MYP Biology 4.8 Hormones Notes

What Are Hormones?

1. Hormones are chemical messengers released by endocrine glands.
2. They travel through the bloodstream to reach specific target cells in different organs.
3. Only cells with the correct receptors respond, which ensures each hormone triggers the right effect.
4. Hormones coordinate slow, long-lasting changes, such as growth, metabolism, and internal balance.

Why Does the Body Need Hormones?

1. Hormones ensure different organ systems work together smoothly.
2. They adjust processes such as blood glucose levels, water balance, growth, and reproduction.
3. Because hormones travel in the blood, one signal can coordinate responses across the whole body.

What Is the Endocrine System?

1. The endocrine system is the network of glands that produce and release hormones.
2. Major endocrine glands:
   1. Pituitary gland: regulates many other glands.; often called the “master gland.”
   2. Pancreas: controls blood glucose using insulin and glucagon.
   3. Adrenal glands: release adrenaline during stress.
   4. Thyroid gland: controls metabolic rate.
   5. Ovaries/testes: produce sex hormones for reproduction and development.

How Does the Body Use Hormones to Maintain Homeostasis?

1. Hormones often work through negative feedback, a system that reverses changes to keep conditions stable.
2. When a factor moves outside a safe range, hormones are released to bring it back to normal.
3. When the factor returns to the correct level, hormone release decreases.

Example

• Just as we covered in homeostasis, blood glucose levels are a good example of negative feedback:
  • High glucose → insulin released → glucose stored → levels return to normal
  • Low glucose → glucagon released → glucose released from liver → levels rise

What Does Adrenaline Do?

1. Adrenaline prepares the body for quick action during stress ("fight or flight").
2. It increases heart rate, widens air passages, and releases stored glucose for immediate energy.
3. These effects act quickly but last only a short time.

How Do Hormones Control Growth and Development?

1. Growth hormone stimulates cell division and protein synthesis.
2. Sex hormones (oestrogen and testosterone) trigger puberty and the development of secondary sexual characteristics.
3. These changes occur gradually because hormones act over long periods.

What Are the Key Differences Between Nerves and Hormones?