A-Level Biology: The Endocrine System and Hormone Signalling | A-Level 生物：内分泌系统与激素信号传导

📚 A-Level Biology: The Endocrine System and Hormone Signalling | A-Level 生物：内分泌系统与激素信号传导

The endocrine system is a network of glands that secrete hormones directly into the bloodstream to regulate physiological processes over long distances. Unlike the nervous system, which transmits rapid electrical impulses, the endocrine system produces slower, longer-lasting effects that coordinate growth, metabolism, reproduction and homeostasis.

内分泌系统是由一系列腺体组成的网络，这些腺体直接将激素分泌进入血液，以远距离调控生理过程。与传递快速电脉冲的神经系统不同，内分泌系统产生较为缓慢但持久的效应，协调生长、代谢、生殖和内稳态。

1. Endocrine Glands and Their Hormones | 内分泌腺及其激素

Key endocrine glands in the human body include the hypothalamus, pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries and testes. Each gland produces specific hormones: the thyroid secretes thyroxine (T₄) and triiodothyronine (T₃); the adrenal medulla secretes adrenaline; and the pancreatic islets of Langerhans produce insulin and glucagon.

人体主要的内分泌腺包括下丘脑、垂体、甲状腺、肾上腺、胰腺、卵巢和睾丸。每个腺体产生特定的激素：甲状腺分泌甲状腺素（T₄）和三碘甲状腺原氨酸（T₃）；肾上腺髓质分泌肾上腺素；胰腺的朗格汉斯岛产生胰岛素和胰高血糖素。

Hormones are specific in their action because target cells possess complementary receptors. A single hormone can affect multiple tissue types, and multiple hormones can act on a single target tissue, enabling complex physiological integration.

激素的作用具有特异性，因为靶细胞具有互补的受体。一种激素可以影响多种组织，多种激素也可以作用于同一靶组织，从而实现复杂的生理整合。

2. Chemical Classification of Hormones | 激素的化学分类

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