Your cervix has actually been opening and changing with every cycle since your very first period. During ovulation, the cervix softens, lifts higher in the body to make it easier for fertilization to occur, and opens slightly for sperm to enter. Then it closes back up. When you bleed, the cervix opens again and lowers in the body to help the uterine lining flow more easily out of the vagina. And then it closes again.
Your cervical fluid, better known as the white stuff on your underwear, does two very important things: One: your cervical fluid changes consistency throughout your cycle (maybe you’ve noticed sometimes it’s more watery and other times more "globby" or "stretchy") to either help, around ovulation, or prevent, the rest of the time, sperm from being able to reach the egg. Sperm won’t survive without your fluid helping it along. Two: the fluid carries out dead cells and bacteria to guard against infection.
During orgasms, your vaginal walls flood with blood and cause the vagina to grow in size. So, your vagina has been growing and shrinking since the beginning of your sexual life.
Lastly, your breasts/chest changes throughout the cycle, practicing for lactation. When you bleed, your milk glands enlarge in case fertilization occurs when you next ovulate (the lumpier boob phase). As you inch toward ovulation, your milk ducts also grow. If no fertilization occurs, the process starts all over again.