The Endocrine System
Glands, Hormones, Humoral Regulation & Comparison with the Nervous System
Recall from our previous lesson: We learned that the nervous system uses fast electrical signals to control the body. Today we dive deep into the endocrine system — the body's slower but longer-lasting chemical messaging network — and see how these two systems work together.
1. What Is the Endocrine System?
The endocrine system is a collection of glands that produce hormones — the body's chemical messengers. These hormones carry information and instructions from one set of cells to another through the bloodstream.
🔬 Endocrine Glands
Endocrine glands are ductless — they release hormones directly into the bloodstream. This is what makes them special.
Examples: Pituitary gland, thyroid, adrenal glands, pancreas
⚠️ Exocrine Glands (NOT Endocrine!)
Exocrine glands release chemicals through ducts (tubes) to specific locations. They are not part of the endocrine system.
Examples: Sweat glands, salivary glands, tear glands
🧠 Key Distinction: Endocrine = ductless, into blood. Exocrine = has ducts, to specific surfaces. Don't confuse them!
2. The Major Endocrine Glands
There are eight major hormone-secreting glands in the human body. Let's explore each one:
| Gland | Location | Key Hormone(s) | Main Function |
|---|---|---|---|
| Hypothalamus | Lower central brain | Releasing & inhibiting hormones | Links nervous & endocrine systems; controls pituitary |
| Pituitary | Base of brain (pea-sized) | Growth hormone (GH), TSH, FSH, LH, and others | "Master gland" — controls many other glands |
| Thyroid | Front of neck | T3, T4 (thyroid hormones) | Regulates metabolism, bone growth, brain development |
| Parathyroids | Behind thyroid (4 tiny glands) | Parathyroid hormone (PTH) | Controls blood calcium levels |
| Adrenal Glands | On top of each kidney | Adrenaline (epinephrine), cortisol | Stress response ("fight or flight"), metabolism |
| Pancreas | Behind stomach | Insulin, glucagon | Regulates blood glucose (sugar) levels |
| Pineal Gland | Middle of brain | Melatonin | Regulates sleep-wake cycle |
| Gonads | Pelvis (ovaries in females, testes in males) | Estrogen, progesterone, testosterone | Sexual development & reproduction |