HUBS1404 Lecture Notes - Lecture 21: Plasma Osmolality, Fluid Balance, Molality
19 Jul 2018
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Icf 2/3 of fluid: ecf 1/3 of fluids. If, plasma, lymph, synovial, serous, git secretion: generally compartments are stable in health, movement of h2o between compartments is driven by osmosis, osmolality is determined by conc. Of solutes that are not freely permeable across membrane(s) separating compartments. If there is a different concentration of solutes between compartments --> water will move to even out the concentration. Principle anion relative to solutes, h2o moves freely between compartments (osmotic & hydrostatic pressure: because na+ is most abundant in ecf - controlling those will lead to control of body fluid osmolality. Water balance: h2o in = h2o out (individual variability in both, h2o in - ingested (tiny bit as by-product of metabolism but negligible, h2o out, urine (60%) Insensible (perspiration, respiratory: skin, sweat faeces, the osmolarity/tonicity/ saltiness of body fluid is precisely regulated. Stronger for adh is the osmolarity (solute concertation) going up rather than just bp dropping - vasodilation causes bp drop.
