# Ovulation, Fertilization & Implantation How an egg is released, fertilized in the fallopian tube, divides into a hollow ball and settles into the womb's lining over about one week\. By gentle\-fox\-147918bc Topic: Human Body & Medicine [Open the interactive Jig](https://ask.jig.com/j/Ru7UjUaY1vRc) ## Transcript ### 1. The first week of a new life Every person began as a single cell, smaller than a grain of sand\. Over about one week, an egg is released, meets a sperm, and the tiny new embryo travels to the womb and settles in\. Drag anywhere to turn the model\. The glowing dot marks the ovary, where the journey starts\. ### 2. Ovulation: an egg is released Each ovary holds thousands of eggs, each inside a fluid\-filled sac called a follicle\. About once a month, usually one follicle swells until it bulges from the surface\. It bursts gently and the egg floats out, wrapped in a sticky cloud of helper cells\. The fingers at the end of the tube, called fimbriae, sweep the egg inside\. ### 3. Meeting in the tube The egg is the largest cell in the human body, yet only about a tenth of a millimetre wide\. Sperm swim up to meet it in the wider part of the fallopian tube\. Many arrive, but they must push through the egg’s helper cells and its clear, glassy shell\. That clear shell is called the zona pellucida\. ### 4. Fertilization: only one gets in One sperm reaches the egg first and its cell joins with the egg’s\. Straight away the shell changes and hardens, so no other sperm can enter\. Inside, the egg’s and the sperm’s sets of genes come together to make one new cell, the zygote\. An egg can only be fertilized for about 12 to 24 hours after it is released\. ### 5. One cell becomes many As it drifts down the tube, the zygote splits into 2 cells, then 4, then 8\. The whole ball does not grow yet: each cell simply gets smaller\. By day 3 or 4 it is a solid cluster of 16 or more cells, like a tiny raspberry, called a morula\. Tiny hairs lining the tube, called cilia, help sweep it toward the womb\. ### 6. A hollow ball: the blastocyst Around day 5, fluid collects inside and the ball becomes hollow\. Now it is a blastocyst, made of about 70 to 100 cells\. The thin outer layer will help make the placenta, and the small clump of cells inside will become the baby\. The clump is called the inner cell mass\. ### 7. Hatching from the shell The blastocyst is still inside its clear shell\. Around day 6 it pushes and squeezes until the shell opens, and it slips out\. Free of its shell, it can now touch the lining of the womb\. Scientists really do call this hatching\. ### 8. Implantation: settling into the lining About 6 days after fertilization, the blastocyst touches the soft lining of the womb, inner cell mass side first\. It sticks, then gently burrows in, and the lining closes over it\. By about day 10 it is fully tucked inside\. Its outer cells start making a hormone called hCG, the signal a pregnancy test looks for\. ### 9. The whole journey Follow the trail: the egg leaves the ovary, is fertilized in the tube, divides on its way down, and settles into the womb’s lining\. All of this takes about one week, and it is the very start of a pregnancy\. Day numbers are typical\. Every body keeps its own timing\.