What is one primary reason water is considered a universal solvent in the body?
It blocks waste excretion pathways
It stores energy for cellular metabolism
It builds structural proteins in tissues
It dissolves solutes to facilitate biochemical reactions
The Correct Answer is D
A. It blocks waste excretion pathways: Water is essential for the clearance of metabolic wastes through the renal and integumentary systems. It serves as the vehicle for excretion rather than a barrier. Dehydration, not water, leads to the accumulation of toxic metabolites in the bloodstream.
B. It stores energy for cellular metabolism: Adenosine triphosphate and glycogen are the molecules responsible for energy storage and transfer. Water is an inorganic molecule that does not contain high-energy phosphate bonds or caloric value. It facilitates the hydrolysis reactions that release energy from these molecules.
C. It builds structural proteins in tissues: Proteins are synthesized from amino acids via translation in the ribosomes. While the hydrophobic effect of water helps proteins fold into their functional shapes, water is not a building block of protein. It provides the medium in which these structures exist.
D. It dissolves solutes to facilitate biochemical reactions: The polar nature of water allows it to dissociate ionic compounds and surround polar molecules. This creates a homogeneous medium where reactants can collide and interact chemically. It is the fundamental solvent for all intracellular and extracellular metabolic pathways.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
A. Promote calcium excretion by the kidneys: While calcitonin can have a mild phosphaturic effect, its primary physiological target for blood calcium reduction is the bone. Renal excretion of calcium is more significantly regulated by parathyroid hormone levels. Calcitonin primarily functions to inhibit osteoclast-mediated bone breakdown.
B. Enhance calcium absorption from the gut: Increased intestinal absorption would elevate serum calcium levels, contradicting the goal of calcitonin during hypercalcemia. Calcitriol is the hormone responsible for upregulating calcium-binding proteins in the enterocytes. Calcitonin does not stimulate the synthesis of active Vitamin D.
C. Encourage calcium deposition into bone: This hormone, secreted by parafollicular C cells of the thyroid, inhibits osteoclast activity and stimulates osteoblastic mineral deposition. It effectively shifts ionized calcium from the plasma into the hydroxyapatite matrix. This decreases the circulating concentration of calcium.
D. Stimulate bone resorption: Bone resorption releases calcium and phosphate into the bloodstream, which would worsen a state of hypercalcemia. Parathyroid hormone is the agent that triggers this process to raise blood calcium. Calcitonin acts as a functional antagonist by suppressing bone mineral release.
Correct Answer is A
Explanation
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.
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