Hormones, the pill and the monthly cycle

The cycle, in four hormones

In a natural cycle of 28 days, four hormones rise and fall. You meet them in the chapter on human reproduction.

• FSH from the pituitary helps a follicle of the ovary to grow.
• The growing follicle makes estrogen.
• A sudden rise of LH, the LH surge, comes near day 14 and causes ovulation.
• The empty follicle becomes the corpus luteum and makes progesterone, which keeps the lining of the uterus ready.

If there is no pregnancy, the hormones fall, the lining is shed, and menstruation begins.

The picture is a teaching model. Its units are arbitrary. Real curves differ from person to person.

What the pill changes

The pills contain a progestogen alone, or a progestogen with estrogen. They keep the level of these hormones in the blood steady and fairly high for 21 days.

The pituitary senses the level of these hormones. When the level is high, it makes less FSH and LH. This is negative feedback. With low FSH, a follicle does not ripen. With no rise of LH, there is no LH surge, and no ovulation.

The hormones also act in two other places, as NCERT says.

• They stop the implantation of an embryo.
• They change the quality of the cervical mucus, so that sperms enter with difficulty.

In the 7 days of the gap, no pills are taken. The level of the hormones falls, and the lining of the uterus is shed. This is the bleeding of the gap.

You should find that, with the pill off, LH peaks on day 14 and ovulation follows, and that with the pill on, LH stays low for the whole cycle.

Other hormonal methods

• Injectables and implants. Progestogens alone, or with estrogen, are given as an injection or an implant under the skin. The action is like that of the pills, and the effect lasts much longer.
• Hormone releasing IUDs. The hormone acts mostly where the device sits. It makes the uterus unsuitable for implantation and the cervix hostile to sperms.
• Emergency contraceptives. A progestogen, a progestogen with estrogen, or an IUD, within 72 hours of coitus.
• Saheli. A non-steroidal pill, taken once a week. It has no steroid hormone, so it does not act in the way that the other pills do. Its active substance is a selective estrogen receptor modulator, called centchroman, and it was developed at the Central Drug Research Institute in Lucknow.

Try it in Python

The program uses the model to compare LH in a natural cycle and on the pill. It decides whether an LH surge, and so ovulation, is expected.

Practise with new numbers

Common mistakes

• Saying that the pill stops the making of ova by killing them. It keeps FSH and LH low, so a follicle does not ripen and ovulation does not take place.
• Saying that the bleeding of the gap is a normal period of an ovulating cycle. It follows the fall in the hormone level when the pills stop.
• Saying that the pill acts only on the ovary. It also acts on implantation and on the cervical mucus.
• Saying that Saheli is a steroid. It is non-steroidal.
• Mixing up emergency pills and daily pills. Emergency methods are used within 72 hours of coitus, for an emergency.

Remember these

• Natural cycle: FSH grows the follicle, the follicle makes estrogen, an LH surge near day 14 causes ovulation, and progesterone follows.
• The pills keep the hormones steady, so FSH and LH stay low. No LH surge, no ovulation.
• They also stop implantation and change the cervical mucus.
• The gap of 7 days brings a bleeding, as the hormone level falls.
• Saheli is non-steroidal, and it is taken once a week.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Which hormone surge causes ovulation in a natural cycle?

2. Why does the pill stop ovulation?

3. Name two other ways in which the pills prevent a pregnancy.

4. Why is there a bleeding in the 7 days with no pill?

5. How is Saheli different from the other pills?

References

• NCERT (2023). Biology, Textbook for Class XII, chapter 3 (contraception) and chapter 2 (the menstrual cycle).
• Betts J. G. et al. (2022). Anatomy and Physiology 2e, OpenStax, chapter 28, section on the female reproductive cycle.
• World Health Organization and Johns Hopkins Bloomberg School of Public Health (2018). Family Planning: A Global Handbook for Providers, 3rd edition, chapter on combined oral contraceptives.