1.1.1 Body Fluids and Electrolytes

Question 1

What happens to water concentrations when solute is added?

Answer 1

It decreases

Question 2

What happens to an RBC when it is placed into a 290 mOsm urea solution? (Hint: urea is permeable)

Answer 2

Urea and water continue to enter cell until cell ruptures.

Question 3

At normal body temp, what is the conversion ratio b/t osmotic pressure and solute concentrations?

Answer 3

20 mm Hg/mOsm solute

Question 4

What will happen to a cell placed in a solution that contains 290 mOsm NaCl and 290 mOsm urea? Describe this solution.

Answer 4

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.

Question 5

Write an equation for cardiac output using the variables: Parteries, Prt atrium and TPR

Answer 5

Question 6

What fraction of TBW (total body water) is in the ECF? ICF?

Answer 6

ECF: 1/3 of TBW

ICF: 2/3 of TBW

Question 7

What system attempts to maintain MAP nearly constant by altering either CO or SVR?

Answer 7

Baroreflex System

Question 8

Write the equation for CO.

Answer 8

CO = HR x SV

Question 9

What are the three types of pressures that affect the movement of H₂0 b/t the body compartments?

Answer 9

Osmotic pressure, Hydrostatic pressure, Oncotic pressure

Question 10

What is the osmotic force provided by proteins in the plasma and ICF?

Answer 10

Oncotic pressure

Question 11

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?

Answer 11

40 mm Hg

Question 12

If MAP decreases due to decreased CO, how will the baroreflex system try to compensate or counteract this change?

Answer 12

Increase TPR to raise MAP

Question 13

Assuming pressure in the right atrium is zero mm Hg,

Write equations for MAP.

Answer 13

MAP = CO x TPR

MAP = (HR x SV) x TPR

Question 14

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?

Answer 14

The Na/K pump activity increases. Pumps more Na out than K inward, so water moves out.

Question 15

Can osmolality accurately predict tonicity of a solution?

Answer 15

Not all of the time. B/c osmolality includes permeable solutes, it may inaccurately predict tonicity.

Question 16

Answer 16

D. The final cell volume is half of its initial size

Question 17

Describe the progression of pressure and fluid movement as the capillary spans from the ateriole to the venule.

Answer 17

Pi sign is oncotic pressure

Question 18

Answer 18

B. Decreased

(Think about equation, TBW = 72% of LBM. LBM = Total Mass (kg) - Fat (kg)

Question 19

What is the distribution of the ECF b/t plasma and ISF?

Answer 19

Plasma: 1/4 of ECF

Intersistial Fluid (ISF): 3/4 of ECF

Question 20

What does MAP stand for?

Answer 20

Mean arterial pressure

Question 21

What is the term for the average pressure in the systemic arteries?

Answer 21

Mean arterial pressure (MAP)

Question 22

Describe how blood pressure and oncotic pressure influence water movement b/t the interstitium and capillary.

Answer 22

Question 23

Write an equation using for flow using change in pressure and resistance.

Answer 23

Flow = Change in pressure/resistance

Question 24

What are the two methods for calculating total body water?

Answer 24

1. As % of BW: TBW = 60% of BW
2. As % of lean body mass (LBM): LBM = Body weight - Fat weight, TBW = 72% of LBM

Question 25

What are the two different types of IV administered fluids and what are their net effects?

Answer 25

O.9% Saline: ECF expands, ICF does not change

Dextrose (5%) in water: ECF expands, ICF expands (good for dehydration)

Question 26

Answer 26

C. 45 Liters

(LBM = 63 Kg, TBW = .72(63)

Question 27

Answer 27

B. 4 liters

LBM = 63 Kg, TBW = .72(63), TBW = 45 L, ECF = 1/3 of TBW, Plasma = 1/4 of ECF

Question 28

What will happen to an RBC placed in a 580 mOsm urea solution? Describe this solution.

Answer 28

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

Question 29

The above calculations for TBW are for adults. How does body fluid change with age?

Answer 29

Question 30

Describe hypotonic, isotonic, and hypertonic in terms of mOsm.

Answer 30

Hypotonic: < 290 mOsm

Isotonic: 290 mOsm

Hypertonic: > 290 mOsm

Question 31

Answer 31

A. 288 mOsm/liter

(Remember the ratio of 20 mm Hg/mOsm)

Question 32

Describe the direction of water diffusion.

Answer 32

Water will diffuse from high water concentration to low water concentration (towards higher solute concentration).

Question 33

Describe the concentrations of Na+, K+, Ca++, Cl-, and Protein in the three compartments (plasma, interstitial, and intracellular).

Answer 33

Question 34

Describe how a cell will change when placed in hypotonic, isotonic, and hypertonic solutions.

Answer 34

Question 35

What is P_{rt atrium} equivalent to?

Answer 35

Central Venous Pressure, which is typically negligible

Question 36

What is the osmolality of 0.9% NaCl?

Answer 36

~ 290 mOsm

Question 37

Describe the flow of blood from the sides of the heart, lungs, and systemic organs.

Answer 37

Right Heart -> Lungs -> Left Heart -> Systemic Organs -> Right Heart

Question 38

Describe the relationship b/t solute and water concentrations.

Answer 38

Water concentration is inversely proportional to solute concentration. (Hence, as solute concentration increases, water concentration decreases.)

Question 39

Define osmotic pressure.

Answer 39

The hydrostatic pressure that prevents water movement from a pure water phase into a solute phase. It is a function of solute concentration.

Question 40

Define osmolality and tonicity. How do they differ?

Answer 40

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.