Chapter 1: Physiology of Body Fluids Flashcards
What is the equation to convert mEq/L to mmol/L?
mEq/L = mmol/L x valence
Intracellular homeostasis is maintained by what?
Shifts in water, solutes and other substances across the cell membrane.
Fill in the blanks in mEq/L: ECF/ICF Na+: K+: Ca2+: Mg2+: Cl-: HCO3-: HPO4 2-, H2PO4-: Protein -:
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
In most disease states, loss of fluids occurs initially where?
ECF
What is the 60:40:20 rule?
An easy way of remembering distribution of body fluids - 60% is water, 40% is ICF and 20% is ECF.
What makes up the transcellular fluid compartment? What percentage of total body fluid does this compartment make up?
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.
Dense connective tissue, bone and cartilage contain approximately ____% of total body water.
15%
These tissues exchange fluid very slowly and this is usually not taken into account when considering fluid therapy.
The vascular endothelium is freely permeable to ________?
Ionic solutes. Therefore, the concentration of these ions is almost the same in ISF as in plasma.
Describe the Gibbs-Donnan equilibrium.
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.
Describe the two ways that sodium can move into or out of cells.
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).
What are the most abundant anions in the ECF?
Chloride and bicarbonate
What enzyme creates bicarbonate from water and CO2?
Carbonic anhydrase
What are the primary cations in the ICF?
Potassium and magnesium
Which ion is primarily responsible for generating the cell membrane at approximately -70 mV?
Potassium. Almost 100% of potassium is exchangeable.
What are the predominant anions in the ICF?
organic phosphates and proteins
Definition of molality:
Number of moles of solute per kilogram of solvent
Definition of molarity:
Number of moles of solute per liter of solution
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?
[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
In clinical medicine, why is osmolality measured in serum and not plasma?
Because the addition of anticoagulants for plasma would increase the solute in the sample.
What is the average measured serum osmolality in the dog? In the cat?
Dog: 300 mOsm/L
Cat: 310 mOsm/L
True or false: glucose is a permeable solute.
False. Glucose is an impermeable solute and therefore an effective osmole.
What is tonicity?
Effective osmolality
True or false: Freezing point depression osmometer measures both effective and ineffective osmoles.
True
Fill in the blank with either , or =
Oftentimes, the tonicity of a solution is ___ than the measured osmolality.
tonicity is often < measured osmolality
Colloid osmotic pressure is only about ___% of the total osmotic pressure.
0.5%. The remainder is made up of impermeable ions, glucose and BUN (if concentration is increased)
What is the formula for calculated osmolality?
2([Na] + [K] + Glucose/18 + BUN/2.8
In the formula for calculated osmolality, why is Na + K multipled by 2?
To account for the contribution of Cl- and HCO3-
In the formula for calculated osmolality, why is glucose divided by 18 and BUN by 2.8?
To convert mg/dL to mmol/L. The molecular of glucose is 180 and that of BUN is 28
What are the types of fluid and solute loss that can occur?
Solute in excess of water (hypertonic fluid), isotonic loss, or water in excess of solute (hypotonic fluid)
What would the effect of hypotonic fluid loss have on the ECF?
The ECF would be hypertonic (and then water would shift from the intracellular space to extracellular to equilibrate)
What would the effect of isotonic fluid loss have on the ECF?
The ECF would be isotonic. No shift of water
What would the effect of hypertonic fluid loss have on the ECF?
Hypotonic ECF. And then fluid would shift from ECF to intracellular to equilibrate.
What is the definition of effective blood volume?
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.
Exchange of solutes and fluid between plasma and interstitial spaces occurs where?
Capillaries
What is Starling’s Law (the OG)?
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)
What is the net filtration pressure in healthy capillaries?
0.3-0.5 mm Hg, at the proximal (arteriolar) end of capillary.
What is the normal anion gap in dogs and cats?
Dogs: 12-24 mEq/L
Cats: 13-27 mEq/L
What is the difference between obligatory water loss and free water loss?
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.
What makes up the majority of urinary solute (two-thirds) in the dog?
Urea
Secretion of ADH is inhibited by a ____% decrease in serum osmolality?
1-2%
If a patient has limited food intake, does their water intake needs increase or decrease?
Decrease.
