Epithelial Tissues

Body Tissues Tissues Groups of cells with similar structure and function Four primary types: Epithelial tissue (epithelium) Connective tissue Muscle tissue Nervous tissue © 2015 Pearson Education, Inc.

Epithelial Tissues Locations: Functions: Body coverings Body linings Glandular tissue Functions: Protection Absorption Filtration Secretion © 2015 Pearson Education, Inc.

Epithelium Characteristics Cells fit closely together and often form sheets The apical surface is the free surface of the tissue The lower surface of the epithelium rests on a basement membrane Avascular (no blood supply) Regenerate easily if well nourished © 2015 Pearson Education, Inc.

Figure 3.17a Classification and functions of epithelia. Apical surface Basal surface Simple Apical surface Basal surface Stratified (a) Classification based on number of cell layers

Classification of Epithelia Number of cell layers Simple—one layer Stratified—more than one layer © 2015 Pearson Education, Inc.

Figure 3.17a Classification and functions of epithelia. Apical surface Basal surface Simple Apical surface Basal surface Stratified (a) Classification based on number of cell layers

Classification of Epithelia Shape of cells Squamous Flattened, like fish scales Cuboidal Cube-shaped, like dice Columnar Column-like © 2015 Pearson Education, Inc.

Figure 3.17b Classification and functions of epithelia. Squamous Cuboidal Columnar (b) Classification based on cell shape

Figure 3.17c Classification and functions of epithelia. Number of layers One layer: simple epithelial tissues More than one layer: stratified epithelial tissues Cell shape Squamous Diffusion and filtration Secretion in serous membranes Protection Cuboidal Secretion and absorption; ciliated types propel mucus or reproductive cells Protection; these tissue types are rare in humans Columnar Secretion and absorption; ciliated types propel mucus or reproductive cells Transitional Protection; stretching to accommodate distension of urinary structures (c) Function of epithelial tissue related to tissue type

Simple Epithelia Simple squamous Single layer of flat cells Location—usually forms membranes Lines air sacs of the lungs Forms walls of capillaries Forms serous membranes (serosae) that line and cover organs in ventral cavity Functions in diffusion, filtration, or secretion in membranes © 2015 Pearson Education, Inc.

Nucleus of squamous epithelial cell Figure 3.18a Types of epithelia and their common locations in the body. Air sacs of lungs Nucleus of squamous epithelial cell Nuclei of squamous epithelial cells Basement membrane Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (275×). (a) Diagram: Simple squamous

Simple Epithelia Simple cuboidal Single layer of cube-like cells Locations: Common in glands and their ducts Forms walls of kidney tubules Covers the surface of ovaries Functions in secretion and absorption; ciliated types propel mucus or reproductive cells © 2015 Pearson Education, Inc.

Nucleus of simple cuboidal epithelial cell Figure 3.18b Types of epithelia and their common locations in the body. Nucleus of simple cuboidal epithelial cell Simple cuboidal epithelial cells Basement membrane Basement membrane Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (250×). (b) Diagram: Simple cuboidal

Simple Epithelia Simple columnar Single layer of tall cells Location: Goblet cells secrete mucus Location: Lines digestive tract from stomach to anus Mucous membranes (mucosae) line body cavities opening to the exterior Functions in secretion and absorption; ciliated types propel mucus or reproductive cells © 2015 Pearson Education, Inc.

Nucleus of simple columnar epithelial cell Figure 3.18c Types of epithelia and their common locations in the body. Mucus of a goblet cell Nucleus of simple columnar epithelial cell Simple columnar epithelial cells Basement membrane Basement membrane Photomicrograph: Simple columnar epithelium of the small intestine (575×). (c) Diagram: Simple columnar

Simple Epithelia Pseudostratified columnar All cells rest on a basement membrane Single layer, but some cells are shorter than others giving a false (pseudo) impression of stratification Location: Respiratory tract, where it is ciliated and known as pseudostratified ciliated columnar epithelium Functions in absorption or secretion © 2015 Pearson Education, Inc.

Pseudo- stratified epithelial layer Figure 3.18d Types of epithelia and their common locations in the body. Cilia Pseudo- stratified epithelial layer Pseudo- stratified epithelial layer Basement membrane Basement membrane Connective tissue Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (560×). (d) Diagram: Pseudostratified (ciliated) columnar

Stratified Epithelia Stratified squamous Named for cells present at the free (apical) surface, which are flattened Functions as a protective covering where friction is common Locations—lining of the: Skin (outer portion) Mouth Esophagus © 2015 Pearson Education, Inc.

Stratified squamous epithelium Stratified squamous epithelium Figure 3.18e Types of epithelia and their common locations in the body. Nuclei Stratified squamous epithelium Stratified squamous epithelium Basement membrane Basement membrane Photomicrograph: Stratified squamous epithelium lining of the esophagus (140×). Connective tissue (e) Diagram: Stratified squamous

Stratified Epithelia Stratified cuboidal—two layers of cuboidal cells; functions in protection Stratified columnar—surface cells are columnar, and cells underneath vary in size and shape; functions in protection Stratified cuboidal and columnar Rare in human body Found mainly in ducts of large glands © 2015 Pearson Education, Inc.

Stratified Epithelia Transitional epithelium Composed of modified stratified squamous epithelium Shape of cells depends upon the amount of stretching Functions in stretching and the ability to return to normal shape Locations: urinary system organs © 2015 Pearson Education, Inc.

Transi- tional epithelium Figure 3.18f Types of epithelia and their common locations in the body. Basement membrane Transi- tional epithelium Transitional epithelium Basement membrane Connective tissue Photomicrograph: Transitional epithelium lining of the bladder, relaxed state (270×); surface rounded cells flatten and elongate when the bladder fills with urine. (f) Diagram: Transitional

Glandular Epithelium Gland One or more cells responsible for secreting a particular product Secretions contain protein molecules in an aqueous (water-based) fluid Secretion is an active process © 2015 Pearson Education, Inc.

Glandular Epithelium Two major gland types Endocrine gland Ductless; secretions diffuse into blood vessels All secretions are hormones Examples include thyroid, adrenals, and pituitary © 2015 Pearson Education, Inc.

Glandular Epithelium Two major gland types Exocrine gland Secretions empty through ducts to the epithelial surface Include sweat and oil glands, liver, and pancreas Includes both internal and external glands © 2015 Pearson Education, Inc.