NO ME CHINGUES.
Yahoo! de por sí es una basca de página. Neta espero que no la cague.
In a paper published in Cell yesterday, scientists from the US and Thailand have, for the first time, successfully produced embryonic stem cells from human skin cells.
That sounds interesting, but what are stem cells and where do they come from?
If you take a limb from a rose tree, and put it in soil, it will grow into a thriving bush.
There is a special type of flatworm that can be cut in half, again and again hundreds of times, and each half grows back into a full worm.
Similarly, if you cut out half a human liver, it will grow back. The story of Prometheus, whose liver was eaten away by eagles and regrew each day, suggests that the Greeks of ancient times knew about regeneration of organs.
This sort of regeneration is attributed to special cells called “stem cells”.
Reprogramming the workers
Most of our cells are like many professional workers – they are hardened in their ways and can’t manage career changes.
Blood cells carry oxygen or fight disease, muscle cells expand and contract to move us around, nerve cells carry signals, skin cells form a protective layer over our bodies, and structures made up of kidney cells filter our blood.
The cells of most organs or tissues are referred to as “terminally differentiated” cells. They have specialised, and many won’t divide again. If they are damaged or die they will disappear. This is very important.
Although we feel like we grow a lot after we are born, we really only double in size two or three times and most of our cells don’t divide much.
If they did we would be at great risk from cancer – the uncontrolled doubling of cells at the wrong time.
We have a lot of cells and it is important that none of them run out of control.
But some cells can double to renew themselves and can also differentiate and give rise to specialised progeny.
These are the stem cells. We need them to produce new skin to replace damaged skin cells. Similarly, we need them in our guts to replace damaged cells on the surface of our intestines.
Our blood cells also get worn out as they race around our bodies so we have blood stem cells that divide and replace themselves. They also differentiate to form the different types of white and red blood cells we need.
Australian researchers identified stem cells in the breast that can proliferate and form a complete functioning breast. There are also stem cells in the brain and in the heart.
While stem cells tend to be very rare, they exist in many of our organs.
Types of stem cells
The ultimate stem cells are embryonic stem cells.
These cells are found in the inner cell mass of the early embryo and are referred to as “totipotent” since they have the ability to form every cell that is needed in the growing embryo.
They can be extracted from the early embryo and grown in culture dishes.
They can also be genetically modified by the addition of DNA, then injected back into other embryos or into adult animals where find their way into localities that suit them and replace themselves by duplication or differentiate into other cell types that may be needed. For a long time this type of work had been done primarily in laboratory mice.
The techniques in yesterday’s Cell paper involved injecting the nucleus from a human skin cell into a human egg (the nucleus of which has been destroyed) then growing the resulting embryo until the inner cell mass cells could be harvested.
The method may still be controversial because it uses unfertilised eggs, but many people will regard it as preferable to using human embryos. And there are other interesting methods for making stem cells.
Somatic cells to stem cells
It is also possible to convert skin cells, and indeed many different terminally differentiated cells, back into what are called “induced pluripotent stem cells” or iPS cells.
One uses the “magic four” or “OKSM” set of DNA-binding proteins that govern normal stem cell biology:
- Octamer-binding transcription factor 4 (OCT4)
- Kruppel-like factor 4 (KLF4)
- SRY (sex determining region Y)-box 2 (SOX2)
- cellular myelocytomatosis virus-like gene (MYC)
In 2012 Shinya Yamanaka won the Nobel Prize for discovering how to convert normal cells into iPS cells using the OKSM regulators to turn on and off the right genes and convert skin cells into stem cells.
Researchers are continuing to investigate whether iPS cells have the same therapeutic potential as embryo derived stem cells.
It is hoped that stem cells may provide therapies for people suffering from degenerative diseases.
Skin cells could be taken from a patient, converted to stem cells, and then these could be injected back into the damaged organ.
Ideally, they would repopulate the damaged organ with new cells.
So why doesn’t this happen in normal biology? Why aren’t our own heart stem cells busy trying to repair broken hearts?
They may be but our natural supply of stem cells is limited and presumably insufficient to tackle severe disease.
So why don’t we just have more stem cells in our bodies?
The down side of having too many stem cells may be cancer.
Stem cells share a number of features with cancer cells – both are able to self-renew and double without limit.
One theory about cancer holds that the disease most often originates not from terminally differentiated cells but from one of the small number of stem cells in the relevant tissues.
The obvious concern about using stem cells for therapy is that injecting too many could increase the chances that some of these cells would proliferate beyond control, and ultimately give rise to cancer.
Stem cell therapy for regenerative medicine is an exciting idea.
Every day we are learning more about stem cells – how to purify or make them, and how to grow them in culture and direct them down particular pathways to repopulate different organs.
Future research will assess the risks and how effective they can be in experimental systems and ultimately in human patients.
Amazing NEW Periodic Table video!
If the Animaniacs and Science had a child, this would be it! Every element of the Periodic Table, sung, in order!
Osteo-chondro-myxosarcoma before and after surgical intervention
Osteogenic tumors develop bone that displaces soft tissue. Osteo- means “bone”, and -genic means “to form”. In addition to the osteogenic behavior, this patient’s tumor has caused disordered cartilage (chondro-) and mucous membrane (myxo-) growth.
The case report states that it took “many” surgeries to completely remove the tumor and partially reconstruct the jaw, but that the patient lived a further 8 years after removal, and experienced no recurrence of the tumor in that time. While his vision suffered, as the left eye was unsalvagable, and his speech was impeded by both the incomplete jaw reconstruction and the excess skin remaining on the face, he was able to hold down a steady job and communicate. He was reported to be of “average-to-high” intelligence.
Tumors of the Jaws. Charles Locke Scudder, 1912.
Consider a failed murder attempt. Or a simple mistake that causes another to die. Is one of these more acceptable than the other?
Neuroscientists don’t pretend to hold the answers as to how people know what is right and what is wrong. But studies show individual biology may influence the ways people process the actions of others.
It turns out we judge others not only for what they do, but also for what we perceive they are thinking while they do it.
Consider the following scenario: Grace and Sally are touring a chemical factory when Grace decides to grab a cup of coffee. Sally asks Grace to pour her a cup as well. Grace spots a container of white powder next to the coffee maker and, knowing that her friend takes sugar in her coffee, she pours some into Sally’s cup. As it turns out, the powder is poison, and Sally dies after a few sips.
Most of us would understand and maybe forgive Grace for accidentally poisoning — or even killing — her friend. But what would you think of Grace if you were to learn that she had a hunch that the powder was toxic, yet decided to add it to her friend’s cup anyway?
“Often, what determines moral blame is not what the outcome is, but what [we think] is going on in the mind of the person performing the act,” says Rebecca Saxe, a neuroscientist at the Massachusetts Institute of Technology who studies how the brain casts judgment.
Scientists are learning the ways the brain responds when we attempt to determine right from wrong. Ultimately, they hope such information will help show how the brain processes difficult situations.
What was she thinking?
One way scientists study how we make right-or-wrong judgments is to look at brain regions that are most active when people attempt to interpret the thoughts of others.
In some studies, participants read stories about characters that either accidentally or intentionally cause harm to others while scientists use functional magnetic resonance imaging (fMRI) to track how brain activity changes. Such studies show that thinking about another’s thoughts increases the activity of nerve cells in a brain region known as the right temporo-parietal junction located behind the right ear.
As it turns out, some of these cells respond differently when presented with an intentional harm versus an accident. By zeroing in on the distinct patterns of activity in these cells, Saxe’s group discovered that they could accurately predict how forgiving the participants would be.
“People who say accidents are forgivable have really different [activity] patterns” than those less willing to overlook the unintentional harm, Saxe says.
Thinking about harm
Neuroscientists also study how people respond when asked how they themselves would act in morally challenging scenarios.
In one popular moral dilemma scenario, scientists ask participants to imagine the following: A runaway train is barreling down on five people. The only way to save these people is to hit a switch that would redirect the train onto tracks where it will kill only one person. Would you hit the switch?
What if, instead, you had to push a man off of a bridge to stop the train, knowing that doing so will kill him but save the lives of the others?
Studies ran these scenarios by people with damage to the ventromedial prefrontal cortex — a region believed to be involved in the processing of emotions — and those without damage. Both groups equally support the decision to hit the switch to redirect the train to save more lives.
However, those with damage to the ventromedial prefrontal cortex are much more likely to endorse pushing the man in front of the train, a more direct and personal harm. These studies, led by neuroscientist Antonio Damasio of the University of Southern California, suggest the important role of emotion in the generation of such judgments.
To test how important the ventromedial prefrontal cortex is when we judge the actions of others, Damasio along with neuroscientist Liane Young of Boston asked a small group of people with damage to this region to evaluate variations of the Grace and Sally story.
When told that Grace deliberately puts powder she believes is toxic into Sally’s cup, only to later learn the powder was sugar, healthy adults regularly condemn Grace’s failed attempt to harm her friend. However, people with ventromedial prefrontal cortex damage shrug off Grace’s action. As they see it, as long as Sally survives, Grace’s actions are no big deal.
Damasio says these results, along with others, reveal the role of the ventromedial prefrontal cortex and emotion in evaluating harmful intent.
That’s not fair
There is also evidence that changes in the chemistry of the brain influence how we behave when others treat us unfairly.
To measure how changes in brain chemistry affect people’s reactions to unfairness, University College London neuroscientist Molly Crockett and others gave study participants a drink to drive down levels of the neurotransmitter serotonin in the brain before asking them to play the ultimatum game.
In the ultimatum game, participants are paired with strangers they are told have been given a lump sum of money to share with them. The stranger determines how to divvy up the money, and proposes a split to the participant. The participant decides whether or not to accept the stranger’s offer. If the participant accepts, both players walk away with some money. However, a participant may reject the offer, believing it to be unfair, leaving both players empty-handed. Crockett found that people with lower levels of serotonin were more likely than others to reject offers they deemed to be unfair.
When the scientists examined the brain activity of participants with depleted serotonin levels as they accepted or rejected the offers, they found that rejecting offers led to increased activity in the dorsal striatum — a region involved in processing reward. Crockett says the findings suggest that dips in serotonin can shift people’s motivations to punish unfairness. For instance, when you deplete serotonin, people who are normally more forgiving may become happier with revenge, she says.
Crockett notes that serotonin levels may fluctuate when people are hungry or stressed. The findings illustrate how individual differences in biology might influence the way people view, and respond to, the actions of others.
Puta mierda corraaaaaa