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The Incredible Human Egg

The human egg is a beautiful and unique masterpiece of biology.

human eggUnlike any other cell in the body, the incredible egg, scientifically called an oocyte, seems to be gifted with amazing superpowers that insure the continuation of the human race. It is a highly specialized cell, uniquely equipped for the single function of generating a new individual. 

But, if you’re like most people, you know more about eggs you buy in a store than about the incredible eggs that human women produce. As cells go, the human egg is truly amazing and worth knowing more about, especially if you are trying to conceive.

Incredible egg facts

If you weren’t listening in high school biology class, you might not know just how unique and special egg cells are. Learn more about human eggs with these amazing facts:

  • It is believed that a female fetus just nine weeks into gestation will start making all the eggs she will have for the rest of her life. At birth, she will have 1-2 million eggs. Crazy fact: the egg that created you was inside your mother when she was inside your grandmother!
  • The egg is one of the biggest cells in the body, at about 100 microns with the relative thickness of a strand of hair. That means you could, in theory, see an egg cell with the naked eye. And, it’s about 20 times the size of a sperm!
  • Many of your eggs will die off before you hit puberty, meaning you’re left with around 700,000 egg cells by the time menstruation begins. At menopause, a woman will likely have fewer than 1,000 egg cells left.
  • Unlike other cells in the body, egg cells take years to “grow up.” That is, they spend years inside the ovaries in an immature state, maturing just before they are released during the process of ovulation.
  • On average, a woman will ovulate, or release, a mere 400-500 mature eggs, or ovum, in her lifetime. Many eggs will begin to develop during the follicular phase of the menstrual cycle each month, but only the largest egg is ovulated while the smaller ones die off. And once released, the egg only lives for about 24 hours, at which time if it’s not fertilized will begin to disintegrate. It’ll later be shed—along with endometrial tissue, vaginal secretions, cervical mucus, and blood—during the menstrual period, as the body gets ready for a new cycle of ovulation.
  • Unlike most other cells in your body that can regenerate and replace themselves, scientists don’t think eggs cannot do this. This can be troublesome as the eggs you are born with age over your lifetime. Young women have plenty of healthy eggs. About 75-90% of the eggs of a 21 year old are viable. But for a woman over 40, only about 5-10% of her eggs are good. This is why many young women who are focused on a career or delaying building a family are considering egg freezing.
  • At fertilization, eggs only allow one sperm inside to fertilize it out of the potentially millions trying to get in. No one knows what biological mechanism decides which sperm will be the lucky one.
  • Despite being one of the largest cells of the human body, egg cells only have half the genes, just 23 of the usual 46 pairs of chromosomes in human cells. But, this is what makes human reproduction and genetics work the way it does. The other half only gets to the egg from the sperm during fertilization. The 23 chromosomes from the egg cell combine with the 23 chromosomes from the sperm cell to form a brand new human being.
  • The egg contains all the instructions for what happens after fertilization. RNA in the egg helps the egg’s nucleus fuse with the sperm’s, guides the fertilized egg through its initial cell divisions, and tells the cells inside the developing embryo how to specialize and what kind of cell they need to become.
  • Egg cells need a lot of energy, especially after they’re fertilized and they start dividing and developing. Because of this high energy use, the egg also contains lots of mitochondria which are the powerhouse of the cell, converting oxygen and nutrients into energy.
  • Egg cells are fragile and can be affected by your general health, which is in turn determined by diet, exercise and habits. Smoking, in particular, has a significantly negative effect on your ovaries and can contribute to degeneration of your egg cells, and can even hasten menopause. The chemicals in cigarettes can also damage the chromosomes in your egg cells, making you more prone to miscarriage or giving birth to babies with birth defects.

So, next time you pick up a carton of eggs in the store, hopefully you will remember some of these incredible human egg facts!

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