Chapter 27 Summary

Summary

Osmotic regulation is the maintenance of a steady osmotic pressure in the blood plasma.
Ionic regulation of any particular inorganic ion is the maintenance of a steady concentration of that ion in the blood plasma.
The concepts of osmotic and ionic regulation can also be applied to the interstitial and intracellular fluids.
Volume regulation is the maintenance of a steady volume (amount) of water in the body as a whole or in a particular fluid compartment. Cell-volume regulation is regulation of the amount of intracellular water in a cell.

The water vapor pressure of air is the partial pressure of water vapor in the air and is the most useful expression of humidity for analysis of evaporation and condensation.
The water vapor pressure of an aqueous solution is the equilibrium water vapor pressure the solution tends to create in juxtaposed air if the solution and air are sealed in a closed system.
Water vapor diffuses from regions of high water vapor pressure to regions of low water vapor pressure. Thus evaporation occurs if the water vapor pressure of an aqueous solution exceeds that of the surrounding air. Evaporation takes place at a rate proportional to the difference in vapor pressure.

The effects of kidney function on the composition of the blood plasma are analyzed using osmotic and ionic U/P ratios. Figure 27.7 summarizes the interpretation of U/P ratios.
Osmotic regulation, volume regulation, and ionic regulation are separable kidney functions in the sense that the kidneys can participate in volume regulation while simultaneously not aiding osmotic regulation, or they can carry out ionic regulation independently of osmotic regulation.

Metabolic water is produced by all animals in amounts determined by the chemical stoichiometry of the oxidation of organic molecules.
To determine the net effect of catabolism on water balance, obligatory respiratory, urinary, and fecal water losses must be subtracted from gross metabolic water production.
The role played by metabolic water in the overall water budget of an animal depends on the animal’s capacity to conserve body water.

For a cell to maintain a constant volume, it must reduce the amounts of osmotically effective dissolved entities in its intracellular fluid when the osmotic pressure of the surrounding extracellular fluid falls, and it must increase its content of dissolved entities when the osmotic pressure of the extracellular fluid rises.
Organic molecules such as free amino acids are the principal intracellular solutes employed for cell-volume regulation by cells of invertebrates. They are also the principal intracellular solutes employed in certain of the tissues (e.g., brain and renal medulla) of vertebrates.
The use of organic molecules as principal agents of cell-volume regulation permits simultaneous ionic and volume regulation of the intracellular fluid.