Tissue: is a group of cells with similar structure and function, along with extracellular substances located between cells.
Changes in tissues can result in development, growth, aging, trauma, or disease.
Histology: is the microscopic study of tissue structure
Epithelial: covers and protects surfaces, both outside and inside the body.
Connective: provides support, protection, and binds other tissues together. A diverse primary tissue type that makes up part of every organ in the body.
Muscle: allows movement by contracting to shorten or lengthen.
Nervous: transmits information throughout the body through electrical impulses. Responsible for coordinating and controlling many body activities.
EPITHELIAL TISSUE: Mostly composed of cells with very little extracellular matrix between them.
EPITHELIAL TISSUE: covers body surfaces that include the exterior surface, lining of digestive, urinary, reproductive, & respiratory tracts, heart & blood vessels, and linings of body cavities.
Distinct epithelial cell surfaces:
Free / Apical Surface – exposed & not attached to other cells.
Lateral Surface – cells attached to other epithelial cells.
Basal Surface – attached to a basement membrane (a specialized type of extracellular material that helps attach the epithelial cells to the underlying tissues and plays an important role in supporting & guiding cell migration during tissue repair.)
Major Functions of Epithelia:
Protecting underlying structures
Acting as a barrier
Permitting the passage of substances
Secreting substances
Absorbing substances
CLASSIFICATION OF EPITHELIUM:
Simple
Stratified
Pseudostratified
Transitional
Simple: one layer of cells only
Stratified: more than one layer of cells
Pseudostratified: special type of simple epithelium; appears to be stratified but is not
Transitional: modification of stratified epithelium that can be greatly stretched
Shape of cells (Simple):
Squamous
Cuboidal
Columnar
Shape of cells (Stratified)
Squamous
Nonkeratinized (moist)
Keratinized
Cuboidal
Columnar
Shape of cells (Transitional):
Roughly cuboidal to columnar when not stretched and squamous-like when stretched.
Simple Squamous: 1 layer of flat, tile-like cells, often hexagonal cells
Simple Cuboidal: 1 layer of square-shaped cells
Simple Columnar: 1 layer of tall, narrow cells
Pseudostratified Columnar: 1 layer of tall, narrow cells, appears stratified but isn’t, almost always ciliated
Stratified Squamous: many layers of flat, tile-like cells
Stratified Cuboidal: many layers, cube-shaped; relatively rare
Stratified Columnar: many layers, but only the surface cells are columnar; deeper layers are irregular or cuboidal in shape; relatively rare
Transitional: special type that changes shape
stretched: squamous
not stretched: cuboidal
Simple epithelium is involved with diffusion, secretion, or absorption.
Stratified epithelium serves a protective role.
Squamous cells function in diffusion or filtration.
Cuboidal or columnar cells, which contain more organelles, secrete or absorb.
Microvilli: increase cell’s surface area (ex: small intestines)
Cilia: move materials across cell’s surface (ex: trachea)
Goblet Cells: produce mucus (ex: stomach)
Tight Junctions: bind adjacent cell together
Desmosomes: mechanical links that bind cells
Hemidesmosomes: bind cells to basement membrane
Gap Junctions: most common; small channels that allow molecules to pass between cells & allow cells to communicate
Glands: structures that secrete substances onto a surface, into a cavity, or into blood; primarily composed of epithelium, with a supporting network of connective tissue.
Exocrine: type of gland with ducts (ex: sweat & oil glands)