2 Body Fluids Flashcards by Anon Anon

What is our total water intake daily?

2100ml

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How much do we urinate daily?

400-2300ml

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Name 5 fluid compartments in the body

intracellular water
interstitial water
fat
plasma
transcellular fluid

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What is total body water?

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

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how much of our total body fluid is extracellular?

Plasma 3L

interstitial 10L

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How much of our total body fluid is intracellular?

28L

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How much of our total body fluid is transcellular?

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Name 4 examples of transcellular compartments

Peritoneal space
CSF
Pleural cavity
synovial fluid

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

weigh a body, desiccate it, then re-weigh

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What is the volume of distribution?

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

large molecules (heparin)
protein binding molecules (insulin)

anything that will stay in the plasma

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What should we do when measuring volume of distribution?

leave the chemical time to equilibrate

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

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

we can use charged / polar molecules (gentamicin)

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Why could you not use tetrahydrocannabinol to measure fat volume?

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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How can we measure total body water?

labellling water with deuterium or tritium

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What marker could you use for plasma volume?

Evan’s blue (labelled protein injected intravascularly)

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What markers could you use for extracellular fluid?

36Cl
Thiosulphate
Thiocyanate

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What is Haematocrit?

the measure of the proportion of the blood occupied by cells

(usually around 45%)

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Why is haematocrit useful in physiology?

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

What is the listed extracellular calcium?

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

What is the rate of filtration of calcium equal to?

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

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

amount of protein

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

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

What is normal albumin level?

40g/L

What is osmole?

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

How many osmoles would 100mmol NaCl form in solution?

100 Na+ + 100 Cl- = 200mOsm

What is osmole useful for?

measuring osmotic forces

What is osmolality?

The number of osmoles per unit mass of the solvent | Osm.kg-1

What is osmolarity?

the number of osmoles per unit volume of solution | Osm-1

Why do osmolarity and osmolality not differ much?

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

what is osmotic pressure?

the force per unit area required to oppose a new movement

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

until the added hydrostatic pressure resist the flow of incoming water

What is the osmotic pressure equal to for practical purposes?

osmolality

How can we prevent large volume shifts in plasma?

Keeping osmolality constant

What does isosmotic mean?

2 solutions share the same osmolality

What does isotonic mean?

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

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

there would be no net movement across the membrane

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

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

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

hydrostatic force and osmotic pressures

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

large proteins, as the small ions are in equilibrium this force is called oncotic pressure

What is the most abundant protein in the blood?

albumin

What might cause a fall in albumin levels?

fall in production - liver failure | increased loss - renal failure

What is the effect of decreased albumin levels?

less of a force keeping water in circulation | water moves out of circulation into other spaces

What might albumin deficiency cause?

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

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

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)