Cell Bio- Lecture #2 (Epithelium and Connective Tissues)

Apical membrane

The free surface of epithelial cells

Microvilli

Increase surface area (to facilitate absorption); found on apical membrane

Cilia

(On ciliated epithelium) move fluids outside the cell; found on apical membrane

Basolateral membrane

The attached surface of epithelial cells

Basal lamina

What epithelial cells are attached to, which facilitates interaction with connective tissue; a narrow strip of dense matrix filled with collagen and laminin proteins that allows strong attachment of epithelia to underlying connective tissue

Simple epithelium

Single layer of cells

Stratified epithelium

Several layers of cells

Squamous epithelia

Thin and flat

Cuboidal epithelia

Cube shaped

Columnar epithelia

Tall, slender rectangles

Adherens junctions

Hold neighboring cells firmly to each other; formed by interaction of cadherin proteins from both cell membranes, attached to actin filaments intracellularly

Desmosomes

Create very strong, localized attachments between neighboring cells; formed by a plaque of specific cadherin proteins from both cells, attached to intermediate filaments like keratin

Tight junctions

Create a semipermeable or impermeable seal in the extracellular space between neighboring cells; formed by claudin proteins from the membranes of both cells

Gap junctions

Create a small pore through the membranes of two neighboring cells, allowing exchange of small cytoplasmic solutes and communication; formed by hemichannels made of 6 connexin proteins in each cell

Cadherin

Proteins from both cell membranes that form adherens junctions

Plaque

Structure formed by specific cadherin proteins from both cells in a desmosome

Claudin

Proteins from the membranes of both cells that form tight junctions

Connexin

Proteins that form hemichannels (6 per cell) making up gap junctions

Fibroblasts

Cells that secrete fibers in connective tissue

Collagen fibers

Strong & flexible; resist force in 1 direction (bundled collagen)

Reticular fibers

Strong & flexible; resist force in many directions (collagen matrix)

Elastic fibers

Stretch and return to original length; made of elastin protein

Structural fibers

large macromolecular fibers that provide a strong structure to maintain tissue structure and organization (collagen, elastin proteins)

Hydrated matrix

Extremely large macromolecular structures that act as flexible 'filler' for the space between cells (proteoglycans, glycosaminoglycans, glycoproteins)

Adhesive molecules

Allow cells to attach to the extracellular structures (integrin and laminin proteins)

Collagen

A trimeric, helical protein that is secreted; assembles into fibrils in the extracellular space, which then associate into very strong but flexible fibers

Procollagen

Assembled in the endomembrane system, but does not associate with other molecules until it is secreted and processed by a peptidase enzyme

Elastins

Protein fibers that are crosslinked with each other; work like springs to help maintain the shape of tissues subject to a lot of movement

Proteoglycans

Fill the remainder of the extracellular space in animals; formed of many glycosaminoglycans (GAGs) attached to an organizing core protein; look like bottle brushes

Glycosaminoglycans (GAGs)

Very long carbohydrates with disaccharide repeats attached to a core protein

Hyaluronic acid

A massive GAG (up to 20,000 disaccharide repeats) that aggregates proteoglycans (the metal core of the bottle brush)

Fibronectins

Large secreted glycoproteins that bind to sugar moieties; form fibrils with each other and attach to both GAGs and to integrin proteins

Laminins

Secreted proteins that allow direct attachment to collagen fibers for maximal support of thin layers of epithelia; one end binds integrins on the basolateral membrane, the other end binds collagen fibers in the ECM

Epithelial Tissue Functions

Provide protection, control access (permeablity), sense phenomena, produce sercretions

Epithelial Tissue Characteristics

Polarized, primarily cellular, cell junctions, attached to connective tissue, avascular, regenerate

Connective tissue characteristics

Doesnt contact external world, specialized and extracellular, highly vascularized

List of loose connective tissue

Areolar, adipose, reticular

Dense Regular list

Tendon, ligament