Fluid/Electrolyte/Acid/Base Balance Questions

-Intracellular fluid (ICF): water contained within cell membranes. [~30L, ~40% of body weight]
-Extracellular fluid (ECF): water contained outside cell membranes. [~14L, ~20% of body weight]
Interstitial [~9L, ~15% of body weight]
Intravascular [~5L, ~5% of body weight]

For the first question,

intracellular fluid (ICF): fluid inside the cell and makes up the body's largest amount of fluid.

extracellular fluid (ECF): fluid outside the cell and includes plasma, serum, and interstitial fluid (ISF).

The simple answer is that if acid-base levels are not maintained, the organism dies.

pH can effect the shape of proteins, the binding of substrates to enzymes, the rate of enzyme catalyzed reactions, etc.

The body's acid–base balance is tightly regulated. Several buffering agents exist which reversibly bind hydrogen ions and impede any change in pH. Extracellular buffers include bicarbonate and ammonia, while proteins and phosphate act as intracellular buffers. The bicarbonate buffering system is especially key, as carbon dioxide (CO2) can be shifted through carbonic acid (H2CO3) to hydrogen ions and bicarbonate (HCO3−) as shown below.

\(\rm HCO_3^- + H^+ \leftrightarrow H_2CO_3 \leftrightarrow CO_2 + H_2O\)

Acid–base imbalances that overcome the buffer system can be compensated in the short term by changing the rate of ventilation. This alters the concentration of carbon dioxide in the blood, shifting the above reaction according to Le Chatelier's principle, which in turn alters the pH. For instance, if the blood pH drops too low (acidemia), the body will compensate by increasing breathing, expelling CO2, and shifting the following reaction to the right such that less hydrogen ions are free – thus the pH will rise back to normal. For alkalemia, the opposite occurs.

The kidneys are slower to compensate, but renal physiology has several powerful mechanisms to control pH by the excretion of excess acid or base. In responses to acidosis, tubular cells reabsorb more bicarbonate from the tubular fluid, collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH3 buffer. In responses to alkalosis, the kidney may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of glutamine metabolism and ammonia excretion.