📚 A-Level CIE Biology: The Endocrine System – Key Points | A-Level CIE 生物：内分泌系统考点精讲
The endocrine system uses hormones to coordinate slow, long-lasting responses, complementing the rapid actions of the nervous system. Understanding hormone action, feedback loops, and specific examples is essential for A-Level CIE Biology.
内分泌系统利用激素来协调缓慢、持久的反应，与神经系统的快速作用互补。理解激素作用、反馈环路及具体实例是 A-Level CIE 生物学的关键。
1. What is the Endocrine System? | 什么是内分泌系统？
Endocrine glands are ductless glands that secrete hormones directly into the bloodstream.
内分泌腺是无导管腺体，直接将激素分泌到血液中。
Hormones are chemical messengers that travel via the blood to target cells, which possess specific receptors for that hormone.
激素是化学信使，通过血液到达靶细胞，靶细胞具有该激素的特异性受体。
Only cells with complementary receptors will respond, giving the system high specificity.
只有具有互补受体的细胞才会响应，使系统具有高度特异性。
The main endocrine glands include the pituitary, thyroid, adrenal, pancreas, ovaries and testes.
主要的内分泌腺包括垂体、甲状腺、肾上腺、胰腺、卵巢和睾丸。
2. Hormone Action: First and Second Messengers | 激素作用：第一信使与第二信使
Peptide hormones, such as adrenaline and insulin, are hydrophilic and cannot cross the plasma membrane.
肽类激素，如肾上腺素和胰岛素，是亲水性的，不能穿过细胞膜。
They bind to receptor proteins on the cell surface, acting as the first messenger.
它们与细胞表面的受体蛋白结合，充当第一信使。
This binding activates a G-protein, which in turn activates the enzyme adenylyl cyclase.
这种结合激活 G 蛋白，G 蛋白接着激活腺苷酸环化酶。
Adenylyl cyclase converts ATP into cyclic AMP (cAMP), the second messenger.
腺苷酸环化酶将 ATP 转化为环磷酸腺苷（cAMP），即第二信使。
cAMP triggers a cascade of reactions, often activating protein kinase A, leading to the cellular response, e.g., glycogen breakdown in liver cells.
cAMP 触发级联反应，通常激活蛋白激酶 A，导致细胞响应，如肝细胞中糖原的分解。
Steroid hormones (e.g., oestrogen) are lipid-soluble and enter cells by diffusion to bind to intracellular receptors, directly affecting gene transcription.
类固醇激素（如雌激素）是脂溶性的，通过扩散进入细胞，与细胞内受体结合，直接影响基因转录。
3. The Pituitary Gland and Its Hormones | 垂体及其激素
The pituitary gland, located below the hypothalamus, is often called the ‘master gland’.
垂体位于下丘脑下方，常被称为“主腺”。
The posterior pituitary releases ADH (antidiuretic hormone) and oxytocin, which are produced in the hypothalamus.
垂体后叶释放抗利尿激素（ADH）和催产素，它们在下丘脑合成。
ADH increases water reabsorption in the kidney collecting ducts, regulating blood water potential.
ADH 增加肾集合管对水的重吸收，调节血液水势。
The anterior pituitary produces and secretes tropic hormones such as TSH, FSH, LH, and growth hormone.
垂体前叶产生并分泌促激素，如促甲状腺激素（TSH）、卵泡刺激素（FSH）、黄体生成素（LH）和生长激素。
TSH stimulates the thyroid to release thyroxine; FSH and LH control the menstrual cycle.
TSH 刺激甲状腺释放甲状腺素；FSH 和 LH 调控月经周期。
4. Regulation of Blood Glucose: Insulin and Glucagon | 血糖调节：胰岛素与胰高血糖素
The pancreas contains islets of Langerhans: α-cells secrete glucagon, β-cells secrete insulin.
胰腺中含有胰岛：α 细胞分泌胰高血糖素，β 细胞分泌胰岛素。
When blood glucose rises (after a meal), β-cells detect the increase and release insulin.
当血糖升高（餐后），β 细胞检测到升高并释放胰岛素。
Insulin binds to receptors on hepatocytes and muscle cells, promoting glucose uptake and glycogenesis (glucose → glycogen).
胰岛素与肝细胞和肌细胞上的受体结合，促进葡萄糖摄取和糖原生成（葡萄糖 → 糖原）。
It also increases the rate of respiration of glucose and stimulates fat synthesis.
它还提高葡萄糖的呼吸速率并刺激脂肪合成。
When blood glucose falls (between meals), α-cells secrete glucagon.
当血糖降低（餐间），α 细胞分泌胰高血糖素。
Glucagon stimulates glycogenolysis (glycogen → glucose) and gluconeogenesis (formation of glucose from non-carbohydrates).
胰高血糖素刺激糖原分解（糖原 → 葡萄糖）和糖异生（从非碳水化合物生成葡萄糖）。
This is a classic negative feedback loop to maintain normoglycemia (around 90 mg 100 mL⁻¹).
这是维持正常血糖（约 90 mg·100 mL⁻¹）的经典负反馈回路。
5. Adrenaline: The Stress Hormone | 肾上腺素：应激激素
Adrenaline is secreted by the adrenal medulla in response to stress, fear, or excitement.
肾上腺素由肾上腺髓质分泌，以响应压力、恐惧或兴奋。
It binds to receptors on target cells (e.g., liver, heart) and uses the cAMP second messenger system.
它与靶细胞（如肝脏、心脏）上的受体结合，并利用 cAMP 第二信使系统。
In liver cells, adrenaline activates glycogen phosphorylase, leading to rapid glycogenolysis and release of glucose.
在肝细胞中，肾上腺素激活糖原磷酸化酶，导致快速糖原分解并释放葡萄糖。
It increases heart rate and stroke volume, dilates bronchioles, and redirects blood to muscles.
它增加心率和搏出量，扩张细支气管，并将血液重新分配到肌肉。
These adjustments prepare the body for ‘fight or flight’, providing extra oxygen and glucose for respiration.
这些调整使身体为“战斗或逃跑”做好准备，为呼吸作用提供额外的氧气和葡萄糖。
The effects are short-lived because adrenaline is rapidly broken down in the liver.
这些效应是短暂的，因为肾上腺素在肝脏中迅速被分解。
6. Thyroid Hormones and Metabolic Control | 甲状腺激素与代谢调控
The thyroid gland secretes thyroxine (T₄) and triiodothyronine (T₃), which contain iodine.
甲状腺分泌甲状腺素（T₄）和三碘甲状腺原氨酸（T₃），它们含有碘。
These hormones increase basal metabolic rate, enhancing oxygen consumption and heat production.
这些激素提高基础代谢率，增加耗氧量和产热量。
Their secretion is controlled by a negative feedback loop involving the hypothalamus and pituitary.
它们的分泌受涉及下丘脑和垂体的负反馈回路控制。
The hypothalamus releases TRH (thyrotropin-releasing hormone), which stimulates the anterior pituitary to secrete TSH.
下丘脑释放促甲状腺激素释放激素（TRH），刺激垂体前叶分泌 TSH。
TSH stimulates the thyroid to release T₄ and T₃. High levels of T₄ and T₃ inhibit TRH and TSH release.
TSH 刺激甲状腺释放 T₄ 和 T₃。高水平的 T₄ 和 T₃ 抑制 TRH 和 TSH 的释放。
A lack of iodine leads to insufficient thyroid hormones, causing TSH overproduction and thyroid gland enlargement (goitre).
缺碘导致甲状腺激素不足，引发 TSH 过度分泌和甲状腺肿大（甲状腺肿）。
7. The Menstrual Cycle: A Hormonal Symphony | 月经周期：激素交响曲
The menstrual cycle is controlled by pituitary and ovarian hormones interacting via feedback.
月经周期由垂体和卵巢激素通过反馈相互作用控制。
FSH from the anterior pituitary stimulates follicle development in the ovary, and the follicle cells secrete oestrogen.
垂体前叶的 FSH 刺激卵巢中的卵泡发育，卵泡细胞分泌雌激素。
Rising oestrogen initially exerts negative feedback on FSH, but at a threshold level it switches to positive feedback on LH.
升高的雌激素最初对 FSH 施加负反馈，但在达到阈值水平时，它对 LH 变为正反馈。
The LH surge triggers ovulation (day 14). After ovulation, the follicle becomes the corpus luteum, which secretes progesterone.
LH 激增触发排卵（第 14 天）。排卵后，卵泡转变为黄体，黄体分泌孕酮。
Progesterone maintains the uterine lining (endometrium) and inhibits FSH and LH release.
孕酮维持子宫内膜，并抑制 FSH 和 LH 的释放。
If no fertilisation occurs, the corpus luteum degenerates, progesterone drops, and menstruation follows.
如果没有受精，黄体退化，孕酮水平下降，随后月经来潮。
Oestrogen also repairs and thickens the endometrium during the follicular phase.
在卵泡期，雌激素还修复和增厚子宫内膜。
8. Endocrine vs Nervous Coordination | 内分泌与神经协调的比较
The nervous system uses electrical impulses and neurotransmitters for rapid, short-lived, localised responses.
神经系统利用电信号和神经递质实现快速、短暂、局部的反应。
The endocrine system uses hormones in the blood for slower, long-lasting, widespread effects.
内分泌系统利用血液中的激素，实现缓慢、持久、广泛的效果。
Nervous signals travel via neurones; endocrine signals travel through the bloodstream.
神经信号经由神经元传递；内分泌信号通过血液流动。
Often, both systems cooperate, such as in the fight-or-flight response where the sympathetic nervous system triggers adrenaline release.
经常两个系统合作，例如在战斗或逃跑反应中，交感神经系统触发肾上腺素释放。
9. Summary of Key Endocrine Glands | 主要内分泌腺总结
The table below summarises the major glands, their hormones, and principal actions.
下表总结了主要腺体、其激素及主要作用。
| Gland / 腺体 | Hormone / 激素 | Main Action / 主要作用 |
|---|---|---|
| Pituitary (anterior) / 垂体前叶 | TSH, FSH, LH, GH | Stimulate thyroid, gonads; growth |
| Pituitary (posterior) / 垂体后叶 | ADH, Oxytocin | Water reabsorption; uterine contraction, milk ejection |
| Thyroid / 甲状腺 | T₄, T₃ | Increase metabolic rate; development |
| Adrenal medulla / 肾上腺髓质 | Adrenaline | Fight-or-flight response; glycogenolysis |
| Pancreas (α-cells) / 胰腺α细胞 | Glucagon | Increase blood glucose; glycogenolysis |
| Pancreas (β-cells) / 胰腺β细胞 | Insulin | Decrease blood glucose; glycogenesis |
| Ovary / 卵巢 | Oestrogen, Progesterone | Menstrual cycle control; secondary sexual characteristics |
| Testis / 睾丸 | Testosterone | Sperm production; male secondary sexual characteristics |
10. Common Exam Pitfalls and Tips | 常见考试误区与提示
Confusing negative and positive feedback: remember that positive feedback (e.g., oestrogen on LH) is rare and amplifies a change.
混淆负反馈和正反馈：记住正反馈（如雌激素对 LH）很少见，它会放大变化。
Forgetting that ADH acts on the collecting ducts, not the loop of Henlé.
忘记 ADH 作用于集合管，而不是髓袢。
Mixing up α- and β-cells of the pancreas; β = insulin, α = glucagon.
混淆胰腺的 α 和 β 细胞；β 分泌胰岛素，α 分泌胰高血糖素。
Using ‘hormones are enzymes’ – they are not; they are signalling molecules that trigger enzyme cascades.
说“激素是酶”——它们不是；激素是触发酶级联反应的信号分子。
Neglecting the second messenger model details: many CIE questions ask you to describe the cAMP cascade step by step.
忽视第二信使模型细节：许多 CIE 试题要求逐步描述 cAMP 级联反应。
Stating that adrenaline directly enters the cell – it does not; it binds to membrane receptors.
声称肾上腺素直接进入细胞——它不会；它与膜受体结合。
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