Water and electrolytes Flashcards
What is hydrostatic pressure?
it is the pressure exerted by an fluid at equilibrium due to the force of gravity
Pressure= force/area
What is the concentration of solutions?
amount of solute per unit volume of solvent
concentration= amount solute/volume solvent
Ion
atom or group of atoms with an electrical charge
cation +
anion-
Valence electrons
the number of electrons in an atom’s outermost energy level (shell)
Valency
the combining power of an atom
the absolute number of electrons that are gained,
lost, or borrowed in order to have a full outermost
energy level
Elements with 4 electrons will share them such as
Carbon
Examples:
oxygen has 6 valence electrons so its valency is 2
sodium has 1 valence electron so its valency is 1
osmosis
the net diffusion of water across a membrane
Osmotic pressure
the pressure that must be applied to a solution to prevent the net flow of water into it
the amount of pressure required to prevent
osmosis is called the osmotic pressure
per k= (m x v^2)/2 large and small particles exert the
same osmotic pressure
Osmotic pressure is directly related to
the solute concentration (osmolality)
What contributes the most to osmotic pressure of body fluids?
electrolytes; they determine the distribution of body water
What is an osmol?
one mole of solute particles dissolved in a solution
indicator of osmotic activity
the term osmole refers to the number of osmotically active particles rather than the molar
1 mole/1 L is equal to
1 osmol/ 1L or 1 osmM
1 osmole is equivalent to
1 mole which is equal to 6.02 x 10^23 particles
What osmolality do we use when referring to the body?
we utilize milliosmoles for body fluids
1 mOsm= 1/1000 osmoles
What is osmolarity?
the osmotic concentration of a solution expressed as OSMOLES of solute per LITER of solution
What is osmolality?
the osmotic concentration of a solution expressed as OSMOLES per KG of solution
285-295 mOsm/kg is normal osmolality for adults
275-290 mOsm/kg is normal osmolality for
children
What is an isotonic solution?
the solution has the same solute concentration as our cells
0.9 NS or LR
What is a hypotonic solution?
the solution has less solute concentration than our cells so water will want to move into cells and cause them to burst
ex.: D5 or .45 NS
What is a hypertonic solution?
the solution has more solute concentration than our cells so water will want to move out of cells and cause them to shrink
Ex. 3%
What is colloid osmotic pressure?
high MW substances such as proteins (albumin) do exert a colloid osmotic pressure (oncotic pressure)
proteins are confined in the vascular space whereas all other dissolved solutes pass freely through the capillary pores
What is the total body weight of water?
60%
in a 70 kg person 3L is plasma, 11 L is ISF, and 28 L is intracellular
We can calculate these for any body weight
What electrolytes have the highest concentrations extracellularly?
Na+, Cl-, and bicarb
What electrolytes have the highest concentrations intracellularly?
K+, Mg+, proteins, phosphate, and organic anions have the highest concentrations inside the cell
Explain the Donnan equilibrium effect.
Proteins that have multiple negative charges attracts cations, cations bring water (hydration spheres) so osmotic pull is much larger than expected for 1 protein
-electroneutrality is maintained in the plasma and ISF
the presence of negatively charged non-diffusible proteins molecules on one side of a membrane leads to an excess of diffusible cations and a deficit of diffusible anions on the same side
What is a colloid solution?
colloids are big proteins that cannot diffuse across the plasma membrane; they have negative ions so they pull water into the plasma
If we have 1 mole of Cl-. How many moles of Ca2+ will balance the charge on 1 mole of chloride?
Ca2+ is divalent thus half a mole of Ca2+ will balance 1 mole of negative charge
Conversion between mEq and moles and milligrams for 222 mg CaCl2 in 1 L of fluid
222 mg CaCl2 & MW is 111 grams/mole
111 grams/mole= 111 mg/mmole
so 222 mg/111 mg/mmole= 2 mmole
2 mmoles/ 1 L
For Ca2+: 2 mmoles in 1 L x valency of 2= 4 mEq/L
For Cl-: 4 mmoles in 1 liter x valency of 1= 4 mEq/L of anion
Why do we use mEq/L over mg/deciliter?
mEq/L shows neutrality
Mg has to be converted to moles of ions and valence to assess neutrality
What is Van Hoff’s Law & it’s relationship to osmotic pressure and fluid movement?
osmotic pressure= CRT
where C is concentration in osmoles/L
R= ideal gas constant of 62.36
T= Temperature in Kelvin
Example of Van Hoff’s Law: what is the osmotic pressure of 0.9% NaCl?
9 grams/ 1 L
9 grams/58 g/mole
0.155 moles/ 1 L or 0.155 molar x 1000= 155 mmoles/Liter
NaCl dissociates into Na+ and Cl- so we have 2 osmoles (155 mmoles x 2)
= 308 mOsmoles/L
= 308 mOsmoles/L x 62.36 x 310 K
=5,954 mmHg
What is the volume of distribution for colloid solutions?
albumin- plasma
PV/Vd = 3/3 so 100% of it stays in the plasma
What is the volume of distribution for isotonic solutions?
NS & LR
Plasma and ISF
3/14= 20% fraction left in plasma
What is the volume of distribution for hypotonic solutions?
D5W
plasma, ISF, ICF
3/42= 7% fraction left in plasma
What is the volume of distribution for hypertonic solutions?
3%
plasma, ISF, and draws fluid in from ICF
cannot calculate d/t this
Be able to calculate the Net Capillary Filtration given the Pc, Pif, πp and πif / determine which way fluid will flow
Net filtration pressure (NFP) = (Pc – Pif) – (πp – πif)
Where Pc = capillary hydrostatic pressure (outward)
Pif = interstitial fluid hydrostatic pressure (inward) (is usually -3mmHg)
Πp = osmotic force due to plasma protein concentration (inward)
Πif = osmotic force due to interstitial fluid protein concentration (outward)
What is the major extracellular ion?
Na+ & it is a good reflection of osmolality
If Na+ goes up sodium is not the issue, H2O is
Electroneutrality is maintained
in plasma and ISF
Conversion of mg/dl to mEq/Liter
mEq/Liter= (mg/dl x 10 x valence)/atomic weight
Proteins are
multi-valent (many negatively charged areas) and thus, can attract multiple cations
Osmotic pressure
is directly related to concentration of the solute and it determines how water moves
The water concentration of a solution depends on
the number of particles in the solution
we define this in osmoles
The amount of pressure required to prevent osmosis is known as
osmotic pressure
increased osmotic pressure
higher solute concentration and lower water concentration
The osmotic pressure is directly proportional
to osmolarity or the concentration of osmotically active particles in the solution
1 molecule of NaCl has XXXX the osmotic effect of 1 molecule of glucose
twice
A large force acts to move H2O across the cell membrane when
intracellular and extracellular fluids are not in osmotic equilibrium
1 mosmole = osmotic pressure of 19.3 mmHg
When the MW of a substance is low
there will be MORE molecules per a given unit weight
more molecules–> greater osmotic pressure
Plasma volume expansion equation
Plasma volume expansion= plasma volume/volume of distribution
