Cell junctions INTERCELLULAR JUNCTION 1 Tight junction 2

Cell junctions

INTERCELLULAR JUNCTION 1. Tight junction 2. Desmosomes 3. Gap junction

�Tight junctions �Ridge like structures between adjacent cells. �Made up of proteins �Cells are bound together. �Found in epithelial cells vintestinal mucosa vrenal tubles �Form selective barrier Eg. Blood brain barrier.

• Functions • Helps in maintaining the functional polarity. • Localizing the membrane proteins in one place.

�They are important in preventing molecules leaking between the cells and providing control of passage for materials through the epithelial sheet. �It is made up of proteins called claudins and occludins.

�Desmosome or maculae adherens • fasten cells together strengthening the tissue. �Desmo (‘bound’), soma (‘body’). �Adjacent membranes become thickened and the space in between is filled with filament like material. �Fibrils arise from this portion to the interior of the membrane. �Hemi desmosome – half desomoses on the basal sides of the cell.

Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Intercellular space Plaque Intermediate filament (keratin) Linker glycoproteins (cadherins) (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. Figure 3. 5 b

• Gap junctions or communicating junctions. • Gap junctions form channels between cells. • Allow ions and small molecules to pass directly from one cell to another. These channels are formed by membrane proteins called connexin. • Six connexins in the cell membrane form a channel called a connexon

�Functions �. Gap junctions permit electrical signals to pass directly from one cell to another. �Gap junctions are found in heart and smooth muscle cells and between some neurons. �To regulate the membrane potential between cells and allow electrical impulses to pass between cells. �Electrical impulses passing between cardiac muscle cells it lead conduction of the beat. �Also gap junctions provide the contractions of the smooth muscle cells of the uterus during birth

Plasma membranes of adjacent cells Microvilli Intercellular space Basement membrane Intercellular space Channel between cells (connexon) (c) Gap junctions: Communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication. Figure 3. 5 c