Chapter 3 Body Tissues • Tissues – Groups of cells with similar structure and function – Four primary types: 1. 2. 3. 4. Epithelial tissue (epithelium) Connective tissue Muscle tissue Nervous tissue © 2015 Pearson Education, Inc. Epithelial Tissues • Locations: – 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 unattached surface • Can be exposed to exterior or cavity of an organ • The lower surface of the epithelium (the basal lamina) rests on a basement membrane – Consists of reticular connective tissue © 2015 Pearson Education, Inc. Epithelium Characteristics • Avascular (no blood supply) – Relies on circulatory system to obtain food and oxygen • Surrounding connective tissues supply via diffusion from nearby capillaries • Regenerate easily if well nourished (through normal cell division) – Those on the exterior of the skin are exposed to friction and other hostile substances and are therefore lost Classification of Epithelia • Two name system: – First name = # of layers – Second name = shape of cells • Names using number of cell layers include: – 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 • Names using 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 Squamous Diffusion and filtration Secretion in serous membranes Protection Cuboidal Secretion and absorption; ciliated types propel mucus or reproductive cells Secretion and absorption; ciliated types propel mucus or reproductive cells Protection; these tissue types are rare in humans Cell shape Columnar Transitional Protection; stretching to accommodate distension of urinary structures (c) Function of epithelial tissue related to tissue type • Remember these general characteristics and you will be able to classify each type a lot easier !! 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. Figure 3.18a Types of epithelia and their common locations in the body. Air sacs of lungs Nucleus of squamous epithelial cell Basement membrane (a) Diagram: Simple squamous Nuclei of squamous epithelial cells Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (275×). 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. Figure 3.18b Types of epithelia and their common locations in the body. Nucleus of simple cuboidal epithelial cell Basement membrane (b) Diagram: Simple cuboidal Simple cuboidal epithelial cells Basement membrane Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (250×). Simple Epithelia • Simple columnar – Single layer of tall cells • 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. Figure 3.18c Types of epithelia and their common locations in the body. Nucleus of simple columnar epithelial cell Basement membrane (c) Diagram: Simple columnar Mucus of a goblet cell Simple columnar epithelial cells Basement membrane Photomicrograph: Simple columnar epithelium of the small intestine (575×). 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. Figure 3.18d Types of epithelia and their common locations in the body. Cilia Pseudostratified epithelial layer Pseudostratified epithelial layer Basement membrane Basement membrane Connective tissue (d) Diagram: Pseudostratified (ciliated) columnar Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (560×). Stratified Epithelia (two or more cell layers) • 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. Figure 3.18e Types of epithelia and their common locations in the body. Nuclei Stratified squamous epithelium Basement membrane (e) Diagram: Stratified squamous Stratified squamous epithelium Basement membrane Connective Photomicrograph: tissue Stratified squamous epithelium lining of the esophagus (140×). 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 – Unique type of epithelium because of its ability to become temporarily modified in arrangement and shape – 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. Figure 3.18f Types of epithelia and their common locations in the body. Basement membrane Transitional epithelium Basement membrane Transitional epithelium Connective tissue (f) Diagram: Transitional Photomicrograph: Transitional epithelium lining of the bladder, relaxed state (270×); surface rounded cells flatten and elongate when the bladder fills with urine. 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.
