Overview
This lecture covers the three main types of cell junctions—tight junctions, desmosomes, and gap junctions—and their structural properties and functions in tissues.
Types of Cell Junctions
- Tight junctions create a watertight seal that blocks water, ions, and molecules from passing between cells.
- Tight junctions are typically found in tissues such as the bladder, intestines, and kidney where barriers are crucial.
- Desmosomes act like spot welds, attaching cells together and connecting to the cytoskeleton inside each cell.
- Desmosomes allow water, ions, and small molecules to flow between cells and are found in tissues undergoing mechanical stress, like skin and intestines.
- Gap junctions form tunnel-like connections between cells, permitting direct flow of water and ions from cell to cell.
- Gap junctions are especially important in tissues that propagate electrical signals, such as cardiac muscle and neurons.
Functional Roles of Junctions
- Tight junctions maintain distinct environments on either side of an epithelial tissue by forming a complete barrier.
- Desmosomes provide structural integrity and resistance to mechanical stress by allowing limited movement between connected cells.
- Gap junctions enable rapid communication and synchronized activity by allowing ions and small molecules to pass directly between adjacent cells.
Multiple Junctions in Tissues
- Some tissues, like the intestines, can have more than one type of cell junction (e.g., both tight junctions and desmosomes).
Key Terms & Definitions
- Tight Junction — A cell junction forming a watertight seal, preventing passage of substances between cells.
- Desmosome — A cell junction providing strong intercellular attachment while allowing water and ions to pass.
- Gap Junction — A cell junction creating tunnels for direct movement of ions and water between cells.
- Epithelial Tissue — Sheets of cells covering surfaces or lining cavities, often containing multiple junction types.
Action Items / Next Steps
- Review examples of tissues with each type of cell junction.
- Practice drawing and labeling the three junction types.
- Read about how cell junction failures contribute to disease.