Thursday, 22 June 2017

How menstruation works

How menstruation works


http://ed.ted.com/lessons/how-menstruation-works-emma-bryce


This might seem hard to believe, but right now,
300 million women across the planet are experiencing the same thing:
a period.
The monthly menstrual cycle that leads to the period
is a reality most women on Earth will go through in their lives.
But why is this cycle so universal?
And what makes it a cycle in the first place?
Periods last anywhere between two and seven days,
arising once within in a 28-day rotation.
That whole system occurs on repeat,
happening approximately 450 times during a woman's life.
Behind the scenes are a series of hormonal controls
that fine tune the body's internal workings
to make menstruation start or stop during those 28 days.
This inner machinery includes two ovaries
stocked with thousands of tiny sacks called follicles
that each contain one oocyte, an unfertilized egg cell.
At puberty, ovaries hold over 400 thousand egg cells,
but release only one each month,
which results in pregnancy or a period.
Here's how this cycle unfolds.
Each month beginning around puberty,
the hormone-producing pituitary gland in the brain
starts releasing two substances into the blood:
follicle stimulating hormone and luteinizing hormone.
When they reach the ovaries,
they encourage the internal egg cells to grow and mature.
The follicles respond by pumping out estrogen.
The egg cells grow and estrogen levels peak,
inhibiting the production of FSH,
and telling the pituitary to pump out more LH.
That causes only the most mature egg cell from one of the ovaries
to burst out of the follicle and through the ovary wall.
This is called ovulation,
and it usually happens ten to sixteen days before the start of a period.
The tiny oocyte moves along the fallopian tube.
A pregnancy can only occur if the egg is fertilized by a sperm cell
within the next 24 hours.
Otherwise, the egg's escapade ends,
and the window for pregnancy closes for that month.
Meanwhile, the now empty follicle begins to release progesterone,
another hormone that tells the womb's lining
to plump up with blood and nutrients
in preparation for a fertilized egg that may embed there and grow.
If it doesn't embed,
a few days later, the body's progesterone and estrogen levels plummet,
meaning the womb stops padding out and starts to degenerate,
eventually falling away.
Blood and tissue leave the body, forming the period.
The womb can take up to a week to clear out its unused contents,
after which, the cycle begins anew.
Soon afterwards, the ovaries begin to secrete estrogen again,
and the womb lining thickens,
getting ready to accommodate a fertilized egg
or be shed.
Hormones continually control these activities
by circulating in ideal amounts delivered at just the right time.
The cycle keeps on turning,
transforming each day and each week into a milestone along its course
towards pregnancy or a period.
Although this cycle appears to move by clockwork,
there's room for variation.
Women and their bodies are unique, after all.
Menstrual cycles occur at diffferent times in the month,
ovulation comes at various points in the cycle,
and some periods last longer than others.
Menstruation even begins and ends at different times in life
for different women, too.
In other words, variations between periods are normal.
Appreciating these differences and learning about this monthly process
can empower women,
giving them the tools to understand and take charge of their own bodies.
That way, they're able to factor this small cycle

into a much larger cycle of life.

这听上去令人难以置信,但是现在全球近3亿的女性正在经历着同样的事情:一段特殊的时期。
这就是每月一次的月经期,是一个全球妇女在她们的一生中必然要面对的现实。
但为什么这个周期如此普遍呢?最开始的周期是怎样形成的呢?
月经会持续2-7天,每28天循环发生。
月经现象会重复不断地出现,
女人的一生大概会有450次的月经。

表象之下,这一切都是由人体激素进行调控的,
激素精密地控制着身体内部的运作,
在这28天里控制经期的起始。
这套内部机制包含两个卵巢,卵巢内存有成千上万的微小袋子,叫做卵泡,
每个卵泡内都含有一个卵母细胞,即未受精卵细胞。
青春期时期,卵巢内含有超过40万的卵细胞,
但每个月只会释放出一个卵细胞,
正是这个卵细胞决定着女性是受孕还是月经。
接下来我们来看看这个循环过程是如何产生的。
青春期的每个月初时候,大脑中的脑下垂体会分泌激素
向血液中释放两种物质:促卵泡激素和黄体化激素。
当它们到达卵巢后,会促进子卵巢内卵泡的发育和成熟。
卵泡的成熟,会进一步促进雌性激素的分泌。
伴随着卵细胞的成长,雌性激素的分泌也将达到峰值,
同时抑制促卵泡激素,
促进垂体释放更多的黄体化激素。
结果就是,只有其中一个卵巢中发育最为成熟的卵细胞,
才能冲出卵泡,穿越子房壁。
这就是排卵现象,排卵通常发生在月经前的1016天。
微小的卵母细胞沿输卵管运动。
只有当卵母细胞(卵子)和精子结合后女性才会受孕,
这需要在排卵后24小时之内发生。
否则,意味着卵子使命的终结,女性在该月受孕的窗口也会关闭。
与此同时,空虚的卵泡开始释放孕酮,另一种激素以刺激子宫内膜
产生血液和营养物质,为受精卵的着床和生长做准备。
如果没有受精卵着床,几天后,身体的孕酮和雌性激素骤降,
刺激子宫停止补充养分,内膜开始退化坏死,渐渐脱落。
血液和脱落的子宫内膜离开身体,形成月经。
子宫清理内部无用物质的过程常常会持续一周,
之后,一个新的周期又开始了。
很快,卵巢又开始分泌雌性激素,
子宫内膜开始变厚,为受精卵着床最准备或再一次脱落。
激素长期控制着整个活动过程,通过在精确的时间输送理想的量。
随着周期的循环前行,令每一天,每个星期,
都是这个受孕或经期过程中的一个里程碑。

虽然这个过程看上去如时钟般精准,但它仍然会有区别。
毕竟每位女性及其身体都是独一无二的。
每个月,月经产生的时间因人而异;
排卵期出现的节点不同;甚至经期持续的时间也各有长短。
另外,对于不同的女性来说,一生中初潮和绝经的时间也不尽相同。
换言之,不同个体的经期有差别是正常的。
欣赏这些不同并学习关于生理周期的过程,
能让女性更加的从容,自主,让女性了解并掌控自己的身体。
这样,她们能够将从这个小周期领会到的东西,
运用在更加复杂的生活周期之中。



http://www.mayoclinic.org/healthy-lifestyle/womens-health/in-depth/menstrual-cycle/art-20047186






Wednesday, 21 June 2017

KITAR HAID (The Menstrual Cycle) ~ video















































Why do women have periods?


Why do women have periods?



http://ed.ted.com/lessons/why-do-women-have-periods







地球上只有极少数的物种 有这种神秘的特质:
月经周期。
人类是便是这少数物种之一。
猴子、猿、蝙蝠、人类, 可能还有象鼩
是地球上仅有的 有月经的哺乳动物。
人类的月经比其他动物更频繁,
即便月经会导致营养流失 和身体上的不便。
那么这种罕见的生理过程 究竟意义何在?
这要从怀孕说起。
在怀孕过程中, 身体的资源被充分地利用
来塑造一个适合胎儿生长的环境,
为胎儿成长提供营养的港湾。
从这方面来看, 怀孕多么神奇啊。
但这只是一方面。
另一方面,怀孕的过程中 母体和胎儿也存在冲突。
和其他所有生物一样,
人类身体进化的目的是 更好地延续物种基因。
对母亲而言,这意味着 她应该给她所有的后代
提供相同的条件。
但母亲和胎儿的基因 不是完全相同的。
胎儿还继承了其父亲的基因。
这些基因为了生存,
会向母亲索取更多的资源。
这种进化中的利益冲突,
让女性和她腹中的孩子
在子宫内展开 一场生理上的拔河比赛。
这场比赛的成因之一是胎盘。
胎盘是连接胎儿和 母体血液系统的器官。
它为胎儿提供发育需要的营养。
大多数哺乳动物的胎盘 被母体内的一层细胞屏障包围。
这层屏障让母体能控制 给胎儿的营养供应。
但对于人类和其他少数物种来说,
胎盘实际上直接进入了 母体的循环系统,
直接接触母体的血液。
通过胎盘, 胎儿向母体的动脉释放荷尔蒙,
这使母体的动脉扩张, 运送营养丰富的血液。
这样无限制的接触, 胎儿能通过控制激素
来增加母体血糖, 扩张母体动脉,
并提高母体血压。
在必要的情况下,大多数哺乳动物的母体 能排出或者再吸收胚胎,
但是对人类来说, 一旦胎儿连接到血液供应,
切断了这种连接 会导致严重内出血。
如果胎儿发育不良或死亡,
则会危及母亲的健康。
胎儿发育和对营养的持续需求
会使母亲极其疲惫,血压升高,
并可能出现 糖尿病和先兆子痫等状况。
因为这些风险的存在,
怀孕是一项重大而危险的投资。
因此身体有理由仔细筛选胚胎,
只留下那些值得为之冒险的胚胎。
月经则随之产生了。
怀孕始于着床这一过程,
胚胎把自己嵌入到子宫内膜上。
子宫内膜不断演化 使得着床变得困难。
这样只有健康的胚胎能够存活。
但这样一来,
它也选择了最有活力的胚胎,
创造了一个进化反馈循环。
胚胎向子宫内膜传递 复杂而精细的激素信号,
使子宫内膜允许它着床。
那么如果胚胎着床失败了呢?
胚胎可能还会附着在子宫内膜上,
甚至部分进入子宫内膜。
但胚胎慢慢死去时, 母体会更容易发生感染。
它可能还会一直释放激素信号, 扰乱母体组织。
身体为了避免这个问题, 会排出所有可能的危险。
每当排卵未能形成健康胚胎,
子宫都会使整个内膜脱落,
同时将未受精的,虚弱的 或濒死的胚胎一并排出。
这个自我保护的过程 就是月经周期,
其结果就是月经来潮。
正是这种奇异的生物特性
使得人类能一直繁衍下去。

A handful of species on Earth share a seemingly mysterious trait:
a menstrual cycle.We're one of the select few.
Monkeys, apes, bats, humans, and possibly elephant shrews
are the only mammals on Earth that menstruate.
We also do it more than any other animal,
even though its a waste of nutrients and can be a physical inconvenience.
So where's the sense in this uncommon biological process?
The answer begins with pregnancy.
During this process, the body's resources are cleverly used to shape a suitable environment for a fetus,
creating an internal haven for a mother to nurture her growing child.
In this respect, pregnancy is awe-inspiring, but that's only half the story.

The other half reveals that pregnancy places a mother and her child at odds.
As for all living creatures, the human body evolved to promote the spread of its genes.
For the mother, that means she should try to provide equally
for all her offspring.
But a mother and her fetus don't share exactly the same genes.
The fetus inherits genes from its father, as well,
and those genes can promote their own survival by extracting
more than their fair share of resources from the mother.
This evolutionary conflict of interests
places a woman and her unborn child in a biological tug-of-war
that plays out inside the womb.
One factor contributing to this internal tussle
is the placenta, the fetal organ that connects to the mother's blood supply and nourishes the fetus while it grows.
In most mammals, the placenta is confined behind a barrier of maternal cells.
This barrier lets the mother control the supply of nutrients to the fetus.
But in humans and a few other species,
the placenta actually penetrates right into the mother's circulatory system to directly access her blood stream.
Through its placenta, the fetus pumps the mother's arteries with hormones that keep them open to provide a permanent flow of nutrient-rich blood.
A fetus with such unrestricted access can manufacture hormones to increase the mother's blood sugar, dilate her arteries, and inflate her blood pressure.
Most mammal mothers can expel or reabsorb embryos if required, but in humans, once the fetus is connected to the blood supply, severing that connection can result in hemorrhage.
If the fetus develops poorly or dies,
the mother's health is endangered.
As it grows, a fetus's ongoing need for resources can cause intense fatigue,
high blood pressure,
and conditions like diabetes and preeclampsia.
Because of these risks,
pregnancy is always a huge, and sometimes dangerous, investment.
So it makes sense that the body should screen embryos carefully to find out which ones are worth the challenge.
This is where menstruation fits in.
Pregnancy starts with a process called implantation,
where the embryo embeds itself in the endometrium that lines the uterus.
The endometrium evolved to make implantation difficult
so that only the healthy embryos could survive.
But in doing so, it also selected for the most vigorously invasive embryos, creating an evolutionary feedback loop.
The embryo engages in a complex, exquisitely timed hormonal dialogue that transforms the endometrium to allow implantation.
What happens when an embryo fails the test?
It might still manage to attach,
or even get partly through the endometrium.
As it slowly dies, it could leave its mother vulnerable to infection, and all the time, it may be emitting hormonal signals that disrupt her tissues.
The body avoids this problem by simply removing every possible risk.
Each time ovulation doesn't result in a healthy pregnancy,
the womb gets rid of its endometrial lining,
along with any unfertilized eggs, sick, dying, or dead embryos.
That protective process is known as menstruation,
leading to the period.
This biological trait, bizarre as it may be,

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