Hormone graphs show which hormone rises and falls when. To read one, take a single hormone at a time, find its peak and name the event it explains.
This lesson follows explaining fertilisation and early development in the reproduction, development and growth chapter. It uses the textbook model of a 28-day cycle, which real cycles do not always follow.
What does each hormone do?
| Hormone | Made by | Main effect in the model |
|---|---|---|
| FSH | Pituitary gland | Stimulates a follicle to develop |
| Oestrogen | Developing follicle | Thickens the uterus lining; helps trigger the LH surge |
| LH | Pituitary gland | A surge triggers ovulation |
| Progesterone | Structure left after ovulation | Keeps the lining thick |
Worked example: read a table of hormone values
The table shows hormone levels in arbitrary units on selected days of a model 28-day cycle.
| Day | 1 | 7 | 13 | 14 | 21 | 28 |
|---|---|---|---|---|---|---|
| Oestrogen | 15 | 40 | 90 | 60 | 70 | 10 |
| Progesterone | 2 | 2 | 3 | 5 | 30 | 3 |
| LH | 5 | 5 | 12 | 45 | 6 | 5 |
Question 1: when is ovulation most likely? LH peaks at 45 on day 14. This surge triggers ovulation, so ovulation is most likely at about day 14.
Question 2: why is the lining thick on day 21? Progesterone is at its highest, 30, on day 21, and oestrogen is also high, 70. These hormones keep the lining thick, ready for an embryo to implant.
Question 3: why does the lining break down by day 28? Both progesterone (3) and oestrogen (10) have fallen. Without them, the lining cannot be maintained, so it breaks down if no embryo implants.
The mistake that costs marks
The common slip is to name the wrong hormone for ovulation, for example “oestrogen causes ovulation because it is highest on day 13”. Oestrogen is the hormone that peaks first, but the LH surge is the direct trigger.
| Wrong | Right | |
|---|---|---|
| Ovulation trigger | Progesterone | The surge of LH |
| Lining on day 21 | Maintained by FSH | Maintained by progesterone and oestrogen |
| Reading a graph | Name all four hormones | Quote the value and day for the hormone asked |
Always quote the day and the value from the graph, for example “LH rises from 12 to 45”.
Check yourself
Using the table, state what happens to the progesterone level between day 14 and day 21, and suggest a reason the change matters.
Answer
Progesterone rises from 5 to 30 between day 14 and day 21.
The rise keeps the uterus lining thick and supplied with blood, so an embryo could implant there. Progesterone stays high only if an embryo is present; otherwise it falls, as on day 28.
What to study next
Continue with reading growth curves and identifying phases, where you read a different kind of graph. The graph evidence and fair-comparison lab offers more graphs to practise on.
Record any wrong-hormone slips in the mistake log and paper-error review. For a teacher to go through graphs with you, see online one-to-one Biology tuition.