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← Theoretical 1

Q42 — Thyrocyte Adenylyl Cyclase — TSH and VIP/PACAP Pathways

Theoretical 1 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Endocrine System Physiology

The following image depicts the pathways which activate the adenylyl cyclase (AC) enzyme in thyrocytes of the thyroid gland. AC — adenylyl cyclase, GS (G protein) — stimulating protein, TSH — thyroid-stimulating hormone.

Diagram showing TSH-receptor and VIP/PACAP receptor both signalling through their own GS proteins to a shared adenylyl cyclase (AC), producing cAMP. TSH-receptor and VIP/PACAP receptors both activate the shared adenylyl cyclase (AC) via their respective GS proteins, producing cAMP and regulating cellular processes in the thyrocytes.

Determine whether the following statements are true or false:

A. The activation of AC, which occurs by TSH binding to its receptors, plays a important role in the production of thyroid hormones (TH).
B. The peptide hormone PACAP activates AC via VIP/PACAP receptors.
C. GS proteins activate AC by catalyzing the synthesis of secondary messenger - cAMP.
D. One of the mechanisms of thyroid hypofunction is the increased sensitivity of the thyrocyte AC system to TSH, as well as the increased number of TSH receptors.
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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)