Regulation of fluids

Question 1

What is the % of water neonates have compared to adults?

Answer 1

75-80% water with proportionately more extracellular fluid (ECF) than adults

Question 2

How much larger is interstitial fluid proportion at birth as compared to an adult?

Answer 2

three times larger

Question 3

What is the % of decrease in TBW (total body water) at 60 years of age in males?

Answer 3

50%

Question 4

What is the reason for the decrease in TBW in males at 60yo mostly due to?

Answer 4

increase in adipose tissue

Question 5

How many litres of fluids are in intracellular (ICF) and extracellular fluid (ECF)?

Answer 5

intra = 23 L
extra = 19 L

Question 6

Describe fluid balance in the ICF:

Answer 6

• cytosol of cells

- makes up two-thirds of total body water

Question 7

Describe fluid balance in the ECF:

Answer 7

• major components includes interstitial fluid and plasma

- minor components include all other extracellular fluids

Question 8

ICF and ECF are separated by?

Answer 8

cell membranes

Question 9

What are the levels of ions in intracellular fluids?

Answer 9

potassium/magnesium = high
sodium/chloride = low

Question 10

Is there a single united compartment of intracellular fluid?

Answer 10

no. this concept is artificial

Question 11

Is the ECF divided into several smaller compartments?

Answer 11

Yes

Question 12

How are the compartments in ECF distinguished?

Answer 12

by different locations and kinetic characteristics

Question 13

What are the levels of ions in extracellular fluids?

Answer 13

potassium/magnesium = low
sodium/chloride = high

Question 14

What does the interstitial fluid contain (ISF)?

Answer 14

all fluids which lie in the interstices of all body tissues

Question 15

What are the ‘functions/purposes’ of the ISF?

Answer 15

• bathes all cells in body
• link between ICF and intravascular compartment
• oxygen, nutrients, wastes, chemical messengers all pass through
• has compositional characteristics of ECF

Question 16

How is the ISF distinguished?

Answer 16

by its usually low protein concentration

Question 17

Is the lymph considered part of ISF?

Answer 17

Yes

Question 18

What is the relation of the lymphatic system with ISF?

Answer 18

• lymphatic system returns protein and excess ISF to circulation
• lymph more easily obtained for analysis than other ISF parts

Question 19

What can we say about the plasma compartment?

Answer 19

the only major fluid compartment that exists as real fluid collection all in one location

Question 20

What is the difference of plasma and ISF?

Answer 20

plasma much higher protein content and its high bulk flow (transport function)

Question 21

What are the normal blood levels of sodium?

Answer 21

135-145 mEq/L

Question 22

What are the normal blood levels of potassium?

Answer 22

3.5-5.5 mmoles/L

Question 23

What are the normal blood levels of chloride?

Answer 23

96-106 mEq/L

Question 24

What makes water move?

Answer 24

osmosis

Question 25

Explain how the osmotic pressure works, making water move:

Answer 25

- it's the hydrostatic (hydraulic) pressure that opposes movement of water through semi-permeable membrane - in response to osmotic gradient

Question 26

What is serum osmolality measured by?

Answer 26

- use of an osmometer OR - calculated as sum of concentration of solutes present in solution

Question 27

How many mL is the insensible loss of water from the body?

Answer 27

800mL

Question 28

How many mL is the minimal sweat loss of water from the body?

Answer 28

100mL

Question 29

How many mL is the faecal loss of water from the body?

Answer 29

200mL

Question 30

How many mL is minimal urine volume to excrete solute load, of water from the body?

Answer 30

500mL

Question 31

So, the daily obligatory water loss in mL is?

Answer 31

1,600mL

Question 32

What are the external fluid inputs?

Answer 32

- oral intake of fluid and foods | - IV fluids

Question 33

What are the internal fluid inputs?

Answer 33

metabolic water production

Question 34

When is metabolic water produced?

Answer 34

during oxidation of food | - carbs are completely metabolised to carbon dioxide and water

Question 35

How much per day of metabolic water is produced?

Answer 35

350-400mls/day

Question 36

Give some examples of fluid loss:

Answer 36

- pure gastric vomiting - bilious vomiting - panting - free water gain - diarrhea

Question 37

What happens in pure gastric vomiting?

Answer 37

- loss of HCl | - volume causes hypochloremic metabolic alkalosis

Question 38

What happens in bilious vomiting?

Answer 38

- loss of K, HCO3, Na | - cause hypokalemia, acidosis (colour of vomit is important)

Question 39

In panting, what are the losses?

Answer 39

- loss of free water | - but no electrolyte loss

Question 40

What can promote ion loss in the free water gain situation?

Answer 40

dilution and diuresis

Question 41

What is by far the most important indication for fluid and electrolyte replacement?

Answer 41

dirrhoea

Question 42

What enhances intestinal absorption of sodium and water?

Answer 42

by glucose (other carbs)

Question 43

What is the solution to replacement of fluid/electrolytes lost through diarrhea?

Answer 43

Oral rehydration therapy (ORT) - give solutions containing Na, K, and glucose (other carbs, starch)

Question 44

What is a result of the oral rehydration solution?

Answer 44

- enhance absorption of water/electrolytes - replace electrolyte deficit - contain alkalinising agent to counter acidosis - be slightly hypo-osmolar (250mmol/L) to prevent possible induction of osmotic diarrhoea - simple to use in hospital/at home - palatable and acceptable to children esp. - readily available

Question 45

What is WHO's rehydration salt formulation containing?

Answer 45

NaCl = 2.6g KCl = 1.5g Na citrate = 2.9g anhydrous glucose = 13.5g (But solutions are lower in sodium for UK since patients suffer less sodium loss)

Question 46

How long is the rehydration process?

Answer 46

3-4hrs

Question 47

What is the maximum rate of sweating?

Answer 47

50mls/min 2000mls/hr 8000mls/day??

Question 48

What is the % losses of TBW through sweating during stress?

Answer 48

25%

Question 49

What is lost through sweating?

Answer 49

- fluid (hot environment, physically active) - solute (acclimatisation) - heat (high latent evaporisation of water)

Question 50

How much of sweat is solute in %?

Answer 50

0.2-1%

Question 51

Where is sweat loss from?

Answer 51

sweat glands, specialised skin appendages

Question 52

Where is insensible fluid loss from?

Answer 52

- skin | - respiratory tract

Question 53

What is the role of sweat?

Answer 53

regulate body temperature

Question 54

Under extreme conditions, how much sodium can be lost in a day?

Answer 54

350mmols/day

Question 55

What is the central controller of water balance?

Answer 55

hypothalamus

Question 56

What are the key parts of the hypothalamus involved in water balance?

Answer 56

- osmoreceptors - thirst center - OVLT and SFO (respond to angiotensin II) - supraoptic and paraventricular nuclei (ADH synthesis)

Question 57

What are the 2 types of thirst?

Answer 57

hypovolemic and osmotic

Question 58

What are the 4 major stimuli to thirst?

Answer 58

1. Hypertonicity 2. Hypovolaemia 3. Hypotension 4. Angiotensin II

Question 59

What is hypertonicity?

Answer 59

cellular dehydration, via osmoreceptor mechanism

Question 60

What is hypovolaemia?

Answer 60

low volume sensed via the low pressure baroreceptors in great veins and right atrium

Question 61

What is hypotension?

Answer 61

high pressure baroreceptors in carotid sinus and aorta provide the sensors for this input

Question 62

what is angiotensin II?

Answer 62

produced consequent to release of renin by kidney (response to renal hypotension)

Question 63

What is ADH?

Answer 63

antidiuretic hormone - nonapeptide synthesised in hypothalamus - vasopressin because vasopressor response to pharmacological doses

Question 64

What is ADH's major role?

Answer 64

regulation of water balance by its effect on kidneys

Question 65

What is the half life of intravascular ADH?

Answer 65

15mins, being rapidly metabolised in liver/kidney to inactive products

Question 66

What properties do both caffeine and alcohol have?

Answer 66

diuretic properties - work by restricting ADH activity - inhibit pituitary secretion of anti-diuretic hormone

Question 67

At what levels of caffeine would there be diuretic effect?

Answer 67

excess of 300mg