Physiology 1: body fluid compartments Flashcards

1
Q

what is osmolarity

A

concentration of osmotically active particles in a solution (osmol/l)

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2
Q

what does high osmolarity mean

A

lots of ions that drive water osmosis eg a concentrated solution (usually weak salts)

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3
Q

what 2 factors must be known to calculate osmolarity

A

molar concentration and number of osmotically active particles

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4
Q

what would the osmolarity of 100mM of MgCl2 be

A

moles = 100mM, active particles = 3: 3x100 = 300mosmol/l

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5
Q

what is the difference between osmolality and osmolarity

A

osmolality is units /kg of water vs osmolarity is units /l

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6
Q

what is the osmolarity of most body fluids

A

300mosmol/l

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7
Q

what is tonicity

A

the effect an osmotic solution has on a cell

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8
Q

what effect does a hypotonic solution have on a a cell

A

hypotonic = not many active particles eg very dilute - causes water to diffuse into cell to higher concentration and cell to swell/ Burst (lysis)

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9
Q

what effect does a hypertonic solution have on a a cell

A

hypertonic = lots of active particles eg very concentrated - causes water to diffuse out of cell to higher concentration and cell to shrink

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10
Q

what is an isotonic solution

A

osmolarity is same inside and outside the cell

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11
Q

what % of males and females are water

A

males 60% and women 50%

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12
Q

what are the 2 major compartments total body water exists as

A

intercellular fluid (66%) and extracellular fluid (33%)

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13
Q

what is extracellular fluid made of

A

interstitial fluid 80% / plasma 20% (liquid component of blood) / negligible lymph and transcellular

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14
Q

what different tracers are used to calculate how much water are in each compartment: TBW, ECF and plasma

A

TBW: titrated water 3H2O / ECF: inulin / plasma: labelled albumin

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15
Q

how would you use a tracer to figure out total volume of compartment (volume of distribution)

A

1) add specific dose of tracer eg D=42mg to unknown water volume (V) 2) mix and take a small sample volume eg 5ml 3) measure concentration and scale back eg 0.005mg/5ml = 1mg/l 4) insert into calculation V = D/C eg 42/1 = 42L

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16
Q

what 3 ions mostly make up the osmolarity of the ECF

A

Na, Cl and HCO3

17
Q

what 2 ions mostly make up the osmolarity of the ICF

A

K and Mg (slightly negative)

18
Q

what effect would an increased ECF osmotic concentration have on the ICF

A

water would move down it’s concentration gradient out of the ICF and into the ECF to maintain the osmolarity of both

19
Q

what are the 3 main challenges to fluid concentration

A

gain or loss of water / gain or loss of Na / gain or loss of isotonic fluid eg NaCl

20
Q

what is an electrolyte

A

a salt that dissociates in a solution to give free ions eg NaCl –> Na+ (ECF) and Cl- (ICF)

21
Q

what is the importance of sodium in the water balance

A

determines ECF osmolarity and therefore volume - too much = hypertonic and too little = hypotonic

22
Q

what is the importance of the potassium balance in the body

A

establishes membrane potential and ICF osmolarity - too much = muscle weakness and paralysis (cell to negative so no depolarisation and APs) and also cardiac irregularities