Principles of fluid balance Flashcards
Water is a polar solvent, true or false?
True
ICF and ECF have exactly the same composition, true or false?
False
Molality refers to the number of moles per _____ of a solvent.
Kg
Osmotic pressure/osmotic potential is the measure of a solution to _____ _____ water.
Take in
What is colloid osmotic pressure?
The osmotic pressure exerted by plasma colloids.
Tonicity is the effective osmolarity of a solution. How can a fluid be described with regard to serum and biological membranes?
Isotonic, hypotonic, hypertonic
What are the properties of water due to?
The presence of hydrogen bonds
How much of total body weight is due to water?
60%
Of the 60% total body weight that water makes up, how much is ICF and how much is ECF?
40% ICF
20% ECF
What makes up ECF and in what constituents?
15% ISF
5% plasma volume
<1% transcellular fluid
How is ICF formed?
Hydrostatic pressure at the arterial end of the capillary forces fluid out into the interstitium
COP at the venous end of the capillary then forces fluid back into the vessels
What ion is found in the highest quantity in the ECF?
Na
What ion is found in highest quantity in the ICF?
K
What is the difference between molarity and molality?
Molarity is the number of moles per litre
Molality is the number of moles per kg of substance
A 5M solution means 5 moles per litre. A 5 molal solution has 5 moles per kg. Molarity and molality are often equivalent as a litre of water has a mass of 1kg.
Molarity may show slight variation, but molality does not change with changes in temperature and pressure- the molality of a solution is always constant.
What is an equivalent?
The amount of material that will combine with 1 mole of OH-, H+ or electrons, e.g. in HCl, 1 mol hydrogen combines wuth 1 mol chlroine, so the amount of chlorine needed is one equivalent. In CaCl2, the combining ratio of calcium to chlorine is 1:2, so 1/2 mol Ca2+ combines with one mole Cl.
What are most solutes in the body measured in?
Milliequivalents
For monovalent ions, 1 meq = _____mmol
1
For divalent ions 1meq = _____ mmol
0.5
For trivalant ions, 1meq = _____ mmol
0.333
What is the definition of osmosis?
The net movement of water from an area of high water potential (high concentration) to an area of low water potential (low concentration).
What is water potential?
The tendancy of the water molecules to move out of a solution.
Water always moves from an area of _____ water potential to an area of _____ water potential.
High
Low
Water potential in a cell = water potential of _____ in the system and water potential _____
Water
Pressure
What are colloids?
Large molecular weight particle present in solution, usually found in plasma
What is oncotic pressure?
The proportion of the total osmotic pressure exerted by colloids, i.e the draw of the proteins in plasma
What will happen to the water within animal cells in a hypertonic solution?
Water will move out of the cell into the surrounding area
What will happen to the water within animal cells in a hypertonic solution?
Nothing
What will happen to the water within animal cells in a hypotonic? solution?
Water will move into the cell eventually causing the cell to lyse
What is an osmole?
The number of ions or particles into which a solute dissosciates in solution
Osmolality is the number of osmoles per _____, and osmolarity is the number of osmoles per _____ of solution.
Kg
Litre
What is tonicity?
The effective osmolality of a solution, i.e. the osmotic pressure of a fluid when compared with plasma
Tonicity is the effective osmolarity and is equal to the sum and concentration of the (effective) solutes which have the capacity to exert an osmotic force across the membrane, i.e. it only concerns solutes that cannot cross the membrane.
Tonicity is a property of a solution in reference to the membrane, i.e. concerned with solutes that cannot cross the membrane. Tonicity dictates the osmolar gradient across a cell.
Fluids with osmolality more than 300mOsm/kg are _____ to plasma.
Hypertonic
Fluids with osmolality less than 300mOsm/kg are _____ to plasma.
Hypotonic
Fluids with osmolality at 300mOsm/kg are _____ to plasma.
Isotonic
What type of fluid would you want to give to a dehydrated animal?
Hypotonic to restore ECF volume (dehydration does not involve loss of plasma volume)
What type of fluid would you give to a hypovolaemic animal?
Hypertonic to draw water into the circulation, colloids would also have the same effect
Rapid changes in ECF tonicity will have no effect on the ICF volume, true or false?
False, it will dramatically alter cell volume
Slow and more moderate changes in ECF tonicity have no effect on ICF volume true or false?
True, the cell will have time to adapt to changes in ECF
If there is an increase in extracellular hypertonicity, how does the cell respond to counter this change and preserve volume?
Cells will increase expression of genes encoding proteins that increase intracellular osmoles (solutes)
