NaCl dissociates into two osmotically active particles in solution (Na + and Cl −) and, thus, a 1 mmol/L–NaCl solution has an osmolarity of ~2 mOsm. Glucose does not dissociate in solution, so a 1-mmol/L glucose solution has an osmolarity of 1 milliOsmole (mOsm). Osmolarity is a measure of a solute's ability to generate osmotic pressure that takes into account how many particles a solute dissociates into when dissolved in water. Osmotic pressure can be measured physically as the amount of pressure required to precisely counter water movement between two solutions with dissimilar solute concentrations ( Figure 3.3). Where n is the number of particles that a given solute dissociates into when in solution, C is solute concentration (in mmol/L), and R and T are the universal gas constant and absolute temperature, respectively. The osmotic pressure of a solution (π measured in mm Hg) can be calculated from: Therefore, two small ions such as Na + generate a higher osmotic pressure than a single complex glucose polymer such as starch (MW >40,000) as shown in Figure 3.2. An apparent peculiarity of the process is that pressure is determined entirely by solute particle number and is largely independent of the size, mass, chemical nature of the solute, or even its electrical valence.
Osmotic pressure gradients are created when solute molecules displace water, thereby decreasing water concentration. Thus, a chemical concentration gradient becomes an osmotic pressure gradient. The concentration difference required to generate physiologically significant water flow across membranes is very small, so, in practice, it is far more convenient to discuss osmosis in terms of the amount of pressure that water is capable of generating as it moves down its concentration gradient. Although cells do not contain pure water, it is nevertheless a superabundant chemical. Pure water has a molarity of >55 moles/L.
Osmosis describes a process by which water moves passively across a semipermeable membrane, driven by a difference in water concentration between the two sides of the membrane.
This approach is effective because water is enslaved to solute concentration by osmosis. The body does not contain a transporter capable of redistributing water between compartments, so its approach to water management at the cellular and tissue level is to manipulate solute concentrations within intracellular fluid (ICF), extracellular fluid (ECF), and plasma. Loss of water from the cell raises intracellular solute concentrations and, thereby, interferes with normal cell function. Although TBW is tightly regulated, water moves freely across cell membranes and between the body's different fluid compartments. Thus, the autonomic nervous system ( ANS) closely monitors total body water ( TBW) and adjusts intake and output pathways (drinking and urine formation, respectively) to maintain water balance (see 28 The biochemistry of life is highly sensitive to solute concentration, which, in turn, is determined by how much water is contained within a cell. Water is the universal solvent, facilitating molecular interactions, biochemical reactions, and providing a medium that supports molecular movement between different cellular and subcellular compartments. The proportion of water in cells is even greater (~80%) as shown in Figure 3.1, the remainder largely comprising proteins.
Review intracellular extracellular body fluid compartments series#
This can be confirmed by the fact that when these persons place their feet on somewhere else rather than the floor, they do not develop an edema.One of the more memorable quotes from the popular television series Star Trek: The Next Generation came from a silicon-based alien life form that referred to the intrepid Captain Picard as an “ugly bag of mostly water.” The average human body comprises 50%–60% water by weight, depending on body composition, gender, and age of the individual. From observations, I do believe that a cemented floor causes the development of feet edema in specific individuals with genetic predisposition. Edema being a sign/symptom as an entity does cause other signs and symptoms in the body. I do believe that it can be classified into appendicular and axial edemas with reference to the body division rather than the present classification of peripheral edema and other edemas. Text Book of Medical Physiology, 11th Edition, Saunders/Elsevier, Philadelphia.ĭevelopment of Feet Edema on Contact with a Cemented Floor in Specific Individuals with Genetic PredispositionĮdema, Appendicular, Axial, Cemented Floor, Feet, Genetic PredispositionĪBSTRACT: Edema is a sign/symptom which has origin diverse causes and mechanisms of installations. Guyton & Hall (2006) The Body Fluid Compartments Extracellular and Intracellular Fluids Interstitial Fluid and Edema.
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