1. Need for communication
Why to communicate/ cordinate
1…….
2…….
3………….
Communication levels
Cellular level
Tissue
Organ level
Environment

2. TYPES OF COMMUNICATION
Cell’s direct signaling or intracellular communication
Direct cell contacts
Extra cellular communication or chemical signaling
Paracrine
Autocrine signaling
Endocrine signaling
Synaptic signaling

3. CELL TO CELL CONTACTS/ JUNCTIONS
vertebrates, 3 Types
1. Anchoring Junctions (connect the cytoskeletons of adjacent cells)
Desmosomes
Hemidesmosomes
Adherens Junctions
Communicating (GAP) junctions (permit small molecules to pass between cells)
3. Tight Junctions (occluding junctions), create sheets of cells

5. A: Anchoring Junctions
VERTEBRATES
A: Anchoring Junctions
Anchoring proteins extend through the plasma membrane to link cytoskeletal proteins in one cell to cytoskeletal proteins in neighbouring cells as well as to proteins in the extracellular matrix .
Junction
Cytoskeletal Anchor
Transmembrane Linker
Ties Cell To
Desmosomes
Intermediate filaments
Cadherin
Other Cells
Hemidesmosomes
Intermediate Filaments
Integrins
EC Matrix
Adherens junctions
Actin Filaments
Cadherin/Integrins
Other Cells / the EC Matrix

6. VERTEBRATES B: Communicating (GAP) junctions
Direct chemical communication between adjacent cellular cytoplasm through diffusion without contact of the extracellular fluid.
Six connexin proteins, interacting to form a cylinder with a pore in the centre. 2 adjacent cell connexons interact, they form the gap junction channel.
Connexon pores vary in size n polarity and therefore can be specific depending on the connexin proteins that constitute each individual connexon
Heart muscle, brain, Retinal and skin cells

7. VERTEBRATES C: Tight junctions
Branching network of sealing strands, each acting independently
tissue, organ or cell specific combination of proteins of the claudin, occluding, tricellulin and JAM families.
Beside transmembrane proteins , a number of cytoplasmatic associated adaptor proteins are present, that mediate the regulation and connection of the tight junctions with the actic cytoskeleton

8. Efficiency of the junction in preventing ion passage increases exponentially with the number of strands.
Regulate the movement of water and solutes between epithelial layers.
Tight epithelia like distal convoluted tubule, and the collecting duct part of the nephron in the kidney and the bile ducts ramifying through liver tissue.
Leaky epithelia have less complex tight junctions. For instance, the tight junction in the kidney proximal tubule, a very leaky epithelium, has only two to three junctional strands, and these strands exhibit infrequent large slit breaks.

11. CELL TO CELL CONTACTS/ JUNCTIONS
Invertebrates: junctions, for example septate junctions or the C. elegans apical junction.
epithelial cells, barrier to solute diffusion through the intracellular space
beneath the apical, lumenal surface of the intestinal cells

12. MULTICELLULAR PLANTS PLASMODESMATA
portions of the endoplasmic reticulum are trapped across the middle lamella in newly dividing plant cells eventually becoming (primary plasmodesmata).
wall is not thickened further, and depressions or thin areas known as pits are formed
Alternatively, plasmodesmata can be inserted into existing cell walls between non-dividing cells (secondary plasmodesmata)