Slide 1
A chemical message in circulation
Hormones are chemical messengers that can travel through blood. A cell responds only when it has the relevant receiving machinery.
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Endocrine glands release their messages into the circulation rather than through a delivery duct. The pancreas illustrates that an organ can have endocrine functions alongside a separate duct-based digestive role.
Slide 2
The receptor makes a target
A receptor is a protein that recognizes a particular signal. Its presence helps determine which cells can respond to a hormone.
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Different target cells can turn the same hormonal message into different actions. Recognition begins the response, but the machinery inside the cell determines what follows.
Slide 3
Some messages stay outside
Many hormones bind receptors at the cell surface. The binding event starts a chain of signals inside the cell.
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Small internal messenger molecules can amplify a response, so one external binding event can influence many downstream molecules. The hormone itself need not enter the cell to have a substantial effect.
Slide 4
Other messages reach inward
Some hormones bind receptors inside cells. The resulting interaction can alter which genes are used to make proteins.
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This route helps explain why hormonal responses can unfold over different timescales. A change in protein production has different timing from rapidly changing the activity of a protein already present.
Slide 5
Feedback limits the response
Hormone systems often use negative feedback: a downstream effect reduces the signal that helped produce it. This supports regulation.
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The number and sensitivity of receptors can also change. A concentration measured in blood is therefore only one part of the story of how a tissue experiences a hormone.
Sources
- Hormones
OpenStax, Rice University
- Glands and Hormones
NCBI, NIH