electrolyte disorder

Question 1

tobal body water (TBW) - general

Answer 1

• 50% female body weight, 60% male body weight
• decreases w age
• increases w body fat (obese > 120% ideal body weight, use TBW to estimate)
• no. of anion = no. of cation in each compartment cuz equilibrium maintained by cell membrane

Question 2

Total body water (TBW) - composition

Answer 2

1) ICF
- 2/3 TBW
- K+, Mg2+, PO42-, proteins

2) ECF
- 1/3 TBW
- rich in Na+, Cl-, HCO3-
- split into 3/4 intravascular (plasma) and 1/4 interstitial (space btwn cell)

Question 3

serum osmolarity

Answer 3

• independent of weight/nature of particle
• serum osmolarity (mmol/kg) = 2 x Na (mmol/L) + Glucose (mmol/L) + blood urea nitrogen (mmol/L)
• normal: 280 - 300 mmol/kg

Question 4

tonicity

Answer 4

• ability of extracellular solution to make water move into/out of cell by osmosis
• dependent on Na conc
• types
  1) isotonic: same as ICF
  2) hypertonic: tonicity > ICF, water shift from ICF into ECF
  3) hypotonic: tonicity < ICF, water shift from ECF to ICF