Building blocks

Cells.

We are made up of about 30 trillion cells. Each is typically about 6µm (micrometres) in size: that is 6 millionths of a metre, or a tenth of the thickness of a human hair, and each carries our entire DNA including a map with details of where it is needed and what it does. (Our original DNA is composed of the cell information from each of our parents.)

There are also spare cells (“stem cells”) in the body which may be required to replace cells that have become damaged.

There are two basic types of stem cell:

Embryonic stem cells (as in developing embryos) can usually become any type of cell the body may need, like part of an eye or part of a liver for instance.

Adult (“somatic”) stem cells are usually limited to become any part of the organ from where they are found.

Cells lining the digestive tract

The normal cells that line the oesophagus are usually smooth and flat (“squamous”) cells to facilitate the smooth passage of foods down it.

The cells that line the stomach and intestines are usually corrugated into ridges and troughs (“columnar”) to provide a larger surface area and hold the acid away from the depths.

The cells that line the intestines usually include some that make a thick mucous (“goblet cells”) to provide lubrication and extra protection against any residual acid that no longer needed.

The Cell Cycle

All the cells in the human body replicate themselves continuously (the “cell cycle”). This process varies in length of time depending on its location and purpose. For those of the oesophagus, stomach and intestines, the cycle is around 22 hours to a day.

During the cell cycle, each cell produces a complete replica of itself and the old cell dies. Each cell contains over a gigabyte of information and during the copying process, it is possible for mistakes to occur. A small error doesn’t really make much difference (For instance, it could be related to the colour of your eyes and the cell is part of your big toe.) and the other cells at that location will probably have replicated okay. However, if repeated errors occur, the cell can mutate. Subsequent mutations can become cancerous when the cell will continue replicating without destroying the old copies. It is this uncontrolled growth that forms the tumour.

Some cells are more prone to replication errors. If our parents had mutated cells, it is likely those mutation possibilities may be in our DNA.

Barrett’s formation

Refluxing acid burns the lining of the oesophagus. Blood rushes to the area to remove damaged cells and provide replacements. That is inflammation called oesophagitis. It can be painful, though not everyone feels it, but it will usually heal if permitted and the source of damage is removed.

Refluxing acid mixed with bile is more serious. It causes deeper damage, penetrating further. If this were to continue, normal cell replacement may not be able to cope.

The stem cells may produce columnar cells to replace the squamous cells as they are better able to cope with the attack.

When one type of cell is replaced with a different type of cell, it is known as metaplasia. If the oesophageal squamous cells are replaced by cells resembling the stomach lining, it is known as “gastric metaplasia (GM)”; if they are replaced with cells resembling the intestines, it is known as “intestinal metaplasia (IM).” The difference is the addition of goblet cells in IM.

Quality control – our immune system.

As previously mentioned, blood will carry away damaged and dead cells and deliver new cells; it also carries specialised cells that look out for damage and respond accordingly. This is our immune system carrying T cells to seek out unwanted interlopers like viruses to destroy. If a particular virus is prevalent, our T cells can learn to identify them easily and increase the number of specialised cells to deal with the intruders. That is how we can gain immunity to some diseases. Once the pattern is recognised, future generations of T cell will be able to find them easier.

T cells also compare the cells with the original DNA map to check for mutations and can usually destroy mutations that could become cancerous. However, Barrett’s cells were not part of our original DNA so the T cells ignore them which means, if they were to mutate, they can go unchecked. That is why, those with Barrett’s have surveillance every few years to look for mutated cells.

It has also been found that PPI medication can reduce the risk of cell mutation by causing mutating cells to self destruct, effectively fulfilling the role of the T cells.

Page updated 5 June 2026

Page updated

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