tissue
assembly of cells that work together to carry out a specific set of functions
organ
composed of several tissues that form a structural unit to serve a physiological function
The major types of tissues:
epithelial, connective, muscle, nerve, blood
Epithelium
- barrier at the surface of organs
- cells predominate the tissue
- cells attach to one another and to a very thin layer of ECM
� Direct cell-cell contacts
� Basal lamina: the ECM component of the tissue
� line the surfaces of body (skin), organs and bloo
Connective tissue
- ECM predominates the tissue
- cells are embedded in ECM
- mechanical support
- No direct cell-cell contact
Muscle
contraction
Nerve
propagate electrical signals
Blood
immunity (white blood cells) and oxygen transport (red blood cells)
Extracellular Matrix (ECM)
� Composed of macromolecules: proteins and polysaccharides
� Synthesized and secreted by cells
� Two forms:
-ECM of connective
tissue: fibrous network
-Basal lamina (epithelium,
muscle, nerve): dense
sheet
Collagens
� Major structural component of ECM
� Provides tensile strength to tissues
� are produced and organized by cells
� molecules are assembled into fibrils/fibers or sheets
� regulate many cellular activities
Glycosaminoglycans (GAGs) (including hyaluronan)
� linear polysaccharides
� provide compressive strength, which depends on the high density of negative changes that attract water
Proteoglycan
Core protein + GAGs (covalently attached)
Proteoglycans and sheet-forming collagens are major structural components of ______
basal lamina
GAG/Proteoglycan complexes in connective tissue
� Provide compressive strength
� Extended conformation: serve as space filler
� major structural components of ECM
� synthesized inside the cells and exported to the extracellular space
Hyaluronan
� a very long GAG
� often serves as the central core of GAG/proteoglycan complexes
� can be used to make hydrogels for tissue engineering applications
Cell junctions
formed by membrane proteins at cell-cell borders
The functions of tight junction
� seal: prevents free paracellular diffusion
� forms paracellular channels for specific ions
� sets the apico-basal boundary: prevent lateral diffusion across the boundary
Gap junctions are intercellular channels
� allow ions and small water-soluble molecules to move from one cell to another
- Ions, sugars, amino
acids, etc.
� Rapid propagation and coupling of electrical and chemical signals among cells
Anchoring junctions
mediate cell adhesion
Cells are subjected to mechanical forces through interactions with neighboring cells and the ECM. The mechanical forces influence:
� mechanical properties of the cells and tissues
� activities of the cells