**Question:** Which of the following is the mechanism of abortion sticks?

A. Ethanol
B. Saline
C. Misoprostol
D. Mifepristone

**Core Concept:**
Abortion sticks, also known as uterine evacuation devices, are medical tools used for inducing uterine contractions and cervical ripening to facilitate termination of a pregnancy. They primarily work by stimulating uterine contractions, dilating the cervix, and causing uterine wall thickening.

**Why the Correct Answer is Right:**
Correct Answer: **D. Mifepristone**.

Mifepristone (also known as RU-486) is a progesterone receptor antagonist. By blocking the effects of progesterone on the uterine lining, mifepristone weakens the uterine lining, making it easier for prostaglandins to act on the uterus. This leads to increased uterine contractions, cervical dilation, and thickening of the uterine wall, ultimately causing uterine evacuation.

**Why Each Wrong Option is Incorrect:**

A. Ethanol (Option A) is a toxic alcohol used for sterilization and disinfection, not for inducing uterine contractions. Ethanol is not a suitable abortion stick.

B. Saline (Option B) is a sterile solution used for irrigating the uterus during surgery or for diagnostic purposes, not for inducing abortions. Saline does not have the desired uterine contracting and cervical dilating effects.

C. Misoprostol (Option C) is a synthetic prostaglandin analogue that directly stimulates uterine contractions and cervical dilation, making it an effective abortion stick. However, it is not the correct answer as mifepristone is a more suitable option for inducing abortion.

**Clinical Pearl:**

Mifepristone is a key component of the mifepristone and misoprostol combination therapy, which is used for medical termination of pregnancy. This combination allows for a safe and effective method of inducing uterine contractions, cervical dilation, and uterine evacuation. Properly understanding these mechanisms can help medical professionals select the appropriate method for inducing abortion in a clinical setting.