5.6 The Endocrine System

The Endocrine System: Chemical Messengers

The endocrine system is a network of glands that release hormones directly into the bloodstream to regulate body functions over longer time spans than the nervous system. It works alongside the nervous system but communicates more slowly and broadly, affecting growth, metabolism, mood, and reproduction.

The Pituitary Gland: Master Gland

The pituitary gland, controlled by the hypothalamus, is called the master gland because it releases hormones that regulate other endocrine glands. It secretes growth hormone and signals for hormone release throughout the body, linking the nervous and endocrine systems together.

Adrenal Glands & Stress Response

The adrenal glands sit atop the kidneys and release epinephrine (adrenaline) and cortisol during stress, triggering the fight-or-flight response — increased heart rate, energy, and alertness. This is regulated by the sympathetic nervous system working with the endocrine system.

Key terms

Endocrine system

A network of glands that secrete hormones into the bloodstream to regulate body processes.

Hormones

Chemical messengers released by endocrine glands that travel through the blood to affect distant organs.

Pituitary gland

The 'master gland,' controlled by the hypothalamus, that regulates other endocrine glands and releases growth hormone.

Adrenal glands

Glands above the kidneys that release epinephrine and cortisol during stress, triggering fight-or-flight.

Hypothalamus

Brain structure that links the nervous and endocrine systems by controlling the pituitary gland.

Try an AP-style question

Which symptom is most likely?

1. Extreme hunger
2. Racing heart and anxiety
3. Fatigue and sluggishness
4. Insomnia