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3 REN > 2 Body Fluids > Flashcards

2 Body Fluids Flashcards

1
Q

What is our total water intake daily?

A

2100ml

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2
Q

How much do we urinate daily?

A

400-2300ml

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3
Q

Name 5 fluid compartments in the body

A 
intracellular water
interstitial water
fat
plasma
transcellular fluid
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4
Q

What is total body water?

A

42L for a 70 kg person
greater in men than women
decreases with age (sarcopenia)

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5
Q

how much of our total body fluid is extracellular?

A

Plasma 3L

interstitial 10L

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6
Q

How much of our total body fluid is intracellular?

A

28L

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7
Q

How much of our total body fluid is transcellular?

A

1L

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8
Q

Name 4 examples of transcellular compartments

A

Peritoneal space
CSF
Pleural cavity
synovial fluid

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9
Q

What techniques would we have used in the past to estimate body fluid consumption?

A

weigh a body, desiccate it, then re-weigh

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10
Q

What is the volume of distribution?

A

the volume of fluid required to contain the total amount of drug in the body at the same concentration as that present in the plasma

V = Q/C

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11
Q

What kinds of molecules would we use to measure plasma volume?

A 
large molecules (heparin)
protein binding molecules (insulin)

anything that will stay in the plasma

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12
Q

What should we do when measuring volume of distribution?

A

leave the chemical time to equilibrate

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13
Q

What kind of molecule would we use to measure the volume of the extracellular space?

A

small enough to get across capillary, but too big to get into cells

we can use charged / polar molecules (gentamicin)

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14
Q

Why could you not use tetrahydrocannabinol to measure fat volume?

A

it is lipophilc yes, but it gives an apparent volume of distribution of 700L

this doesn’t work, as the plasma is not part of fat distribution

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15
Q

How can we measure total body water?

A

labellling water with deuterium or tritium

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16
Q

What marker could you use for plasma volume?

A

Evan’s blue (labelled protein injected intravascularly)

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17
Q

What markers could you use for extracellular fluid?

A

36Cl
Thiosulphate
Thiocyanate

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18
Q

What is Haematocrit?

A

the measure of the proportion of the blood occupied by cells

(usually around 45%)

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19
Q

Why is haematocrit useful in physiology?

A

in physiology plasma flow rate is often used over blood flow rate, haematocrit allows us to switch between the two

20
Q

What is the listed extracellular calcium?

A

the sum of the bound and free calcium, they are roughly equal

21
Q

What is the rate of filtration of calcium equal to?

A

half the listed extracellular volume, so 1.2mM from 2.4 mM, as the kidney does not easily remove protein bound substances

22
Q

What do we need to watch out for when we get a blood count of calcium?

A

amount of protein

23
Q

What is used to calculate the ‘free calcium’ by clinicians?

A

‘corrected calcium’, which is just a modified form of free calcium

24
Q

What is normal albumin level?

A

40g/L

25
Q

What is osmole?

A

a measure of the number of molecules that a compound dissociates into when dissolved in solution

26
Q

How many osmoles would 100mmol NaCl form in solution?

A

100 Na+ + 100 Cl- = 200mOsm

27
Q

What is osmole useful for?

A

measuring osmotic forces

28
Q

What is osmolality?

A

The number of osmoles per unit mass of the solvent

Osm.kg-1

29
Q

What is osmolarity?

A

the number of osmoles per unit volume of solution

Osm-1

30
Q

Why do osmolarity and osmolality not differ much?

A

the density of water is very close to 1kg/L

when you dissolve a solvent in a solute, the volume doesn’t change very much

31
Q

what is osmotic pressure?

A

the force per unit area required to oppose a new movement

32
Q

How long will water keep moving into an area with more water?

A

until the added hydrostatic pressure resist the flow of incoming water

33
Q

What is the osmotic pressure equal to for practical purposes?

A

osmolality

34
Q

How can we prevent large volume shifts in plasma?

A

Keeping osmolality constant

35
Q

What does isosmotic mean?

A

2 solutions share the same osmolality

36
Q

What does isotonic mean?

A

applying the solution to cells (traditionally RBC’s) will not cause net fluid movement

37
Q

What would happen if a semipermeable membrane separated 2 isotonic soluions?

A

there would be no net movement across the membrane

38
Q

If a membrane permeable only to urea and water separated a solution of urea, and a solution of something else, what would happen?

A

the urea would move into the other compartment, and water would follow

39
Q

What is the net movement of water across capillary walls a balance between?

A

hydrostatic force and osmotic pressures

40
Q

Across the capillary membrane what is the main osmotic pressure due to?

A

large proteins, as the small ions are in equilibrium

this force is called oncotic pressure

41
Q

What is the most abundant protein in the blood?

A

albumin

42
Q

What might cause a fall in albumin levels?

A

fall in production - liver failure

increased loss - renal failure

43
Q

What is the effect of decreased albumin levels?

A

less of a force keeping water in circulation

water moves out of circulation into other spaces

44
Q

What might albumin deficiency cause?

A

peripheral / pulmonary oedema
abdomen swelling (ascites)
brain swelling - pretty bad

45
Q

How is albumin deficiency treated?
Why?
What other use does it have?

A

mannitol

inert
transiently increases plasma osmotic pressure, pulling water back
it is cleared by the kidney, taking water with it

an inhaled cystic fibrosis management (dilutes airways by moving water)

3 REN (21 decks)

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