Why do women have periods?

Prevodilac: Ivana Korom Lektor: Mile Živković

A handful of species on Earth share a seemingly mysterious trait:

Nekoliko vrsta na Zemlji deli jednu naizgled misterioznu osobinu:

a menstrual cycle.

menstrualni ciklus.

We're one of the select few.

Mi smo jedni od malobrojnih.

Monkeys, apes, bats, humans, and possibly elephant shrews

Majmuni, gorile, slepi miševi, ljudi, i možda rovčice

are the only mammals on Earth that menstruate.

jedini su sisari na Zemlji koji menstruiraju.

We also do it more than any other animal,

Takođe to činimo češće od drugih životinja,

even though its a waste of nutrients and can be a physical inconvenience.

iako je to traćenje nutrijenata i može biti fizička nelagodnost.

So where's the sense in this uncommon biological process?

Pa, u čemu je smisao ovog neuobičajenog biološkog procesa?

The answer begins with pregnancy.

Odgovor počinje trudnoćom.

During this process, the body's resources are cleverly used to shape

Tokom ovog procesa, resursi tela se pametno koriste da stvore

a suitable environment for a fetus,

odgovarajuću okolinu za fetus,

creating an internal haven for a mother to nurture her growing child.

stvarajući unutrašnje utočište u kom majka neguje svoje rastuće dete.

In this respect, pregnancy is awe-inspiring,

Na ovaj način, trudnoća je zadivljujuća,

but that's only half the story.

ali to je samo polovina priče.

The other half reveals that pregnancy places a mother and her child at odds.

Druga polovina otkriva da trudnoća postavlja majku i dete u rizik.

As for all living creatures,

Kao i kod svih živih bića,

the human body evolved to promote the spread of its genes.

ljudsko telo se razvilo da pospeši širenje svojih gena.

For the mother, that means she should try to provide equally

Za majku, to znači da bi trebalo da svim svojim potomcima

for all her offspring.

pruži jednako.

But a mother and her fetus don't share exactly the same genes.

Ali majka i njen fetus ne dele potpuno iste gene.

The fetus inherits genes from its father, as well,

Fetus nasleđuje gene i od oca,

and those genes can promote their own survival by extracting

a ti geni mogu da pospešuju svoj opstanak

more than their fair share of resources from the mother.

uzimajući od majke i više resursa nego što je neophodno.

This evolutionary conflict of interests

Ovaj evolutivni konflikt interesa

places a woman and her unborn child in a biological tug-of-war

stavlja ženu i njeno nerođeno dete u biološko rivalstvo

that plays out inside the womb.

koje se odigrava unutar materice.

One factor contributing to this internal tussle

Jedan faktor koji doprinosi ovoj unutrašnjoj borbi

is the placenta, the fetal organ that connects to the mother's blood supply

je posteljica, organ koji povezuje fetus sa majčinim izvorom krvi

and nourishes the fetus while it grows.

i hrani ga dok raste.

In most mammals, the placenta is confined behind a barrier of maternal cells.

Kod većine sisara, posteljica je skrivena iza barijere majčinih ćelija.

This barrier lets the mother control the supply of nutrients to the fetus.

Ta barijera dozvoljava majci da kontroliše dopremanje nutrijenata do fetusa.

But in humans and a few other species,

Ali kod ljudi i još nekih vrsta,

the placenta actually penetrates right into the mother's circulatory system

posteljica zapravo prodire unutar majčinog sistema krvotoka,

to directly access her blood stream.

da bi mu direktno pristupila.

Through its placenta, the fetus pumps the mother's arteries with hormones

Kroz posteljicu, fetus u majčine arterije upumpava hormone

that keep them open to provide a permanent flow of nutrient-rich blood.

koji ih održavaju otvorenim kako bi stalno dobijao nutrijente.

A fetus with such unrestricted access can manufacture hormones

Fetus sa takvim neograničenim pristupom može da proizvodi hormone

to increase the mother's blood sugar, dilate her arteries,

kako bi povećao majčin nivo šećera u krvi, proširio njene arterije

and inflate her blood pressure.

i povisio njen krvni pritisak.

Most mammal mothers can expel or reabsorb embryos if required,

Većina majki sisara može da izbaci ili vrati embrion ako je potrebno,

but in humans, once the fetus is connected to the blood supply,

ali kod ljudi, jednom kad se fetus poveže sa dotokom krvi,

severing that connection can result in hemorrhage.

presecanje te veze može da dovede do krvarenja.

If the fetus develops poorly or dies,

Ako se fetus ne razvije dovoljno ili umre,

the mother's health is endangered.

majčino zdravlje je ugroženo.

As it grows, a fetus's ongoing need for resources can cause intense fatigue,

Kako raste, potrebe fetusa za resursima mogu da uzrokuju intenzivan zamor,

high blood pressure,

visok krvni pritisak

and conditions like diabetes and preeclampsia.

i stanja poput dijabetesa i preeklampsije.

Because of these risks,

Zbog ovih rizika,

pregnancy is always a huge, and sometimes dangerous, investment.

trudnoća je uvek ogromna, ponekad i rizična investicija.

So it makes sense that the body should screen embryos carefully

Tako da ima smisla da telo pažljivo proverava embrione

to find out which ones are worth the challenge.

kako bi našlo one koji su vredni tog izazova.

This is where menstruation fits in.

Ovde se menstruacija uklapa.

Pregnancy starts with a process called implantation,

Trudnoća počinje procesom zvanim implantacija,

where the embryo embeds itself in the endometrium that lines the uterus.

kada se embrion ugrađuje u endometrijum koji obavija matericu.

The endometrium evolved to make implantation difficult

Endometrijum se razvio da oteža implantaciju,

so that only the healthy embryos could survive.

kako bi samo zdravi embrioni mogli da prežive.

But in doing so,

Ali u tom procesu

it also selected for the most vigorously invasive embryos,

je izabrao i najinvazivnije embrione,

creating an evolutionary feedback loop.

stvarajući evolutivnu povratnu spregu.

The embryo engages in a complex, exquisitely timed hormonal dialogue

Embrion ulazi u složen, izuzetno precizan hormonalni dijalog

that transforms the endometrium to allow implantation.

koji transformiše endometrijum da bi dozvolio implantaciju.

What happens when an embryo fails the test?

Šta se dešava kad embrion padne na testu?

It might still manage to attach,

Možda će ipak uspeti da se veže,

or even get partly through the endometrium.

ili će delimično proći kroz endometrijum.

As it slowly dies, it could leave its mother vulnerable to infection,

Dok polako umire, svoju majku može učiniti podložnom infekcijama

and all the time, it may be emitting hormonal signals that disrupt her tissues.

i svo vreme može da emituje hormonske signale koji remete njena tkiva.

The body avoids this problem by simply removing every possible risk.

Telo ovaj problem izbegava jednostavno uklanjajući svaki mogući rizik.

Each time ovulation doesn't result in a healthy pregnancy,

Saki put kada ovulacija ne dovede do zdrave trudnoće,

the womb gets rid of its endometrial lining,

materica se otarasi postave endometrijuma

along with any unfertilized eggs, sick, dying, or dead embryos.

zajedno za neoplođenom jajnom ćelijom, bolesnim, umirućim ili mrtvim embrionima.

That protective process is known as menstruation,

Taj zaštitni proces je poznat kao menstruacija,

leading to the period.

koji dovodi do krvarenja.

This biological trait, bizarre as it may be,

Ova biološka osobina, koliko god bila bizarna,

sets us on course for the continuation of the human race.

je početak nastavka ljudske rase.