1. Through meiosis every gamete we produce is unique. Women are born with 2 million immature eggs. Men produce 100 million sperm a day and more than 2 trillion in a lifetime.
2. It’s a good thing we produce so many because it turns out our gametes aren’t very reliable. Up to 60% of sperm produced can be non-functional. At puberty, 80% of a woman’s eggs have already died, and during her lifetime only 0.1% (400) of her remaining eggs will be ovulated. 3. The egg must be fertilized within a very small window. If it is not fertilized within a couple hours of being ovulated it will die. 4. The female reproductive organs are an extremely hostile environment for sperm. Her immune response can be triggered to a foreign body, the vagina is acidic and can kill sperm. Cilia (small hairs) in the fallopian tubes capture sperm as well. 5. The cervix is only passable for sperm a few days a month during ovulation. The rest of the time mucous protects the entrance to the uterus. Only when the right hormones are present, are small channels created allowing sperm to pass through one by one. 6. Normally it would take sperm 2 days to swim 6 inches through the uterus to reach an egg in the fallopian tubes. This would waste valuable time and limited energy that sperm have. However during menstruation, undulations of the uterus shorten this trip to 30 minutes. 7. The egg is highly protected and the body provides barriers for sperm to reach it. Outer layers of chaperone cells surrounding the egg only allow a few sperm through. 8. Beneath the layers of chaperone cells, a thick membrane called the zona protects the egg. Proteins on the sperm cap must match precisely to proteins on the zona to allow the sperm to enter the egg. 9. 50% of fertilized eggs fail to develop properly and the body aborts the pregnancy early on. 10. If the fertilized egg survives long enough to become a blastocyst, it could be attacked by the mother’s own immune system when the blastocyst tries to implant into the uterus wall. 11. What starts out as a handful of cells, develops into tissues, organs, and body parts. Every cell has the same 46 chromosomes containing the same genes and the same unique DNA in all 26 billion cells of a newborn. 12. As the cells multiply, they “know” based on their location in the embryo and fetus what they are to become. This is possible because cells can communicate with chemical signals. These chemical signals turn on and off particular genes that leads to specialized tissues and organs. 13. Gene SRY on the Y chromosome is thought to be responsible for sending instructions for a developing 6-week-old embryo to start becoming a boy. This is the only time this gene is active in a man’s life and the gene is only turned on for a couple of days. 14. At 6 months a fetus needs so much fat the mother often cannot keep up. This fat is being used to form myelin sheaths around neurons in our brains. Myelin sheaths are a fatty covering that protects the neuron and increases the speed nerve signals can travel 100 times. 15. Human birth is extremely dangerous compared to other species. This is true for both the mother and the baby and is due to our large head size in comparison to our bodies, which makes delivery a challenge and risk. This information was taken from a PBS/NOVA film called "Life's Greatest Miracle" which aired Nov 20, 2001. If you find this stuff interesting you can watch the full video at the link below. It really is quite an incredible production, the shots they get of development inside the womb are amazing. **Disclaimer** The film is a bit graphic at the end and shows an actual pregnancy so if that isn't something you want to see, avoid the last 5 minutes or so. My guess is if you read all 15 facts and decided to watch the movie, you probably are prepared to see something of that nature though anyways. :) http://www.pbs.org/wgbh/nova/body/life-greatest-miracle.html
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Alexander McNaChronicles of my journey into the nursing profession. Archives
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