Intro: tissue: a group of cells that usually have a common origin in an embryo and function together to carry out specialized activities, histology: the science that deals with the study of tissues. Cell junctions: cell junctions are contact points between the plasma membranes of tissue cells, there are many types but we consider 5: tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions. Tight junctions: consist of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes, tight junctions inhibit the passage of substances between cells and prevent the contents of these organs from leaking. Desmosomes: also contain plaque and have cadherins that extend to attach to adjacent cells, unlike adherens junctions, the plaque of desmosomes does not attach to microfilaments. Instead they attach to intermediate filaments, which consist of the protein keratin. Intermediate filaments span the entire cell and contribute to its stability: desmosomes prevent separating under tension/pulling.