Biology – Page 2 – GOLLYGEE!

09.18.2018

sperm counts are falling

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.

09.05.2018

airport trays are full of germs

Trays at airport security stations are loaded with microbes. A new study shows they can contain more viruses than toilets.

Air travel is a well known culprit in the spread of infectious diseases, such as the common cold and the flu. We can now add another potential mechanism for the spread of these types of infections, thanks to a new study published in BMC Infection Diseases last month.

Scientists from the University of Nottingham in England and the Finnish National Institute for Health and Welfare swabbed the trays and other airport surfaces after peak travel times, then identified traces of common respiratory viruses that were found in those samples. They looked at a variety of surfaces including toilets, pay machines, hand rails and luggage trays. Of all of the surfaces that they sampled, the luggage trays contained the most identifiable traces of respiratory viruses. Out of the 8 tray samples, 4 of them were positive for respiratory viruses like rhinovirus, which causes the common cold, and influenza, or the flu. Out of the 14 samples from the toilet flush button, zero gave positive results.

We know that objects that are frequently handled or manipulated with our hands tend to be laden with bacteria. Mobile phones, tv remotes and computer keyboards have been identified as having high bacterial counts. It now appears that the same applies to airport trays.

One caveat of the study is that although traces of viral DNA were found on various surfaces, this does not necessarily mean that they were contagious or able to infect humans. However, viruses and microbes have been known to survive for a few days on surfaces.

What can you do to minimize your risk of infection? The best advice still applies: Wash your hands!

08.31.2018

the persistent myth of the super sperm

Fertilization occurs when a sperm cell fuses with an egg.

Over at Aeon, Robert 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.

GOLLYGEE!

Category: Biology (page 2 of 63)

sperm counts are falling

airport trays are full of germs

the persistent myth of the super sperm