📚 Endocrine System Revision for IB Biology | IB 生物内分泌系统考点精讲
The endocrine system is a collection of glands that secrete hormones directly into the bloodstream, regulating processes such as metabolism, growth, reproduction, and stress responses. In the IB Biology curriculum, understanding the molecular mechanisms of hormone action, specific glands and their products, and the principles of feedback control is essential. This guide breaks down the core content into manageable sections, pairing each English explanation with a Chinese translation to support bilingual learners.
内分泌系统是由一组腺体组成的系统，这些腺体将激素直接分泌到血液中，调节新陈代谢、生长、生殖和应激反应等过程。在 IB 生物课程中，理解激素作用的分子机制、特定腺体及其产物，以及反馈控制原理至关重要。本指南将核心内容分解为易于掌握的小节，并为每个英文解释配上中文翻译，以支持双语学习者。
1. Overview of the Endocrine System | 内分泌系统概述
The endocrine system works alongside the nervous system to maintain homeostasis. Unlike the rapid, short-lived signals of the nervous system, endocrine signals are slower but longer lasting because hormones travel through the blood to target cells anywhere in the body. A target cell responds only if it possesses a specific receptor for that hormone, ensuring precise control.
内分泌系统与神经系统协同工作以维持体内平衡。与神经系统快速而短暂的信号不同，内分泌信号较慢但持续时间更长，因为激素通过血液传播到全身各处的靶细胞。靶细胞只有在拥有该激素的特异性受体时才会做出反应，从而确保精确控制。
Major endocrine glands include the pituitary, thyroid, parathyroid, adrenal glands, pancreas, ovaries, and testes. Some organs, such as the hypothalamus, heart, and kidneys, also have secondary endocrine functions. The hypothalamus acts as a bridge between the nervous and endocrine systems by secreting releasing hormones that control the pituitary gland.
主要的内分泌腺包括垂体、甲状腺、甲状旁腺、肾上腺、胰腺、卵巢和睾丸。一些器官，如下丘脑、心脏和肾脏，也具有次要的内分泌功能。下丘脑通过分泌控制垂体的释放激素，充当神经系统和内分泌系统之间的桥梁。
The IB syllabus emphasises the distinction between lionine and non‑lionine hormones. Lionine hormones bind to membrane receptors and activate second messenger cascades, while steroid hormones pass through the plasma membrane and alter gene expression directly.
IB 教学大纲强调亲水性激素和疏水性激素的区别。亲水性激素与膜受体结合并激活第二信使级联反应，而类固醇激素则穿过质膜直接改变基因表达。
2. Hormone Structure and Classification | 激素的结构与分类
Hormones are chemically diverse. Peptide and protein hormones (e.g., insulin, glucagon, growth hormone) are chains of amino acids and are water‑soluble, so they cannot cross the phospholipid bilayer. They bind to receptors on the cell surface. Amino acid derivatives include thyroid hormones and catecholamines (adrenaline). Thyroid hormones are lipid‑soluble and act intracellularly, whereas adrenaline behaves like a peptide hormone.
激素在化学结构上多种多样。肽类和蛋白质激素（如胰岛素、胰高血糖素、生长激素）由氨基酸链构成，为水溶性，因此无法穿过磷脂双分子层。它们与细胞表面受体结合。氨基酸衍生物包括甲状腺激素和儿茶酚胺（肾上腺素）。甲状腺激素是脂溶性的，在细胞内起作用，而肾上腺素的行为类似肽类激素。
Steroid hormones (e.g., oestrogen, testosterone, cortisol) are derived from cholesterol and are lipid‑soluble. They cross the membrane readily and bind to intracellular receptors in the cytoplasm or nucleus, forming a hormone‑receptor complex that acts as a transcription factor to regulate gene expression.
类固醇激素（如雌激素、睾酮、皮质醇）来源于胆固醇，是脂溶性的。它们很容易穿过细胞膜，并与细胞质或细胞核内的细胞内受体结合，形成激素‑受体复合物，该复合物作为转录因子调控基因表达。
- Peptide / Protein Hormones → cell surface receptor → second messenger (e.g. cAMP)
- Steroid Hormones → intracellular receptor → direct gene activation
- 肽类/蛋白质激素 → 细胞表面受体 → 第二信使（如 cAMP）
- 类固醇激素 → 细胞内受体 → 直接基因激活
3. Mechanism of Peptide Hormone Action | 肽类激素的作用机制
When a peptide hormone arrives at its target cell, it binds to a specific receptor protein on the plasma membrane. This binding activates a G‑protein on the inner side of the membrane, which in turn activates an effector enzyme such as adenylyl cyclase. Adenylyl cyclase converts ATP into cyclic AMP (cAMP), the second messenger. cAMP then activates a cascade of protein kinases, leading to amplification of the signal and ultimately a cellular response, such as enzyme activation or secretion of a product.
当肽类激素到达其靶细胞时，它会与质膜上的特异性受体蛋白结合。这种结合激活了膜内侧的 G 蛋白，G 蛋白又激活效应酶，如腺苷酸环化酶。腺苷酸环化酶将 ATP 转化为环磷酸腺苷（cAMP），即第二信使。cAMP 随后激活一系列蛋白激酶，导致信号放大，并最终产生细胞响应，例如酶激活或分泌产物。
The beauty of this system is signal amplification — one hormone molecule binding to a receptor can trigger many cAMP molecules, each activating several kinases, so a tiny hormone concentration can produce a large effect. The response is terminated when cAMP is broken down by phosphodiesterase, returning the cell to its resting state.
该系统之美在于信号放大——一个激素分子与受体结合可触发许多 cAMP 分子，每个 cAMP 又激活多种激酶，因此极低的激素浓度就能产生巨大效应。当 cAMP 被磷酸二酯酶分解时，反应终止，细胞恢复到静息状态。
Hormone + Receptor → G‑protein activation → Adenylyl cyclase → ATP → cAMP → Protein kinase cascade → Response
激素 + 受体 → G 蛋白激活 → 腺苷酸环化酶 → ATP → cAMP → 蛋白激酶级联 → 响应
4. Mechanism of Steroid Hormone Action | 类固醇激素的作用机制
Steroid hormones are lipid‑soluble, so they diffuse directly through the plasma membrane. Once inside, they bind to receptor proteins in the cytoplasm or nucleus. The hormone‑receptor complex undergoes a conformational change and moves into the nucleus (if not already there), where it binds to specific DNA sequences called hormone response elements (HREs). This binding stimulates or inhibits the transcription of specific genes, resulting in altered protein synthesis.
类固醇激素是脂溶性的，因此可直接通过质膜扩散。进入细胞后，它们与细胞质或细胞核中的受体蛋白结合。激素‑受体复合物发生构象变化并进入细胞核（如果尚未在核内），在那里与称为激素响应元件（HRE）的特定 DNA 序列结合。这种结合刺激或抑制特定基因的转录，从而改变蛋白质合成。
Because steroid hormones alter gene expression, their effects are relatively slow (hours to days) but long‑lasting. IB exam questions often ask candidates to compare the speed and duration of effects between peptide and steroid hormones and to explain the difference in terms of the signalling mechanisms.
由于类固醇激素改变基因表达，其效应相对较慢（数小时至数天）但持续时间长。IB 考试题目常要求考生比较肽类激素和类固醇激素作用的速度和持续时间，并从信号传递机制的角度解释这种差异。
5. The Hypothalamus–Pituitary Axis | 下丘脑‑垂体轴
The pituitary gland, often called the ‘master gland’, is divided into the anterior and posterior lobes. The anterior pituitary synthesises and secretes hormones under the control of releasing (or inhibiting) hormones from the hypothalamus, carried by a portal blood system. Key anterior pituitary hormones include thyroid‑stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), luteinising hormone (LH), follicle‑stimulating hormone (FSH), growth hormone (GH), and prolactin.
垂体常被称为“主腺”，分为前叶和后叶。腺垂体在下丘脑释放（或抑制）激素的控制下合成和分泌激素，这些激素通过门脉血液系统输送。主要的腺垂体激素包括促甲状腺激素（TSH）、促肾上腺皮质激素（ACTH）、黄体生成素（LH）、卵泡刺激素（FSH）、生长激素（GH）和催乳素。
The posterior pituitary does not synthesise hormones; it stores and releases oxytocin and antidiuretic hormone (ADH) produced by the hypothalamus. Both are peptide hormones released in response to nerve impulses from the hypothalamus.
神经垂体不合成激素；它储存并释放由下丘脑产生的催产素和抗利尿激素（ADH）。两者都是响应下丘脑神经冲动而释放的肽类激素。
Negative feedback loops involving the target glands tightly regulate the hypothalamic‑pituitary axis. For instance, when thyroid hormone levels fall, the hypothalamus releases thyrotropin‑releasing hormone (TRH), which stimulates the anterior pituitary to release TSH, which in turn stimulates the thyroid gland to secrete thyroxine (T₄) and triiodothyronine (T₃). Rising thyroid hormone levels then inhibit TRH and TSH release.
涉及靶腺的负反馈回路严格调控下丘脑‑垂体轴。例如，当甲状腺激素水平下降时，下丘脑释放促甲状腺激素释放激素（TRH），刺激腺垂体释放 TSH，TSH 转而刺激甲状腺分泌甲状腺素（T₄）和三碘甲状腺原氨酸（T₃）。升高的甲状腺激素水平随后抑制 TRH 和 TSH 的释放。
6. Thyroid Hormones and Metabolic Control | 甲状腺激素与代谢调控
The thyroid gland, located in the neck, produces thyroxine (T₄) and triiodothyronine (T₃), both derived from the amino acid tyrosine and iodine. These hormones increase the basal metabolic rate, enhance protein synthesis, and are essential for normal growth and development, especially of the nervous system.
甲状腺位于颈部，产生甲状腺素（T₄）和三碘甲状腺原氨酸（T₃），两者均来源于氨基酸酪氨酸和碘。这些激素可提高基础代谢率，增强蛋白质合成，并对正常的生长和发育（尤其是神经系统发育）至关重要。
The secretion of thyroid hormones is controlled by a classic negative feedback loop. Cold environments stimulate the hypothalamus to release more TRH, raising TSH and thus T₃/T₄ production. When body temperature rises, the opposite occurs. Iodine deficiency can lead to hypothyroidism and goitre because the gland cannot produce enough hormone and is over‑stimulated by TSH.
甲状腺激素的分泌受经典负反馈回路控制。寒冷环境会刺激下丘脑释放更多 TRH，升高 TSH 并因此增加 T₃/T₄ 的产生。体温升高时则发生相反过程。碘缺乏可导致甲状腺功能减退和甲状腺肿，因为腺体无法产生足够激素并受到 TSH 的过度刺激。
7. Regulation of Blood Glucose — Insulin and Glucagon | 血糖调节——胰岛素与胰高血糖素
The pancreas contains clusters of endocrine cells called the islets of Langerhans. Beta (β) cells secrete insulin, and alpha (α) cells secrete glucagon. These two peptide hormones work antagonistically to maintain blood glucose concentration within a narrow range (about 4–6 mmol dm⁻³).
胰腺含有称为胰岛的内分泌细胞团。β 细胞分泌胰岛素，α 细胞分泌胰高血糖素。这两种肽类激素拮抗作用，将血糖浓度维持在一个狭窄的范围内（约 4–6 mmol dm⁻³）。
- After a meal → blood glucose rises → β cells release insulin → insulin stimulates uptake of glucose by liver and muscle cells and promotes glycogen synthesis (glycogenesis) → glucose level falls.
- 餐后 → 血糖升高 → β 细胞释放胰岛素 → 胰岛素刺激肝细胞和肌肉细胞摄取葡萄糖并促进糖原合成（糖原生成） → 血糖水平下降。
- During fasting → blood glucose falls → α cells release glucagon → glucagon stimulates glycogen breakdown (glycogenolysis) in the liver and conversion of amino acids and fats into glucose (gluconeogenesis) → glucose level rises.
- 禁食期间 → 血糖下降 → α 细胞释放胰高血糖素 → 胰高血糖素刺激肝脏中的糖原分解（糖原分解）以及将氨基酸和脂肪转化为葡萄糖（糖异生） → 血糖水平升高。
Insulin also increases the permeability of muscle and adipose cell membranes to glucose by causing more GLUT4 transporter proteins to be inserted into the plasma membrane. This detail is frequently assessed in IB exams.
胰岛素还通过促使更多 GLUT4 转运蛋白插入质膜，增加肌肉和脂肪细胞膜对葡萄糖的通透性。这一细节在 IB 考试中经常被考查。
8. Diabetes Mellitus — Type 1 and Type 2 | 糖尿病——1 型与 2 型
Diabetes mellitus is a condition characterised by chronic hyperglycaemia (high blood glucose). Type 1 diabetes is an autoimmune disease in which the immune system destroys the pancreatic β cells, leading to absolute insulin deficiency. It usually develops in childhood or adolescence and requires lifelong insulin injections.
糖尿病是一种以慢性高血糖为特征的疾病。1 型糖尿病是一种自身免疫性疾病，免疫系统破坏胰腺 β 细胞，导致绝对胰岛素缺乏。它通常发生在儿童期或青春期，需要终身注射胰岛素。
Type 2 diabetes is largely associated with obesity and a sedentary lifestyle. In this form, target cells become resistant to insulin, meaning that normal insulin levels fail to trigger glucose uptake. Over time, the β cells may become exhausted. Type 2 diabetes can often be managed with dietary changes, exercise, and oral medications that improve insulin sensitivity or stimulate insulin secretion.
2 型糖尿病主要与肥胖和久坐生活方式有关。在这种类型中，靶细胞对胰岛素产生抗性，即正常的胰岛素水平无法触发葡萄糖摄取。随着时间推移，β 细胞可能耗竭。2 型糖尿病通常可通过改变饮食、锻炼以及改善胰岛素敏感性或刺激胰岛素分泌的口服药物来管理。
| Feature 特征 | Type 1 1型 | Type 2 2型 |
|---|---|---|
| Onset 起病 | Childhood / adolescence 儿童/青少年 | Adulthood (increasingly in youth) 成年（逐渐年轻化） |
| Cause 原因 | Autoimmune β‑cell destruction 自身免疫性 β 细胞破坏 | Insulin resistance + eventual β‑cell decline 胰岛素抵抗 + 最终 β 细胞功能衰退 |
| Treatment 治疗 | Insulin injections 胰岛素注射 | Diet, exercise, medication 饮食、运动、药物 |
9. Leptin and Appetite Control | 瘦素与食欲控制
Leptin is a peptide hormone secreted by adipose (fat) cells. Its discovery added a new dimension to our understanding of energy balance. Leptin acts on receptors in the hypothalamus to reduce appetite and increase energy expenditure. As fat mass increases, leptin levels rise, acting as a satiety signal to prevent overeating.
瘦素是一种由脂肪细胞分泌的肽类激素。它的发现为我们理解能量平衡增添了新维度。瘦素作用于下丘脑中的受体，降低食欲并增加能量消耗。随着脂肪量增加，瘦素水平升高，作为饱腹感信号防止过量进食。
In most cases of obesity, however, circulating leptin is high, indicating leptin resistance rather than deficiency. Mouse models have been pivotal in understanding leptin: ob/ob mice lack functional leptin and become severely obese; when injected with leptin, their body mass normalises. This finding illustrates the power of endocrine feedback in body weight regulation.
然而，在大多数肥胖病例中，循环瘦素水平较高，表明存在瘦素抵抗而非缺乏。小鼠模型在理解瘦素方面至关重要：ob/ob 小鼠缺乏功能性瘦素，变得严重肥胖；注射瘦素后，其体重恢复正常。这一发现说明了内分泌反馈在体重调节中的威力。
10. Sex Hormones and Reproductive Control | 性激素与生殖调控
The gonads produce steroid sex hormones. In males, the testes produce testosterone under the influence of LH. Testosterone stimulates sperm production (together with FSH) and is responsible for secondary sexual characteristics. In females, the ovaries produce oestrogen and progesterone in a cyclic pattern controlled by FSH and LH from the anterior pituitary.
性腺产生类固醇性激素。在男性中，睾丸在 LH 影响下产生睾酮。睾酮刺激精子生成（与 FSH 共同作用）并负责第二性征。在女性中，卵巢在腺垂体 FSH 和 LH 的控制下，以周期性模式产生雌激素和孕酮。
IB students must understand the regulation of the menstrual cycle. FSH stimulates follicle development and oestrogen secretion; a surge in oestrogen triggers a surge in LH, which induces ovulation. After ovulation, the ruptured follicle forms the corpus luteum, secreting progesterone to maintain the uterine lining. Negative and positive feedback loops interplay to coordinate these events.
IB 学生必须了解月经周期的调控。FSH 刺激卵泡发育和雌激素分泌；雌激素的急剧升高触发 LH 激增，诱导排卵。排卵后，破裂的卵泡形成黄体，分泌孕酮以维持子宫内膜。负反馈与正反馈回路相互作用，协调这些事件。
Pregnancy tests detect human chorionic gonadotropin (hCG), a hormone secreted by the developing embryo that maintains the corpus luteum and thus progesterone production. hCG is structurally similar to LH and can be detected in urine shortly after implantation.
妊娠检测试剂检测人绒毛膜促性腺激素（hCG），这是一种由发育中的胚胎分泌的激素，可维持黄体从而维持孕酮产生。hCG 在结构上与 LH 相似，可在着床后不久的尿液中检测到。
11. Feedback Mechanisms — Negative and Positive | 反馈机制——负反馈与正反馈
Negative feedback is the predominant mechanism in endocrinology. It ensures that a deviation from the set point causes a corrective response that returns the system to normal. Virtually all hypothalamic‑pituitary‑target gland axes rely on negative feedback. When the final hormone level rises, it inhibits the secretion of the releasing and tropic hormones.
负反馈是内分泌学中的主要机制。它确保偏离设定点的偏差引发纠正反应，使系统恢复正常。几乎所有下丘脑‑垂体‑靶腺轴都依赖负反馈。当最终激素水平升高时，会抑制释放激素和促激素的分泌。
Positive feedback is rarer but important. The best‑known example is the pre‑ovulatory LH surge. Rising oestrogen from the maturing follicle initially exerts negative feedback on the pituitary, but beyond a threshold concentration it switches to positive feedback, causing a massive release of LH that triggers ovulation. Another example is oxytocin during childbirth: uterine contractions stimulate more oxytocin release, intensifying contractions until the baby is born.
正反馈较罕见但很重要。最著名的例子是排卵前 LH 激增。来自成熟卵泡的雌激素升高最初对垂体产生负反馈，但超过阈值浓度后转为正反馈，引发 LH 的大量释放，触发排卵。另一个例子是分娩时的催产素：子宫收缩刺激更多催产素释放，增强收缩，直到婴儿出生。
12. Endocrine Disruptors and Environmental Link | 内分泌干扰物与环境关联
In the IB options or as part of nature of science discussions, candidates may explore endocrine‑disrupting chemicals (EDCs). These are substances in the environment, such as bisphenol A (BPA) from plastics, that can mimic or block natural hormones. Exposure to EDCs has been linked to reproductive disorders, metabolic diseases, and developmental abnormalities in wildlife and humans.
在 IB 选修内容或科学本质的讨论中，考生可能会探索内分泌干扰化学物（EDC）。这些是环境中的物质，如来自塑料的双酚 A（BPA），可以模拟或阻断天然激素。接触 EDC 与野生动物和人类的生殖障碍、代谢疾病及发育异常有关。
Studying the endocrine system therefore extends beyond pure physiology into public health and environmental science, helping students appreciate the real‑world relevance of hormonal regulation and the importance of tightly controlled signalling pathways.
因此，对内分泌系统的研究从纯生理学延伸到公共卫生和环境科学，帮助学生理解激素调节在现实世界中的相关性以及严格控制的信号通路的重要性。
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