Lecture 4- Body Fluids, Diffusion and Osmosis

Question 1

Body Fluid Content

Answer 1

• Average total body water (TBW) is 60% for males, 50% for females (bc have more fat)
• decreases w age

Question 2

Distribution of Adult Body Fluid

Answer 2

TBW= .5x body weight or .6x body weight 
ECF: TBW x 1/3 
ICF: TBWx 2/3 
Blood Plasma Volume (BPV): ECFx1/4 
Interstital Volume (ISF): ECF-BPV

Question 3

Hematocrit Level

Answer 3

Plasma = 1- hematocrit

-varies w age

Question 4

Composition of Body Fluids

Answer 4

• Water (universal solvent)
• Non electrolyte solutes: uncharged moieties (glucose, lipids, creatin, urea, neutral proteins
• Electrolyte solutes: charged molecules (inorganic salts, all acids/bases, charged proteins)

Question 5

Electrolyte Composition

Answer 5

ECF: Na+: 140, K+:4 Cl-: High Ca2+: High
ICF: Na+:14 K+:120 Ca2+: Negligible CL-: Low

Question 6

Units of Concentration

Answer 6

• mol/L= grams of solute in 1 L of solution/molecular weight
• mmol/L= mol/Lx1000
• Eq/L=mol/Lx number/charge of atoms
• % solution= grams of S/100mL
• For Eq/L, multiply by 2 for divalent ions

Question 7

Osmolarity and Osmolality

Answer 7

-Osmole (osm) is # of moles of solute that contribute to osmotic pressure
-Osmolarity expressed as osm/L of solvent
osm/L =[S] x Number of particles S dissociates into in solution Ex: NaCl-> Na+ +CL-=> 15 mmol/L NaCl is 30mOsm/L solution
-Osmolality is Osm/kg H20, not varied by temperature
-Negligible in this situation

Question 8

Diffusion

Answer 8

• Rate is proportional to 1/distance^2

- Inversely related to mechanism size

Question 9

Osmotic Pressure

Answer 9

-Pressure that must be applied to oppose osmosis
-(pi) measured in units of atmospheres (atm) or millimeter of mercury (mm Hg)
1 atm=760 mm Hg

Question 10

Plasma Osmolarity

Answer 10

-290 mOsm/L
-Can be estimated from plasma concentrations of Na+ Plasma osmolarity= 2[Na+]
More accurate: 2[Na+] + [glucose]/18 + [urea]/2.8

Question 11

Osmolarity of Body Fluids

Answer 11

• Same in ICF and ECF at equilibrium
• Regulates distribution of water among compartments, water goes to higher osmolarity
• Isosmotic: same as plasma osmolarity
• Hyposmotic: lower than plasma osmolarity <290 mOsm/L
• Hyperosmotic: higher than plasma osmolarity > 290mOsm/L

Question 12

Tonicity

Answer 12

-Depends on permeability of solutes across cell membrane
For solute that does not cross membrane:
-Isotonic if cell volume hasnt changed at equilibriu,
-Hypertonic, if cell shrunk at equilibrium
-Hypotonic, if cell is swollen at equilibrium

Question 13

Tonicity as Function of Permeability

Answer 13

• If impermeable, only water will move
• Impermeable substance is osmotically active
• If permeable, solute can move too

Question 14

Tonicity of Complex Solutions

Answer 14

• Solutes will move in and out of cell to balance penetrating solutes
• Water will move in or out of cell to balance nonpenetrating solutes

Question 15

Fluid Infusion

Answer 15

• Addition of Isotonic NaCl: ECF will increase, ICF will not increase because there is no net movement of fluid into cells
• Addition of Hypotonic NaCl: ICF and ECF will increase bc/ solution has more water, osmolarity will decrease
• Addition of Hypertonic NaCl: ICF volume will shrink bc water leaves cell, ECF increases from water leaving cell, overall osmolarity increases