Correction of hypoxemia is regulated by
a positive feedback loop
an enzymatic amplification
a negative feedback loop
a self-amplifying mechanism
a cascade effect
The Correct Answer is C
A. A positive feedback loop: Positive feedback amplifies a response (e.g., oxytocin in labor); oxygen regulation requires balance, not amplification.
B. An enzymatic amplification: This refers to intracellular signaling cascades, not whole-body oxygen regulation.
C. A negative feedback loop: Hypoxemia stimulates chemoreceptors → increases respiratory drive → raises oxygen levels. Once oxygen is restored, stimulation decreases, demonstrating a classic negative feedback loop.
D. A self-amplifying mechanism: This is another way of describing positive feedback, which does not apply to oxygen regulation.
E. A cascade effect: Cascade effects occur in clotting or enzyme cascades, not in oxygen regulation.
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Related Questions
Correct Answer is {"dropdown-group-1":"D"}
Explanation
A. thymus: The thymus secretes thymosins that influence T-cell maturation (immune function), not hormones that raise blood calcium - so it does not respond to hypocalcemia.
B. thyroid gland: The thyroid’s parafollicular (C) cells secrete calcitonin, which lowers blood calcium in response to hypercalcemia, not hypocalcemia.
C. pituitary gland: The pituitary releases many trophic hormones, but it does not directly secrete the primary hormone (PTH) that corrects hypocalcemia.
D. parathyroid glands: The parathyroid glands secrete parathyroid hormone (PTH) in response to low blood Ca²⁺; PTH raises serum calcium by acting on bone, kidney, and vitamin D activation.
E. pineal gland: The pineal gland secretes melatonin to regulate circadian rhythms, not calcium homeostasis.
Correct Answer is D
Explanation
A. CP: Creatine phosphate (phosphocreatine) is an energy-reserve molecule in muscle that donates phosphate to ADP to regenerate ATP; it is not a second messenger in hormone signal transduction and would not appear as the intracellular signaling oval shown.
B. DPG: 2,3-diphosphoglycerate (2,3-DPG) is an RBC metabolite that modulates hemoglobin’s O₂ affinity; it is not produced as a cytoplasmic second messenger following receptor activation.
C. PEP: Phosphoenolpyruvate (PEP) is a glycolytic intermediate involved in metabolism, not a hormone-activated intracellular signaling molecule.
D. CAMP: Cyclic AMP (cAMP) is a common second messenger produced by adenylate cyclase after many peptide hormones bind cell-surface receptors; the diagram’s small oval (C) inside the cytoplasm leading to downstream effects (D) fits cAMP.
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