Hormonal Communication

The endocrine system provides chemical communication via hormones — molecules secreted by endocrine glands into the blood, which travel to target cells bearing specific receptors. Hormonal responses are typically slower to initiate but longer-lasting than nervous responses. This topic covers the endocrine system, blood glucose regulation, and the detailed structure and function of the kidneys.

Key Definition: A hormone is a chemical messenger produced by an endocrine gland, secreted into the blood, and transported to distant target cells that possess specific complementary receptors for that hormone.

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Nervous vs Endocrine Communication

Feature	Nervous System	Endocrine System
Signal type	Electrical impulses (action potentials)	Chemical (hormones in the blood)
Speed	Very fast (milliseconds)	Slower (seconds to hours)
Duration	Short-lived (milliseconds)	Longer-lasting (hours, days, or even weeks)
Target	Specific (individual muscles/glands via neurones)	Widespread (all cells with the specific receptor)
Pathway	Along neurones	Via the bloodstream
Nature of response	Precise, localised	More general, often affecting multiple organs