The single female reproductive cell released from the ovary, if not joined by a sperm cell, is scientifically known as an ovum (plural: ova). This cell is the largest in the human body. The ovum is responsible for contributing the genetic material and the necessary cellular machinery to begin development if fertilization occurs. The terms “ovum” and “egg cell” are often used interchangeably to describe this mature, unfertilized gamete.
What Is It Called?
The most accurate biological term for the mature, unfertilized female gamete is the secondary oocyte. This cell is released during the process of ovulation, typically once per menstrual cycle, from one of the two ovaries. The term oocyte refers to the egg cell in its various stages of development, with the secondary oocyte representing the stage ready for potential fertilization. An unfertilized ovum contains half the genetic material needed for a new organism, carrying 23 chromosomes.
The formation of this cell involves a lengthy process called oogenesis, which begins before a female is even born. The ovum carries the maternal DNA and large reserves of cytoplasm and nutrients required to sustain the earliest stages of embryonic growth.
The State of the Unfertilized Egg
Upon release from the ovary, the secondary oocyte is in a state of suspended animation, arrested at metaphase II of meiosis. Meiosis is a specialized cell division that reduces the chromosome number by half. This arrest is maintained by a biochemical system within the cell to prevent further division before fertilization.
The egg waits in this poised state, containing its half-set of chromosomes, and only completes the final stage of meiosis upon the entry of a sperm. This final division results in the formation of a mature ovum and a second polar body, a small, non-functional cell that quickly degenerates. The successful fusion of the ovum’s nucleus and the sperm’s nucleus then forms a single-celled zygote, marking the beginning of a genetically unique individual.
The Lifespan After Ovulation
The unfertilized ovum has a short window of viability after its release into the fallopian tube. The lifespan of the human egg is estimated to be between 12 and 24 hours. If a sperm cell does not successfully penetrate the ovum within this timeframe, the egg loses its capacity to be fertilized.
This narrow window means that successful conception relies on precise timing between the release of the egg and the presence of live sperm. Sperm can survive within the female reproductive tract for up to five days. Therefore, the fertile window spans several days leading up to and including the day of ovulation, with the egg’s short viability being the limiting factor.
What Happens Next?
If the secondary oocyte remains unfertilized after its brief lifespan, it begins a process of degeneration. The cell breaks down, and its remnants are naturally reabsorbed by the surrounding tissues of the fallopian tube and the uterine lining. This cellular disintegration signals that pregnancy will not occur during that cycle.
The subsequent drop in the reproductive hormones progesterone and estrogen triggers the shedding of the thickened lining of the uterus. This shedding process is known as menstruation, which marks the start of a new menstrual cycle. The body efficiently clears the unfertilized egg and the prepared uterine lining to begin preparing a new egg and uterine environment for the next cycle.