 cell and extracellular matrix interaction occurs via transmembrane proteins known as integrins. Transmembrane means it traverses through the membrane and has extracellular binding site as well as a cytoplasmic binding domain. At extracellular domain, it binds with extracellular proteins like fibrin, then proteoglycans, laminin. All of them have certain common amino acid sequences to which the extracellular domain of integrin receptor binds. At the cytoplasmic domains, it can bind either with the actin filament or with the intermediate filaments which are cytoskeletal proteins. So we will discuss two types of cell extracellular matrix interaction, focal additions and hemidesmosomes. Focal additions are transient pliable cell matrix interaction. In focal additions, the intracellular binding domain of integrin binds with actin filaments and extracellular domain can bind with all kinds of extracellular matrix proteins as we have already discussed. The affinity of extracellular domain to its ligand is not always same. What signal from inside can change the shape of this protein causing it to bind with extracellular protein with higher affinity. This signal which is coming from inside the cell to change the affinity of the extracellular domain of integrin protein is known as inside out signaling. It is coming from inside and changing something outside. After binding with its ligand, again there may be change in the shape of the integrin receptor mainly at the cytoplasmic domain and in turn change its interaction with the actin. This change in the inside of the cell which is coming due to binding of extracellular domain of integrin protein to its ligand is known as outside in signaling. It is coming from outside, changing something inside. This inside out and outside in signaling basically means cell and extracellular matrix are talking to each other. There is an active dialogue going on between the two. So it can convey a lot of things like it can convey to the cell. Like it binds with the proper extracellular matrix protein that yes I am at my home. This will activate some proteins which will move to nucleus of the cell and it can lead to expression or inhibition of some proteins and lead to cell proliferation or differentiation or it can interact with other cells also. So one example of this is when platelet at a site of vessel injury they bind with the outside defibrinogen which in turn binds with the other platelets. So some kind of signal is conveyed to the platelets at that site and they all aggregate at that site and form platelet plug. So here we see how a dialogue is going on between cells and its extracellular environment. To contrast to focal adhesion hemi-desmosomes are quite tight junctions between cells and its extracellular matrix. In hemi-desmosomes the cytoplasmic domain of integrin binds with intermediate filaments which primarily have supporting function. So in this video we discussed two types of cell matrix interactions focal adhesions and hemi-desmosomes in the next video we will talk about cell-cell interactions.