It’s true: At some point, all of us looked the same.
We all began as a zygote.
But in 9 months, this single cell became a rapidly-dividing clump of cells and soon developed into a newborn—with a complete set of fingers and toes, not to mention complex circulatory and nervous systems.
What’s more, in a few years, the baby grew big and strong—into an adult with tough bones, toned muscles, and thoughtful intellect.
How do humans achieve this?
Cell division and Stem cells!
In this post, we are going to talk about stem cells.
What Are Stem Cells?
Our bodies are made up of many different kinds of cells. About 200 of them. Under a microscope, these cells would look very different—from our red blood cells which are disk-like, to the more elongated spindle cells of the muscles.
Not only do these cells look different, but they also have varying functions. Their forms and features give us a clue as to their functions. For example, muscle cells are more elongated so that they can relax and contract. Red blood cells, true to their oxygen-delivering function, do not have a nucleus inside them to maximize the space for the oxygen that they deliver throughout the body.
But regardless of form, or how distinct their tasks are, all these cells come from the same entities. We call them “stem cells.”
Stem cells are sometimes called “master cells” because they can turn into any type of cell in the body. These cells enter a period of specialization where they take on specific features. So a stem cell destined to be a part of the kidney will develop differently from, say, one that will become part of the brain.
There are two major types of stem cells: embryonic stem cells and adult stem cells.
Let’s look at each briefly.
Embryonic Stem Cells
When the sperm and the egg cell meet (usually in the fallopian tube), they fuse and form a single cell called the zygote. The zygote then heads to the uterus, rapidly undergoing cell division (mitosis) along the way.
By the time it reaches the uterus, it has now become a small clump of cells called the blastocyst. This group of cells implants into the uterine wall, part of it becoming the placenta, which provides the nourishment for the embryo, and the other develops into the embryo itself.
The latter contains the all-important embryonic stem cells.
Embryonic stem cells are known as “pluripotent,” which means they can turn into practically any type of cell of the human body. Around the 3rd or 4th week since conception, the different layers of embryonic stem cells begin to specialize into different tissues and organs of the fetus.
Because of their “pluripotency,” embryonic stem cells have tremendous potential in curing a host of diseases. But a lot of research is still needed to unlock all the secrets they hide.
So, where do we get embryonic stem cells for research?
See, when couples are having a difficult time having babies, some of them visit fertility clinics where doctors help them conceive via in vitro fertilization. Egg cells and sperm cells are taken from the prospective parents. And because there’s no guarantee of conception, several zygotes are created, say, 10 of them, for example.
The doctor will then choose the best ones, say 5 of the fittest zygotes, and implant them in the uterus. The remaining 5 (zygotes) are usually discarded. But some couples, with their full consent, donate these extra zygotes for research. And these become the source of embryonic stem cells.
If you sense an ethical dilemma here, we will have more to say about that later.
Adult Stem Cells
You get a cut, and it heals. Your back gets sunburned, and your body replaces dead skin cells with fresh and healthy new ones.
Billions of cells are being replaced every day, with different cells and tissues regenerating at different rates. For example, the lining in the gut, due to the wear-and-tear, is replaced every 5 days. Red blood cells have a lifespan of about 120 days. The heart cells, on the other hand, are replaced every 3 years.
The body regenerates itself continuously, giving rise to the idea that there’s a new “you” every 7 years.
Cell division plays a significant part in this. But another vital component to the replacement and repair of cells is done by stem cells. These somatic stem cells or adult stem cells are referred to as “multipotent.”
We need to differentiate between “pluripotent” embryonic stem cells with “multipotent” adult stem cells. “Pluripotent” stem cells, the ones we talked about earlier, which give rise to the fetus, are capable of turning into the different tissues and organs of the body. On the other hand, “multipotent” stem cells found in the adult human body are more limited and are only capable of replacing similar tissues and cells.
Adult stem cells can be found in the bone marrow, brain, muscles, heart, liver, and skin, among others. They help renew and maintain the organs and tissues in which they are found. For example, neural stem cells in the brain give rise to glial and neuronal cells while hepatic stem cells work in the liver.
Because of the limited agency of adult stem cells, scientists look to embryonic stem cells for resolving some of the most challenging medical issues humanity is facing.
There is, however, one very big caveat: Ethics.
Knots In Stem Cell Research
Embryonic stem cells, of course, in the appropriate environment, like a womb, will soon develop into another human being.
And so scientists wondered, by studying and researching embryonic stem cells, “Are we killing off potential human beings?”
When is the onset of personhood? Where are the margins of human life?
These are charged questions that are being asked and answered by scientists, philosophers, religious leaders, government regulators, and the medical establishment. Their answer would mean a “green” or “red” light for embryonic stem cell research.
The dilemma is that because of their pluripotent nature, embryonic stem cells have great potential in finding the cure/treatment for the human condition. There is great interest and hope for embryonic stem cells to unlock some of mankind’s problematic diseases.
Alzheimer’s, stroke, diabetes, cancer, heart disease, kidney disease, Parkinson’s, cerebral palsy, cancer, rheumatoid arthritis, leukemia, lymphoma, and autism. These are just some of the diseases that can be cured by stem cells. For example, if a patient has a malfunctioning kidney, stem cells can be used to regenerate the organ—bringing in fresh batches of life-saving nephrons.
There are no easy answers to these questions, but so far, the leaders in the field have compromised on a “14-day rule.” It says that embryonic research is allowed only within a 14-day limit. After the two-week window, the specimens have to be discarded. It is not a perfect solution, but it at least gives chance to researchers to peek into the potential of embryonic stem cells.
However, there are bright lights coming from research in Japan. Dr. Shinya Yamanaka, co-recipient of the 2012 Nobel Prize in Physiology or Medicine, has some breakthroughs in the field.
He discovered that adult stem cells can be “reprogrammed” to go back to a pluripotent state. This means that cells taken from adults can be made to function like embryonic stem cells, precluding the need to experiment with true embryonic ones. This finding has tremendous potential in dealing with conditions formerly thought “incurable” or “untreatable” and has possible applications in spinal cord injuries, brain damage, muscular dystrophy, and organ failures.
But Dr. Yamanaka’s research on Induced Pluripotent Stem Cells (iPSC) is still in its nascent stage and there are a lot more breakthroughs like it to be made. Still, it shines a bright light on the prospects of humanity finally taming long-puzzled diseases. And hopefully, in the coming years, it would render the whole ethical dilemma on embryonic stem cell research obsolete.
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