Flashcards in Physiology of Body Fluids Deck (31):
What components make up the extracellular fluid? What separates them?
1. Interstitial fluid - minimal protein - 75%
2. Plasma - 20%
3. Transcellular fluid - 5% - minimal, includes synovial fluid, CSF, intraocular fluid, digestive secretions, etc
Interstitial fluid and plasma separated by capillary wall, relatively permeable to small solutes but not large solutes (proteins)
What is blood volume vs hematocrit?
Blood volume - total volume of intravascular compartment -> plasma + blood cells
Hematocrit - fraction of blood volume occupied by cells
(Hematocrit*BV) + Plasma = BV
Why do women have less body water than men? How do their relative TBW / TBWt's compare?
They tend to have more adipose tissue due to breasts and buttocks. As adipose tissue increases, percent water content goes down.
Male - ~60%, about 42L in a healthy man of 70 kg
Female - ~50%
What are the relative volumes of ICF / ECF and why?
ICF = 2x ECF, thus ICF makes up 2/3 of TBW (total body water). This is because ICF has about 2x as much solute, and water moves by osmosis
How does water content of kidney, muscle, bone, and adipose compare?
Kidney (84%) > muscle > bone > adipose (10%)
How do you calculate plasma volume with hematocrit + blood volume?
PV = BV (1-hct)
How does total body water / total body weight (TBW / TBWt) change with age?
Decreases, so old people have a problem with heat and staying hydrated -> less water to lose
What are the normal sources of daily fluid loss and where might they be severe in each case?
1. Respiration - 1-2L, exercise + extreme cold
2. Perspiration - 1-2L, exercise / hot weather
3. Urination - 1-2L, varies with hydration
4. Defecation - 0.1 L - 25L losses with cholera
What are the major cation differences between ICF and ECF?
ICF: High K+, Low Na+. Gradient maintained by Na+/K+ ATPase
ECF: High Na+, Low K+
ICF also has extra Mg+2
What are the major anion differences between ICF and ECF?
ICF: Proteins and inorganic phosphates, make the cell swell and give overall negative membrane potential
ECF: Chloride and bicarbonate
How are chloride and bicarbonate kept out of the cell?
Negative charge on inside of membrane keeps anions out. Proteins are very negatively charged inside the cell as it is, so the cell has a net negative potential.
How does ionized Ca+2 compare in ICF vs ECF?
ECF is four orders of magnitude higher than ICF so you don't have muscles contracting
How does the osmolality of ICF compare to ECF?
This is the total solute concentration. It is the same in both, because the cell membranes are very permeable to water. ~290 mM / kg H20
What is the major difference between plasma and interstitial fluid (ISF)? How does this affect ion concentrations?
Plasma contains soluble proteins, whereas ISF does not
1. Occupy space - make all solutes more concentrated in the remaining water
2. Carry negative charge - attracts cations from ISF, repels anions into ISF
What percent of plasma volume do proteins + lipids take in plasma solution and how does the relate to protein free plasma?
They take about 7%. Thus, to calculate protein-free plasma, you take the concentrations of ions per liter solution and divide by (1-.07) = 0.93.
Protein-free plasma = plasma water
What is an equivalent? Why is it important?
moles * valence of solute. Valence = charge. I.e. calcium would have a valence of two.
It is important for keeping track of net charge.
What are normal lab values for Na+ in protein-free plasma and cell?
Protein-Free Plasma: 153 mM
Cell: 15 mM
What are normal lab values for K+ in protein-free plasma and cell?
Protein-Free Plasma: 4.7 mM
Cell: 120 mM
What are normal lab values for Ca+2 in protein-free plasma and cell?
Protein-Free Plasma: 1.3 mM
Cell: 1 x 10^-7 M (4 orders of magnitude)
What are normal lab values for Mg+2 in protein-free plasma and cell?
Protein-Free Plasma: 0.6 mM
Cell: 18 mM (total), 1 ionized
What are normal lab values for Cl- in protein-free plasma and cell?
Protein-Free Plasma: 110 mM
Cell: 20 mM
What are normal lab values for HCO3- in protein-free plasma and cell?
Protein-Free Plasma: 24 mM
Cell: 15 mM
How tightly regulated are phosphates?
Not regulated, about 0.7 mM all around
What are normal lab values for protein in protein-free plasma and cell?
Protein-Free Plasma: (None) - 1 mM in regular
Cell: 4 mM
What is normal blood glucose and what is it in cells?
5.9 mM in protein-free plasma, it is very low in cells as it is readily used.
How does pH differ from ECF to ICF?
ICF: ~7.2, slightly lower
What is meant by electroneutrality?
All body fluids are electrically neutral
What is the anion gap?
[Na+] + [K+] > [Cl-] + [HCO3-]. This gap normally amounts to about 9-14 mEq/L, but it works out because the proteins + smaller organic ions have a net negative charge
What are some problems with clinical extracellular Na+ disorders?
Causes abnormal shifts of water between body fluid compartments, especially in brain which can cause seizures, coma, and death
What are some problems resulting from failed K+ gradient?
Coordination problems, muscle weakness