📚 IB Biology: Endocrine System Key Points | IB 生物：内分泌系统 考点精讲
The endocrine system is a network of ductless glands that produce and secrete hormones directly into the bloodstream. Hormones serve as chemical messengers that regulate processes such as metabolism, growth, reproduction, and homeostasis, acting over minutes to days. In IB Biology, a detailed understanding of key glands, hormone classes, signalling mechanisms, and feedback loops is essential for mastering Topic 6 and Option D content. This article distills the core concepts, pairing clear English explanations with precise Chinese translations to reinforce bilingual comprehension.
内分泌系统是由无导管腺体组成的网络，能直接向血液中合成并分泌激素。激素作为化学信使，调节新陈代谢、生长、生殖和稳态等过程，作用时间从几分钟到几天不等。在IB生物学中，深刻理解关键腺体、激素类别、信号传导机制及反馈环路是掌握Topic 6与Option D内容的基础。本文提炼核心概念，将清晰的英文阐释与准确的中文翻译成对呈现，强化双语掌握。
1. Introduction to the Endocrine System | 内分泌系统简介
A hormone is defined as a chemical messenger produced by endocrine cells, released into the bloodstream, and capable of eliciting a specific response in distant target cells that possess matching receptors.
激素被定义为由内分泌细胞产生、释放入血并能在具有相应受体的远距离靶细胞中引发特异反应的化学信使。
Endocrine glands (e.g., pituitary, thyroid, adrenal) are ductless and secrete hormones directly into the interstitial fluid, from which they diffuse into capillaries. In contrast, exocrine glands (e.g., salivary, sweat) deliver their products via ducts to a body surface or cavity.
内分泌腺（如垂体、甲状腺、肾上腺）无导管，将激素直接分泌到组织液中，再扩散入毛细血管。相反，外分泌腺（如唾液腺、汗腺）通过导管将产物输送到体表或体腔。
Hormonal communication is generally slower but more sustained than neural communication, which relies on electrical impulses and neurotransmitters for rapid, short‑term adjustments. A single hormone can trigger coordinated, widespread changes across multiple tissues.
激素通讯通常比神经通讯慢，但更持久；神经通讯依赖电冲动和神经递质进行快速、短期的调整。单一种激素就能在多个组织中引发协调一致的广泛变化。
2. Hormone Types and Intracellular Signalling | 激素类型与胞内信号传导
Hormones are classified chemically into two major categories: lipid‑soluble (steroid and thyroid hormones) and water‑soluble (peptide, protein, and amine hormones). Their solubility dictates how they interact with target cells.
激素按化学性质分为两大类：脂溶性（类固醇与甲状腺激素）和水溶性（肽类、蛋白质及胺类激素）。其溶解性决定了它们与靶细胞相互作用的方式。
Lipid‑soluble hormones, such as oestrogen, testosterone, and cortisol, diffuse freely across the plasma membrane and bind to intracellular receptors in the cytoplasm or nucleus. The hormone‑receptor complex acts as a transcription factor, directly modulating gene expression—typically a slower but long‑lasting response.
脂溶性激素，如雌激素、睾酮和皮质醇，能自由扩散穿过细胞膜，与胞质或胞核中的胞内受体结合。激素‑受体复合物作为转录因子直接调节基因表达，通常反应较慢但持久。
Water‑soluble hormones (e.g., insulin, glucagon, adrenaline) cannot cross the phospholipid bilayer; instead they bind to cell‑surface receptors, initiating a second‑messenger cascade. A common pathway involves G‑protein activation, adenylate cyclase, and cyclic AMP (cAMP), which triggers a phosphorylating enzyme cascade leading to rapid cellular changes.
水溶性激素（如胰岛素、胰高血糖素、肾上腺素）无法穿过磷脂双分子层，而是与细胞表面受体结合，启动第二信使级联反应。常见的通路包括G蛋白激活、腺苷酸环化酶及环磷酸腺苷(cAMP)，进而引发磷酸化酶级联反应，产生快速的细胞变化。
Peptide hormone → Receptor → G‑protein → Adenylate cyclase → cAMP → Protein kinase A → Cellular response
肽类激素 → 受体 → G蛋白 → 腺苷酸环化酶 → cAMP → 蛋白激酶A → 细胞应答
3. The Hypothalamus‑Pituitary Axis | 下丘脑‑垂体轴
The hypothalamus serves as the bridge between the nervous and endocrine systems. It synthesises releasing and inhibiting hormones that are transported through a portal blood system to the anterior pituitary, controlling its secretion of trophic hormones.
下丘脑是神经与内分泌系统之间的桥梁。它合成释放激素和抑制激素，经门脉血管系统运送至垂体前叶，调控其促激素的分泌。
Key hypothalamic‑anterior pituitary axes include: TRH → TSH, CRH → ACTH, GnRH → FSH/LH, and GHRH/somatostatin → GH. Each trophic hormone then acts on a peripheral target gland or tissue.
关键的下丘脑‑垂体前叶轴包括：TRH → TSH，CRH → ACTH，GnRH → FSH/LH，以及 GHRH/生长抑素 → GH。每种促激素再作用于外周靶腺或组织。
The posterior pituitary does not synthesise hormones; it stores and releases vasopressin (antidiuretic hormone, ADH) and oxytocin, which are originally produced by neurosecretory cells in the hypothalamus and transported down axons.
垂体后叶不合成激素，它储存并释放血管升压素（抗利尿激素，ADH）和催产素，这两种激素由下丘脑的神经分泌细胞产生并沿轴突运输至此。
ADH increases water reabsorption in the kidney collecting ducts, thereby concentrating urine and maintaining blood osmolarity. Oxytocin stimulates uterine contractions during childbirth and milk ejection during lactation.
ADH增加肾脏集合管对水的重吸收，从而浓缩尿液并维持血液渗透压。催产素在分娩时刺激子宫收缩，并在哺乳期促进排乳。
4. Thyroid Gland: T3, T4, and Calcitonin | 甲状腺：T3、T4与降钙素
The thyroid gland produces two iodine‑containing hormones: thyroxine (T4) and triiodothyronine (T3). T4 is a prohormone largely converted into the more active T3 in target tissues. These hormones elevate the basal metabolic rate, promote protein synthesis, and are critical for normal growth and neural development.
甲状腺产生两种含碘激素：甲状腺素(T4)和三碘甲状腺原氨酸(T3)。T4是一种激素原，大多在靶组织中转化为活性更强的T3。这些激素提高基础代谢率，促进蛋白质合成，并对正常生长和神经发育至关重要。
TSH from the anterior pituitary stimulates all steps of thyroid hormone synthesis and release. Negative feedback occurs when elevated T3 and T4 levels suppress TRH secretion from the hypothalamus and TSH from the pituitary, maintaining a stable set point.
垂体前叶分泌的TSH刺激甲状腺激素合成与释放的每一步。当T3和T4升高时，会通过负反馈抑制下丘脑TRH和垂体TSH的分泌，从而维持稳定的设定点。
Iodine deficiency limits hormone production, leading to insufficient negative feedback, persistent TSH overstimulation, and enlargement of the thyroid—a condition known as endemic goitre. In infants, severe deficiency can cause cretinism, characterised by intellectual disability and growth retardation.
缺碘会限制激素生成，导致负反馈不足、TSH持续过度刺激和甲状腺增大，即地方性甲状腺肿。在婴儿，严重缺碘可导致呆小症，表现为智力障碍和生长迟缓。
Parafollicular C‑cells of the thyroid secrete calcitonin, which slightly lowers blood Ca²⁺ by inhibiting osteoclast activity and promoting calcium deposition in bone. Its role in adult humans is minor compared with parathyroid hormone.
甲状腺的滤泡旁C细胞分泌降钙素，通过抑制破骨细胞活性和促进骨钙沉积而轻度降低血Ca²⁺。在成年人体内，其作用远不如甲状旁腺激素重要。
5. Parathyroid Hormone and Calcium Homeostasis | 甲状旁腺激素与钙稳态
Parathyroid hormone (PTH) is the dominant regulator of extracellular calcium concentration. It is secreted by the chief cells of the four small parathyroid glands embedded in the posterior surface of the thyroid whenever blood Ca²⁺ falls below the normal range.
甲状旁腺激素(PTH)是细胞外钙浓度的主要调节者。它由位于甲状腺后表面的四枚微小甲状旁腺的主细胞在血Ca²⁺低于正常范围时分泌。
PTH elevates blood Ca²⁺ through three synergistic mechanisms: (1) stimulating osteoclasts to resorb bone, releasing Ca²⁺ and phosphate; (2) increasing renal tubular reabsorption of Ca²⁺ while promoting phosphate excretion; (3) enhancing the activation of vitamin D in the kidney, which augments intestinal absorption of Ca²⁺.
PTH通过三种协同机制升高血Ca²⁺：(1) 刺激破骨细胞溶骨，释放Ca²⁺与磷酸盐；(2) 增加肾小管对Ca²⁺的重吸收，同时促进磷酸盐排泄；(3) 增强肾脏中维生素D的活化，从而提高肠道对Ca²⁺的吸收。
Calcitonin from the thyroid and PTH act as physiological antagonists, fine‑tuning plasma calcium levels. The primary variable sensed by the parathyroid cells is the ionised Ca²⁺ concentration, detected by calcium‑sensing receptors.
甲状腺的降钙素与PTH互为生理拮抗剂，精细调节血浆钙水平。甲状旁腺细胞感知的主要变量是离子化Ca²⁺浓度，通过钙敏感受体检测。
6. Adrenal Glands: Adrenaline and Cortisol | 肾上腺：肾上腺素与皮质醇
Each adrenal gland consists of two functionally distinct regions: an outer cortex and an inner medulla. The medulla contains chromaffin cells that are directly innervated by sympathetic preganglionic fibres, allowing a rapid, neural‑like release of catecholamines.
每个肾上腺由外部的皮质和内部的髓质两个功能不同的区域构成。髓质内的嗜铬细胞受交感神经节前纤维直接支配，能以类似神经的方式快速释放儿茶酚胺。
Adrenaline (epinephrine) and noradrenaline (norepinephrine) are catecholamines released during the ‘fight‑or‑flight’ response. They bind to adrenergic receptors, triggering effects such as increased heart rate, bronchodilation, vasoconstriction in non‑essential organs, and glycogenolysis in the liver, all of which prepare the body for intense physical activity.
肾上腺素与去甲肾上腺素是在“战斗或逃跑”反应中释放的儿茶酚胺。它们结合肾上腺素能受体，引发心率加快、支气管扩张、非必需器官血管收缩以及肝糖原分解等效应，为激烈体力活动做好准备。
The adrenal cortex synthesises corticosteroids from cholesterol. Glucocorticoids, principally cortisol in humans, elevate blood glucose through gluconeogenesis, suppress the immune response, and aid the body in coping with long‑term stress. Mineralocorticoids, mainly aldosterone, promote Na⁺ reabsorption and K⁺ secretion in the kidney, thereby regulating blood pressure and electrolyte balance.
肾上腺皮质从胆固醇合成皮质类固醇。糖皮质激素（主要是人体中的皮质醇）通过糖异生提高血糖，抑制免疫反应，并帮助身体应对长期应激。盐皮质激素（主要是醛固酮）促进肾脏对Na⁺的重吸收并分泌K⁺，从而调节血压与电解质平衡。
Cortisol secretion follows a diurnal rhythm and is controlled by the hypothalamic‑pituitary‑adrenal (HPA) axis: CRH from the hypothalamus stimulates ACTH release from the anterior pituitary, which in turn induces cortisol synthesis. Negative feedback by cortisol inhibits both CRH and ACTH secretion.
皮质醇的分泌具有昼夜节律，受下丘脑‑垂体‑肾上腺(HPA)轴调控：下丘脑的CRH刺激垂体前叶释放ACTH，ACTH再诱导皮质醇合成。皮质醇通过负反馈抑制CRH和ACTH的分泌。
7. Pancreatic Islets and Glucose Regulation | 胰岛与血糖调节
The endocrine pancreas consists of clusters of cells called the islets of Langerhans. Within each islet, α‑cells secrete glucagon, β‑cells secrete insulin, and δ‑cells secrete somatostatin. Insulin and glucagon work in opposition to maintain blood glucose within a narrow physiological range (approximately 4–6 mmol L⁻¹).
内分泌胰腺由称为胰岛的细胞团组成。每个胰岛内，α细胞分泌胰高血糖素，β细胞分泌胰岛素，δ细胞分泌生长抑素。胰岛素与胰高血糖素相互拮抗，将血糖维持在狭窄的生理范围内（约4–6 mmol L⁻¹）。
Insulin is released in response to elevated blood glucose. It binds to tyrosine kinase receptors, promoting glucose uptake in muscle and adipose tissue via GLUT4 translocation, stimulating glycogen synthesis (glycogenesis) in the liver and muscles, and inhibiting gluconeogenesis. These actions collectively lower blood glucose.
胰岛素在血糖升高时分泌。它结合酪氨酸激酶受体，通过GLUT4转位促进肌肉和脂肪组织摄取葡萄糖，刺激肝和肌肉中的糖原合成（糖生成），并抑制糖异生。这些作用共同降低血糖。
Glucagon is released when blood glucose falls. It acts mainly on the liver to stimulate glycogenolysis and gluconeogenesis, thereby increasing glucose output into the bloodstream. It also promotes lipolysis in adipose tissue.
胰高血糖素在血糖下降时分泌。主要作用于肝脏，刺激糖原分解与糖异生，从而增加肝脏向血液中输出的葡萄糖。它还促进脂肪组织的脂解。
High blood glucose → β‑cells release insulin → glucose uptake & glycogenesis → blood glucose drops → insulin secretion declines
高血糖 → β细胞释放胰岛素 → 葡萄糖摄取与糖生成 → 血糖下降 → 胰岛素分泌减少
Disruption of this balance leads to diabetes mellitus. Type 1 diabetes results from autoimmune destruction of β‑cells, causing absolute insulin deficiency. Type 2 diabetes is characterised by insulin resistance and relative insulin deficiency, often associated with obesity and lifestyle factors.
这种平衡的破坏导致糖尿病。1型糖尿病由β细胞的自身免疫破坏引起，导致绝对的胰岛素缺乏。2型糖尿病的特点是胰岛素抵抗和相对胰岛素缺乏，常与肥胖和生活方式因素有关。
8. Reproductive Hormones and the Menstrual Cycle | 生殖激素与月经周期
Hypothalamic gonadotropin‑releasing hormone (GnRH) stimulates the anterior pituitary to release follicle‑stimulating hormone (FSH) and luteinising hormone (LH), which are pivotal in gamete production and sex hormone secretion in both males and females.
下丘脑的促性腺激素释放激素(GnRH)刺激垂体前叶分泌促卵泡激素(FSH)与黄体生成素(LH)，这两种激素对两性配子生成和性激素分泌至关重要。
In males, FSH acts on Sertoli cells to support spermatogenesis, while LH acts on Leydig cells to stimulate testosterone production. Testosterone promotes the development of male secondary sexual characteristics and maintains libido and sperm maturation.
在男性，FSH作用于支持细胞以促进精子生成，LH作用于间质细胞以刺激睾酮生成。睾酮促进男性第二性征发育，并维持性欲和精子成熟。
In females, the menstrual cycle is divided into the follicular phase, ovulation, and the luteal phase. FSH stimulates growth of ovarian follicles, which secrete oestrogen. Rising oestrogen levels initially exert negative feedback on FSH, but a sustained high level triggers a positive feedback switch that elicits the LH surge, causing ovulation.
在女性，月经周期分为卵泡期、排卵和黄体期。FSH刺激卵泡生长，卵泡分泌雌激素。升高的雌激素一开始对FSH实施负反馈，但持续高水平会触发正反馈开关，引发LH峰，导致排卵。
After ovulation, the ruptured follicle forms the corpus luteum, which secretes progesterone and some oestrogen. Progesterone thickens and maintains the endometrium, preparing it for potential implantation. If fertilisation does not occur, the corpus luteum degenerates, progesterone levels fall, and menstruation ensues.
排卵后，破裂的卵泡形成黄体，分泌孕酮和少量雌激素。孕酮增厚并维持子宫内膜，为可能的着床做准备。若未受精，黄体退化，孕酮水平下降，月经来潮。
9. Feedback Mechanisms in Endocrine Control | 内分泌调控中的反馈机制
Negative feedback is the most prevalent control mechanism in
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