WJEC生物 稳态 体温 血糖 肾脏 负反馈
稳态（Homeostasis）是 WJEC A-Level 生物学的核心模块，占据 Unit 3 (A2) 考试的重要比重。本清单涵盖体温调节、血糖控制、肾脏功能与渗透调节三大子系统，逐个拆解超滤、选择性重吸收、逆流倍增及激素反馈环路的关键考点。无论你正在备考 Paper 1 或 Paper 2，这 10 项知识点清单都能帮你系统梳理全模块，锁定高分。
Homeostasis is a core module in WJEC A-Level Biology, carrying significant weight in the Unit 3 (A2) examination. This checklist covers the three major subsystems - thermoregulation, blood glucose control, and kidney function with osmoregulation - breaking down ultrafiltration, selective reabsorption, the countercurrent multiplier, and hormonal feedback loops item by item. Whether you are revising for Paper 1 or Paper 2, these 10 knowledge items will help you systematically review the entire module and lock in top marks.
1. Thermoregulation 体温调节
人体核心温度维持在 37 deg C 左右，由下丘脑（hypothalamus）的体温调节中枢控制。皮肤与血液中的温度感受器持续向中枢发送信号，中枢通过比较「设定点」与实际体温，启动效应器做出响应。散热机制包括皮肤血管舒张（vasodilation）、出汗（sweating）及立毛肌松弛（erector pili relaxation）；产热机制包括血管收缩（vasoconstriction）、战栗产热（shivering thermogenesis）及甲状腺素（thyroxine）加速代谢。WJEC 常考的是 thermoregulatory centre 定位在下丘脑的具体区域（preoptic area），以及 brown adipose tissue 在新生儿非战栗产热中的特殊作用。
The human core body temperature is maintained around 37 deg C, controlled by the thermoregulatory centre in the hypothalamus. Thermoreceptors in the skin and blood continuously send signals to this centre, which compares the actual body temperature against a set point and activates effectors accordingly. Heat-loss mechanisms include cutaneous vasodilation, sweating, and relaxation of erector pili muscles; heat-gain mechanisms include vasoconstriction, shivering thermogenesis, and increased metabolism driven by thyroxine. WJEC frequently tests the specific hypothalamic location of the thermoregulatory centre (the preoptic area) and the special role of brown adipose tissue in non-shivering thermogenesis in newborns.
2. Negative Feedback 负反馈原理
负反馈（negative feedback）是稳态调节的通用机制：当某一生理变量偏离设定点时，系统启动反向调节过程将其拉回正常范围。关键结构包括感受器（receptor）、协调中枢（coordination centre）和效应器（effector）。以体温调节为例：体温升高-感受器检测-下丘脑整合-皮肤血管舒张+出汗-体温下降-回到设定点。需要区分正反馈（positive feedback）：：在分娩（oxytocin-driven uterine contractions）和动作电位（action potential depolarisation）中出现，推动过程远离平衡态，而非维持稳定。
Negative feedback is the universal mechanism underlying homeostatic regulation: when a physiological variable deviates from its set point, the system initiates corrective processes that restore it to the normal range. The key components are receptors, a coordination centre, and effectors. Take thermoregulation as an example: temperature rises → receptors detect change → hypothalamus integrates signal → cutaneous vasodilation plus sweating → temperature falls → return to set point. Distinguish this from positive feedback, which drives processes away from equilibrium and occurs in childbirth (oxytocin-driven uterine contractions) and action potential depolarisation, rather than maintaining stability.
3. Blood Glucose Regulation 血糖调节
血糖浓度正常范围为 4-6 mmol dm sup3。进食后血糖升高时，胰腺 beta 细胞释放胰岛素（insulin），促进肝细胞和肌细胞通过 GLUT4 转运蛋白摄取葡萄糖，并将多余葡萄糖转化为糖原（glycogenesis）。血糖过低时，胰腺 alpha 细胞释放胰高血糖素（glucagon），激活糖原分解（glycogenolysis）和糖异生（gluconeogenesis），使肝脏释放葡萄糖入血。WJEC 考试常要求描述胰岛素作用的第二信使机制（second messenger model）：胰岛素与受体结合-激活酪氨酸激酶-磷酸化级联反应-GLUT4 囊泡转运至细胞膜-葡萄糖内流。
Normal blood glucose concentration ranges from 4-6 mmol dm sup3. After a meal when blood glucose rises, pancreatic beta cells release insulin, which promotes glucose uptake by hepatocytes and muscle cells via GLUT4 transporter proteins and converts excess glucose to glycogen through glycogenesis. When blood glucose falls too low, pancreatic alpha cells release glucagon, which activates glycogenolysis and gluconeogenesis, causing the liver to release glucose into the blood. WJEC exams often require describing the second messenger model of insulin action: insulin binds to receptor → activates tyrosine kinase → phosphorylation cascade → GLUT4 vesicles translocate to the cell membrane → glucose influx.
4. Osmoregulation and Kidney Structure 渗透调节与肾脏结构
渗透调节（osmoregulation）维持血液水势（water potential）在狭窄范围内，主要由肾脏执行。WJEC 要求掌握肾脏宏观结构：皮质（cortex）含肾小体（Bowman's capsule + glomerulus）及近曲小管和远曲小管；髓质（medulla）含亨氏袢（loop of Henle）及集合管（collecting duct）；肾盂（pelvis）收集尿液通向输尿管。一个肾单位（nephron）是肾脏的功能单位，血液按「入球小动脉-肾小球-出球小动脉-管周毛细血管-肾静脉」路径流动。注意出球小动脉直径小于入球小动脉：：这一结构特点产生肾小球内高压，是超滤的驱动力。
Osmoregulation maintains blood water potential within a narrow range and is primarily executed by the kidneys. WJEC requires mastery of kidney gross anatomy: the cortex contains renal corpuscles (Bowman's capsule + glomerulus), proximal convoluted tubules, and distal convoluted tubules; the medulla contains the loop of Henle and collecting ducts; the pelvis collects urine en route to the ureter. A nephron is the functional unit of the kidney, with blood flowing along the path: afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → renal vein. Note that the efferent arteriole has a smaller diameter than the afferent arteriole - this structural feature generates high hydrostatic pressure inside the glomerulus, which is the driving force for ultrafiltration.
5. Ultrafiltration in the Bowman's Capsule 超滤作用
超滤（ultrafiltration）发生在肾小体，依靠肾小球毛细血管内的高静水压（hydrostatic pressure）将血浆中的水和小分子溶质推过滤过屏障。滤过屏障由三层结构组成：毛细血管内皮的有孔窗（fenestrated endothelium）、基底膜（basement membrane，关键过滤层，含胶原蛋白和糖蛋白）以及足细胞（podocytes）的足突裂孔（filtration slits）。正常情况下，血细胞和血浆蛋白（如白蛋白、球蛋白）因分子量过大被保留在血液中，而水、葡萄糖、氨基酸、尿素、离子等自由滤过。肾小球滤过率（GFR）约为 125 cm sup3 min sup1。WJEC 常考基底膜阻挡蛋白质通过的结构原理。
Ultrafiltration occurs in the renal corpuscle, where high hydrostatic pressure in the glomerular capillaries forces water and small dissolved solutes from the plasma across the filtration barrier. This barrier consists of three layers: the fenestrated endothelium of the capillary, the basement membrane (the critical filtration layer, composed of collagen and glycoproteins), and the filtration slits between the foot processes of podocytes. Under normal conditions, blood cells and plasma proteins (such as albumin and globulins) are retained in the blood due to their large molecular size, while water, glucose, amino acids, urea, and ions pass freely into the filtrate. The glomerular filtration rate (GFR) is approximately 125 cm sup3 min sup1. WJEC frequently examines the structural principle by which the basement membrane blocks protein passage.
6. Selective Reabsorption in the PCT 选择性重吸收
近曲小管（proximal convoluted tubule, PCT）是选择性重吸收的主要场所：：约 85 percent 的滤液在此被重吸收。PCT 上皮细胞具有微绒毛（microvilli）形成的刷状缘，极大增加表面积；胞内含有大量线粒体，为主动运输提供 ATP。葡萄糖和氨基酸通过钠离子协同转运蛋白（Na sup+ cotransporter）从管腔进入上皮细胞（次级主动运输），再由基底侧的易化扩散进入血液。水通过渗透作用（osmosis）跟随。尿素中约 50 percent 被动扩散回血液。注意 WJEC 需要区分重吸收发生的具体部位和运输方式：PCT 的 Na sup+ cotransport 是次级主动运输，而非初级主动运输。
The proximal convoluted tubule (PCT) is the primary site of selective reabsorption, where approximately 85 percent of the filtrate is reclaimed. PCT epithelial cells possess a brush border formed by microvilli, greatly increasing the surface area; they contain abundant mitochondria providing ATP for active transport. Glucose and amino acids are transported from the lumen into epithelial cells via Na sup+ cotransporter proteins (secondary active transport), then move into the blood via facilitated diffusion at the basal membrane. Water follows by osmosis. Approximately 50 percent of urea diffuses passively back into the blood. Note that WJEC requires distinguishing the specific location and transport mechanism involved: Na sup+ cotransport in the PCT is secondary active transport, not primary active transport.
7. Loop of Henle and Countercurrent Multiplier 亨氏袢与逆流倍增
亨氏袢（loop of Henle）是形成肾髓质渗透梯度的关键结构，通过逆流倍增机制（countercurrent multiplier）实现。降支（descending limb）对水通透但对 Na sup+ 和 Cl sup- 不通透，滤液下行时水被周围高渗髓质间质吸出，管腔内液逐渐浓缩。升支粗段（thick ascending limb）对水不通透但主动泵出 Na sup+ 和 Cl sup- 进入间质，建立从皮质表面（300 mOsm）到髓质深处（1200 mOsm）的递增渗透梯度。WJEC 需要区分降支细段与升支粗段的通透性差异，以及为什么升支被称为「稀释段」。这个梯度是后续集合管中水重吸收的驱动力。
The loop of Henle is the key structure that establishes the osmotic gradient in the renal medulla, achieved through the countercurrent multiplier mechanism. The descending limb is permeable to water but impermeable to Na sup+ and Cl sup-, so as filtrate descends, water is drawn out into the hypertonic medullary interstitium, progressively concentrating the luminal fluid. The thick ascending limb is impermeable to water but actively pumps Na sup+ and Cl sup- into the interstitium, establishing an increasing osmotic gradient from the cortical surface (300 mOsm) to the deep medulla (1200 mOsm). WJEC requires distinguishing the permeability differences between the thin descending limb and the thick ascending limb, and understanding why the ascending limb is called the diluting segment. This gradient is the driving force for water reabsorption in the subsequent collecting duct.
8. ADH and Collecting Duct Regulation ADH与集合管调节
抗利尿激素（antidiuretic hormone, ADH）由下丘脑合成、垂体后叶（posterior pituitary）释放，是渗透调节的终极激素控制器。当血液水势降低（脱水或高盐摄入）时，下丘脑渗透压感受器检测到变化，触发 ADH 释放。ADH 与集合管和远曲小管主细胞基底侧的 V2 受体结合，激活 cAMP 第二信使级联，促使含有水通道蛋白-2（aquaporin-2, AQP2）的囊泡插入顶膜，大幅增加管壁对水的通透性，水顺渗透梯度重吸收，尿液浓缩。水势恢复后，ADH 分泌减少，AQP2 通过胞吞作用内化，管壁重新变为水不通透，产生稀释尿液。
Antidiuretic hormone (ADH), synthesised by the hypothalamus and released from the posterior pituitary, is the ultimate hormonal controller of osmoregulation. When blood water potential falls (dehydration or high salt intake), hypothalamic osmoreceptors detect the change and trigger ADH release. ADH binds to V2 receptors on the basolateral membrane of principal cells in the collecting duct and distal convoluted tubule, activating a cAMP second messenger cascade that promotes the insertion of vesicles containing aquaporin-2 (AQP2) water channels into the apical membrane. This greatly increases the tubule wall's permeability to water; water is reabsorbed down the osmotic gradient, producing concentrated urine. When water potential is restored, ADH secretion decreases, AQP2 is internalised by endocytosis, and the tubule wall returns to being water-impermeable, producing dilute urine.
9. Diabetes Mellitus 糖尿病
糖尿病是稳态调节失败的典型临床实例。1 型糖尿病（Type 1 diabetes）由自身免疫攻击胰腺 beta 细胞导致胰岛素绝对缺乏，典型发病于儿童/青少年期，需终身胰岛素注射治疗。2 型糖尿病（Type 2 diabetes）由胰岛素抵抗（insulin resistance）和 beta 细胞功能逐渐衰退引起，与肥胖和久坐生活方式密切相关，可通过饮食控制和运动管理。WJEC 需要说明二者在病理生理上的本质区别：Type 1 是胰岛素产生不足，Type 2 是靶细胞对胰岛素不敏感。还需提及血糖监测（blood glucose monitoring）和糖化血红蛋白（HbA1c）作为长期血糖控制的诊断指标。注意不要把糖尿病与尿崩症（diabetes insipidus, ADH 缺乏或 ADH 受体缺陷导致）混淆。
Diabetes mellitus represents a classic clinical example of homeostatic failure. Type 1 diabetes results from autoimmune destruction of pancreatic beta cells, causing absolute insulin deficiency; it typically presents in childhood or adolescence and requires lifelong insulin therapy. Type 2 diabetes is caused by insulin resistance combined with a gradual decline in beta cell function, is strongly associated with obesity and sedentary lifestyle, and can be managed through dietary control and exercise. WJEC requires explaining the fundamental pathophysiological difference: Type 1 involves insufficient insulin production, while Type 2 involves target cell insensitivity to insulin. Blood glucose monitoring and glycated haemoglobin (HbA1c) as diagnostic markers for long-term glycaemic control should also be mentioned. Do not confuse diabetes mellitus with diabetes insipidus, which results from ADH deficiency or ADH receptor defects.
10. Homeostasis and Exercise 运动中的稳态整合
剧烈运动是对稳态系统的终极压力测试：肌肉活动产热使核心体温上升，出汗增加导致水分和电解质流失，血糖被快速消耗。此时多个稳态系统协同工作：：体温调节通过皮肤血管舒张和大量出汗散热；血糖调节通过胰高血糖素和肾上腺素（adrenaline）促进肝糖原分解维持血糖；渗透调节通过 ADH 分泌增加保留水分，同时 RAAS（renin-angiotensin-aldosterone system）系统激活以保留 Na sup+ 和水。WJEC 的综合分析题常以运动场景为背景，要求考生将体温、血糖和渗透调节三个子系统的响应整合成完整的稳态应答模型。
Vigorous exercise is the ultimate stress test for homeostatic systems: muscular activity generates heat that raises core temperature, increased sweating causes fluid and electrolyte loss, and blood glucose is rapidly consumed. In this scenario, multiple homeostatic systems work in concert: thermoregulation dissipates heat through cutaneous vasodilation and profuse sweating; blood glucose regulation maintains levels via glucagon and adrenaline-promoted glycogenolysis; osmoregulation conserves water through increased ADH secretion, while the renin-angiotensin-aldosterone system (RAAS) is activated to retain Na sup+ and water. WJEC integrative analysis questions frequently use exercise scenarios as a context, requiring candidates to synthesise the responses of all three subsystems - temperature, glucose, and osmoregulation - into a complete homeostatic response model.
Key Bilingual Terms 关键双语术语
Homeostasis 稳态 | Negative feedback 负反馈 | Thermoregulation 体温调节 | Hypothalamus 下丘脑 | Vasodilation 血管舒张 | Vasoconstriction 血管收缩 | Insulin 胰岛素 | Glucagon 胰高血糖素 | Glycogenesis 糖原合成 | Glycogenolysis 糖原分解 | Gluconeogenesis 糖异生 | Osmoregulation 渗透调节 | Nephron 肾单位 | Glomerulus 肾小球 | Bowman's capsule 肾小囊 | Ultrafiltration 超滤 | Podocyte 足细胞 | Proximal convoluted tubule (PCT) 近曲小管 | Loop of Henle 亨氏袢 | Countercurrent multiplier 逆流倍增器 | Collecting duct 集合管 | Antidiuretic hormone (ADH) 抗利尿激素 | Aquaporin 水通道蛋白 | Diabetes mellitus 糖尿病 | Set point 设定点
Exam Tips for WJEC 考试技巧
WJEC A-Level 生物的稳态模块在 Unit 3 考试中通常以结构化简答题和数据分析题形式出现，偶尔出现在长篇论述题（9-mark essay）中。第一要点：区分描述题与解释题：：Describe 只需陈述观察事实，Explain 必须提供因果机制（例如：体温上升-血管舒张-散热增加-体温下降，而非只说体温下降）。第二要点：多系统整合题务必逐一模块回答，先体温、再血糖、后渗透调节，避免交叉跳跃导致逻辑混乱。第三要点：ADH 的 cAMP 第二信使通路和胰岛素第二信使模型是 WJEC 高频考点，掌握囊泡运输和磷酸化级联的准确步骤。第四要点：数据处理题给出的血糖浓度曲线或尿液渗透压图表，务必标注上升段/下降段对应哪种激素的作用。
The Homeostasis module in WJEC A-Level Biology typically appears in Unit 3 as structured short-answer and data-analysis questions, occasionally as part of extended-response 9-mark essays. First key point: distinguish between describe and explain questions. Describe only requires stating observed facts; Explain demands causal mechanisms (e.g., temperature rises → vasodilation → increased heat loss → temperature falls, not just stating that temperature falls). Second key point: for multi-system integration questions, answer module by module - thermoregulation first, then blood glucose, then osmoregulation - to avoid cross-jumping that confuses the logical flow. Third key point: the cAMP second messenger pathway for ADH and the second messenger model for insulin are high-frequency WJEC examination topics; master the precise sequence of vesicle trafficking and phosphorylation cascades. Fourth key point: for data-handling questions presenting blood glucose curves or urine osmolarity charts, always annotate which hormone is responsible for each rising or falling segment.
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