0305 fluid compartments Flashcards
• Outline the different fluid compartments • Summarise the approximate compartment volumes • Describe how volumes of different fluid compartments are measured • recognise major ionic components in different compartments (cations and anions) • Outline the concept of free and bound ions
What is the average total body water percentage an adult
Male = 60% and females = 55%
As you get older, does your total body water percentage increase or decrease
As we get older our TBW decreases
What are the 2 sub categories of total body water and what is their relative percentages
Intracellular fluid (60%) and Extracellular fluid (40%)
What is functional extracellular fluid and what is it’s relative percentage of total body water
fECF (function ECF) is the water in ECF minus the immovable/very slow to move water (e.g. those in bone and dense connective tissue). It is 30% of total body water. Therefore, it is 75% of ECF
List the components of extracellular fluid. Which of these components have slow exchange rates of water
Plasma, interstitial fluid (transcellular water, bone water and dense connective tissue water). All but plasma have slow exchange rates of water
What is the ratio of intracellular fluid : extracellular fluid? What about Intracellular fluid : functional ECF
ICF:ECF = 3:2. ICF : fECF = 2:1
What is the principle behind using tracers to measure compartments? What are some traits of ideal tracers
Put a known volume of indicator into a compartment, extract a sample of compartment and measure [indicator]. Calculate volume based on dilution. Ideal tracers are non toxic, not excreted during equilibrium period, evenly distributed, will not enter other compartments, not metabolised, easy to measure and will not interfere with bodily distribution
What is the formula for determining compartment size from an administered tracer
Compartment size = administered volume of tracer / [tracer]
List some properties for tracers of total body water and it’s compartments
TBW (must penetrate all compartments), ECF (must no enter cells), plasma (anything that binds to albumin), ICF (no direct tracer, TBW - ECF)
What are the major cations, anions and buffer of extracellular fluid
Major cation = Na+, Ca2+, major anion = Cl-, major buffer = HCO3
What is the major difference in ion compositon of plasma and interstitial fluid (both ECF)
The major difference is that plasma contains plasma proteins and interstitial fluid does not
What are the major cations, anions and buffer of intracellular fluid
Major cation = K+, major anion = HPO4-, major buffer = HPO4-
What is electroneutrality
Electro-neutrality is the even matching of positively and negatively charged ions in a compartment
What is total intracellular ratio of [anion/cation] higher than extracellular ratio? What maintains the ionic gradients between intracellular and extracellular compartments (hint: maintain means going against gradient)
ICF is higher because there are intracellular proteins. Ionic gradients are maintained by the actions of active transporters that use ATP
What is special about Ca2+ and Mg2+ ions within the body
Both ions are generally 50% ionized (free) and 50% bound to protein or organic matter. This means they are free to contribute to cellular machinery
