Human life activities are not chaotic but rather a symphony orchestrated by thenervous systemandendocrine systemworking together. From instinctively pulling your hand away from a hot pot to drooling at the sight of delicious food, these responses reveal how life precisely adapts to environmental changes.
I. Core Term: Hormone (hormone)
Beyond the nervous system, the body produces a special chemical messengerโhormonesโviaendocrine glandswhich secrete a unique chemical signal moleculeโhormones.Summary: Hormones are present in extremely small quantities in the blood but play crucial roles in regulating metabolism, growth, development, and reproduction.
II. Fundamental Difference Between Glands
Understanding the regulatory mechanism hinges on distinguishing gland structures:
- Exocrine glands: possess dedicatedducts. For example, salivary and sweat glands release their secretions onto the body surface or into the digestive tract.
- endocrine glands:no ducts. Secretions (hormones) are released directly into capillaries and travel throughout the body via the bloodstream.
Deep Dive: The Evolution of Responses
Withdrawing your hand is an innate 'instinct' (unconditioned reflex), while salivating at the sight of sour plums results from learned experience (conditioned reflex). Neural regulation governs 'instant reactions,' whereas hormonal regulation acts like a gentle caretaker, quietly managing your height and heart rate.