Tag: fertilization (page 1 of 2)

sperm counts are falling

sperm egg fertilization

Some studies  show declining sperm counts in many Western societies. Is humanity doomed?

Continuing our recent exploration of human fertility, Julia Belluz atVox reports on the continued decline in human sperm counts.

In 2017, Hagai Levine et al.  published a meta-analysis in Human Reproduction Update detailing how sperm counts were halved between the 1970s and 2011 in North America, Europe, Australia and New Zealand. Since then, there has been lots of hand-wringing about what the results mean for the future of human fertility and reproduction. After talking wtih epidemiologists and men’s health professionals, Julia breaks down what these observed trends might mean.

First even though sperm counts have declined they are still within in normal range. The observed decrease was from 60 million to 30 million sperm per mL of ejaculate. To be in the normal range, counts should be above 15 million/mL.

Continuing on, she points out the limited scope of the problem. The decline only seemed apparent in Western countries:

The study authors also found the slope of the sperm count decline wasn’t as significant in the non-Western countries (in South America, Asia, and Africa), where sperm count even went up among men who were known to have fathered a child. (They thought this may be because men in non-Western countries haven’t been exposed to the same chemicals from industrial development as Western men have; more on that later.) But this raises the question of whether there’s something else that’s different about the groups or studies that might explain this variation.

And there is always the possibility of confounding variables in meta-analyses like this where experiments from over many decades and in many different countries are analyzed to discern a pattern. Male doctors that she was able to speak with have not noticed a decline that would correlate with what was observed in the publication.

Read Julia’s artcle here to get the rest of the details. And she ends with some tips for enhancing sperm quality, for if and when you are trying to conceive.

the persistent myth of the super sperm

sperm egg fertilization

Fertilization occurs when a sperm cell fuses with an egg.

Over at AeonRobert D Martin debunks a persistent myth of biology. Many people, including scientists, believe that during fertilization, sperm are in competition, racing to be the first to fertilize an egg. Because sperm competition is observed in chimpanzees and other mammals closely related to humans, people think that the same holds true for men. But Robert points out all the evidence against this theory.

First, human sperm contains a higher proportion of deformed or abnormal sperm compared to chimpanzees. If sperm were in competition to fertilize an egg, you would expect for there to be fewer nonmotile sperm than are observed. Chimpanzees, have relatively few abnormalities in their sperm cells.

Secondly, much of the sperm’s transport to the ovary is achieved passively. Through the womb and oviducts, a wafting and pumping motions propel sperm through the female tract. And in fact much of the selection of intact sperm is happens because of  environment in the woman’s vagina and cervix.

Many sperm do not even make it into the neck of the womb (cervix). Acid conditions in the vagina are hostile and sperm do not survive there for long. Passing through the cervix, many sperm that escape the vagina become ensnared in mucus. Any with physical deformities are trapped. Moreover, hundreds of thousands of sperm migrate into side-channels, called crypts, where they can be stored for several days. Relatively few sperm travel directly though the womb cavity, and numbers are further reduced during entry into the oviduct. Once in the oviduct, sperm are temporarily bound to the inner surface, and only some are released and allowed to approach the egg.

Robert continues from there, explaining what happens when too many sperm reach an egg and how cervical mucus can contain and release viable intact sperm for up to 5-10 day. The essay is quite interesting and well worth a read, so I won’t spoil it all. It’s an interesting counterargument to the manly notion that the best sperm gets the egg.

spermbots


Fortune magazine reports on some exciting research related to male infertility. As the headline says, “This Robot Is Like a Chauffeur for Slow Sperm”. Basically, researchers have developed tiny metal helices that wrap around the tail of a sperm cell. The helix effectively turns the sperm into a micromotor that can be directed a magnetic field. They are calling the invention a “spermbot”.

The video above lets you see how spermbots can propel once immobile sperm toward an egg.  So far scientists haven’t been able to actually fertilize an egg using the spermbot, but they are optimistic that with further study and development, this might someday improve success of in vitro fertilizations.

Take a look at the original research paper here in Nano Letters.  Caged Oligo explains some of the science behind the machine.

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