Unit I

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Macula adherens (Desmosome)Zonula adherens (Intermediate junction)Zonula occludens (Tight junction)Macula communicans (Gap junction)10
Intercellular contactsThe plasma membrane is the surface, which establishes contact with other cells and promotes variouskinds of cellular interaction. Structurally there are two main classes of contact:- Nonspecialised andSpecialised. The nonspecialised contacts are more common, which enable them to form loose aggregationat the same time permitting some movements. Here membrane surfaces are separated by 20nm. Followingare the types of specialised cell junctional complexes.They are seen only under electron microscope and are the regions of reciprocally adherent cellsIntercellular contactsNonspecialised Specialised/ Junctional ComplexesOccluding Adhesive CommunicatingZonula occludens Zonula adherens Macula adherens Macula communicans(Tight junction) (Intermediate junction) (Desmosome) (Gap junctions)Zonula occludens: It is a continuous zone present around the apices of epithelial cells, endothelial cells andat other sites where there is a barrier to prevent diffusion through the intercellular space. Colloidal tracersfail to move from the lumen of the intestine into the spaces between the epithelial cells. Here the membranesof the adjacent cells come into contact obliterating the gap between them. Contacts lie along branching andanastomosing ridges formed by the particles within the membrane. These junctions prevent the leakage oftoxic substances from the lumen into the tissue.Zonula adherens:It is a continuous belt formed around the apices of epithelial cells. Microfilaments areoften inserted into a dense coat on the cytoplasmic side of the membrane. No filaments span the gapbetween the cell surfaces but an adhesive material may intervene at this point which anchor the cells e.g.Intercalated discs of cardiac muscles.Macula adherens:It is a plaque like structure where the plasma membrane is coated internally with alayer of dense proteins in to which intracytoplasmic tonofilaments are inserted. The intercellular gap isbridged by thin interlocked filaments and is rich in glycoprotein (desmoglea). Single sided orhemidesmosome are also found e.g. epidermis.Macula communicans: The opposed membranes are separated by an apparent gap of 3mm. This gap istraversed by numerous dense beads arranged in hexagonal arrays on the two surfaces. Such junctionsform limited attachment of plaques rather than continuous zones thereby allowing free passage of substancesalong the cleft between the cells e.g. Hepatocytes and connective tissue.11
Page 4: Mitochondrion Golgi apparatusSmooth
Page 7 and 8: . Nonmembrane bound: These organell
Page 9: Nucleus: It is made up of deoxyribo
Page 13 and 14: 3. Epithelial tissueHuman body is m
Page 15: Compound epithelium: They have two
Page 18 and 19: 4. Connective tissueFibroblast. Fib
Page 20 and 21: Collagen fibres Elastic fibresLoose
Page 22: 5. Muscular TissueStriated muscle L
Page 25 and 26: Sarcomere (Relaxed): Each myofibril
Page 27 and 28: Smooth muscle (LP): Smooth muscle f
Page 30 and 31: Astrocyte (Fibrous) Astrocyte (Prot
Page 32: Peripheral nerve T.S: (Epineurium -
Page 35 and 36: 7. CartilageIt is a specialised con
Page 37 and 38: White fibrocartilage: It shows bund
Page 40 and 41: Decalcified bone T.S.: (Fibrous and
Page 42 and 43: 9. Blood VesselsElastic artery: (Tu
Page 44 and 45: VeinCapillaries: (Endothelium- Basa
Page 46 and 47: 10. Lymphoid TissueLymph node (LP):
Page 48 and 49: Spleen (LP): ( Capsule - Trabeculae
Page 50 and 51: Thymus: (Capsule-Septa-Lobules-Cort
Page 52 and 53: Palatine Tonsil (LP): (Stratified s
Page 54 and 55: Morphological classification of exo
Page 56 and 57: Serous salivary gland e.g Parotid g
Page 58 and 59: Mucous salivary gland (LP): (Interl
Page 61 and 62:
Mixed salivary gland (LP): A saliva
Page 63 and 64:
12. Integumentary SystemSkin, the l
Page 65 and 66:
Hair: In humans, hairs are not impo
Page 67 and 68:
Sebaceous gland: It is seen on the
Page 69:
Tooth: The tooth shows a projected
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Unit I

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