Question

What is the function of the adipokine Leptin?

• A. To increase the appetite of an individual
• B. To decrease the appetite of an individual
• C. To release neuropeptide Y
• D. To act on orexigenic neurons

Hint:

Leptin acts as the "satiety" signal (suppressing appetite), whereas Ghrelin, secreted by the stomach, acts as the primary "hunger" signal (stimulating appetite).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Leptin is a peptide hormone primarily synthesized and secreted by adipocytes (fat cells) in proportion to the amount of body fat.
As an adipokine, it serves as a long-term signal of energy storage, communicating the status of adipose tissue reserves to the central nervous system.

Step 2: Detailed Explanation:
Leptin circulates in the blood and crosses the blood-brain barrier to bind to specific leptin receptors located in the hypothalamus.
Its primary target is the arcuate nucleus, which contains two distinct populations of neurons regulating energy balance:
Orexigenic neurons, which secrete Neuropeptide Y (NPY) and Agouti-related peptide (AgRP) to stimulate appetite and promote weight gain.
Anorexigenic neurons, which secrete pro-opiomelanocortin (POMC) to promote satiety and suppress food intake.
When fat stores are high, leptin levels increase.
The binding of leptin to its receptors in the hypothalamus results in the inhibition of the orexigenic neurons, reducing the synthesis and release of Neuropeptide Y.
Concurrently, leptin activates the anorexigenic neurons, stimulating the release of $\alpha$-melanocyte-stimulating hormone ($\alpha$-MSH).
The biological outcome of these coordinated neural pathways is a significant decrease in appetite and food consumption, alongside an increase in metabolic rate and energy expenditure.
Conversely, when fat stores drop, leptin levels decline, which triggers hunger and conserves energy.

Step 3: Final Answer:
Thus, the direct physiological function of leptin is to decrease the appetite of an individual.