Final answer:
Adjacent cells in an epithelium are joined by specialized cell junctions, including tight junctions, anchoring junctions (desmosomes, hemidesmosomes, and adherens), and gap junctions, which provide watertight seals, strong connections and intercellular communication respectively.
Step-by-step explanation:
Adjacent cells in an epithelium are joined by cell junctions that allow various degrees of interaction. There are three main types of junctions: tight junctions, anchoring junctions, and gap junctions. Tight junctions create a watertight seal, preventing materials from leaking between cells and effectively separating the apical and basal compartments of cells. These junctions are crucial for maintaining selective barriers in tissues such as the lining of internal organs.
Anchoring junctions, which include desmosomes, hemidesmosomes, and adherens, provide strong and flexible connections. Desmosomes are like spot welds using cadherin proteins that link cells together, vital for tissues subjected to stretching. Hemidesmosomes are similar but connect cells to the extracellular matrix using integrin proteins. Adherens junctions may utilize either cadherins or integrins, with the contractile protein actin, helping to shape and fold the epithelial tissue.
In contrast, gap junctions form intercellular passageways for the exchange of small molecules and ions between cells, facilitating intercellular communication. Collectively, these specialized junctions enable epithelial tissue to adhere to itself and the underlying connective tissue, forming a cohesive layer that supports tissue integrity and function.