Question

question 85 (0.5 points)
during hypocalcemia, parathyroid glands release parathyroid hormone (pth) in response to low plasma ca²⁺ concentration.
which type of stimulus best describes the mechanism that triggers pth release?
neural
hormonal
humoral
autocrine

Explanation:

To determine the stimulus type for PTH release:

• Neural: Requires nervous system input (not here, as it’s about ion concentration).
• Hormonal: Triggered by another hormone (not the case, as it’s triggered by $Ca^{2+}$ levels).
• Humoral: Triggered by changes in blood/extracellular fluid composition (e.g., ion levels). Hypocalcemia (low $Ca^{2+}$) in plasma directly triggers PTH release, fitting humoral stimulus.
• Autocrine: Hormone acts on the same cell that secretes it (not applicable here, as PTH is released in response to plasma $Ca^{2+}$, not self - signaling).

Answer:

C. Humoral