**Question:** Zygote with zona pellucida reaches uterine cavity by-

A. Ovulation
B. Oviposition
C. Ectropion
D. Intrusion

**Correct Answer:** C. Ectropion

**Core Concept:**

The process by which a fertilized egg (zygote) reaches the uterine cavity after fertilization is known as fertilization. In humans, fertilization typically occurs in the fallopian tube, and the zona pellucida is a glycoprotein shell surrounding the egg. The zona pellucida plays a crucial role in protecting the egg and allowing sperm to penetrate it.

**Why the Correct Answer is Right:**

The correct answer, "ectropion," refers to the process of the fallopian tube's cilia (tiny, hair-like projections) propelling the fertilized egg (zygote) into the uterine cavity. This is a crucial step in the process of fertilization and embryo implantation, allowing the zygote to reach its final destination for implantation and development.

**Why Each Wrong Option is Incorrect:**

A. Ovulation: This refers to the process of an egg being released from the ovary, not the method by which it reaches the uterus. Ectropion is the correct term for that process.

B. Oviposition: This is incorrect terminology and does not describe the mechanism by which the zygote enters the uterine cavity.

D. Intrusion: This term refers to the action of a pathogen entering the body, not the movement of the fertilized egg into the uterine cavity.

**Clinical Pearl:**

Understanding the process of fertilization and embryo implantation is crucial for obstetricians and gynecologists, as it relates to fertility treatments, contraceptive methods, and reproductive health management. Adequate knowledge of these mechanisms helps in preventing potential complications, guiding medical interventions, and providing accurate information to patients.