the tissue level of organization

Tissue

Collection of specialized cells and cell products working together to perform a limited number of functions

Histology

The study of tissues

Epithelial tissue

Covers exposed surfaces, intestinal passageways and forms glands

Connective tissue

Fills internal spaces, provides structural support, Transports material, and stores energy

Muscle tissue

Specialized for contraction; includes skeletal muscle, cardiac muscle, and smooth muscle

Neural tissue

Carries electrical impulses throughout the body

Epithelia

Layers of cells that cover internal or external surfaces

Glands

Structures that produce fluid-like secretions; either are attached to or are derived from epithelia

Cellularity

Epithelial is composed almost entirely of cells

Polarity

Structural and functional differences between apical and basal surfaces

Attachment

Basal surfaces are attached to a basal lamina

Avascularity

Epithelia lack a blood supply

Regeneration

Cell division and replacement occurs at a faster rate than most other tissues

Functions of epithelial tissue

1. Provided physical protection

2. Control permeability

3. Provide sensation

4. Produces specialized secretions

Three types of cell junctions

1. Tight junctions

2. Gap junctions

3. Desmosomes

Tight junctions

The lipid portion of the plasma membranes fo two cells are tightly bound together by interlocking membrane proteins; so tight they prevent the passage of water and ions between cells

Gap junction

Composed of channel called connexons; form narrow passageways that allow small molecules and ions to pass from cell to cell

Desmosomes

Very strong connections made of CAM’s and proteoglycans that can resist stretching and twisting

Cell adhesion molecule (CAM)

Proteins that attach large areas of opposing plasma membranes

Three types of epithelial cell shapes

1. Squamous

2. Cuboidal

3. Columnar

Squamous

Thin and flat in appearance

Cuboidal

Appears as boxes or cubes

Columnar

Tall and relatively slender in appearance

Simple epithelium

Of only one layer of cells covers the basements membrane

Are fragile and don’t provide mechanical protection

Line internal compartments and passageways such as the ventral body cavities, heart chambers, and blood vessels

Stratified epithelium

Several layers of cells are present along the basements membrane membrane

Generally located in areas that are exposed to chemical and mechanical stresses such as the surface of the skin and linings of the mouth

Simple squamous epithelium

Stratified squamous epithelium

Simple cuboidal epithelium

Stratified cuboidal epithelium

Simple columnar epithelium

Stratified columnar epithelium

Pseudostratified columnar epithelium

Transitional epithelium

Endocrine glands

Release secretions into interstitial fluid

Exocrine glands

Release secretions into passageways called ducts

1. Merocrine secretion: product is released by exocytosis

2. Apocrine secretion: involves the loss of cytoplasm as well as secretory product

3. Holocrine secretion: involves cell destruction during secretion

Serous glands

Secrete a watery secretion that contains enzymes; the parotid glands are examples

Mucous glands

Secrete mucin that hydrate to form mucous; the sub mucosal glands of the small interstice are examples

Mixed glands

Contain more than one type of gland cell; the submandibular glands are an example

Simple gland

Doesn’t have a branching duct

Compound gland

Has at least one branching duct

Connective tissue

Connects the epithelium to the rest of the body

Three basic components

1. Specialized cells

2. Extracellular protein fibers

3. Ground substance

Matrix

Extracellular fibers and ground substance combined; typically makes up the majority of a connective tissue

Connective tissue proper

Broad category divided into loose connective tissue and dense connective tissue based on the number of cell types present and the proportion of fiber and ground substance

Fluid connective tissue

Have distinct populations of cells suspended in a watery matrix; blood and lymph