🩸 The Menstrual Cycle – 28 days of biological precision
Your menstrual cycle isn’t just a calendar date — it’s a carefully timed sequence of hormonal changes preparing the body for possible pregnancy. Here’s what you need for your IGCSE exam:
🔍 Day 1–5: Menstrual Phase
The uterus lining (endometrium) breaks down and is shed through the vagina — this is menstruation.
Oestrogen and progesterone levels are low.
🔍 Day 6–13: Proliferative Phase
FSH (Follicle Stimulating Hormone) from the pituitary stimulates an egg follicle to develop in the ovary.
The growing follicle releases oestrogen, which thickens the uterus lining.
🔍 Day 14: Ovulation
A surge in LH (Luteinising Hormone) causes the egg to be released from the ovary into the oviduct.
💡 Exam tip: Ovulation usually happens mid-cycle, but stress, illness, or hormonal changes can shift the timing.
🔍 Day 15–28: Secretory Phase
The empty follicle becomes the corpus luteum, releasing progesterone to maintain the thick uterus lining.
If fertilisation does not occur, the corpus luteum breaks down, hormone levels fall, and the cycle restarts.
🌟 Key survival link: These hormonal changes ensure the uterus is ready if an embryo implants — but waste no time resetting if pregnancy doesn’t happen.
📚 Get crystal-clear diagrams, animations, and exam tips on topics like this with Chimera Biology — designed exactly for Cambridge IGCSE Biology.
🌐 Check us out at: www.chimerabiology.com
#IGCSEBiology #CambridgeIGCSE #StudyTok #RevisionTips #BiologyRevision #ExamSuccess #StudentLife #ChimeraBiology #MenstrualCycle #Hormones #Oestrogen #Progesterone #LH #FSH #ScienceTok #StudyMotivation
The menstrual cycle involves changes to the uterus lining over a period of 28 days. It has three phases. Menstrual, proliferative, and secrettory phases. Days 0 to 5 involve the menstrual phase. Here the uterus lining breaks down and is shed. Levels of the hormones estrogen, progesterone, FSH, and LH are low. Days 6 to 13 involve the proliferative phase. Here estrogen produced in the follicle in the ovary increases. This is caused by the hormone FSH. LH peaks at day 14 causing ovulation, the release of the egg from the ovary. The cycle now enters the secrettory phase. LH, FSH, and estrogen levels decrease. Progesterone levels increase, maintaining the thickness of the uterus lining. Progesterone is produced by the remains of the follicle after ovulation, now called a corpus lutium. If no fertilization of the egg occurs, the corpus lutium breaks down, progesterone levels drop, and the menstrual phase occurs again at the start of the next month when the uterus lining is shed.