PHED-2507EL Lecture Notes - Lecture 10: Body Water, Plasma Osmolality, Serous Fluid
29 Apr 2019
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Infants are 73% or more water (low body fat, low bone mass) Adult females: ~50% (higher fat content, less skeletal muscle mass: adipose tissue is least hydrated of all, total body water in adults averages ~40l. Water content declines to ~45% in old age. Intracellular fluid (icf) compartment: fluid inside cells accounts for 2/3 of total body fluid. Extracellular fluid (ecf) compartment: fluid in two main ecf compartments outside cells accounts for 1/3 of total body fluid: plasma 3 l. Interstitial fluid (if): 12 l in spaces between cells: also considered part of if: lymph, csf, humors of the eye, synovial fluid, serous fluid, and gastrointestinal secretions. Osmotic and hydrostatic pressures regulate continuous exchange and mixing of fluids. All body fluid osmolality is almost always equal. Change in solute concentration of any compartment leads to net water flow. Increase ecf osmolality water leaves cell: decrease osmolality water enters cell.
