Sperm: 15 crazy things you should know

When it comes to sperm, people always seem to have an agenda.

Some want to kill sperm cells. Some want to buy or sell them. Some fret over their failure to get the job done.

Why can't we just appreciate sperm for the amazing little wrigglers that they are? After all, without sperm, the world would be a very lonely place.

So here are 15 fascinating facts about sperm, from Dr. Craig Niederberger, professor of urology at the University of Illinois at Chicago.

Abnormal Sperm? That's Normal

Human sperm-making machinery is a bit lazy. How else to explain the fact that 90 percent of the sperm in a man's ejaculate are deformed? Two heads, two tails, huge heads, pinheads, coiled tails - the list of common deformities is a long one.

It's the price of monogamy, Dr. Niederberger says. "For those species where more than one male's sperm can find itself in a female at the same time, the sperm are much more uniform in appearance," he says. "In humans, Joe and Sam's sperm don't usually find themselves in Betty at the same time."

Half a Teaspoon

teaspoon, spoon, tablespoon — istockphoto

That's how much a man typically ejaculates. It isn't much, but - for better or worse - it often does the job.

Sperm Wear Hard Hats

You might not call sperm dapper, but they do wear hats.

Well, not really a hat but an oval-shaped structure called the acrosome. It contains strong chemicals that are released once the sperm attaches to the egg. The chemicals melt the egg's outer surface, drilling a hole so that the sperm can penetrate the egg to release its genetic cargo.

Sperm vs. Semen

Some people use the terms sperm and semen interchangeably. But sperm cells are only one component. Semen also contains substances from the prostate and a pair of rabbit ear-shaped organs inside the pelvis called the seminal vesicles.

Sperm cells - which are made in the testicles - need lots of high-octane fuel to whip their tails. Lucky for them (and us), sperm get the fuel they need in the form of sugar fructose, which is supplied by the seminal vesicles.

Fluid from the prostate contains chemicals that cause semen to liquefy once it's inside the female. Without it, sperm would be locked in place and unable to swim.

One Testicle Is Enough

If a guy loses one testicle, the other is generally able to make enough sperm to create a baby. Often the remaining testicle grows a bit to boost sperm output.

Lance Armstrong, shown here, is perhaps the most high profile person to have lost a testicle to cancer. He has fathered five children since then, three from banked sperm, but two, he says, were concieved naturally.

200 Million Competitors

It takes only one sperm cell to fertilize a woman's egg - but there's stiff competition for that honor. In fact, the average ejaculate contains 200 million sperm. Best of luck to each of you.

The Factory Never Closes

old man, happy, optimistic — istockphoto

Women are born with all the eggs they'll ever have. It's different for men. Men produce sperm all day, every day - throughout their lives.

As men age, their sperm may become a little sluggish and their DNA a bit more fragmented. But the factory never closes.

Hope springs eternal.

Sperm Are Tiny

Want to see a sperm cell? Better have a microscope, because sperm are far too tiny to see with the naked eye. How tiny? Each one measures about 0.002 inch from head to tail, or about 50 micrometers.

Of course, what sperm lack in size they more than make up in sheer numbers. If a guy could coax all the sperm in one ejaculate to line up end to end, they'd stretch six miles.

That's a lot of sperm.

Sperm Need Protection

Sperm start out looking pretty much like any cell in the body. But by the time they're ready to leave the testicles, they have half as much DNA as other cells in the body. That makes them look a bit suspicious to the body's immune system.

To keep immune cells from wiping out "invading" sperm, the testicles employ specialized cells to surround them with a sort of "picket fence."

Dead Sperm Can Make Live Babies

ivf, in vitro fertilization — istockphoto

To fertilize an egg the old-fashioned way, sperm need to be able to swim. Not so with in-vitro (test tube) fertilization. In fact, when IVF technicians use tiny, robotically controlled glass straws to insert a single sperm inside an egg, they sometimes beat the sperm with the glass until it stops moving. The only thing that matters is the DNA inside the sperm.

Which Way Do We Go?

Sperm can certainly whip their tails, but many have a hard time swimming in a straight line. In fact, only about half do. The rest swim around in circles or bob along with the motion of the semen.

But because so many start their journey, plenty make it to the egg. And that's despite the fact that the tubes connecting the uterus to the ovaries contain tiny hair cells that beat against the sperm.

Ever seen salmon swim upstream? It's a bit like that.

Sperm Live for Days

female, woman, body clock, bra, underwear — istockphoto

How long can a sperm cell live once inside a woman's body? About two days.

The Y Stands Alone

xy chromosome, y chromsome — istockphoto

Once a sperm fuses with an egg, the chromosomes swap bits of DNA, meaning that each becomes a mash-up of mom's and dad's DNA. But there's one exception: the Y chromosome has no counterpart within the egg's DNA, so it's passed along essentially unchanged from father to son.

In fact, a man's Y chromosome looks just like his father's and his father's father's, and so on, back through the generations.

Refrigerator Testicles

cold, freezing, man, chilly, chilled, chill — istockphoto

Sexual passion may be hot, but a guy's testicles stay cool - about 7 degrees Fahrenheit cooler than ordinary body temperature. That's just right for producing healthy sperm.

A man's body keeps the ideal testicle temperature with radiator-like veins that pull heat away and muscles in the scrotum that raise and lower the testicles to bring them closer to the body's warmth - or farther away.

If a guy crosses his legs, his scrotal temperature increases by about 2 degrees. Ditto if he wears briefs. But lots of guys who cross their legs become dads, and Dr. Niederberger says the idea that wearing boxers will help boost fertility is probably misguided.

Two Months to Make Sperm

How long does it take to make sperm? About two months, according to the latest studies.

"Sperm are being started all the time, just like an assembly line," says Dr. Niederberger. "You don't wait for a truck to finish the assembly line before starting to build another, right? But just like an assembly line, it takes time to go from the start to the end."

So get busy.