Which of the following is considered part of the extracellular fluid (ECF)?

A. equation shifts left, respiratory acidosis, hypoventilation: Respiratory acidosis is caused by the retention of carbon dioxide, not the loss of gastric hydrochloric acid. A leftward shift would occur to consume excess hydrogen ions, which contradicts the loss of acid. Hypoventilation is a response to alkalosis.

B. equation shifts right, metabolic alkalosis, hypoventilation: Loss of gastric protons causes a rise in systemic pH, characterizing metabolic alkalosis. To replace the lost hydrogen ions, the carbonic acid-bicarbonate equation shifts right. The lungs then slow the breathing rate to retain carbon dioxide and lower pH.

C. equation shifts right, metabolic acidosis, hyperventilation: Metabolic acidosis involves an excess of hydrogen ions, which is the opposite of what occurs during vomiting. Hyperventilation is the compensation for acidemia, intended to blow off carbon dioxide. Vomiting specifically depletes acids, leading to an alkaline state.

D. equation shifts left, metabolic alkalosis, hyperventilation: While metabolic alkalosis is the correct diagnosis, a leftward shift would only occur if there were an excess of hydrogen and bicarbonate. Furthermore, hyperventilation would worsen alkalosis by removing more acid. The body compensates by slowing respiration to retain acid.

A. The buffering ability of proteins is due to their charged amino acid side chains: Proteins contain carboxyl and amino groups that can donate or accept protons depending on the surrounding pH. Hemoglobin and plasma albumin are major contributors to the body's total buffering capacity. This allow proteins to stabilize both intracellular and extracellular fluids.

B. Proteins act only in acidic environments: Proteins are amphoteric molecules, meaning they can function as both acids and bases. They neutralize excess hydrogen ions in acidic states and release hydrogen ions in basic states. This versatility makes them effective across a wide spectrum of physiological pH disturbances.

C. Protein buffering is insignificant compared to other mechanisms: Intracellular proteins and hemoglobin represent one of the largest buffering pools in the human body. While the bicarbonate system is the primary extracellular buffer, proteins provide massive buffering power within the cells. They are a critical component of acid-base homeostasis.

D. Proteins buffer by converting to enzymes under pH stress: Enzymes are proteins with specific catalytic functions, but they do not "convert" into new forms to provide buffering. Buffering is an inherent chemical property of the protein structure itself. pH stress actually risks denaturing enzymes and destroying their functional capacity.