1.1.1 Body Fluids and Electrolytes Flashcards
What happens to water concentrations when solute is added?
It decreases
What happens to an RBC when it is placed into a 290 mOsm urea solution? (Hint: urea is permeable)
Urea and water continue to enter cell until cell ruptures.
At normal body temp, what is the conversion ratio b/t osmotic pressure and solute concentrations?
20 mm Hg/mOsm solute
What will happen to a cell placed in a solution that contains 290 mOsm NaCl and 290 mOsm urea? Describe this solution.
Intitally the cell will shrink in size, but the cell will return to its original form.
(Important Point: In the presence of impermeant solutes, the permeant solute has no effect on final cell volue.
Write an equation for cardiac output using the variables: Parteries, Prt atrium and TPR
What fraction of TBW (total body water) is in the ECF? ICF?
ECF: 1/3 of TBW
ICF: 2/3 of TBW
What system attempts to maintain MAP nearly constant by altering either CO or SVR?
Baroreflex System
Write the equation for CO.
CO = HR x SV
What are the three types of pressures that affect the movement of H20 b/t the body compartments?
Osmotic pressure, Hydrostatic pressure, Oncotic pressure
What is the osmotic force provided by proteins in the plasma and ICF?
Oncotic pressure
If compartment A has an osmotic pressure of 300 mOsm and compartment B has an osmotic pressure of 298mOsm, what would be the needed hydrostatic pressure needed to result in zero fluid movement?
40 mm Hg
If MAP decreases due to decreased CO, how will the baroreflex system try to compensate or counteract this change?
Increase TPR to raise MAP
Assuming pressure in the right atrium is zero mm Hg,
Write equations for MAP.
MAP = CO x TPR
MAP = (HR x SV) x TPR
When water moves into a cell and the cell swells, the activity of what will increase? What will be the net effect on water movement?
The Na/K pump activity increases. Pumps more Na out than K inward, so water moves out.
Can osmolality accurately predict tonicity of a solution?
Not all of the time. B/c osmolality includes permeable solutes, it may inaccurately predict tonicity.
D. The final cell volume is half of its initial size
Describe the progression of pressure and fluid movement as the capillary spans from the ateriole to the venule.
Pi sign is oncotic pressure
B. Decreased
(Think about equation, TBW = 72% of LBM. LBM = Total Mass (kg) - Fat (kg)
What is the distribution of the ECF b/t plasma and ISF?
Plasma: 1/4 of ECF
Intersistial Fluid (ISF): 3/4 of ECF
What does MAP stand for?
Mean arterial pressure
What is the term for the average pressure in the systemic arteries?
Mean arterial pressure (MAP)
Describe how blood pressure and oncotic pressure influence water movement b/t the interstitium and capillary.
Write an equation using for flow using change in pressure and resistance.
Flow = Change in pressure/resistance
What are the two methods for calculating total body water?
- As % of BW: TBW = 60% of BW
- As % of lean body mass (LBM): LBM = Body weight - Fat weight, TBW = 72% of LBM
What are the two different types of IV administered fluids and what are their net effects?
O.9% Saline: ECF expands, ICF does not change
Dextrose (5%) in water: ECF expands, ICF expands (good for dehydration)
C. 45 Liters
(LBM = 63 Kg, TBW = .72(63)
B. 4 liters
LBM = 63 Kg, TBW = .72(63), TBW = 45 L, ECF = 1/3 of TBW, Plasma = 1/4 of ECF
What will happen to an RBC placed in a 580 mOsm urea solution? Describe this solution.
Cell will initially shrink in size, but, as urea enters cell by diffusion, water will ultimately cause the cell to swell then rupture.
Hyperosmotic but Hypotonic
The above calculations for TBW are for adults. How does body fluid change with age?
Describe hypotonic, isotonic, and hypertonic in terms of mOsm.
Hypotonic: < 290 mOsm
Isotonic: 290 mOsm
Hypertonic: > 290 mOsm
A. 288 mOsm/liter
(Remember the ratio of 20 mm Hg/mOsm)
Describe the direction of water diffusion.
Water will diffuse from high water concentration to low water concentration (towards higher solute concentration).
Describe the concentrations of Na+, K+, Ca++, Cl-, and Protein in the three compartments (plasma, interstitial, and intracellular).
Describe how a cell will change when placed in hypotonic, isotonic, and hypertonic solutions.
What is Prt atrium equivalent to?
Central Venous Pressure, which is typically negligible
What is the osmolality of 0.9% NaCl?
~ 290 mOsm
Describe the flow of blood from the sides of the heart, lungs, and systemic organs.
Right Heart -> Lungs -> Left Heart -> Systemic Organs -> Right Heart
Describe the relationship b/t solute and water concentrations.
Water concentration is inversely proportional to solute concentration. (Hence, as solute concentration increases, water concentration decreases.)
Define osmotic pressure.
The hydrostatic pressure that prevents water movement from a pure water phase into a solute phase. It is a function of solute concentration.
Define osmolality and tonicity. How do they differ?
Osmolality: Property is determined by the total concentration of solute molecules in solution (Permeable and impermeable)
Tonicity: Property is defined by how the volume of cell changes when the cell is placed in the solution (Impermeable solutes)
Tonicity differs from osmolality in that is dependent solely upon impermeable solutes. This is important b/c impermeable solutes cannot cross the cell membrane leading to net change depending on the concentration of those solutes.
