Direct action of parathyroid hormone include everything EXCEPT

JIPMER Nursing Officer-2017

Applied Physiology

Medium

Appeared in: JIPMER Nursing Officer-2017

Explanation

The primary function of Parathyroid Hormone (PTH) is to increase blood calcium levels.
PTH's effect on the intestine is indirect; it does not have receptors on intestinal cells.
PTH directly stimulates the kidneys to produce 1,25-dihydroxyvitamin D (calcitriol), the active form of Vitamin D.
It is this active Vitamin D, not PTH, that directly acts on the small intestine to increase the absorption of dietary calcium.

Option A: This is a primary and direct action of PTH. The hormone binds to receptors on osteoblasts, which in turn signal osteoclasts to increase bone resorption, releasing calcium into the blood.
Option C: This is a direct action of PTH. The hormone acts on the distal convoluted tubules of the kidneys to increase the reabsorption of calcium, reducing its excretion in urine.
Option D: This is a direct action of PTH. The hormone stimulates the enzyme 1-alpha-hydroxylase in the proximal tubules of the kidneys, which is the final step in activating Vitamin D.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Direct and Indirect Actions of Parathyroid Hormone (PTH) as background academic context rather than a clinical decision trigger.
Understanding PTH's mechanism is crucial for managing calcium disorders. In hyperparathyroidism, excess PTH leads to hypercalcemia (high blood calcium), causing symptoms like kidney stones, bone pain, and constipation.
In hypoparathyroidism, insufficient PTH leads to hypocalcemia (low blood calcium), causing neuromuscular irritability, which can be assessed with Chvostek's sign (facial muscle twitch) and Trousseau's sign (carpal spasm).
What if the patient has chronic kidney disease? The kidneys' ability to activate Vitamin D in response to PTH would be impaired. This would lead to decreased intestinal calcium absorption, contributing to hypocalcemia and secondary hyperparathyroidism, a common complication in CKD.

How to Approach the Question

First, identify the keywords in the question stem: 'direct action', 'parathyroid hormone', and the negative keyword 'EXCEPT'.
The word 'EXCEPT' signals that three of the options are correct descriptions of PTH's direct actions, and your task is to find the one that is not.
Systematically evaluate each option. Recall the main target organs of PTH.
Remember that PTH acts directly on bone and kidneys.
Consider the action on the intestine. Recall that this action is mediated by another hormone that PTH activates.
This identifies the indirect action, which is the correct answer for this 'EXCEPT' question.

Concept Tested & Keywords

Concept Tested: Direct and Indirect Actions of Parathyroid Hormone (PTH)
Stem keywords: parathyroid hormone, direct action
Lead-in keywords: EXCEPT
Negative lead-in flag: The question asks to identify the action that is NOT a direct effect of Parathyroid Hormone, which requires careful elimination of the direct actions.

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