Which three hormones are primarily responsible for maintaining calcium and phosphate balance in the human body?

A. Heart rate: Tachycardia often serves as a compensatory mechanism for decreased stroke volume in hypovolemic states. While sensitive to changes in fluid status, it does not directly measure the hydrostatic force against arterial walls. It reflects sympathetic nervous system activation.

B. Respiratory rate: Tachypnea may occur in response to metabolic acidosis associated with severe perfusion deficits. It is a secondary indicator of systemic distress rather than a direct measurement of vascular volume. It does not provide data regarding blood pressure fluctuations.

C. Skin turgor: This physical examination technique assesses the elasticity of the dermis and underlying interstitial fluid. Decreased turgor or tenting indicates significant extracellular fluid depletion. It provides a qualitative measure of hydration but does not quantify systemic arterial pressure.

D. Blood pressure: Measuring systolic and diastolic pressures directly evaluates the hemodynamic impact of total circulating volume. Hypotension often reflects intravascular depletion, while hypertension can signify fluid resuscitation excess or volume overload. It is the definitive parameter for monitoring these conditions.

A. Hypotonic; swelling or lysis: Rapid ingestion of free water dilutes the extracellular fluid, reducing its osmolarity relative to the intracellular compartment. Water moves into the cells via osmosis to balance the concentration gradient. This influx causes cellular edema and potentially ruptures the plasma membrane.

B. Isotonic; no change to the cells: An isotonic state occurs when the solute concentration in the plasma matches that of the intracellular fluid. Pure water lacks the electrolytes necessary to maintain this equilibrium. Therefore, cellular volume would not remain stable following the rapid intake of large volumes.

C. Hypotonic; crenation: While the plasma becomes hypotonic, crenation is the result of water leaving the cell, not entering it. Crenation occurs only in hypertonic environments where the exterior solute concentration is higher than the interior. Hypotonicity always leads to expansion rather than shrinkage.

D. Hypertonic; swelling or lysis: A hypertonic plasma would possess a higher osmolarity than the cytoplasm, which would pull water out of the cell. This choice incorrectly pairs a hypertonic state with cellular swelling. Swelling is strictly a consequence of a lower external osmotic pressure.

E. Hypertonic; crenation: Ingesting plain water decreases plasma osmolarity, making it hypotonic, not hypertonic. Hypertonicity typically follows dehydration or excessive salt intake. While crenation is the correct cellular response to hypertonicity, the initial premise of the plasma state is incorrect.