Sperm are often thought of as mere DNA carriers, but these tiny cells have so much more to offer. In this article, discover 5 incredible things to know about these tiny, fascinating beings that play an essential role in human reproduction.
1. The toughest race in the world: the sperm race
The competition between spermatozoa is fierce, as they have to travel a long distance to reach the egg and fertilize it. In fact, it’s probably the most complex and exhausting microscopic race imaginable.
The obstacle course for spermatozoa
At the moment of ejaculation, several million sperm cells are released into the vagina. However, only a few reach the egg. To get there, they have to cross a hostile environment, work their way through the cervical mucus, up the uterus and finally into the fallopian tube.
Top-level athletes
In the face of these obstacles, spermatozoa demonstrate exceptional endurance and strength. They can swim at an average speed of 2 to 5 millimeters per minute, equivalent to a human covering several kilometers. What’s more, they can use powerful tail strokes to propel themselves forward and break through barriers in their path.
2. Spermatozoa vary in longevity
Contrary to what you might think, not all spermatozoa are equal in terms of lifespan. In fact, their longevity depends on a number of factors, not least the environment in which they evolve.
In the male body
In the testicles, sperm can survive for several weeks, even months. However, their quality and ability to fertilize an egg gradually diminish over time.
Outside the body
Once released during ejaculation, spermatozoa have only a short window of opportunity to accomplish their mission. Outside the vagina, they quickly die: their lifespan is generally less than a few hours in the open air or on the skin.
Inside the female body
When introduced into the vagina, spermatozoa benefit from an environment more favorable to their survival. They can live for up to five days in the female reproductive tract, giving them a chance to meet an ovum for fertilization.
3. Sperm quality can be influenced by lifestyle
Interestingly, certain aspects of a man’s lifestyle and environment can affect sperm quality. Here are just a few examples:
- Diet: a balanced diet rich in essential nutrients promotes the production of healthy, viable sperm.
- Exercise: regular physical activity can improve sperm quality, notably by increasing their concentration and mobility.
- Temperature: the testicles are sensitive to heat, and prolonged exposure to high temperatures (e.g. when using a laptop on the knees) can adversely affect sperm production.
- Stress: chronic stress has been shown to reduce the quantity and quality of sperm produced.
4. Spermatozoa have a sophisticated navigation system
To successfully reach the egg, spermatozoa must be able to navigate precisely through the female reproductive tract. To achieve this, they have a complex navigation system that enables them to detect the chemical signals emitted by the ovum and gradually approach it.
Sperm chemotaxis
Spermatozoa are able to perceive the concentration gradients of certain molecules (such as progesterone) present in the environment around them. Based on this information, they adjust their trajectory towards the egg.
The crucial role of calcium
Calcium plays a central role in the sperm navigation process. When they detect a progesterone gradient, the calcium channels on their membrane open, triggering a sudden increase in calcium concentration inside the cell. This cascade of biochemical reactions then leads to a change in the frequency and amplitude of the sperm tail beats, enabling it to modify its direction and speed.
5. Spermatozoa are morphologically diverse
Did you know that not all spermatozoa resemble those usually seen on diagrams? In fact, their shape can vary considerably from one individual to another, and even from one spermatozoon to another within the same sperm sample.
Atypical shapes
Sperm with a larger or smaller than normal head, a curled tail or abnormalities in the nucleus can be observed. Some sperm even have two heads or tails!
Impact on fertility
These morphological differences can affect the sperm’s ability to fertilize an egg. In general, the more abnormal a spermatozoon is, the less likely it is to fulfill its mission. However, given the large number of spermatozoa present in each ejaculate, only one needs to be able to reach and penetrate the egg for conception to take place.
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