📚 Hormonal Regulation of Blood Glucose Concentration | 血糖浓度的激素调节
The maintenance of blood glucose concentration within a narrow physiological range is one of the most critical examples of homeostasis in the human body. This process is primarily regulated by hormones secreted from the islets of Langerhans in the pancreas, ensuring that cells receive a constant supply of glucose for respiration while preventing the damaging effects of hyperglycaemia or hypoglycaemia.
将血糖浓度维持在一个狭窄的生理范围内，是人体内稳态最重要的范例之一。这一过程主要由胰腺朗格汉斯岛分泌的激素调控，确保细胞获得持续供应的葡萄糖用于呼吸作用，同时防止高血糖或低血糖带来的损害。
1. Why Blood Glucose Concentration Must Be Regulated | 为何必须调节血糖浓度
Glucose is the primary respiratory substrate for most mammalian cells, particularly neurons, which rely almost exclusively on glucose under normal conditions. Maintaining blood glucose around 80–120 mg/dL (4.4–6.7 mmol/L) is essential because too little glucose deprives the brain of energy, leading to confusion, unconsciousness, and potentially death, whereas too much glucose causes osmotic water loss from tissues, dehydration, and long-term damage to blood vessels and nerves.
葡萄糖是大多数哺乳动物细胞的主要呼吸底物，尤其是神经元，在正常情况下几乎完全依赖葡萄糖供能。维持血糖在80–120 mg/dL（4.4–6.7 mmol/L）至关重要，因为葡萄糖过少会使大脑缺乏能量，导致意识混乱、昏迷甚至死亡；而葡萄糖过多则会引起组织渗透性失水、脱水，并对血管和神经造成长期损害。
Two pancreatic hormones achieve this balance: insulin, which lowers blood glucose, and glucagon, which raises it. These hormones work antagonistically, forming a negative feedback system that responds rapidly to changes in blood glucose concentration.
两种胰腺激素实现这一平衡：降低血糖的胰岛素和升高血糖的胰高血糖素。这两种激素相互拮抗，构成一个对血糖浓度变化作出快速反应的负反馈系统。
2. The Islets of Langerhans | 朗格汉斯岛
The pancreas contains clusters of endocrine cells called the islets of Langerhans, which are scattered among the exocrine acinar cells that secrete digestive enzymes. Each islet contains several distinct cell types, the most important being α-cells and β-cells, which are identifiable by their position within the islet and their secretory products.
胰腺中含有称为朗格汉斯岛的内分泌细胞群，散布在分泌消化酶的外分泌腺泡细胞之间。每个胰岛包含多种不同细胞类型，其中最重要的是α细胞和β细胞，可通过它们在胰岛内的位置及其分泌物加以识别。
| Cell type | Position in islet | Hormone secreted | Effect on blood glucose |
| α-cell | Peripheral | Glucagon | Raises blood glucose |
| β-cell | Central | Insulin | Lowers blood glucose |
The ratio of β-cells to α-cells is approximately 3:1 in humans, reflecting the more frequent physiological challenge of hyperglycaemia after meals compared with hypoglycaemia between meals.
人体中β细胞与α细胞的比例约为3:1，这反映了餐后高血糖的生理挑战比餐间低血糖更为常见。
3. Insulin: Structure and Synthesis | 胰岛素：结构与合成
Insulin is a peptide hormone composed of 51 amino acids arranged in two polypeptide chains — the A chain (21 amino acids) and the B chain (30 amino acids) — linked by two disulphide bridges, with an additional disulphide bridge within the A chain. It is synthesised as preproinsulin, which is cleaved to proinsulin, then folded and processed to active insulin in the Golgi apparatus of β-cells.
胰岛素是一种肽类激素，由51个氨基酸组成，排列成两条多肽链——A链（21个氨基酸）和B链（30个氨基酸）——通过两个二硫键连接，A链内部还有一个二硫键。它以胰岛素原前体的形式合成，被切割为胰岛素原，随后在高尔基体中折叠加工为活性胰岛素。
Insulin secretion is triggered primarily by elevated blood glucose. Glucose enters β-cells via GLUT2 transporters and is metabolised by glucokinase, increasing the ATP/ADP ratio. This ATP-sensitive K⁺ channel closure depolarises the membrane, opening voltage-gated Ca²⁺ channels; the influx of Ca²⁺ stimulates exocytosis of insulin-containing vesicles.
胰岛素分泌主要由血糖升高触发。葡萄糖通过GLUT2转运蛋白进入β细胞，经葡萄糖激酶代谢，使ATP/ADP比值升高。ATP敏感K⁺通道关闭导致膜去极化，开放电压门控Ca²⁺通道；Ca²⁺内流刺激含胰岛素的囊泡胞吐。
Glucose → GLUT2 → Glucokinase → ATP↑ → KATP channel closes → Depolarisation → Ca²⁺ influx → Insulin exocytosis
4. Glucagon: The Hyperglycaemic Hormone | 胰高血糖素：升糖激素
Glucagon is a 29-amino-acid peptide hormone secreted by α-cells when blood glucose falls below approximately 70 mg/dL (3.9 mmol/L). Its secretion is also stimulated by sympathetic nervous activity during stress or exercise. Glucagon acts primarily on the liver, where it promotes glycogenolysis, gluconeogenesis, and the release of glucose into the bloodstream.
胰高血糖素是一种由29个氨基酸组成的肽类激素，当血糖降至约70 mg/dL（3.9 mmol/L）以下时由α细胞分泌。交感神经活动在应激或运动时也会刺激其分泌。胰高血糖素主要作用于肝脏，促进糖原分解、糖异生以及葡萄糖释放入血。
The signalling pathway for glucagon involves binding to a G-protein-coupled receptor that activates adenylate cyclase, increasing intracellular cyclic AMP (cAMP) and activating protein kinase A (PKA). PKA then phosphorylates glycogen phosphorylase kinase, which activates glycogen phosphorylase, the enzyme that catalyses glycogen breakdown, while simultaneously inhibiting glycogen synthase.
胰高血糖素的信号通路涉及与G蛋白偶联受体结合，激活腺苷酸环化酶，增加细胞内环状AMP（cAMP）并激活蛋白激酶A（PKA）。PKA随后磷酸化糖原磷酸化酶激酶，激活催化糖原分解的糖原磷酸化酶，同时抑制糖原合酶。
Glucagon also stimulates gluconeogenesis — the synthesis of glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids — by increasing the expression of key enzymes including phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-bisphosphatase.
胰高血糖素还通过增加磷酸烯醇式丙酮酸羧激酶（PEPCK）和果糖-1,6-二磷酸酶等关键酶的表达，刺激糖异生——即从乳酸、甘油和氨基酸等非碳水化合物前体合成葡萄糖。
5. Target Tissues and Receptors | 靶组织和受体
Insulin exerts its effects through the insulin receptor, a transmembrane tyrosine kinase receptor. Binding of insulin causes autophosphorylation of tyrosine residues, initiating a cascade that recruits insulin receptor substrates (IRS-1 and IRS-2), which activate the PI3K-Akt pathway. This pathway promotes the translocation of GLUT4 glucose transporters to the cell membrane, particularly in muscle and adipose tissue, increasing glucose uptake.
胰岛素通过跨膜酪氨酸激酶受体——胰岛素受体发挥作用。胰岛素结合引起酪氨酸残基自身磷酸化，启动级联反应，募集胰岛素受体底物（IRS-1和IRS-2），激活PI3K-Akt通路。该通路促进GLUT4葡萄糖转运蛋白向细胞膜转位，尤其在肌肉和脂肪组织中，从而增加葡萄糖摄取。
The insulin receptor is a heterotetramer composed of two extracellular α-subunits and two transmembrane β-subunits. The α-subunits bind insulin, while the β-subunits possess intrinsic tyrosine kinase activity that is activated upon insulin binding.
胰岛素受体是由两个细胞外α亚基和两个跨膜β亚基组成的异源四聚体。α亚基结合胰岛素，而β亚基具有固有的酪氨酸激酶活性，在胰岛素结合时被激活。
| Tissue | Insulin effect | Glucagon effect |
| Liver | Glycogenesis, lipogenesis; inhibits gluconeogenesis | Glycogenolysis, gluconeogenesis |
| Muscle | GLUT4 translocation → glucose uptake; glycogen synthesis | No significant effect |
| Adipose tissue | GLUT4 translocation; lipogenesis | Lipolysis (minor) |
6. The Negative Feedback System | 负反馈系统
The regulation of blood glucose exemplifies a classic negative feedback system. When blood glucose rises after a carbohydrate-rich meal, insulin secretion increases and glucagon secretion decreases, restoring normal glucose levels. Conversely, when blood glucose falls during fasting or exercise, glucagon secretion increases and insulin decreases, raising glucose levels back to normal.
血糖调节是经典负反馈系统的例证。当富含碳水化合物的餐后血糖升高时，胰岛素分泌增加，胰高血糖素分泌减少，将血糖恢复至正常水平。反之，当禁食或运动期间血糖下降时，胰高血糖素分泌增加而胰岛素减少，使血糖回升至正常水平。
This antagonistic relationship ensures that the two hormones respond in opposite directions to the same stimulus, providing finer control than a single hormone could achieve. The system also exhibits rapid response times — insulin secretion changes within minutes of glucose ingestion — and self-limiting behaviour, as the effects of each hormone suppress its own further secretion.
这种拮抗关系确保两种激素对同一刺激作出相反方向的响应，比单一激素能实现更精细的控制。该系统还具有快速响应特点——胰岛素分泌在摄入葡萄糖后数分钟内即发生变化——以及自我限制行为，因为每种激素的作用会抑制其自身进一步分泌。
7. Adrenaline and Cortisol: Secondary Regulators | 肾上腺素与皮质醇：次级调节因子
While insulin and glucagon are the primary regulators, two other hormones contribute to blood glucose homeostasis. Adrenaline (epinephrine), secreted by the adrenal medulla during the fight-or-flight response, raises blood glucose rapidly by activating glycogen phosphorylase in the liver and muscle via the cAMP pathway. It also inhibits insulin secretion and stimulates glucagon release, coordinating a rapid mobilisation of energy reserves.
虽然胰岛素和胰高血糖素是主要调节因子，但另外两种激素也参与血糖稳态的维持。肾上腺素（epinephrine）在应激反应期间由肾上腺髓质分泌，通过cAMP途径激活肝脏和肌肉中的糖原磷酸化酶，迅速升高血糖。它还抑制胰岛素分泌并刺激胰高血糖素释放，协调能量储备的快速动员。
Cortisol, a glucocorticoid secreted by the adrenal cortex, raises blood glucose over a longer timescale by stimulating gluconeogenesis in the liver and reducing glucose uptake in peripheral tissues. Cortisol acts through a nuclear receptor that modulates gene transcription, explaining its slower onset and longer duration of action compared with peptide hormones.
皮质醇是由肾上腺皮质分泌的糖皮质激素，通过刺激肝脏糖异生和减少外周组织葡萄糖摄取，在较长时间尺度上升高血糖。皮质醇通过核受体调节基因转录，这解释了其与肽类激素相比起效较慢但作用时间更长的特点。
8. Glycogenolysis and Gluconeogenesis: Molecular Mechanisms | 糖原分解与糖异生：分子机制
Glycogenolysis is the process by which glycogen is broken down into glucose-1-phosphate, catalysed by glycogen phosphorylase. This enzyme cleaves α-1,4-glycosidic bonds sequentially from the non-reducing ends of glycogen branches. The debranching enzyme removes the α-1,6-branch points, allowing complete degradation of glycogen.
糖原分解是由糖原磷酸化酶催化的、将糖原分解为1-磷酸葡萄糖的过程。该酶从糖原分支的非还原端依次切割α-1,4-糖苷键。脱支酶移除α-1,6-分支点，使糖原能够完全降解。
In the liver, glucose-1-phosphate is converted to glucose-6-phosphate by phosphoglucomutase, then hydrolysed to free glucose by glucose-6-phosphatase — an enzyme absent from muscle, which explains why muscle glycogen is used locally rather than exported to the blood.
在肝脏中，1-磷酸葡萄糖由磷酸葡萄糖变位酶转化为6-磷酸葡萄糖，然后被葡萄糖-6-磷酸酶水解为游离葡萄糖——肌肉中缺乏该酶，这解释了为什么肌糖原供局部使用而非释放入血。
Gluconeogenesis is the de novo synthesis of glucose from non-carbohydrate precursors, occurring mainly in the liver during prolonged fasting. Key substrates include lactate (via the Cori cycle), glycerol (from triglyceride breakdown), and glucogenic amino acids (mainly alanine). The pathway largely reverses glycolysis but bypasses three irreversible reactions using distinct enzymes.
糖异生是从非碳水化合物前体从头合成葡萄糖的过程，主要在长时间禁食期间于肝脏中进行。主要底物包括乳酸（通过Cori循环）、甘油（来自甘油三酯分解）和生糖氨基酸（主要是丙氨酸）。该途径大体上是糖酵解的逆转，但使用不同的酶绕过三个不可逆反应。
Lactate → Pyruvate → Oxaloacetate → PEP → … → Glucose-6-phosphate → Glucose
Key regulatory enzymes of gluconeogenesis include pyruvate carboxylase, PEPCK, fructose-1,6-bisphosphatase, and glucose-6-phosphatase. These enzymes are upregulated by glucagon and cortisol but downregulated by insulin.
糖异生的关键调节酶包括丙酮酸羧化酶、PEPCK、果糖-1,6-二磷酸酶和葡萄糖-6-磷酸酶。这些酶被胰高血糖素和皮质醇上调，被胰岛素下调。
9. Diabetes Mellitus | 糖尿病
Diabetes mellitus is a group of metabolic disorders characterised by chronic hyperglycaemia resulting from defects in insulin secretion, insulin action, or both. Type 1 diabetes, accounting for about 5–10% of cases, results from autoimmune destruction of β-cells, leading to absolute insulin deficiency. Onset is typically in childhood or adolescence, and patients require lifelong exogenous insulin.
糖尿病是一组以慢性高血糖为特征的代谢紊乱疾病，由胰岛素分泌缺陷、胰岛素作用缺陷或两者共同引起。1型糖尿病约占病例的5–10%，由自身免疫性破坏β细胞导致绝对胰岛素缺乏所致。起病通常在儿童期或青春期，患者需要终身外源性胰岛素治疗。
Type 2 diabetes, accounting for 90–95% of cases, is characterised by insulin resistance — the failure of target tissues to respond adequately to insulin — combined with relative insulin deficiency. Risk factors include obesity, physical inactivity, genetic predisposition, and ageing. Management typically begins with lifestyle modification, advancing to oral hypoglycaemic agents and eventually insulin therapy.
2型糖尿病约占病例的90–95%，以胰岛素抵抗（靶组织对胰岛素反应不足）合并相对胰岛素缺乏为特征。危险因素包括肥胖、缺乏运动、遗传易感性和衰老。治疗通常从调整生活方式开始，进展到口服降糖药，最终需要胰岛素治疗。
The diagnostic criteria for diabetes include a fasting plasma glucose of ≥126 mg/dL (7.0 mmol/L), a 2-hour plasma glucose of ≥200 mg/dL (11.1 mmol/L) during an oral glucose tolerance test, or an HbA1c ≥6.5% (48 mmol/mol). HbA1c reflects the average blood glucose over the preceding 2–3 months and is used for both diagnosis and monitoring.
糖尿病的诊断标准包括空腹血浆葡萄糖≥126 mg/dL（7.0 mmol/L），口服葡萄糖耐量试验2小时血浆葡萄糖≥200 mg/dL（11.1 mmol/L），或HbA1c≥6.5%（48 mmol/mol）。HbA1c反映过去2–3个月的平均血糖水平，用于诊断和监测。
10. Clinical Correlations and Examinations | 临床相关性与考试考点
Understanding the hormonal regulation of blood glucose is essential for interpreting clinical scenarios in both written and practical examinations. Common examination questions may require you to: identify the cells and hormones involved in blood glucose regulation; explain the signalling pathways activated by these hormones; predict the effects of pancreatic lesions or pharmacological interventions on blood glucose; and evaluate the relative merits of different treatments for diabetes.
理解血糖的激素调节对于解读书面和实验考试中的临床情境至关重要。常见考点包括：识别参与血糖调节的细胞和激素；解释这些激素激活的信号通路；预测胰腺病变或药物干预对血糖的影响；以及评估糖尿病不同治疗方案的相对优劣。
When answering questions about glucose homeostasis, always state the stimulus, the receptor, the integrating centre (pancreas), the effector response, and the return to normal — the full negative feedback loop. Avoid the common error of describing only insulin’s actions without mentioning glucagon and the antagonistic relationship. Also remember that insulin has both rapid (membrane transport) and long-term (gene expression) effects.
回答血糖稳态相关问题时应始终阐明刺激、感受器、整合中枢（胰腺）、效应器反应以及恢复正常的完整负反馈环路。避免只描述胰岛素作用而不提胰高血糖素及其拮抗关系的常见错误。还需记住胰岛素既有快速效应（膜转运）又有长期效应（基因表达）。
11. Common Examination Questions | 常见考题类型
- Describe the negative feedback control of blood glucose concentration, including the roles of insulin and glucagon in your answer.
- Explain how insulin promotes glucose uptake in muscle and adipose tissue, with reference to the insulin receptor and GLUT4.
- Compare and contrast the mechanisms of action of insulin and glucagon at the molecular level.
- Suggest how Type 1 and Type 2 diabetes differ in their causes, and explain how this affects treatment strategies.
- A patient has a pancreatic tumour that destroys all α-cells. Predict the effects on blood glucose regulation.
- Explain why glucagon has a greater effect on liver cells than on muscle cells.
For extended-response questions, it is advisable to structure your answer using a systems approach: stimulus → detection → signalling → response → recovery. This demonstrates both breadth of knowledge and the ability to integrate multiple concepts — the hallmark of top-band answers.
对于扩展性回答题，建议采用系统方法组织答案：刺激→检测→信号传导→反应→恢复。这既展示了知识的广度，也体现了整合多个概念的能力——这是高分答案的标志。
12. Summary and Revision Checklist | 总结与复习清单
- Blood glucose is maintained within 4.4–6.7 mmol/L by negative feedback involving insulin and glucagon.
- Insulin is secreted by β-cells; lowers blood glucose via glycogenesis, GLUT4-mediated uptake, and inhibition of gluconeogenesis.
- Glucagon is secreted by α-cells; raises blood glucose via glycogenolysis and gluconeogenesis in the liver.
- Adrenaline amplifies the hyperglycaemic response; cortisol provides a slower, more sustained effect.
- Type 1 diabetes = insulin deficiency; Type 2 diabetes = insulin resistance with relative deficiency.
- Molecular mechanisms: insulin receptor tyrosine kinase + PI3K-Akt pathway; glucagon receptor G-protein + cAMP-PKA pathway.
By mastering these key concepts and practising application questions, you will be well prepared for any examination question on the hormonal regulation of blood glucose concentration.
掌握这些核心概念并练习应用型题目后，你将充分准备好应对关于血糖浓度激素调节的任何考试题目。
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