How cells and tissues grow
This page tells you about how normal cells and tissues grow. You can read information about
Each one of us is made up of roughly a hundred million million (100,000,000,000,000) tiny cells that can only be seen under a microscope.
Cells are grouped together to make up the tissues and organs of our bodies. They are a bit like building blocks.
Different types of body tissues are made up of different types of body cells. For example, there are bone cells in bone and breast cells in the breast. There are more than 200 different types of cells in the body.
You can read about different types of cells and cancer.
Body tissues grow by increasing the number of cells that make them up. Cells in many tissues in the body divide and grow very quickly between conception and adulthood. Once we are grown up, many cells mature and become specialised for their particular job in the body and they don't reproduce so often. But some cells, such as skin cells or blood cells are constantly being replaced.
If cells are damaged in any way or killed, new cells are produced to replace them. This process is called cell division. One cell doubles by dividing into two. Two cells become four and so on.
It seems that human cells are programmed to reproduce up to 50 or 60 times at most. Then they usually die.
Stem cells provide a pool of dividing cells that the body uses to restock damaged or old cells. Stem cells are a kind of ‘starter cell’. They have the potential to develop into different cell types in the body. When a stem cell multiplies, the resulting cells may remain as stem cells. But under the right conditions they become a type of cell with a more specialised function, such as a muscle cell, red blood cell or brain cell.
Stem cells occur naturally in the body in various places and stages during our lifetime. In the embryo they give rise to all the different tissues and organs of the body. In adults each type of stem cell is usually only able to develop into a few specific types of cell. For example, adult stem cells in the bone marrow, known as haematopoietic stem cells, usually only give rise to different types of blood cell.
Cancer stem cells
Scientists now believe that stem cells may play a role in the development of cancer, as some tumours are thought to develop from faulty stem cells. This has led to the idea of cancer stem cells, which have now been identified in a range of cancer types. The types include bowel, breast and prostate cancer as well as leukaemia.
Researchers are looking at whether some treatments could target cancer stem cells.
When cells divide and grow they do this very precisely so that the new cells are exactly the same as the old ones.
Each cell makes copies of all its genes. Then each cell splits into two with one set of genes in each new cell. During the process, there are lots of checks to make sure that everything has copied correctly. But sometimes mistakes happen, which can lead to cancer.
You can read about genes and cancer on the page about how cancer starts.
The video shows how healthy cells divide.
View a transcript for the video about how healthy cells divide.
If more cells are needed, the new cells will rest for a while and then divide again. The cells carry on doing this until enough cells have been made.
To divide, the cell goes through a process called the cell cycle. There are four main stages, or phases.
- Gap 1 or G1 phase, where the cell grows in size, and checks that everything is OK for it to divide.
- Synthesis or the S phase, where the cell copies its DNA.
- Gap 2 or G2 phase, where the cells checks that all its DNA has been correctly copied.
- Mitosis or M phase, where the cell finally divides in two.
During mitosis the copied DNA is shared out equally. This means that all the chromosomes must be duplicated and separated into two full sets, one at each end of the cell that is splitting in two. The other material that makes up the cell also splits in two. The result is two identical daughter cells.
Normal growth and healing is very orderly and precise. The cells know when there are enough new cells to mend a cut or when a structure such as a finger is fully grown. They send chemical messages to each other so that they stop growing and dividing when growth or healing is complete. The diagram below shows this happening.
Cells in the body have a natural ability to stick together in the right place so that the tissues and structures of the body form correctly. Scientists call this cell adhesion or 'stickiness'.
Molecules on the surface of the cell match those on its neighbours. It is a bit like having a post code. The code makes it very difficult for the cell to move to the wrong place. But if it does find itself in a place where its post code is different from its neighbours, it dies.
When cells are damaged or worn out, they will self destruct. This is called apoptosis, and helps to protect us from developing cancer. Cells can also undergo apoptosis if they have broken away from their proper place in the body.
Scientists are doing a lot of work on apoptosis. If they can understand what makes a cell self destruct, they might be able to use this to develop cancer treatments in the future.
Cancer cells are different from normal cells in a number of very important ways.
Find information about how cancer cells are different on the page about cancer cells.