Question at position 15 Giving leptin to a person who has no receptors for this hormone will most likely cause ___weight gainincreased fat free massweight lossnone of the aboveSingle choice
A
weight gain
B
increased fat free mass
C
weight loss
D
none of the above

Question

Question at position 15 Giving leptin to a person who has no receptors for this hormone will most likely cause ___weight gainincreased fat free massweight lossnone of the above

BlackTom AI · Accepted Answer

Leptin acts on hypothalamic leptin receptors (the Ob-Rb form) to suppress appetite and increase energy expenditure, so its physiological effects require functional receptors and intact downstream signaling (JAK-STAT pathway).

1) Relevant knowledge points and concepts
- Leptin is an adipocyte-derived hormone that signals body energy stores to the brain, primarily via Ob-Rb receptors in the hypothalamus.
- Binding of leptin to its receptor triggers intracellular signaling that reduces food intake and can increase energy expenditure.
- Two distinct clinical situations: leptin deficiency (no hormone) and leptin receptor deficiency (no functional receptor). Replacement therapy works in leptin-deficient patients but not in receptor-deficient patients.

2) Complete step-by-step reasoning
- Step 1: Identify the patient’s problem: absence of leptin receptors (no functional Ob-Rb).
- Step 2: Determine mechanism: exogenous leptin requires receptor binding to produce anorectic and metabolic effects.
- Step 3: Predict outcome: without receptors, injected leptin cannot bind and cannot activate hypothalamic signaling pathways.
- Step 4: Conclude the most likely clinical effect: no direct change in weight or body composition caused by leptin administration.

3) Calculations
- No quantitative calculation is required; this is a mechanistic, qualitative inference.

4) Why the correct answer is correct
- “None of the above” is correct because all listed physiological effects of leptin (weight loss via appetite suppression, increased fat-free mass, weight gain) depend on receptor-mediated signaling. With absent receptors, leptin cannot exert these effects; therefore administration is unlikely to cause the listed changes.

5) Why the other options are incorrect
- Weight loss: incorrect because leptin cannot trigger anorectic pathways without receptors.
- Increased fat-free mass: incorrect because anabolic or body-composition effects are mediated through receptor signaling; absent receptors prevent this.
- Weight gain: incorrect because exogenous leptin does not promote weight gain via any receptor-independent pathway; if anything leptin signaling normally opposes weight gain, but without receptors there is no change.

6) Conclusion
Because leptin requires its receptor to function and the patient has no receptors, administering leptin will most likely produce no of the listed effects. Final answer: none of the above.

Question at position 15 Giving leptin to a person who has no receptors for this hormone will most likely cause ___weight gainincreased fat free massweight lossnone of the aboveSingle choice

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