Lecture 3: Tissue architecture



assembly of cells that work together to carry out a specific set of functions


composed of several tissues that form a structural unit to serve a physiological function

The major types of tissues:

epithelial, connective, muscle, nerve, blood


- 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




propagate electrical signals


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


� 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


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


� 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