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NOVA scienceNOW: Obesity
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Program Overview
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Scientists
discuss leptin, a hormone made in the body's fat cells. Leptin is involved in
appetite—when the brain detects low levels of leptin, it causes a person
to feel hungry. However, mutations can interfere with the delivery of leptin's
signal to the brain. When the body produces little or no leptin or when leptin
receptors are nonfunctional, the brain never receives the signal that the body
has sufficient amounts of fat. As a result, the brain continues to prompt the
person to keep eating. Researchers have found that humans and other animals
with low leptin levels or a diminished ability to detect leptin tend to become
obese.
This NOVA scienceNOW segment:
discusses that most adults have a "set point"—a stable,
maintainable weight that fluctuates very little. This set point is different
for different people. points out that leptin may affect appetite by turning off neural circuits
in the brain that stimulate appetite and by turning on neural circuits that
allow one to feel satiated. explains that the MC4R receptor is faulty or nonfunctioning in some obese
people, and that one in 1,000 people may carry this MC4R mutation. states that mice that do not produce leptin are obese. notes that it is important to try to stay at the lower end of one's
optimal weight range, to exercise regularly, eat a heart-healthy diet, and
recognize that for some people, maintaining a healthy weight is more difficult
than for others.
Key Terms
endocrine system: A chemical communication system in the body that controls
physiologic processes, such as growth, development, and appetite. hormones: Chemical messengers made by one type of cell that
regulate the function of other types of cells (and sometimes the cell that made
the hormone). Hormones have a specific structure that can bind to specific
receptors, allowing for precise control of the cells they regulate. leptin: A hormone produced by fatty tissue (adipocytes) that acts
on the brain, ultimately influencing appetite, body fat storage, and other
physiologic processes. mutation: A change in a gene that alters the message carried by
the gene. The gene product (often a protein) may be altered so that it
functions differently or not at all. plasma membrane: The outer membrane of animal cells, made of a
lipid bi-layer. It controls the movement of substances in and out of the cell.
receptor: A molecule on the plasma membrane or inside a cell that
binds a specific substance, such as a hormone, and triggers a cellular
response. For peptide hormones, receptors are in the plasma membrane. For
steroid and thyroid hormones, the receptors are in the cytoplasm and
nucleus. target tissue: A tissue with a receptor for a specific hormone
that responds chemically to the hormone.
Taping Rights: Can be used up to one year after the program is taped off the air.
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