📚 Hormonal Control of the Menstrual Cycle | 月经周期的激素调控
The menstrual cycle is a regular, hormone-driven process that prepares the female body for pregnancy. In this article, we explain the key hormones, their sources and the feedback mechanisms that control ovulation and the uterine lining – a core requirement of the Edexcel IGCSE Biology specification (specification point 3.5.4).
月经周期是一个由激素调控、为女性身体准备怀孕的规律性过程。本文将解释Edexcel IGCSE生物考纲（知识点3.5.4）要求掌握的关键激素、其来源，以及控制排卵和子宫内膜的反馈机制。
1. What Is the Menstrual Cycle? | 什么是月经周期？
The menstrual cycle lasts about 28 days on average, although it can range from 21 to 35 days. It involves coordinated changes in the ovary, the uterus and the hormones released by the pituitary gland and the ovaries.
月经周期平均约为28天，但可在21至35天范围内变化。它涉及卵巢、子宫以及垂体和卵巢所释放激素之间的协同变化。
The cycle can be divided into two main phases: the follicular phase (days 1–14) and the luteal phase (days 14–28). Day 1 is counted as the first day of menstruation, when the uterine lining is shed.
该周期可分为两个主要阶段：卵泡期（第1–14天）和黄体期（第14–28天）。第1天被计为月经开始的第一天，此时子宫内膜脱落。
2. Key Hormones and Where They Are Produced | 关键激素及其产生部位
- FSH (follicle-stimulating hormone) – produced by the pituitary gland. It stimulates the growth of an egg-containing follicle in the ovary and stimulates the production of oestrogen.
- LH (luteinising hormone) – produced by the pituitary gland. It triggers ovulation and stimulates the formation of the corpus luteum.
- Oestrogen – produced by the developing follicle in the ovary. It repairs the uterine lining and inhibits FSH release at high levels.
- Progesterone – produced by the corpus luteum. It maintains the thick uterine lining and inhibits both FSH and LH release.
FSH（促卵泡激素） – 由垂体产生。它刺激卵巢中含卵泡的生长，并刺激雌激素的生成。
LH（黄体生成素） – 由垂体产生。它触发排卵并刺激黄体的形成。
雌激素 – 由卵巢中发育的卵泡产生。它修复子宫内膜，并在高水平时抑制FSH的释放。
孕酮（黄体酮） – 由黄体产生。它维持增厚的子宫内膜，并抑制FSH和LH的释放。
3. The Follicular Phase | 卵泡期
At the start of the cycle, FSH levels are relatively high. FSH stimulates a few follicles in the ovary to grow and mature. As the follicles develop, they secrete increasing amounts of oestrogen.
在周期开始时，FSH水平相对较高。FSH刺激卵巢中的少数卵泡生长和成熟。随着卵泡发育，它们分泌越来越多的雌激素。
At this stage, oestrogen has a negative feedback effect on the pituitary gland, keeping FSH levels low. However, many follicles degenerate, and usually only one dominant follicle continues to mature.
在此阶段，雌激素对垂体产生负反馈作用，使FSH维持在较低水平。然而，许多卵泡会退化，通常只有一个优势卵泡继续成熟。
4. Oestrogen and the Repair of the Uterine Lining | 雌激素与子宫内膜的修复
Oestrogen also acts on the uterus. It causes the endometrium (the uterine lining) to become thicker and more vascularised, repairing the damage caused by menstruation.
雌激素也作用于子宫。它使子宫内膜变厚、血管增多，修复月经造成的损伤。
By day 14, the endometrium has been restored and is ready to receive an embryo. The increasing concentration of oestrogen from the dominant follicle now changes its feedback effect.
到第14天，子宫内膜已修复，为接受胚胎做好准备。来自优势卵泡的雌激素浓度不断增加，其反馈作用也随之改变。
5. The LH Surge and Ovulation | LH激增与排卵
When oestrogen levels become very high, they trigger a positive feedback mechanism on the pituitary gland. This causes a sudden, rapid release of LH – known as the LH surge.
当雌激素水平变得非常高时，它会对垂体触发正反馈机制，导致LH突然大量释放——称为LH激增。
High oestrogen → LH surge → ovulation
The LH surge causes the mature follicle to burst and release an egg (ovum) into the oviduct. This process is called ovulation and usually occurs around day 14 in a 28-day cycle.
LH激增使成熟卵泡破裂，将一个卵子释放到输卵管中。这个过程称为排卵，通常在28天周期的第14天左右发生。
6. The Luteal Phase and the Corpus Luteum | 黄体期与黄体
After ovulation, the empty follicle develops into a structure called the corpus luteum. The corpus luteum secretes large amounts of progesterone and some oestrogen.
排卵后，空卵泡发育为称为黄体的结构。黄体分泌大量孕酮和少量雌激素。
Progesterone maintains the thick uterine lining and prevents menstruation from occurring. It also inhibits the release of FSH and LH from the pituitary gland, preventing another ovulation during this phase.
孕酮维持增厚的子宫内膜，并防止月经发生。它还抑制垂体释放FSH和LH，从而防止在这个阶段再次排卵。
If the egg is not fertilised, the corpus luteum degenerates after about 14 days. Progesterone levels then fall, causing the uterine lining to break down and menstruation to begin.
如果卵子未受精，黄体约在14天后退化。随后孕酮水平下降，导致子宫内膜解体，月经开始。
7. What Happens If Fertilisation Occurs? | 如果受精发生会怎样？
If the egg is fertilised, the embryo implants into the uterine lining. The developing embryo produces human chorionic gonadotropin (hCG), which maintains the corpus luteum so that progesterone levels stay high.
如果卵子受精，胚胎植入子宫内膜。发育中的胚胎会分泌人绒毛膜促性腺激素（hCG），以维持黄体，使孕酮保持高水平。
High progesterone levels continue to support the pregnancy and prevent further menstrual cycles. This is the basis of many pregnancy tests, which detect hCG in urine.
高水平的孕酮继续支持妊娠，并阻止后续月经周期。这也是许多妊娠检测试纸检测尿液中hCG的基础。
8. Summary of the 28-Day Cycle | 28天周期总结
| Day(s) | Event | Key Hormones |
|---|---|---|
| 1–5 | Menstruation | Oestrogen and progesterone low |
| 6–13 | Follicle matures, uterus lining thickens | FSH and oestrogen rise |
| 14 | Ovulation | LH surge |
| 15–28 | Corpus luteum forms, uterus lining maintained | Progesterone high |
The table above summarises the main events in a typical 28-day cycle. Candidates should be able to interpret graphs showing changing hormone concentrations, a common exam skill.
上表总结了典型28天周期中的主要事件。考生应能够解读显示激素浓度变化的曲线图，这是一项常见的考试技能。
9. Negative vs Positive Feedback | 负反馈与正反馈
Negative feedback reverses a change. For example, high levels of oestrogen before day 14 suppress FSH release; high progesterone in the luteal phase suppresses FSH and LH, preventing ovulation.
负反馈 逆转变化。例如，第14天前高水平的雌激素抑制FSH释放；黄体期高水平的孕酮抑制FSH和LH，从而阻止排卵。
Positive feedback amplifies a change. The surge in oestrogen around day 14 stimulates LH release, which in turn causes more oestrogen release from the follicle, leading to the LH peak that triggers ovulation.
正反馈 放大变化。第14天前后的雌激素激增刺激LH释放，LH又促使卵泡释放更多雌激素，从而形成触发排卵的LH峰值。
Remember that feedback pathways involve the hypothalamus? In this specification, only the pituitary gland and ovary are required, but understanding the direction of each feedback loop is essential.
请记住，反馈通路是否涉及下丘脑？在本考纲中，只需要掌握垂体和卵巢，但理解每条反馈回路的方向至关重要。
10. Common Mistakes and Exam Tips | 常见错误与考试提示
- Do not confuse FSH and LH: FSH stimulates follicle growth; LH triggers ovulation.
- Do not say that oestrogen is produced by the corpus luteum – the corpus luteum mainly produces progesterone.
- Remember that negative feedback keeps hormone levels stable, while positive feedback creates a sharp peak.
- When drawing graphs, label peaks clearly and state the feedback direction for each stage.
不要混淆FSH和LH：FSH刺激卵泡生长；LH触发排卵。
不要误以为雌激素由黄体产生——黄体主要产生孕酮。
记住负反馈使激素水平保持稳定，而正反馈产生尖锐的峰值。
绘图时，清晰标注峰值，并说明每个阶段的反馈方向。
In the exam, pay attention to questions that ask you to “describe hormonal changes”. Use the four hormone names and link each to an event with a time frame.
在考试中，注意那些要求你“描述激素变化”的问题。要使用四种激素的名称，并将每种激素与带时间范围的事件关联起来。
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