Hormonal Communication | 激素通讯

📚 Hormonal Communication | 激素通讯

Hormonal communication is a form of cell signalling in which endocrine glands release chemical messengers into the blood, allowing coordinated responses across distant target organs. It is slower than nervous communication but produces longer-lasting and often widespread effects on metabolism, growth, reproduction and homeostasis.

激素通讯是一种细胞信号传递方式，内分泌腺将化学信使释放到血液中，从而对远距离靶器官产生协调反应。它比神经通讯慢，但对代谢、生长、生殖和稳态产生更持久且往往更广泛的影响。

1. Endocrine System Overview | 内分泌系统概述

The endocrine system consists of ductless glands that secrete hormones directly into the bloodstream. Major glands include the pituitary, thyroid, adrenal glands, pancreas, ovaries and testes. Each hormone travels in the blood plasma until it binds to specific receptors on or inside target cells.

内分泌系统由无管腺组成，这些腺体将激素直接分泌到血液中。主要腺体包括垂体、甲状腺、肾上腺、胰腺、卵巢和睾丸。每种激素在血浆中运输，直到与靶细胞表面或内部的特定受体结合。

Hormones can affect cells throughout the body, but only cells with complementary receptor proteins respond to a given hormone. This explains why a hormone such as insulin affects liver and muscle cells strongly, while many other cell types show little or no response to it.

激素可以影响全身细胞，但只有具有互补受体蛋白的细胞才会对某种激素产生反应。这解释了为什么胰岛素等激素对肝细胞和肌肉细胞作用强烈，而许多其他细胞类型对其反应很小或没有反应。

Endocrine glands are ductless and highly vascularised.
内分泌腺无管道且血管丰富。
Hormones are transported in blood plasma, not in ducts.
激素通过血浆运输，而不是通过管道运输。
Receptor specificity determines which cells respond.
受体特异性决定哪些细胞产生反应。

2. Hormone Classes and Properties | 激素类别与特性

Hormones fall into two broad chemical groups: peptide/protein hormones and steroid hormones. Peptide hormones, such as insulin, glucagon and adrenaline, are hydrophilic and cannot cross the phospholipid bilayer, so they bind to cell surface receptors. Steroid hormones, such as oestrogen and testosterone, are lipid-soluble and enter cells to bind intracellular receptors.

激素分为两大类化学类别：肽类/蛋白质激素和类固醇激素。胰岛素、胰高血糖素和肾上腺素等肽类激素是亲水性的，不能穿过磷脂双分子层，因此与细胞表面受体结合。雌激素和睾酮等类固醇激素是脂溶性的，可进入细胞与细胞内受体结合。

Peptide hormones are often made in advance and stored in secretory vesicles, allowing rapid release by exocytosis. Steroid hormones are synthesised from cholesterol on demand and diffuse out of the cell, so their secretion rate depends mainly on the rate of synthesis.

肽类激素通常预先合成并储存在分泌囊泡中，可通过胞吐作用快速释放。类固醇激素根据需要由胆固醇合成，并扩散出细胞，因此其分泌速率主要取决于合成速率。

Property	Peptide hormones	Steroid hormones
Solubility	Hydrophilic	Hydrophobic/lipid-soluble
Receptor location	Cell surface membrane	Intracellular receptor
Response speed	Rapid, often seconds to minutes	Slower, often hours

特性 | 肽类激素 | 类固醇激素

溶解度 | 亲水性 | 疏水性/脂溶性

受体位置 | 细胞表面膜 | 细胞内受体

反应速度 | 快，通常数秒至数分钟 | 较慢，通常数小时

3. Target Cells and Receptors | 靶细胞与受体

A target cell is any cell that possesses a specific receptor protein complementary to a given hormone. The receptor and hormone fit together by a mechanism similar to enzyme-substrate specificity, involving non-covalent interactions such as hydrogen bonding and ionic bonding.

靶细胞是任何具有与特定激素互补的特异性受体蛋白的细胞。受体与激素通过类似于酶-底物特异性的机制结合，包括氢键和离子键等非共价相互作用。

Cell surface receptors for peptide hormones are transmembrane glycoproteins. When a hormone binds, the receptor changes conformation, which triggers events inside the cell. The number of receptors on a target cell can be up-regulated or down-regulated, altering sensitivity to the hormone.

肽类激素的细胞表面受体是跨膜糖蛋白。当激素结合时，受体构象发生变化，从而触发细胞内部事件。靶细胞上的受体数量可以上调或下调，从而改变对激素的敏感性。

4. First and Second Messengers | 第一信使与第二信使

The hormone itself is called the first messenger because it carries a signal from an endocrine gland through the blood to the target cell surface. However, most peptide hormones do not enter the cell, so a second messenger must relay the signal to the cytoplasm.

激素本身被称为第一信使，因为它将信号从内分泌腺通过血液传递到靶细胞表面。然而，大多数肽类激素不会进入细胞，因此第二信使必须将信号传递到细胞质中。

Common second messengers include cyclic AMP (cAMP), calcium ions (Ca²⁺) and inositol trisphosphate (IP₃). These small molecules diffuse rapidly and activate enzyme cascades, greatly amplifying the original signal. One hormone molecule can lead to thousands of product molecules.

常见的第二信使包括环磷酸腺苷（cAMP）、钙离子（Ca²⁺）和三磷酸肌醇（IP₃）。这些小分子迅速扩散并激活酶级联反应，大大放大了原始信号。一个激素分子可以导致成千上万个产物分子的产生。

hormone (first messenger) → receptor → second messenger → enzyme cascade → cellular response

激素（第一信使）→ 受体 → 第二信使 → 酶级联 → 细胞反应

5. cAMP Signalling Pathway | cAMP 信号通路

In the cAMP pathway, a hormone such as adrenaline or glucagon binds to a G-protein-coupled receptor. The receptor activates a G protein, which in turn activates the membrane enzyme adenylyl cyclase. Adenylyl cyclase catalyses the conversion of ATP to cAMP.

在 cAMP 通路中，肾上腺素或胰高血糖素等激素与 G 蛋白偶联受体结合。该受体激活 G 蛋白，G 蛋白又激活膜上的腺苷酸环化酶。腺苷酸环化酶催化 ATP 转化为 cAMP。

ATP → cAMP + PPᵢ

cAMP then activates protein kinase A (PKA). In liver cells during glucagon signalling, PKA phosphorylates and activates enzymes involved in glycogen breakdown, leading to glucose release. The cascade is switched off when phosphodiesterase converts cAMP to AMP.

cAMP 随后激活蛋白激酶 A（PKA）。在胰高血糖素信号转导过程中，肝细胞内的 PKA 磷酸化并激活参与糖原分解的酶，导致葡萄糖释放。当磷酸二酯酶将 cAMP 转化为 AMP 时，该级联反应被关闭。

6. Blood Glucose Regulation: Insulin and Glucagon | 血糖调节：胰岛素与胰高血糖素

Blood glucose concentration is normally maintained at around 90 mg per 100 cm³. The pancreas detects changes in blood glucose and secretes two antagonistic hormones from the islets of Langerhans: insulin from β cells and glucagon from α cells.

血糖浓度通常维持在约 90 mg/100 cm³。胰腺检测血糖变化，并从胰岛分泌两种拮抗激素：β 细胞分泌胰岛素，α 细胞分泌胰高血糖素。

After a meal, blood glucose rises. β cells secrete insulin, which increases the permeability of muscle and adipose cells to glucose, activates glycogen synthase, and stimulates fatty acid synthesis. In the liver, insulin promotes glycogenesis, converting glucose into glycogen.

进食后血糖升高。β 细胞分泌胰岛素，增加肌肉和脂肪细胞对葡萄糖的通透性，激活糖原合酶，并刺激脂肪酸合成。在肝脏中，胰岛素促进糖原生成，将葡萄糖转化为糖原。

During fasting or exercise, blood glucose falls. α cells secrete glucagon, which activates the cAMP pathway in hepatocytes. This stimulates glycogenolysis and gluconeogenesis, increasing glucose output from the liver into the blood.

禁食或运动期间血糖下降。α 细胞分泌胰高血糖素，激活肝细胞中的 cAMP 通路。这刺激糖原分解和糖异生，增加肝脏向血液中输出的葡萄糖量。

Insulin lowers blood glucose by increasing cellular uptake and glycogenesis.
胰岛素通过增加细胞摄取和糖原生成来降低血糖。
Glucagon raises blood glucose by glycogenolysis and gluconeogenesis.
胰高血糖素通过糖原分解和糖异生升高血糖。
Negative feedback returns blood glucose to the set point.
负反馈使血糖恢复到设定点。

7. Adrenaline and Fight-or-Flight | 肾上腺素与战斗或逃跑反应

Adrenaline is released from the adrenal medulla in response to stress, danger or excitement. It prepares the body for rapid physical action by binding to cell surface receptors on liver, heart, muscle and adipose tissue.

肾上腺素在压力、危险或兴奋时由肾上腺髓质释放。它通过与肝脏、心脏、肌肉和脂肪组织上的细胞表面受体结合，使身体为快速的身体活动做好准备。

In hepatocytes, adrenaline activates the same cAMP pathway as glucagon, stimulating glycogenolysis and raising blood glucose. In heart muscle, it increases heart rate and stroke volume. In bronchial smooth muscle, it causes relaxation, widening the airways.

在肝细胞中，肾上腺素激活与胰高血糖素相同的 cAMP 通路，刺激糖原分解并升高血糖。在心肌中，它增加心率和每搏输出量。在支气管平滑肌中，它引起松弛，使气道扩张。

The widespread effects of adrenaline demonstrate how one hormone can coordinate several tissues at once. This is a key difference from nervous communication, where individual effectors are usually targeted through specific neurone pathways.

肾上腺素的广泛作用表明一种激素可以同时协调多个组织。这是与神经通讯的一个关键区别，后者通常通过特定的神经通路作用于个别效应器。

8. Hormonal vs Nervous Communication | 激素与神经通讯比较

Nervous communication uses action potentials in neurones and neurotransmitters at synapses, allowing extremely rapid responses measured in milliseconds. Hormonal communication uses hormones in the blood, so responses take seconds, minutes or even days to develop.

神经通讯利用神经元中的动作电位和突触中的神经递质，使反应极快，以毫秒计。激素通讯利用血液中的激素，因此反应需要数秒、数分钟甚至数天才能产生。

Nervous responses are short-lived because neurotransmitters are quickly removed or broken down. Hormonal responses are longer-lasting because hormones can remain in the blood and continue activating pathways until they are metabolised by the liver or excreted by the kidneys.

神经反应是短暂的，因为神经递质会被迅速移除或分解。激素反应更持久，因为激素可以留在血液中并继续激活通路，直到被肝脏代谢或由肾脏排出。

Nervous communication is described as localised, with signals directed to specific cells. Hormonal communication is described as widespread, with hormones potentially reaching all cells in the body but only influencing those with the correct receptors.

神经通讯被描述为局部化的，信号指向特定细胞。激素通讯被描述为广泛性的，激素可能到达体内所有细胞，但只影响具有正确受体的细胞。

Feature	Nervous	Hormonal
Signal type	Action potential, neurotransmitter	Chemical hormone in blood
Speed	Very fast	Slower
Duration	Short	Long

特征 | 神经 | 激素

信号类型 | 动作电位、神经递质 | 血液中的化学激素

速度 | 非常快 | 较慢

持续时间 | 短 | 长

9. Endocrine Glands and Hormone Examples | 内分泌腺与激素实例

The pituitary gland is often called the master gland because it secretes hormones that control other endocrine glands, including TSH, FSH, LH and ACTH. The hypothalamus controls the pituitary through releasing factors and inhibitory factors.

垂体常被称为主腺，因为它分泌控制其他内分泌腺的激素，包括 TSH、FSH、LH 和 ACTH。下丘脑通过释放因子和抑制因子控制垂体。

The thyroid gland produces thyroxine, which regulates metabolic rate. The adrenal cortex produces cortisol and aldosterone, while the adrenal medulla produces adrenaline. The ovaries and testes produce oestrogen, progesterone and testosterone, which control secondary sexual characteristics and reproduction.

甲状腺产生甲状腺素，调节代谢率。肾上腺皮质产生皮质醇和醛固酮，而肾上腺髓质产生肾上腺素。卵巢和睾丸产生雌激素、孕酮和睾酮，控制第二性征和生殖。

10. Control of Hormone Secretion | 激素分泌的调控

Hormone secretion is controlled mainly by negative feedback. In many cases the product or condition regulated by a hormone feeds back to inhibit further secretion. For example, high blood glucose stimulates insulin release, but when glucose falls back to normal, insulin secretion decreases.

激素分泌主要通过负反馈控制。在许多情况下，受激素调节的产物或状态会反馈抑制进一步分泌。例如，高血糖刺激胰岛素释放，但当血糖回落到正常水平时，胰岛素分泌减少。

Some endocrine pathways involve several levels of control. The hypothalamus secretes releasing hormones, which stimulate the anterior pituitary to secrete trophic hormones, which in turn stimulate target glands. The final hormone then inhibits the hypothalamus and pituitary, forming a classic negative-feedback loop.

一些内分泌通路涉及多个控制层级。下丘脑分泌释放激素，刺激垂体前叶分泌促激素，促激素进而刺激靶腺。最终激素随后抑制下丘脑和垂体，形成典型的负反馈回路。

hypothalamus → anterior pituitary → target gland → hormone → negative feedback to hypothalamus and pituitary

下丘脑 → 垂体前叶 → 靶腺 → 激素 → 对下丘脑和垂体的负反馈

11. Diabetes and Homeostatic Failure | 糖尿病与稳态失调

Diabetes mellitus is a condition in which blood glucose concentration cannot be controlled effectively. Type 1 diabetes is caused by autoimmune destruction of pancreatic β cells, so the body produces little or no insulin. Type 2 diabetes typically involves reduced insulin sensitivity or insufficient insulin secretion.

糖尿病是一种血糖浓度无法有效控制的疾病。1 型糖尿病由自身免疫破坏胰腺 β 细胞引起，因此身体几乎不产生胰岛素。2 型糖尿病通常涉及胰岛素敏感性降低或胰岛素分泌不足。

Type 1 diabetes is treated with regular insulin injections, allowing glucose uptake by cells and preventing hyperglycaemia. Blood glucose monitoring and controlled carbohydrate intake are essential parts of management. Without insulin, cells cannot take up enough glucose, leading to fatigue, weight loss and ketoacidosis.

1 型糖尿病通过定期注射胰岛素治疗，使细胞能摄取葡萄糖并防止高血糖。血糖监测和控制碳水化合物摄入是管理的重要组成部分。没有胰岛素，细胞无法摄取足够的葡萄糖，导致疲劳、体重减轻和酮症酸中毒。

Type 1 diabetes involves insulin deficiency, often with an autoimmune cause.
1 型糖尿病涉及胰岛素缺乏，通常由自身免疫原因引起。
Type 2 diabetes involves insulin resistance and is associated with obesity and inactivity.
2 型糖尿病涉及胰岛素抵抗，并与肥胖和缺乏运动有关。
Untreated diabetes leads to hyperglycaemia and long-term damage to blood vessels and nerves.
未治疗的糖尿病会导致高血糖以及对血管和神经的长期损害。

12. Exam Focus: Key Concepts | 考点聚焦

In A-Level Cambridge Biology, exam questions on hormonal communication often ask you to describe the action of a named hormone, explain cell signalling using cAMP, compare hormonal and nervous control, or interpret blood glucose regulation data.

在 A-Level 剑桥生物学中，关于激素通讯的考题常要求你描述某种激素的作用、解释使用 cAMP 的细胞信号传递、比较激素与神经控制，或分析血糖调节数据。

Always link the hormone to its receptor, the second messenger, the enzyme cascade and the final cellular response. Use precise terms such as glycogenesis, glycogenolysis, gluconeogenesis, negative feedback, first messenger and second messenger. Avoid vague phrases like ‘the body makes sugar’ without naming pathways.

始终将激素与其受体、第二信使、酶级联和最终细胞反应联系起来。使用精确术语，如糖原生成、糖原分解、糖异生、负反馈、第一信使和第二信使。避免使用模糊表述，例如不提通路就说“身体制造糖”。

When comparing hormonal and nervous communication, a table with speed, duration, signal type and distribution is an efficient way to gain full marks. For blood glucose questions, state the stimulus, the endocrine cells involved, the hormone released and the effect on liver or muscle cells.

在比较激素通讯与神经通讯时，使用包含速度、持续时间、信号类型和分布方式的表格是获得满分的高效方法。对于血糖问题，要写出刺激、涉及的内分泌细胞、释放的激素以及对肝细胞或肌肉细胞的影响。

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Hormonal Communication | 激素通讯