Leptin is a hormone released by fat cells that signals the hypothalamus about how much body fat you have. Higher leptin tells your brain you've stored enough energy, which reduces hunger and helps keep body weight stable.
Leptin is a hormone made by your fat (adipose) cells. The more fat you store, the more leptin you release, and that leptin travels through the blood to your hypothalamus, the brain's hunger-control center. Think of leptin as your body's "fuel gauge" hormone. When it's high, your brain reads the tank as full and dials down appetite.
Leptin is part of the endocrine system, the network of glands and hormones covered in Topic 2.2. Hormones act more slowly than nerve signals but can affect the whole body. Leptin's specific job is long-term energy balance: keeping your body weight in a stable range over time rather than minute-to-minute. That's why it pops up again in Topic 7.2 when AP Psych explains the biological side of hunger and motivation.
Leptin sits at the intersection of two units. In Unit 2 it's a concrete example of how the endocrine system uses hormones to communicate, and in the motivation material it explains why your body pushes you to eat. The exam uses leptin to test whether you understand the biological perspective on motivation, that hunger isn't just willpower but a hormone-driven feedback loop. Pairing leptin (the "I'm full" signal) with ghrelin (the "I'm hungry" signal) is the classic setup for showing you grasp how the body regulates eating.
Keep studying AP Psychology Unit 7
Ghrelin and the Hunger Hormone Pair (Unit 7)
Ghrelin and leptin are opposites that work as a team. Ghrelin (from the stomach) shouts "eat now," while leptin (from fat cells) says "we have enough stored." Knowing both gives you the full hunger-regulation picture the exam wants.
Drive-Reduction Theory (Unit 7)
Leptin is the biology behind a drive. When energy stores drop and leptin falls, your body creates a hunger drive that motivates you to eat and restore balance, which is exactly what drive-reduction theory describes.
Circadian Rhythm and Sleep (Unit 2)
Sleep loss messes with leptin and ghrelin levels, lowering leptin and raising ghrelin so you feel hungrier than you should. This links the endocrine system to your daily biological clock.
Biological Perspective (Units 2 and 7)
Leptin is a textbook example of explaining behavior through biology. Instead of treating overeating as a choice, the biological perspective points to hormones and brain signaling.
Leptin shows up almost entirely in multiple-choice questions about hunger and hormones. Expect stems like "Which hormone signals the body it is full?" or trickier ones like "Which of the following does NOT tell your body it is hungry?" (leptin is the odd one out there, since it suppresses hunger). A common variation asks how sleep deprivation changes ghrelin and leptin levels. No released FRQ has used leptin by name, but it's solid evidence for any free-response prompt asking you to explain hunger from the biological perspective. Your main job: remember leptin = full/satiety, not hunger.
This is the trap. Ghrelin makes you hungry; leptin makes you feel full. A quick memory hook: ghrelin "growls" like an empty stomach, while leptin comes from fat cells and tells your brain to ease up on eating. Mix these up and you'll miss the "which hormone" MCQs every time.
Leptin is a hormone made by fat cells that tells the hypothalamus how much body fat you have.
High leptin signals "full" and reduces appetite, so it's a satiety hormone, not a hunger hormone.
Leptin and ghrelin are opposites: leptin suppresses hunger, ghrelin stimulates it.
Sleep deprivation lowers leptin and raises ghrelin, which makes you feel hungrier.
Leptin is a go-to example for explaining hunger through the biological perspective in Topic 7.2.
Leptin is a hormone released by fat cells that signals your hypothalamus about your body fat level. When leptin is high, your brain reads it as "we have enough energy stored" and reduces hunger, helping keep your weight stable.
No, that's the opposite of what it does. Leptin suppresses hunger by telling your brain you have enough stored energy. The hormone that makes you hungry is ghrelin.
Ghrelin comes from the stomach and stimulates hunger; leptin comes from fat cells and signals fullness. On the exam, leptin is the "satiety" hormone and ghrelin is the "hunger" hormone.
Lack of sleep lowers leptin and raises ghrelin. With less leptin signaling fullness and more ghrelin signaling hunger, you feel hungrier, which is why sleep deprivation is linked to overeating.
Yes, it shows up in multiple-choice questions about the endocrine system (Topic 2.2) and hunger motivation (Topic 7.2). The most common question type asks you to identify which hormone signals fullness versus hunger.
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