30mmol/L

Question 66

Hypokalaemia is defined at which mmol/l?

Answer 66

<3.5mmol/L