When Walt Whitman wrote that he contained “many,” he was probably referring to the possibility of individuals. But the 19th century American poet may have been referring to cells.
Cells are the smallest biological units that can survive on their own, and they are also the building blocks of all living things. These contain instructions that can generate over 200 different types, each with unique functionality. These instructions include rules about what types of cells can divide.
Understand the basics: What is a cell?
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This comparison is appropriate because the youngest cells within a fertilized egg can actually be numerous, both in terms of number and type. They are often called the building blocks of life.
But that explanation may be a bit too simplistic, he says Kuen AoAssociate Professor of Biology at Gannon University in Erie, Pennsylvania. She prefers to call them robots.
like a robot all cells contain membranes — The outer layer that defines the cell and contains its parts. This layer is porous, allowing nutrients to be supplied to the cells and waste products to be removed from them.
Inside the skin is a region called the cytoplasm that contains the parts that keep the robot moving. This includes a framework called . cytoskeleton It gives the cell its shape.
At the center of the cell is a nucleus, which acts like a robot’s hard drive. That hard drive stores DNA, the genetic code that tells each cell what to do or become.
read more: atlas of our cells
How many cells are there in the human body?
We all start as a single cell called a zygote, which is created after a sperm fertilizes an egg.
The zygote is the first embryonic stem (ES) cell. These cells are thought to be “totipotent,” meaning they can produce any type of cell. At first, it’s more of the same. “When you turn on the robot, it thinks it has a better chance of survival if it has friends, so it makes more of itself,” Ao says.
Once the embryo has grown into approximately 32 ES cells, it begins to differentiate, producing more diverse cell types, each with its own specialization. “As the number of robots increases, they think they can survive better if different groups of robots do different things instead of doing the same thing,” Ao says.
As the embryo grows, it produces more specialized cells, such as blood, tissue, and neurons. When the embryo grows into an adult, the maximum value is approximately Men have 36 trillion cells, women have 28 trillion cells..
read more: 5 amazing things about the human body
What do cells do?
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Each cell is alive, but depends on both itself and its neighbors for survival. Cells provide many of the basic needs of larger, more complex organisms.
“You have to take in nutrients, build things, maintain things, and remove waste,” Ao says. “You have to be able to communicate both inside and outside the cell.”
Another main job of cells is to make more cells. The question is when, what kind, and how many.
read more: What is regeneration? Can other organs regenerate like the liver?
Explore different types of cells in the body
This is where the “software” contained in each cell’s DNA comes into play. Genes (individual pieces of “code” in your hard drive) contain rules about how and what each person can become. For example, as cells become more specialized, they are no longer able to generate ES cells.
Additionally, broad categories of cells are unable to change their developmental trajectory. For example, the category of cells that make blood cells can produce red blood cells and white blood cells, but cannot arbitrarily divide into skin cells or neurons. This applies even further down the line. For example, red blood cells cannot divide to form white blood cells.
Differentiation into specific cell types is similar to how robots create societies with different professions. Some people band together to do one job. That’s how certain organizations are formed.
Some people quit and choose another job. “Soon, they built a self-sustaining robot civilization,” Ao said. “The amazing thing is that they didn’t have to change any of the information in their hard drives to do all of this. As civilizations grew, they changed their programs to use them more effectively. That’s all.”
Ultimately, this “civilization” would contain more than 200 specialized cell types. Some types “replace” faster than others, essentially dying and being replaced by replacements. The rate of turnover varies depending on cell type and function. For example, the cells lining the intestines are replaced almost constantly to fight “invaders” such as: intestinal microorganisms in a hostile environment. Cells in the skin are also replaced, but not as quickly as cells in the stomach because the level and intensity of environmental “attacks” are not as frequent or severe.
Generally, the number of each type of cell increases as we move from childhood to adulthood. However, there are some counterintuitive exceptions. For example, we are born with more neurons than we have as adults.
“That may sound very scary,” says Ao. “But one of the really amazing things about the neurons in our brains is that our brains find more efficient ways to establish connections between neurons.”
At some point, cells are no longer able to differentiate into other cell types and eventually lose their ability to divide.
read more: How does the brain think?
When cells go out of control
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However, there are exceptions. “Sometimes a robot breaks down and decides it’s better to act alone than with a fellow robot,” Ao says. “But it can’t work with everyone anymore, so as it replicates itself more and more, it puts a strain on all the other robots. And soon those malfunctioning robots… It causes normal robots to malfunction more often than expected. This is cancer.”
Cancer is originally cell division It’s out of control. Cells that need to be split to create more of their own type will start creating another cell type instead. “Cancer cells can somehow turn on programs that should be turned off,” Ao says. Instead, the software is essentially corrupted, causing new types of cells to divide uncontrollably.
Each type of cancer is caused by a combination of different abnormalities. These defects can include DNA damage or mutations in genes that tell cells to stop dividing. This is why there is no unified treatment for cancer. Instead, scientists are finding ways to counter each type using different weapons and approaches.
read more: Number of bones in the human body and other interesting facts about the skeleton
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Prior to joining Discover Magazine, Paul spent more than 20 years as a science journalist, specializing in U.S. life sciences policy and global scientist career issues. He started his career in newspapers but switched to scientific magazines. His research has appeared in publications such as Science News, Science, Nature, and Scientific American.
