📚 IGCSE OCR Biology: Endocrine System Exam Essentials | IGCSE OCR 生物：内分泌系统考点精讲
The endocrine system is a chemical coordination network using hormones to regulate slow, long-lasting processes such as growth, metabolism, and reproduction. In IGCSE OCR Biology, you need to understand the key glands, the hormones they secrete, their target organs, and the principle of negative feedback.
内分泌系统是利用激素进行化学协调的网络，调节生长、代谢和生殖等缓慢而持久的过程。在IGCSE OCR生物学中，你需要掌握关键腺体、它们分泌的激素、靶器官以及负反馈原理。
1. What Are Hormones? | 什么是激素？
Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream. They travel to target organs where they bind to specific receptors and trigger a response. Unlike nervous impulses, hormones are slower but have longer-lasting effects.
激素是由内分泌腺直接分泌到血液中的化学信使。它们随血液到达靶器官，与特定受体结合，引发反应。与神经冲动不同，激素作用较慢但效果更持久。
2. Endocrine Glands Overview | 内分泌腺概述
Key endocrine glands include the pituitary (master gland), thyroid, adrenal glands, pancreas, ovaries, and testes. Each produces specific hormones. The pituitary gland secretes ADH, FSH, LH, and growth hormone, among others.
关键的内分泌腺包括垂体（主腺体）、甲状腺、肾上腺、胰腺、卵巢和睾丸。每个腺体分泌特定的激素。垂体分泌抗利尿激素(ADH)、促卵泡激素(FSH)、促黄体生成素(LH)和生长激素等。
- Pituitary: FSH, LH, ADH, GH
- Thyroid: Thyroxine
- Adrenal medulla: Adrenaline
- Pancreas (islets of Langerhans): Insulin and glucagon
- Ovaries: Oestrogen, progesterone
- Testes: Testosterone
- 垂体: FSH, LH, ADH, 生长激素
- 甲状腺: 甲状腺素
- 肾上腺髓质: 肾上腺素
- 胰腺（胰岛）: 胰岛素和胰高血糖素
- 卵巢: 雌激素、孕酮
- 睾丸: 睾酮
3. The Hypothalamus and Pituitary Gland | 下丘脑与垂体
The hypothalamus in the brain links the nervous and endocrine systems. It secretes releasing hormones that control the pituitary gland. The pituitary then releases hormones that regulate other glands, acting as a master gland.
大脑中的下丘脑连接神经系统和内分泌系统。它分泌释放激素来控制垂体。垂体随后释放调节其他腺体的激素，起着主腺体的作用。
4. Negative Feedback | 负反馈机制
Negative feedback maintains a steady internal environment. When a hormone level rises, it inhibits further production; when it falls, production increases. This is crucial for thyroxine, blood glucose, and reproductive hormones.
负反馈维持稳定的内环境。当激素水平升高，会抑制进一步产生；当水平下降，产生就会增加。这对甲状腺素、血糖和生殖激素至关重要。
A typical example: blood glucose regulation – high glucose triggers insulin release, lowering glucose; low glucose triggers glucagon release, raising glucose. This keeps levels within a narrow range.
典型例子：血糖调节——高血糖触发胰岛素分泌，降低血糖；低血糖触发胰高血糖素分泌，升高血糖。这使血糖水平维持在狭窄范围内。
5. Blood Glucose Regulation: Insulin & Glucagon | 血糖调节：胰岛素与胰高血糖素
The pancreas detects blood glucose concentration. Beta cells in the islets of Langerhans secrete insulin when glucose is high (e.g., after a meal). Insulin stimulates liver and muscle cells to convert glucose into glycogen (glycogenesis) and increases glucose uptake by cells, lowering blood glucose.
胰腺检测血糖浓度。胰岛中的β细胞在血糖高时（如餐后）分泌胰岛素。胰岛素刺激肝和肌肉细胞将葡萄糖转化为糖原（糖生成），并增加细胞对葡萄糖的摄取，从而降低血糖。
Alpha cells secrete glucagon when blood glucose is low. Glucagon stimulates the liver to convert glycogen back to glucose (glycogenolysis) and release it into the blood, raising blood glucose.
当血糖低时，α细胞分泌胰高血糖素。胰高血糖素刺激肝脏将糖原转化为葡萄糖（糖原分解）并释放入血，从而升高血糖。
| Hormone | Stimulus | Source | Action | Effect on blood glucose |
|---|---|---|---|---|
| Insulin | High glucose | Beta cells (pancreas) | Glycogenesis, ↑ glucose uptake | Decreases |
| Glucagon | Low glucose | Alpha cells (pancreas) | Glycogenolysis | Increases |
| 激素 | 刺激 | 来源 | 作用 | 对血糖影响 |
|---|---|---|---|---|
| 胰岛素 | 高血糖 | β细胞（胰腺） | 糖生成， ↑ 葡萄糖摄取 | 降低 |
| 胰高血糖素 | 低血糖 | α细胞（胰腺） | 糖原分解 | 升高 |
Type 1 diabetes results from the destruction of beta cells, so insulin is not produced. Blood glucose remains high, and it must be managed with insulin injections.
1型糖尿病是由于β细胞被破坏，无法产生胰岛素。血糖持续升高，必须通过注射胰岛素加以控制。
6. Adrenaline: The Fight-or-Flight Response | 肾上腺素：战斗或逃跑反应
Adrenaline is secreted by the adrenal medulla in response to stress or fear. It prepares the body for intense physical activity by increasing heart rate, breathing rate, and blood flow to muscles while diverting blood from non-essential systems like digestion.
肾上腺素由肾上腺髓质在应对压力或恐惧时分泌。它通过提高心率、呼吸速率和肌肉血流量，同时减少消化等非必需系统的血液供应，为身体进行剧烈体力活动做好准备。
Adrenaline also stimulates the liver to break down glycogen to glucose for extra energy. Pupils dilate to improve vision. This is a rapid response activated by the sympathetic nervous system.
肾上腺素还刺激肝脏将糖原分解为葡萄糖以提供额外能量。瞳孔放大以改善视力。这是一种通过交感神经系统激活的快速反应。
7. Thyroxine and Metabolic Rate | 甲状腺素与代谢率
Thyroxine (T4) is produced by the thyroid gland and regulates metabolic rate – the speed at which chemical reactions occur in the body. It also plays a role in growth and development.
甲状腺素(T4)由甲状腺产生，调节代谢率——即体内化学反应发生的速度。它还在生长发育中起作用。
Negative feedback controls thyroxine levels: Low thyroxine stimulates the hypothalamus to release TRH, which causes the pituitary to release TSH. TSH stimulates the thyroid to produce more thyroxine. As thyroxine rises, it inhibits TRH and TSH release.
负反馈控制甲状腺素水平：低甲状腺素刺激下丘脑释放TRH，引起垂体释放TSH。TSH刺激甲状腺产生更多甲状腺素。当甲状腺素升高，会抑制TRH和TSH的释放。
A deficiency in iodine can lead to an underactive thyroid (hypothyroidism) because thyroxine contains iodine. This can cause goitre (swollen thyroid) as the gland enlarges trying to capture more iodine.
碘缺乏可导致甲状腺功能减退，因为甲状腺素含碘。这可能导致甲状腺肿（甲状腺肿大），因为腺体为了摄取更多碘而增大。
8. Reproductive Hormones: FSH, LH, Oestrogen, Testosterone | 生殖激素：FSH、LH、雌激素、睾酮
Follicle-stimulating hormone (FSH) is secreted by the pituitary gland. In females, it stimulates the growth and maturation of ovarian follicles and triggers oestrogen production. In males, FSH promotes sperm production.
促卵泡激素(FSH)由垂体分泌。在女性中，它刺激卵巢卵泡的生长和成熟，并引发雌激素产生。在男性中，FSH促进精子生成。
Luteinising hormone (LH) also from the pituitary. In females, a surge in LH triggers ovulation (release of a mature egg) and stimulates the remains of the follicle to develop into the corpus luteum, which secretes progesterone. In males, LH stimulates the testes to produce testosterone.
黄体生成素(LH)也来自垂体。在女性中，LH的激增触发排卵（释放成熟卵子），并刺激卵泡残余物发育为黄体，分泌孕酮。在男性中，LH刺激睾丸产生睾酮。
Oestrogen is produced by the ovaries and is responsible for the development of secondary sexual characteristics in females and the repair and thickening of the uterus lining during the menstrual cycle.
雌激素由卵巢产生，负责女性第二性征的发育，以及在月经周期中修复和增厚子宫内膜。
Testosterone is produced by the testes and promotes male secondary sexual characteristics and sperm production.
睾酮由睾丸产生，促进男性第二性征和精子生成。
9. The Menstrual Cycle | 月经周期
The menstrual cycle is controlled by the interplay of FSH, LH, oestrogen, and progesterone. There are four stages: menstruation (lining sheds), the follicular phase (follicle develops, oestrogen rises), ovulation (triggered by LH surge), and the luteal phase (corpus luteum secretes progesterone maintaining lining).
月经周期由FSH、LH、雌激素和孕酮的相互作用控制。主要有四个阶段：月经期（内膜脱落）、卵泡期（卵泡发育，雌激素升高）、排卵期（由LH激增触发）和黄体期（黄体分泌孕酮维持内膜）。
If fertilisation does not occur, the corpus luteum breaks down, oestrogen and progesterone levels fall, and menstruation begins again.
如果未发生受精，黄体退化，雌激素和孕酮水平下降，月经再次开始。
Negative feedback is evident: rising oestrogen initially inhibits FSH but then stimulates LH release. Progesterone inhibits FSH and LH production.
负反馈明显：升高的雌激素最初抑制FSH，但随后刺激LH释放。孕酮抑制FSH和LH的产生。
10. Plant Hormones: Auxin and Tropisms | 植物激素：生长素与向性运动
Plants also use chemical coordination. Auxin is a plant hormone produced in shoot and root tips. Unequal distribution of auxin causes tropisms – directional growth responses to stimuli.
植物也利用化学协调。生长素是一种在茎尖和根尖产生的植物激素。生长素的不均匀分布导致向性运动——对刺激的方向性生长反应。
In phototropism (response to light), auxin accumulates on the shaded side of the shoot, causing cells there to elongate faster than on the light side, bending the shoot towards the light. This is advantageous for photosynthesis.
在向光性（对光的反应）中，生长素在背光侧积累，导致该侧细胞比向光侧伸长更快，使茎向光弯曲。这有利于光合作用。
In gravitropism (response to gravity), auxin accumulates on the lower side of a root. In roots, high auxin inhibits cell elongation, so the lower side grows slower, bending the root downwards.
在向地性（对重力的反应）中，生长素在根的下侧积累。在根中，高浓度生长素抑制细胞伸长，因此下侧生长较慢，使根向下弯曲。
Key experiments using agar blocks or removing tips demonstrate that auxin diffuses from the tip and controls growth.
使用琼脂块或切除尖端的实验证明，生长素从尖端扩散并控制生长。
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