Chapter 1: Physiology of Body Fluids

Question 1

What is the equation to convert mEq/L to mmol/L?

Answer 1

mEq/L = mmol/L x valence

Question 2

Intracellular homeostasis is maintained by what?

Answer 2

Shifts in water, solutes and other substances across the cell membrane.

Question 3

Fill in the blanks in mEq/L: 
ECF/ICF
Na+: 
K+:
Ca2+: 
Mg2+:
Cl-: 
HCO3-: 
HPO4 2-, H2PO4-:
Protein -:

Answer 3

Na+: 145/12
K+: 4/140
Ca2+: 2.5/4
Mg2+: 1/34
Cl-: 110/4
HCO3-: 24/12
HPO4 2-, H2PO4-: 2/40
Protein -: 15 (interstitial)/50

Question 4

In most disease states, loss of fluids occurs initially where?

Answer 4

ECF

Question 5

What is the 60:40:20 rule?

Answer 5

An easy way of remembering distribution of body fluids - 60% is water, 40% is ICF and 20% is ECF.

Question 6

What makes up the transcellular fluid compartment? What percentage of total body fluid does this compartment make up?

Answer 6

Fluids produced by specialized cells, such as CSF, GI fluid, respiratory secretion, glandular secretions and synovial fluid. This fluid is estimated to be 1% of body weight, or 2% of total body water.

Question 7

Dense connective tissue, bone and cartilage contain approximately ____% of total body water.

Answer 7

15%

These tissues exchange fluid very slowly and this is usually not taken into account when considering fluid therapy.

Question 8

The vascular endothelium is freely permeable to ________?

Answer 8

Ionic solutes. Therefore, the concentration of these ions is almost the same in ISF as in plasma.

Question 9

Describe the Gibbs-Donnan equilibrium.

Answer 9

Negatively charged, non-diffusible proteins affect the distribution of other small charged solutes and create a small difference in anions and cations across the vascular endothelium.

Question 10

Describe the two ways that sodium can move into or out of cells.

Answer 10

Sodium commonly will diffuse intracellularly due to the high concentration gradient. The Na, K, ATPase pump will also remove sodium from cells to maintain the steep gradient (3 sodium out, 2 potassium in).

Question 11

What are the most abundant anions in the ECF?

Answer 11

Chloride and bicarbonate

Question 12

What enzyme creates bicarbonate from water and CO2?

Answer 12

Carbonic anhydrase

Question 13

What are the primary cations in the ICF?

Answer 13

Potassium and magnesium

Question 14

Which ion is primarily responsible for generating the cell membrane at approximately -70 mV?

Answer 14

Potassium. Almost 100% of potassium is exchangeable.

Question 15

What are the predominant anions in the ICF?

Answer 15

organic phosphates and proteins

Question 16

Definition of molality:

Answer 16

Number of moles of solute per kilogram of solvent

Question 17

Definition of molarity:

Answer 17

Number of moles of solute per liter of solution

Question 18

If at the normal pH of ECF, 80% of phosphate is in HPO4^2- and 20% is in H2PO4^-, what would the phosphate concentration be in mEq/L if the normal phosphate concentration is 4 mg/dL?

Answer 18

[0.8 x (-2)] + [0.2 x (-1)] = -1.8
[4 x 10]/31 x 1.8 = 2.3 mEq/L

Tip:
First calculate average valence
Then convert 4 mg/dL to mg/L
Then to convert to mEq-->divide by molecular weight and multiply by average valence
P molecular weight = 31

Question 19

In clinical medicine, why is osmolality measured in serum and not plasma?

Answer 19

Because the addition of anticoagulants for plasma would increase the solute in the sample.

Question 20

What is the average measured serum osmolality in the dog? In the cat?

Answer 20

Dog: 300 mOsm/L
Cat: 310 mOsm/L

Question 21

True or false: glucose is a permeable solute.

Answer 21

False. Glucose is an impermeable solute and therefore an effective osmole.

Question 22

What is tonicity?

Answer 22

Effective osmolality

Question 23

True or false: Freezing point depression osmometer measures both effective and ineffective osmoles.

Answer 23

True

Question 24

Fill in the blank with either , or =

Oftentimes, the tonicity of a solution is ___ than the measured osmolality.

Answer 24

tonicity is often < measured osmolality

Question 25

Colloid osmotic pressure is only about ___% of the total osmotic pressure.

Answer 25

0.5%. The remainder is made up of impermeable ions, glucose and BUN (if concentration is increased)

Question 26

What is the formula for calculated osmolality?

Answer 26

2([Na] + [K] + Glucose/18 + BUN/2.8

Question 27

In the formula for calculated osmolality, why is Na + K multipled by 2?

Answer 27

To account for the contribution of Cl- and HCO3-

Question 28

In the formula for calculated osmolality, why is glucose divided by 18 and BUN by 2.8?

Answer 28

To convert mg/dL to mmol/L. The molecular of glucose is 180 and that of BUN is 28

Question 29

What are the types of fluid and solute loss that can occur?

Answer 29

Solute in excess of water (hypertonic fluid), isotonic loss, or water in excess of solute (hypotonic fluid)

Question 30

What would the effect of hypotonic fluid loss have on the ECF?

Answer 30

The ECF would be hypertonic (and then water would shift from the intracellular space to extracellular to equilibrate)

Question 31

What would the effect of isotonic fluid loss have on the ECF?

Answer 31

The ECF would be isotonic. No shift of water

Question 32

What would the effect of hypertonic fluid loss have on the ECF?

Answer 32

Hypotonic ECF. And then fluid would shift from ECF to intracellular to equilibrate.

Question 33

What is the definition of effective blood volume?

Answer 33

The component of blood volume to which the volume-regulatory system responds by causing renal sodium adn water retention in the setting of cardiac and hepatic failure even though measured total blood and plasma volume may be increased.

Question 34

Exchange of solutes and fluid between plasma and interstitial spaces occurs where?

Answer 34

Capillaries

Question 35

What is Starling's Law (the OG)?

Answer 35

Net filtration = Kf [(Pcap - Pif) - (π p-π if)] ``` Kf = net permeability of the capillary wall P = hydrostatic pressure generated by heart (cap) or tissues (if) π = oncotic pressure generated by plasma proteins (p) or filtered proteins and mucopolysaccharides in interstitium (if) ```

Question 36

What is the net filtration pressure in healthy capillaries?

Answer 36

0.3-0.5 mm Hg, at the proximal (arteriolar) end of capillary.

Question 37

What is the normal anion gap in dogs and cats?

Answer 37

Dogs: 12-24 mEq/L Cats: 13-27 mEq/L

Question 38

What is the difference between obligatory water loss and free water loss?

Answer 38

Obligatory water loss is the water needed to excrete the daily renal solute load. Free water loss is the water excreted unaccompanied by solute under the control of ADH.

Question 39

What makes up the majority of urinary solute (two-thirds) in the dog?

Answer 39

Urea

Question 40

Secretion of ADH is inhibited by a ____% decrease in serum osmolality?

Answer 40

1-2%

Question 41

If a patient has limited food intake, does their water intake needs increase or decrease?

Answer 41

Decrease.