Compartment and Composition of Body Fluid

What is osmolarity

PARTICLES in a solution → 1 mmol of NaCl = 2 mOsm

What is the 60:40:20 rule

60% of the body is water, 40% is ICF, 20% is ECF

What solutes are in ECF and ICF

ECF: Na, Cl, HCO3-, ICF: K, Ca

What is the dilution method

Using substances that settle in specific compartments to measure concentration

What substances are found specifically in ICF

Mannitol and inulin

What substances are found specifically in ECF

Albumin

What are the 3 steps to approach changes in fluid compartments

1. How did ECF and its osmolarity change

2. Does water shift in our out of ICF

3. What are the consequences (Plasm v, plasm conc, Hct)

What occurs in diarrhea (3 step approach)

1. Loss of fluid and solutes but osmolarity same → Isosmotic

2. ECF volume DECREASE but osmolarity is UNCHANGED → NO water shift → Contraction

3. Plasma vol and AP decrease, plasma conc and Hct increase

What occurs in marathon (3 step approach)

1. Loss of water > solutes = hyperosmolarity

2. ECF volume decrease , osmolarity increase → Water shift from ICF to ECF → Contraction

3. Plasma vol decrease, plasma conc increase, Hct unchanged

What occurs in adrenal insufficiency (3 step approach)

1. Higher sodium reabsorption → loss of sodium into urine → hypoosmotic

2. Na OUTSIDE cell → ECF Osm < ICF Osm → Water moves from ECF to ICF → Contraction

3. Plasma vol decrease, plasma conc increase, Hct increase (RBC get bigger)

What occurs in isotonic NaCl infusion (3 step approach)

1. Solution is ISOTONIC → Isoosmotic

2. ECF volume increase, osmolarity same → No water movement → Expansion

3. Plasma volume increase, plasma conc decrease, Hct decrease (more volume)

What occurs when you eat salty chips (3 step approach)

1. More ECF solutes → ECF Osm increase → Hyperoosmotic

2. ECF Osm > ICF → Water moves from ICF to ECF (ICF volume decrease, ECF vol increase) → Expansion

3. Plasma volume increase, plasma protein conc decrease, Hct decrease

What occurs in SIADH (3 step approach)

1. More water reabsorption → More water → Osmolarity decrease → Hypoosmotic

2. ECF and ICF volume increase, Osmolarity decrease → Expansion

3. Plasma volume increase, plasma protein conc decrease, Hct unchanged

What determines whether something is expansion or contraction

ECF Increase = expansion, ECF volume decrease = contraction