📚 Endocrine System | 内分泌系统
The endocrine system is a network of glands that secrete hormones directly into the bloodstream to regulate processes such as growth, metabolism, and reproduction. Unlike the nervous system, it brings about slower but longer-lasting changes in the body. Mastering this topic is essential for IGCSE CCEA Biology as it links closely with homeostasis, coordination, and response.
内分泌系统是一个由腺体组成的网络，这些腺体将激素直接分泌到血液中，以调节生长、代谢和生殖等过程。与神经系统不同，它带来的变化较慢但更持久。掌握该主题对 IGCSE CCEA 生物学至关重要，因为它与稳态、协调与反应等章节紧密相关。
1. Overview of the Endocrine System | 内分泌系统概述
The endocrine system consists of ductless glands that produce hormones. These hormones travel in the blood plasma to target organs, where they bind to specific receptors and trigger a response. Key glands include the pituitary, thyroid, adrenal, pancreas, ovaries, and testes.
内分泌系统由无管腺体组成，这些腺体产生激素。激素随血浆运输到靶器官，在那里与特异性受体结合并引发反应。重要的腺体包括垂体、甲状腺、肾上腺、胰腺、卵巢和睾丸。
Because hormones circulate throughout the body, a single hormone can affect multiple tissues, but only cells with complementary receptors will respond. The system works in parallel with the nervous system to maintain a stable internal environment.
由于激素在全身循环，一种激素可影响多种组织，但只有具备互补受体的细胞才会响应。该系统与神经系统协同工作，以维持稳定的内环境。
2. Hormones: Chemical Messengers | 激素：化学信使
Hormones are chemical substances produced in minute quantities. They are either proteins (e.g., insulin, glucagon, ADH) or steroids (e.g., oestrogen, testosterone). Protein hormones bind to receptors on the cell membrane and activate second messengers inside the cell, while steroid hormones pass through the membrane and bind to receptors in the cytoplasm or nucleus.
激素是微量产生的化学物质。它们要么是蛋白质（如胰岛素、胰高血糖素、抗利尿激素），要么是类固醇（如雌激素、睾酮）。蛋白质激素与细胞膜上的受体结合，激活细胞内的第二信使；而类固醇激素穿过细胞膜，与细胞质或细胞核内的受体结合。
The action of hormones is highly specific. For example, insulin lowers blood glucose by promoting glucose uptake in liver and muscle cells, but it does not affect red blood cells. Hormones are broken down by the liver and excreted by the kidneys, so their effects are temporary.
激素的作用具有高度特异性。例如，胰岛素通过促进肝细胞和肌细胞摄取葡萄糖来降低血糖，但不影响红细胞。激素在肝脏中被分解并由肾脏排出，因此其效应是暂时的。
3. Comparing Nervous and Hormonal Control | 神经与激素控制比较
It is common to compare the two coordination systems. The nervous system uses electrical impulses along neurones and is fast, precise, and short-lived. In contrast, the endocrine system uses hormones in the blood, which take longer to act but produce more widespread and prolonged effects.
常会将两种协调系统进行比较。神经系统通过神经元的电脉冲传递信息，反应迅速、精确且短暂。相反，内分泌系统利用血液中的激素，作用较慢，但影响范围更广、持续时间更长。
- Speed: Nervous: very rapid (milliseconds); Hormonal: slower (seconds to days).
- 速度： 神经：极快（毫秒级）；激素：较慢（数秒至数天）。
- Duration: Nervous: short-lived; Hormonal: long-lasting.
- 持续时间： 神经：短暂；激素：持久。
- Message type: Nervous: electrical and chemical (at synapses); Hormonal: chemical only.
- 信号类型： 神经：电信号和化学信号（突触处）；激素：仅化学信号。
4. Pituitary Gland and ADH | 垂体与抗利尿激素
The pituitary gland at the base of the brain is often called the 'master gland' because it secretes hormones that control other glands, such as TSH (thyroid-stimulating hormone) and FSH (follicle-stimulating hormone). It also produces antidiuretic hormone (ADH), which regulates water content of the blood.
位于大脑底部的垂体常被称为'主腺'，因为它分泌控制其他腺体的激素，如促甲状腺激素（TSH）和促卵泡激素（FSH）。它还产生抗利尿激素（ADH），调节血液中的水含量。
ADH is released when the blood becomes too concentrated. It acts on the collecting ducts of the kidney, making them more permeable to water. More water is reabsorbed, producing a small volume of concentrated urine. This is part of negative feedback involving the hypothalamus.
当血液变得太浓时，ADH 被释放。它作用于肾脏的集合管，增加其对水的通透性。更多的水被重吸收，产生少量浓缩尿液。这是下丘脑参与的负反馈的一部分。
5. Thyroid Gland and Thyroxine | 甲状腺与甲状腺素
The thyroid gland, located in the neck, produces thyroxine, a hormone that contains iodine. Thyroxine controls the basal metabolic rate – the speed at which the body uses energy. It is vital for growth and development.
甲状腺位于颈部，产生甲状腺素，一种含碘的激素。甲状腺素控制基础代谢率——身体消耗能量的速度。它对生长发育至关重要。
Underproduction of thyroxine (hypothyroidism) leads to weight gain, tiredness, and slow growth. In infants, it can cause cretinism (delayed mental development). Overproduction (hyperthyroidism) results in weight loss, increased heart rate, and anxiety. Iodine deficiency in the diet can cause goitre – a swollen thyroid gland.
甲状腺素分泌不足（甲状腺功能减退）导致体重增加、疲劳和生长缓慢。在婴儿中，可引起克汀病（智力发育迟缓）。分泌过多（甲状腺功能亢进）则导致体重减轻、心率加快和焦虑。饮食缺碘可引起甲状腺肿——甲状腺肿胀。
6. Adrenal Glands and Adrenaline | 肾上腺与肾上腺素
The adrenal glands sit on top of the kidneys. The medulla secretes adrenaline (epinephrine) in response to stress or danger. This is the 'fight or flight' hormone, preparing the body for rapid action.
肾上腺位于肾脏顶部。髓质在压力或危险情况下分泌肾上腺素。这是'战斗或逃跑'激素，为身体快速行动做准备。
Effects of adrenaline include: increased heart rate and breathing rate, dilated pupils, raised blood glucose (by stimulating breakdown of glycogen to glucose in the liver), and redirection of blood flow to muscles and away from the digestive system. All these changes supply more oxygen and glucose to muscle cells for higher respiration.
肾上腺素的效应包括：心率和呼吸频率加快、瞳孔放大、血糖升高（通过刺激肝脏中糖原分解为葡萄糖），以及血液流向肌肉而远离消化系统。所有这些变化为肌细胞提供更多氧和葡萄糖以满足更高的呼吸作用。
7. Pancreas: Insulin and Glucagon | 胰腺：胰岛素与胰高血糖素
The pancreas has both exocrine (digestive enzymes) and endocrine functions. The islets of Langerhans contain alpha cells that secrete glucagon and beta cells that secrete insulin. These two hormones work antagonistically to regulate blood glucose concentration.
胰腺兼具外分泌（消化酶）和内分泌功能。胰岛中的 α 细胞分泌胰高血糖素，β 细胞分泌胰岛素。这两种激素相互拮抗，调节血糖浓度。
After a meal, blood glucose rises. Beta cells release insulin, which stimulates liver and muscle cells to convert excess glucose into glycogen for storage. It also increases cellular uptake of glucose. When blood glucose drops, alpha cells release glucagon, which promotes the breakdown of glycogen back into glucose in the liver (glycogenolysis).
进餐后，血糖升高。β 细胞释放胰岛素，刺激肝细胞和肌细胞将多余的葡萄糖转化为糖原储存，并增加细胞对葡萄糖的摄取。当血糖下降时，α 细胞释放胰高血糖素，促进肝脏中糖原分解为葡萄糖（糖原分解）。
8. Negative Feedback and Blood Glucose Regulation | 负反馈与血糖调节
Negative feedback is a fundamental principle in homeostasis. A change from the set point triggers a response that counteracts the change, returning the system to normal. Blood glucose regulation is a classic example.
负反馈是稳态的基本原则。偏离设定点的变化会触发抵消该变化的反应，使系统恢复正常。血糖调节就是一个经典例子。
When blood glucose rises above a normal level (about 90 mg per 100 cm³), insulin is secreted; glucose is stored as glycogen, bringing the level down. When blood glucose falls below normal, glucagon is secreted; glycogen is converted to glucose, raising the level. Both responses are part of a continuous negative feedback loop.
当血糖升至正常水平（约 90 毫克每 100 立方厘米）以上时，胰岛素分泌；葡萄糖以糖原形式储存，使水平下降。当血糖降至正常以下时，胰高血糖素分泌；糖原转化为葡萄糖，使水平升高。这两种反应都是持续负反馈回路的一部分。
High Glucose → Insulin released → Glucose → Glycogen (liver) → Glucose falls↓
高葡萄糖 → 胰岛素释放 → 葡萄糖 → 糖原（肝脏）→ 葡萄糖降低↓
Low Glucose → Glucagon released → Glycogen → Glucose (liver) → Glucose rises↑
低葡萄糖 → 胰高血糖素释放 → 糖原 → 葡萄糖（肝脏）→ 葡萄糖升高↑
9. Diabetes: Type 1 and Type 2 | 糖尿病：1 型和 2 型
Diabetes mellitus is a condition where the body cannot control blood glucose effectively. In Type 1 diabetes, the immune system destroys the pancreatic beta cells, so little or no insulin is produced. It typically develops in childhood and must be treated with insulin injections.
糖尿病是一种身体不能有效控制血糖的状况。在 1 型糖尿病中，免疫系统破坏胰腺 β 细胞，因此产生极少或根本不产生胰岛素。它通常在儿童期发病，必须通过注射胰岛素治疗。
Type 2 diabetes occurs when body cells lose their responsiveness to insulin (insulin resistance). It is linked to obesity, poor diet, and lack of exercise. It can often be controlled by a carbohydrate-controlled diet and regular physical activity. Severe cases may require medication.
2 型糖尿病发生的原因是身体细胞对胰岛素的反应性降低（胰岛素抵抗）。它与肥胖、不良饮食和缺乏运动有关。通常可通过控制碳水化合物的饮食和规律体育锻炼来管理。严重病例可能需要药物治疗。
| Feature 特征 | Type 1 1型 | Type 2 2型 |
|---|---|---|
| Onset 发病年龄 | Usually young 通常年轻 | Usually over 40 通常40岁以上 |
| Insulin production 胰岛素产生 | None / very little 无/极少 | Normal or high 正常或偏高 |
| Cause 病因 | Autoimmune 自身免疫 | Insulin resistance 胰岛素抵抗 |
| Treatment 治疗 | Insulin injections 胰岛素注射 | Diet, exercise, medication 饮食、运动、药物 |
10. Ovaries, Testes and Secondary Sexual Characteristics | 卵巢、睾丸与第二性征
The ovaries and testes are endocrine glands that produce sex hormones. Ovaries secrete oestrogen and progesterone, while the testes secrete testosterone. These hormones are responsible for the development of secondary sexual characteristics at puberty.
卵巢和睾丸是产生性激素的内分泌腺体。卵巢分泌雌激素和孕激素，而睾丸分泌睾酮。这些激素负责青春期第二性征的发育。
In females, oestrogen prompts breast development, widening of hips, and the start of menstrual cycles. In males, testosterone stimulates growth of facial and pubic hair, deepening of the voice, and increased muscle mass. Both are steroid hormones that exert their effects by entering target cells and activating genes.
在女性中，雌激素促进乳房发育、臀部变宽和月经周期的开始。在男性中，睾酮刺激胡须和阴毛生长、声音变低沉和肌肉量增加。两者都是类固醇激素，通过进入靶细胞并激活基因来发挥作用。
11. The Menstrual Cycle | 月经周期
The menstrual cycle is controlled by a complex interaction of hormones. It lasts approximately 28 days and involves the pituitary hormones FSH and LH, and the ovarian hormones oestrogen and progesterone. Understanding the roles at each stage is key for CCEA exams.
月经周期受复杂的激素相互作用控制。它大约持续 28 天，涉及垂体激素 FSH 和 LH，以及卵巢激素雌激素和孕激素。理解各阶段的作用是 CCEA 考试的关键。
- FSH (follicle-stimulating hormone): secreted by pituitary, stimulates follicle development in the ovary and oestrogen secretion.
- FSH（促卵泡激素）： 由垂体分泌，刺激卵巢中卵泡发育和雌激素分泌。
- Oestrogen: produced by growing follicle, thickens the uterus lining (endometrium) and inhibits FSH (negative feedback) while stimulating LH release just before ovulation.
- 雌激素： 由发育中的卵泡产生，使子宫内膜增厚，并抑制 FSH（负反馈），同时在排卵前刺激 LH 的释放。
- LH (luteinising hormone): a surge triggers ovulation on day 14; also forms the corpus luteum.
- LH（黄体生成素）： 急剧升高触发第 14 天的排卵；同时形成黄体。
- Progesterone: secreted by the corpus luteum, maintains the thick uterus lining and inhibits both FSH and LH. If no implantation, corpus luteum breaks down, progesterone falls, menstruation occurs.
- 孕激素： 由黄体分泌，维持子宫内膜厚度，抑制 FSH 和 LH。若未着床，黄体退化，孕激素下降，月经来潮。
Hormonal contraceptives use synthetic oestrogen and progesterone to inhibit FSH and LH, preventing ovulation. Fertility treatments may involve giving FSH and LH to stimulate egg production.
激素类避孕药利用合成雌激素和孕激素抑制 FSH 和 LH，阻止排卵。生育治疗则可能使用 FSH 和 LH 来刺激卵子生成。
12. Plant Hormones: Auxins | 植物激素：生长素
Plants also use chemical messengers called plant hormones or plant growth regulators. Auxins, such as indoleacetic acid (IAA), are produced in the shoot tip and control phototropism and gravitropism. Unlike animal hormones, auxins are not produced in discrete glands but in meristematic regions.
植物也使用称为植物激素或植物生长调节剂的化学信使。生长素，如吲哚乙酸（IAA），在茎尖产生，控制向光性和向地性。与动物激素不同，生长素不是在离散的腺体中产生，而是在分生组织区域。
In phototropism, light causes auxin to redistribute to the shaded side of the shoot. Higher auxin concentration on the shaded side stimulates cell elongation, causing the shoot to bend towards the light. In roots, however, high auxin inhibits cell growth, so the root bends away from light (negative phototropism).
在向光性中，光照导致生长素重新分布到茎的背光侧。背光侧较高的生长素浓度刺激细胞伸长，导致茎向光弯曲。然而，在根中，高浓度生长素抑制细胞生长，因此根背光弯曲（负向光性）。
In gravitropism, auxin accumulates on the lower side of a horizontal root or shoot. In shoots, this stimulates growth, bending the shoot upwards (negative gravitropism). In roots, it inhibits growth, bending the root downwards (positive gravitropism). This ensures shoots grow towards light and roots anchor firmly into soil.
在向地性中，生长素积聚在水平放置的根或茎的下侧。在茎中，这促进生长，使茎向上弯曲（负向地性）。在根中，它抑制生长，使根向下弯曲（正向地性）。这确保了茎朝光生长，根牢固扎入土壤。
Weedkillers often contain synthetic auxins that cause uncontrolled growth, leading to the plant's death. Selective weedkillers exploit the fact that broad-leaved weeds absorb more auxin than narrow-leaved crops.
除草剂通常含有合成生长素，导致植物生长失控而死亡。选择性除草剂利用了阔叶杂草比窄叶作物吸收更多生长素这一特点。
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