Fluid Compartments and Osmolarity - Anatomy and Physiology
- A 70 kg man's body is 60 percent water. What is his total body water?
- 42 L, because 0.60 x 70 kg = 42 kg of water, and 1 kg of water is about 1 L.
- What fraction of total body water is intracellular fluid?
- About two-thirds; the remaining one-third is extracellular fluid.
- A person rapidly drinks a large volume of pure water. How do ECF osmolarity and ICF volume change?
- ECF osmolarity falls, so water moves into cells by osmosis and ICF volume increases (ECF volume rises as well).
- A patient receives an infusion of hypertonic saline. How do ICF and ECF volumes change?
- ECF osmolarity rises, so water moves out of cells: ICF volume decreases and ECF volume increases.
- What are the two main subdivisions of the extracellular fluid, and which is larger?
- Interstitial fluid and plasma. Interstitial fluid is larger, about three-quarters or more of the ECF.
- How does tonicity differ from osmolarity?
- Osmolarity counts all solute particles; tonicity reflects only solutes that cannot cross the cell membrane, so it determines whether cells swell or shrink.
- About what percentage of body weight is water in an average young adult male?
- About 60 percent.
- What is transcellular fluid?
- A small part of the ECF found in epithelium-lined spaces, such as cerebrospinal, synovial, pleural, and intraocular fluids.
- A patient receives an IV infusion of isotonic (0.9 percent) saline. How do ECF volume, ICF volume, and osmolarity change?
- ECF volume increases, while ICF volume and osmolarity stay essentially unchanged, because no osmotic gradient forms across cell membranes.
- Why do people with a higher proportion of body fat have a lower percentage of body water?
- Adipose tissue contains little water compared with lean tissue such as muscle.
- A person has 42 L of total body water, two-thirds of it intracellular. What is the intracellular fluid volume?
- 28 L (two-thirds of 42 L), leaving 14 L of extracellular fluid.
- What is the normal osmolarity of plasma?
- About 285 to 295 mOsm/L (roughly 290), essentially equal in the ICF and ECF at steady state.