1.2 The Endocrine System

The Endocrine System Basics

The endocrine system is a network of glands that produce and secrete hormones directly into the bloodstream. Hormones travel through the blood and affect distant organs and tissues, working more slowly than the nervous system but producing longer-lasting effects. This system regulates growth, metabolism, mood, and reproduction.

Pituitary Gland: The Master Gland

The pituitary gland, controlled by the hypothalamus, is called the 'master gland' because it releases hormones that direct other endocrine glands. It secretes growth hormone and oxytocin, and signals glands like the thyroid and adrenals to release their own hormones, coordinating body-wide regulation.

Key Glands and Hormones

The adrenal glands release adrenaline (epinephrine) and cortisol, triggering the fight-or-flight stress response. The thyroid gland regulates metabolism via thyroxine. The gonads (testes and ovaries) produce sex hormones like testosterone and estrogen, influencing sexual development and behavior.

Key terms

Endocrine system

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

Pituitary gland

The 'master gland,' controlled by the hypothalamus, that regulates other endocrine glands.

Adrenal glands

Glands that release adrenaline and cortisol, triggering the fight-or-flight response.

Hormones

Chemical messengers released into the bloodstream that affect organs and tissues throughout the body.

Hypothalamus

A brain structure that links the nervous and endocrine systems by directing the pituitary gland.

Try an AP-style question

Which gland released the hormone most responsible?

1. Thyroid gland
2. Pituitary gland
3. Adrenal glands
4. Pineal gland