The human egg cell, or ovum, is the female reproductive cell. Its journey involves storage, monthly preparation, release, and travel through the reproductive tract. This sequence details how the egg develops and is either fertilized or expelled.
The Primary Storage Location
The egg cell is housed within the two small, oval-shaped ovaries, situated on either side of the uterus. These organs house the female reproductive cells and produce hormones. Females are born with their entire supply of hundreds of thousands of immature eggs, stored within tiny fluid-filled sacs called follicles.
At birth, these cells are dormant, paused in an early stage of development. By the time a female reaches puberty, a significant number of follicles have degenerated, leaving approximately 300,000 to 400,000 remaining. The vast majority of these stored eggs will never fully mature or be released.
Preparing the Egg for Release
The maturation process is a monthly event known as folliculogenesis, which transforms a dormant follicle into a structure capable of releasing a mature cell. Hormonal signals trigger a small group of six to twenty follicles to begin growing each cycle.
As the follicular phase progresses, these follicles increase in size and develop fluid-filled spaces. A single dominant follicle is selected, which continues to mature while the others degenerate. This dominant follicle produces hormones that prepare the body for potential pregnancy. The egg cell inside completes its first major cell division just before the follicle ruptures to release the egg.
The Journey After Ovulation
The physical release of the mature egg, known as ovulation, is triggered by a sudden surge in a pituitary hormone. This spike causes the dominant follicle to rupture, ejecting the egg from the ovary’s surface into the abdominal cavity. Finger-like projections (fimbriae) at the end of the fallopian tube capture the released egg.
Once inside the fallopian tube, the egg is propelled toward the uterus by cilia lining the tube’s walls. The released egg is viable for approximately 12 to 24 hours, during which fertilization must occur. If fertilization takes place, the resulting zygote begins to divide rapidly. This developing cell cluster travels for several days, eventually reaching the uterus to attempt implantation into the prepared uterine lining.
If fertilization does not happen, the egg cell quickly degenerates within the fallopian tube. The body ceases preparation for pregnancy, causing a drop in hormone levels. This change triggers the shedding of the uterine lining, and the unfertilized egg is expelled during menstruation.