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Chapter 16 — Chapter 16 — Human Endocrine System
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📘Easy summary
The nervous system carries out high-speed coordination, while the endocrine system controls long-term processes like growth, metabolism and reproduction by sending chemical instructions (hormones) — chemical coordination. A hormone is a regulatory chemical secreted into the blood or tissue fluid by an endocrine gland. Blood carries it to every cell, but it shows its effects only in specific target cells, which respond in a specific way; so hormones are called chemical messengers or signalling molecules. Exocrine glands secrete into ducts; endocrine glands are ductless. Target cells have receptors, each binding a specific hormone; binding triggers changes inside the cell. Receptors may be on the cell membrane, in the cytoplasm or in the nucleus. Bayliss and Starling (1902) discovered the first hormone, secretin.
⭐Key points
- Hormone: secreted into blood by ductless gland.
- Acts only on target cells with receptors.
- Slower and longer-lasting than neurotransmitters.
🔬Diagram
🌿Real-life example
Acidic chyme in the small intestine releases secretin, which makes the pancreas secrete pancreatic juice.
💡Exam tip
- Exocrine = ducts; endocrine = ductless.
✅Quick check
1. Endocrine glands secrete into:
2. First hormone discovered:
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