Cells adhesion is the process of cells connecting with each other and with their matrix. This connection happens because of the existence of cell adhesion molecules (CAMs), which are proteins. (μόρια κυτταρικής προσκόλλησης). Some important functions that are regulated by cell adhesion include cell migration and tissue development.  If the process of cell adhesion changes (example : mutation) this can lead to diseases, like cancer.

 Cell adhesion molecules  are proteins within the membrane of the cell and they are classified in two main categories: 1)  Molecules  dependent on Calcium ions  which are Cadherins and selectins. 2) Molecules non- dependent on calcium ions which are : intergins and immunoglobulin (lg) superfamily. Cells are able to use different adhesion molecules according to their functions.

Integrins: Are mainly involved with the interaction of cells with their extracellular substance. Basically their role is to bind the intracellular cytoskeleton of the cell and the external substance.

Cadherins : These molecules bind cells with each other.  They are group of transmembrane proteins dependent on Calcium ions. If Calcium ions are missing cadherins can’t bond with each other. There are more than 40 different cadherins molecules and many groups of cells produce different kind of Cadherins. For example : In the previous article, the basic parts of embryogenesis were explained. During the final stages, when the neural tube is being formed, a bunch of group cells get detached from the ectoderm and end up in the mesoderm and create a different cell line (neural crest cells). This is a party of cells that wants to stop being connected to one specific group of cells ( the ectoderm cells) and wants to bind to another cell group (the mesoderm cells). The cadherin molecules that are binding the ectoderm cells with each other, get ruptured, their bonds are breaking of, while new cadherin molecules are created between the neural crest cells in the mesoderm.

Cadhering molecules  are categorized  based on their unique ability to bind. They develop homophilic binding ( N-cadherin with N-cadherin). They also, provide a lot of strength to cells and to the cellular connection of tissues. Once cadherins are attached to each other the binding site inside the cell, changes Essentially, the inside part of each protein is attached to the cytoskeleton. The cytoplasmic part of cadherins connects with actin through intracellular binding proteins , known was catenins. (catenin complex).

Celectins : they get attached to carbohydrates.

Immunoglobulin (lg) superfamily : they are commonly associated with roles in the immune system. 

Cell adhesion molecules create cell junctions.

 Cell junctions are essential for cell stability. They are symmetrical structures that are formed, between two adjacent  cells. There are three types of cell junction. 

Tight-occluding junctions , anchoring junctions and gap junctions.

Anhoring junctions : they are located above the tight junctions and they have three sub junctions : 1) zonula adherens or belt desmosome) , 2) macula adgerens or spot desmosome) and 3) hemidesmosome.

Gap junction: These structures are necessary to cells, since they give them the ability to create tissues and directly connect the cytoplasm of two cells (cell to cell junction).  Gap junctions are composed  of transmembrane proteins called connexin which are organized in groups. They all create a structure of a pore called the connexon which looks like a channel. Connexons bind to other connexons through their pores, their proteins bind to each other. This conformation results in molecules moving from the cytoplasm of one cell to the cytoplasm of another. And that’s how a tissue is being made, since many cells are able to function are one.

Tight junctions : Tight-occluding junctions have a very important function:  Τhey determine the polarity of the cells  by segregating the basal region from the apical region. Epithelial cells are polarized, which means that the polarity of one cell isn’t symmetrical, one half is different from the other.