Welcome back to another week of Biology!
This week some of you will be completing a Planaria lab while others will be completing some models to talk more about cell differentiation. Last week all of you were exposed to the need of cell division to help grow and heal multicellular organisms. While there are a couple of types of cell division that we have touched upon (asexual vs. sexual), all cells in an organisms composed of many, must know what job or role they will play. For example, our bodies need to have different cells. The cells in our stomach must be specialized enough to withstand the acidic environment of the gastric juices. On the other hand, our eye cells must be specialized enough to capture the different wavelengths of color that radiates from the different objects across the room.
So what is cell differentiation? It is simply when cells decide to become a specific type and they develop characteristics special to their job. For example, a neuron needs to be long and thin, with many dendrites (arm-like extensions) to quickly pass the information from neuron to neuron. After all, your brain needs to work quickly!! As defined by Kumar, in “Textbook of Human Embryology”, cell differentiation “is the process of a cell changing from one cell type to another. Most commonly this is a less specialized type becoming a more specialized type, such as during cell growth.”
(Figure 1: Stem cell can develop into any of the types of cells shown)
These cells that can turn into any of kind of cell, are called stem cells. Stem cells are commonly found in developing embryos. As humans develop during the nine months of gestation, these stem cells differentiate into the many different types of cells that will make your legs, your lungs, your brain and many more.
Stem cells differ from other cells in the body in several ways
1. Stem cells are unspecialised. They have not developed into cells that perform a specific
function.
2. Stem cells can specialise. They can divide and produce cells that have the potential to become other more specialised cell types or tissues. These new cells and tissues are used to repair or replace damaged or diseased cells in the body.
3. Unspecialised stem cells are capable of self renewal. Stem cells are able to divide and produce many copies of themselves. Many cell types once they have become completely specialised (terminally differentiated) have a limited capacity to produce new cells of the same type. If a mature nerve or blood cell is damaged it cannot replace itself.
4. When stem cells divide, each daughter cell can either: a. stay as a stem cell, or b. the daughter cell can undergo many more cell divisions. With each division the cell becomes more specialised until it finally becomes a terminally specialised cell type. There are many intermediate cell types between the pluripotent stem cell and the final specialised cell type. Stem cells play a critical role in normal growth and development by providing new cells for growth and for replacing and repairing used and damaged tissues. Once stem cells have been obtained from the body they can, in the right conditions, be grown in a laboratory. Scientists can then influence what type of cell a stem cell grows into by adding chemicals to the cell culture or changing how the cells are grown.
Where are we most likely to find these cells? A developing embryo!! Yet the use of embryonic stem cells is rather controversial because this would require the destruction of an embryo.
So let’s take a look at these questions to help you write your post:
Does life begin at fertilization, in the womb, or at birth?
Is a human embryo equivalent to a human child?
Does a human embryo have any rights?
Might the destruction of a single embryo be justified if it provides a cure for a countless number of patients?
Since ES cells can grow indefinitely in a dish and can, in theory, still grow into a human being, is the embryo really destroyed?
