Body Fluid Compartments

Question 1

describe what osmolality is

Answer 1

conc. of osmotically active particles present in a solution

can be calculated

Question 2

describe what tonicity is

Answer 2

the effect a solution has on cell volume

isotonic(no effect), hypotonic(swelling of cell) or hypertonic(shrinking of cell)

Question 3

what are the 2 major compartments total body water(TBW) exists in

Answer 3

extracellular fluid(ECF) and intracellular fluid(ICF)

Question 4

what portion of total body water is in the ECF and ICF

Answer 4

ECF = 33%
ICF = 66%

Question 5

what is included in extracellular fluid(ECF)

Answer 5

plasma(~20%), interstitial fluid(~80%), lymph + transcellular fluid(negligible)

Question 6

describe how you can measure body fluid compartment volumes

Answer 6

using ‘tracers,’ you can obtain the distribution volume of these tracers to measure body compartment volume, ie add known amount of substance and measure the conc. in the compartment

Question 7

what is a suitable tracer for measuring total body water(TBW)

Answer 7

tritiated water(3H2O)

Question 8

what is a suitable tracer for measuring ECF and for plasma

Answer 8

ECF = inulin
plasma = labelled albumin

Question 9

how can you measure ICF

Answer 9

by obtaining TBW and ECF using tracers can calculate ICF

TBW = ECF + ICF

Question 10

what is an imbalance in water homeostasis(balance), ie input and output, manifested as

Answer 10

as changes in body fluid osmolarity

Question 11

how are the ECF and ICF separated into different compartments

Answer 11

the cell membrane and membrane transport mechanisms allow them to exist as 2 different environments

Question 12

how do the osmotic conc. of the ECF and ICF compare with each other

Answer 12

they are identical at around 300mosmol/l

Question 13

what does the term fluid shift mean

Answer 13

refers to movement of water between the ICF and ECF compartments in response to an osmotic gradients

Question 14

describe what would happen if the osmotic conc. of the ECF increased

Answer 14

too little water in ECF so would be hypertonic, cells would shrink as water moves from ICF to ECF, until homeostasis returns
(eg if very dehydrated and not enough water intake)

Question 15

describe what would happen if the osmotic conc. of the ECF decreased

Answer 15

too much water in ECF so would be hypotonic, cells would swell as water enters them, so increased ICF, until homeostasis returns
(eg if too much water intake)

Question 16

what are the 3 challenges to body fluid homeostasis

Answer 16

1) gain or loss of water
2) gain or loss of sodium
3) gain or loss of isotonic fluid

Question 17

what body fluid compartment do the kidneys influence

Answer 17

they alter composition and volume of the ECF