The hormone suppressed by oral contraceptive pills:

Oral contraceptive pills (OCPs), commonly known as birth control pills, work by suppressing certain hormones in the female body to prevent pregnancy. The primary hormone that is suppressed by these pills is Luteinizing Hormone (LH).

Explanation:

1. Luteinizing Hormone (LH):
Luteinizing Hormone (LH) is a hormone produced by the pituitary gland in the brain. In the female reproductive system, LH plays a crucial role in the menstrual cycle and ovulation.

2. Menstrual Cycle:
The menstrual cycle is a series of hormonal changes that occur in women of reproductive age. It consists of different phases, including the follicular phase, ovulation, and the luteal phase.

3. Follicular Phase:
During the follicular phase, which occurs in the first half of the menstrual cycle, the pituitary gland releases Follicle Stimulating Hormone (FSH) and LH. FSH stimulates the growth of ovarian follicles, which contain the eggs. LH helps in the maturation of the ovarian follicles.

4. Ovulation:
When the ovarian follicle reaches maturity, it releases an egg through a process called ovulation. LH surge triggers the release of the mature egg from the ovary into the fallopian tube. This is the fertile period when fertilization can occur if sperm is present.

5. Luteal Phase:
After ovulation, the empty follicle transforms into a structure called the corpus luteum. The corpus luteum produces progesterone, which prepares the uterus for possible pregnancy by thickening the uterine lining.

6. Mechanism of Oral Contraceptive Pills:
Oral contraceptive pills contain synthetic hormones, usually a combination of estrogen and progestin (synthetic progesterone). These hormones work together to prevent pregnancy by suppressing the natural hormonal fluctuations of the menstrual cycle.

7. Suppression of LH:
The synthetic progestin in oral contraceptive pills primarily acts by suppressing the release of LH from the pituitary gland. This prevents the LH surge that triggers ovulation. Without the LH surge, the ovaries do not release an egg, thus preventing fertilization and pregnancy.

8. Additional Effects:
In addition to suppressing LH, oral contraceptive pills also thicken the cervical mucus, making it difficult for sperm to reach the egg. They also alter the lining of the uterus, making it unfavorable for implantation of a fertilized egg.

Conclusion:
Oral contraceptive pills suppress the release of Luteinizing Hormone (LH) from the pituitary gland. This prevents ovulation and, along with other mechanisms, helps to prevent pregnancy. It is important to note that the specific hormonal composition of different oral contraceptive pills may vary, but the suppression of LH is a common mechanism.