The endocrine system is a network of glands and organs that produce and release hormones—chemical messengers that regulate major body functions like growth, metabolism, reproduction, mood, and homeostasis (balance of internal systems).
🧠 Main Components of the Endocrine System
🧬 1. Hypothalamus (in the brain)
- Master regulator that links the nervous system to the endocrine system.
- Controls the pituitary gland via releasing and inhibiting hormones.
- Regulates body temperature, hunger, thirst, circadian rhythms.
📍 2. Pituitary Gland ("Master Gland") – base of the brain
- Controlled by the hypothalamus.
- Releases growth hormone, thyroid-stimulating hormone (TSH), ACTH, prolactin, FSH, LH, and oxytocin (via posterior pituitary).
- Controls many downstream glands.
🧠 3. Pineal Gland – deep in the brain
- Secretes melatonin, which regulates sleep-wake cycles.
🦋 4. Thyroid Gland – in the neck, front of trachea
- Produces T3 and T4 (thyroid hormones), regulating metabolism, temperature, and energy.
🧫 5. Parathyroid Glands – 4 small glands behind the thyroid
- Produce parathyroid hormone (PTH), which controls calcium and phosphate levels in blood and bone.
⚖️ 6. Adrenal Glands – on top of each kidney
- Adrenal cortex: Produces cortisol, aldosterone, and androgens (stress, salt balance, sex hormones).
- Adrenal medulla: Produces epinephrine (adrenaline) and norepinephrine (fight-or-flight).
🩸 7. Pancreas (Endocrine and Exocrine)
- Endocrine portion (Islets of Langerhans):
- Beta cells: Insulin
- Alpha cells: Glucagon
- Regulates blood sugar
- Exocrine portion: Digestive enzymes (not part of endocrine system)
🧬 8. Gonads (Sex glands)
- Testes (in males): Produce testosterone, regulate sperm production.
- Ovaries (in females): Produce estrogen and progesterone, regulate menstrual cycle and pregnancy.
🫀 9. Thymus (behind sternum, in childhood)
- Produces thymosin, important for T-cell (immune) development.
- Active in childhood, shrinks after puberty.
📜 Summary Table
| Gland/Organ | Hormones Secreted | Primary Function |
|---|---|---|
| Hypothalamus | Releasing/inhibiting hormones | Controls pituitary, homeostasis |
| Pituitary (Ant./Post.) | GH, TSH, ACTH, LH, FSH, prolactin, oxytocin | Controls other glands, growth, lactation |
| Pineal | Melatonin | Regulates sleep cycle |
| Thyroid | T3, T4 | Metabolism, energy, development |
| Parathyroids | PTH | Calcium/phosphate balance |
| Adrenals | Cortisol, aldosterone, epinephrine | Stress, fluid balance, metabolism |
| Pancreas (Islets) | Insulin, glucagon | Blood sugar regulation |
| Gonads (Ovaries/Testes) | Estrogen, progesterone, testosterone | Sexual development, reproduction |
| Thymus (childhood) | Thymosin | Immune system maturation |
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