The decrease of estrogen and progesterone, coupled with a rise in prostaglandin, are the key hormones that trigger the start of a period.
How Hormones Influence Menstruation
The menstrual cycle is a complex process regulated by several hormones. Here’s a breakdown of the hormonal interplay that leads to menstruation:
- Estrogen and Progesterone Levels: Throughout the menstrual cycle, levels of estrogen and progesterone fluctuate. If conception doesn't occur, both of these hormones decrease.
- Uterine Lining: The fluctuation of estrogen and progesterone prepares the uterine lining for a possible pregnancy. When these hormone levels drop it signals to the uterus that a pregnancy has not occurred.
- Prostaglandin: As you approach the end of the menstrual cycle, prostaglandin, a type of progesterone hormone, increases.
- Uterine Contractions: The surge in prostaglandin triggers uterine contractions.
- Shedding: These contractions cause the uterine lining to shed, resulting in menstrual bleeding – your period.
Summary of Hormonal Influence on Period Onset
| Hormone | Role | Impact on Menstruation |
|---|---|---|
| Estrogen | Regulates the menstrual cycle and prepares the uterine lining. | Decreases before menstruation starts. |
| Progesterone | Prepares the uterus for pregnancy. | Decreases before menstruation starts; a type, prostaglandin, rises. |
| Prostaglandin | A type of progesterone hormone that increases prior to menstruation. | Triggers uterine contractions and shedding. |
Example of Hormonal Impact
- If pregnancy occurs, estrogen and progesterone levels remain high, preventing the uterine lining from shedding, and therefore, no period occurs.
- However, if fertilization does not happen, the decrease in estrogen and progesterone allows the rise of prostaglandin which stimulates uterine contractions, leading to menstruation.
