📚 Edexcel Biology 5.4 Hormonal Communication | Edexcel 生物 5.4 激素通讯
Hormonal communication is a key topic in Edexcel A level Biology. It explains how endocrine glands use hormones to coordinate physiological responses. This article summarises the main mechanisms and examples required for 5.4.
激素通讯是 Edexcel A level 生物学中的一个重要主题。它解释内分泌腺如何利用激素协调生理反应。本文总结了 5.4 所需的主要机制和实例。
1. The Endocrine System and Hormones | 内分泌系统与激素
Endocrine glands secrete hormones directly into the bloodstream, rather than through ducts. Hormones are chemical messengers that travel in the blood and bind to specific receptors on target cells.
内分泌腺将激素直接分泌到血液中，而不是通过导管。激素是随血液流动的化学信使，并与靶细胞上的特异性受体结合。
Compared with the nervous system, hormonal communication is slower but produces longer-lasting changes, such as growth, metabolism and reproduction.
与神经系统相比，激素通讯较慢，但会产生更持久的变化，例如生长、代谢和生殖。
2. Hormone Classes: Peptide vs Steroid | 激素分类：多肽类与类固醇类
Hormones fall into two main chemical classes relevant to their mechanism of action. Peptide and amino acid-derived hormones are hydrophilic, so they cannot cross the plasma membrane. Steroid hormones are hydrophobic and can diffuse through the lipid bilayer.
激素根据作用机制可分为两大类。多肽类和氨基酸衍生物激素是亲水性的，因此不能穿过质膜。类固醇激素是疏水性的，可以通过脂双层扩散。
Examples of peptide hormones include insulin, glucagon and adrenaline (an amino acid derivative). Examples of steroid hormones include oestrogen and testosterone.
多肽激素的例子包括胰岛素、胰高血糖素和肾上腺素（一种氨基酸衍生物）。类固醇激素的例子包括雌激素和睾酮。
3. Target Cells and Receptors | 靶细胞与受体
A hormone circulates throughout the body, but only target cells respond. Target cells possess receptor proteins with a shape complementary to the hormone. The hormone-receptor interaction is specific.
激素在全身循环，但只有靶细胞做出反应。靶细胞具有与激素形状互补的受体蛋白。激素与受体的结合具有特异性。
Cells can regulate their sensitivity by increasing or decreasing the number of receptors. This is known as up-regulation or down-regulation.
细胞可以通过增加或减少受体数量来调节敏感性。这分别称为上调或下调。
4. Mechanism of Peptide Hormones: Second Messenger | 多肽激素的作用机制：第二信使
Because peptide hormones cannot enter the cell, they bind to receptors on the cell surface. The hormone acts as the first messenger. Receptor activation triggers a G-protein to activate adenylate cyclase.
由于多肽激素不能进入细胞，它们与细胞表面受体结合。激素充当第一信使。受体激活后触发 G 蛋白激活腺苷酸环化酶。
Adenylate cyclase catalyses the conversion of ATP to cyclic AMP (cAMP). cAMP acts as the second messenger inside the cell, relaying the signal to enzymes and transcription factors.
腺苷酸环化酶催化 ATP 转化为环磷酸腺苷 (cAMP)。cAMP 在细胞内充当第二信使，将信号传递给酶和转录因子。
ATP → cAMP + PPᵢ
5. cAMP and Amplification Cascade | cAMP 与级联放大效应
cAMP activates protein kinase A (PKA). PKA then phosphorylates target enzymes, altering their activity. A single activated enzyme molecule can catalyse many reactions downstream.
cAMP 激活蛋白激酶 A (PKA)。PKA 随后使靶酶磷酸化，改变其活性。一个被激活的酶分子可以催化下游许多反应。
This sequence of enzyme activations produces a large amplification of the original hormone signal. A
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