Which statement about plasma osmolality is true?
It measures the volume of blood plasma only.
It is influenced by the balance of solutes and water in the blood.
It has no relationship to hydration status.
It varies greatly in healthy individuals.
The Correct Answer is B
A. It measures the volume of blood plasma only: Osmolality refers to the concentration of particles per kilogram of solvent rather than the total volume of the compartment. Volume is a quantitative measure of space, while osmolality is a qualitative measure of solute density. These are distinct hemodynamic parameters.
B. It is influenced by the balance of solutes and water in the blood: The ratio of dissolved particles, primarily sodium, glucose, and urea, to the volume of water determines the osmotic pressure. High water intake decreases osmolality through dilution. Conversely, water loss through perspiration or diuresis increases the concentration of these solutes.
C. It has no relationship to hydration status: Plasma osmolality is the primary physiological indicator used by the hypothalamus to monitor hydration. Rising osmolality triggers the thirst mechanism and the release of antidiuretic hormone to conserve water. It is the most sensitive marker for systemic water balance.
D. It varies greatly in healthy individuals: Homeostatic mechanisms maintain plasma osmolality within a very narrow range, typically 280 to 295 mOsm/kg. Tight regulation ensures that cells do not experience osmotic shock or volume shifts. Significant variations usually indicate underlying pathological states or severe dehydration.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. Lipids used for long-term energy storage: Triglycerides and fatty acids comprise the primary lipid stores within adipose tissue for metabolic fuel. Electrolytes are inorganic mineral salts that do not contain the hydrocarbon chains characteristic of lipids. They serve electrochemical rather than caloric functions.
B. Proteins that form cell membranes: Structural proteins and phospholipids constitute the lipid bilayer and associated transport channels. While some membrane proteins act as ion pumps, they are macromolecular organic compounds. Electrolytes are the specific charged particles transported by these proteins.
C. Ions from dissociated salts that carry electrical charges: Compounds such as sodium chloride dissociate in aqueous solutions into cations and anions like Na+ and Cl-. These particles are essential for maintaining osmotic pressure and facilitating action potentials across excitable membranes. They conduct electrical currents within physiological fluids.
D. Hormones that regulate metabolic rate: Thyroxine and triiodothyronine are organic signaling molecules produced by the thyroid gland to modulate cellular metabolism. Electrolytes are not chemical messengers but rather the foundational solutes that maintain homeostatic balance. They influence the environment in which hormones function.
Correct Answer is A
Explanation
True: Water molecules spontaneously diffuse across a semipermeable membrane down a water potential gradient. This process moves solvent from a hypotonic environment to a hypertonic environment to achieve osmotic equilibrium. It is a fundamental mechanism for maintaining cellular volume and homeostasis.
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