Hormones are chemical messages that help different parts of the body communicate. They are made by endocrine glands, released into the bloodstream, and carried to cells that can respond to them. Hormones help control growth, energy use, sleep, stress, mood, and body changes during life.
Understanding hormones helps students see how the body stays balanced and reacts to daily needs.
A hormone works only when it reaches a target cell with the correct receptor, similar to a key fitting a lock. After the hormone binds to its receptor, the cell changes its activity, such as taking in more sugar, growing, or releasing another signal. The body uses feedback loops to adjust hormone levels so they do not get too high or too low.
Healthy habits like sleep, balanced meals, physical activity, and stress management support normal hormone signaling.
Key Facts
- Hormones = chemical messengers made by endocrine glands.
- Endocrine glands release hormones directly into the blood.
- Target cells respond only if they have the correct receptor.
- Insulin helps cells take in glucose from the blood for energy.
- Negative feedback helps keep hormone levels balanced, such as high blood sugar causing more insulin release.
- Major endocrine glands include the pituitary, thyroid, adrenal glands, pancreas, ovaries, and testes.
Vocabulary
- Hormone
- A hormone is a chemical messenger that travels through the blood and changes the activity of target cells.
- Endocrine gland
- An endocrine gland is an organ or tissue that releases hormones directly into the bloodstream.
- Target cell
- A target cell is a cell that can respond to a hormone because it has the correct receptor.
- Receptor
- A receptor is a molecule on or in a cell that binds to a specific hormone and starts a response.
- Feedback loop
- A feedback loop is a control system that adjusts hormone release to keep body conditions within a healthy range.
Common Mistakes to Avoid
- Thinking hormones are the same as nerves. Hormones usually travel through blood and often act more slowly, while nerve signals travel through neurons and can act very quickly.
- Assuming every cell responds to every hormone. A cell responds only if it has the matching receptor for that hormone.
- Believing more hormone is always better. Hormones need to stay in a healthy range because too much or too little can disrupt growth, energy, mood, or metabolism.
- Forgetting that glands work together. The endocrine system uses feedback loops, so one gland can affect another and the whole system must stay balanced.
Practice Questions
- 1 A hormone is released by a gland into 5 liters of blood. If 20 milligrams of the hormone are released, what is the concentration in milligrams per liter?
- 2 After a meal, a student's blood glucose rises from 90 mg/dL to 140 mg/dL. By how many mg/dL did the blood glucose increase, and which hormone helps cells take in glucose?
- 3 Explain why a hormone can travel throughout the bloodstream but affect only certain cells in the body.