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Chapter 3 Body Tissues

• Tissues– Groups of cells with similar structure and function– Four primary types:

1. Epithelial tissue (epithelium)2. Connective tissue3. Muscle tissue4. Nervous tissue

Epithelial Tissues

• Locations:– Body coverings– Body linings– Glandular tissue

• Functions:– Protection– Absorption– Filtration– Secretion

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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

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

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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

Figure 3.17a Classification and functions of epithelia.

Basalsurface

Apical surface

Basalsurface

Apical surface

Simple

Stratified(a) Classification based on number of cell layers

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Classification of Epithelia

• Names using shape of cells– Squamous• Flattened, like fish scales

– Cuboidal• Cube-shaped, like dice

– Columnar• Column-like

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.

• Remember these general characteristics and you will be able to classify each type a lot easier !!

Diffusion and filtrationSecretion in serous membranes

Protection

Secretion and absorption; ciliatedtypes propel mucus orreproductive cellsSecretion and absorption; ciliatedtypes propel mucus or reproductive cells

Protection; these tissue types are rarein humans

Protection; stretching to accommodatedistension of urinary structures

(c) Function of epithelial tissue related to tissue type

Number of layers

Cell shapeOne layer: simple epithelialtissues

More than one layer: stratifiedepithelial tissues

Squamous

Cuboidal

Columnar

Transitional

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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

Figure 3.18a Types of epithelia and their common locations in the body.

Nucleus ofsquamousepithelial cell

Basementmembrane

Air sacs oflungs

Nuclei ofsquamousepithelialcells

(a) Diagram: Simple squamous

Photomicrograph: Simple squamous epithelium forming partof the alveolar (air sac) walls (275×).

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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

Figure 3.18b Types of epithelia and their common locations in the body.

Nucleus ofsimplecuboidalepithelialcellBasementmembrane

Simplecuboidalepithelialcells

Basementmembrane

Connectivetissue

(b) Diagram: Simple cuboidalPhotomicrograph: Simple cuboidalepithelium in kidney tubules (250×).

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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

Figure 3.18c Types of epithelia and their common locations in the body.

Basementmembrane

Basementmembrane

Mucus of agoblet cellNucleus of

simple columnarepithelial cell

Simplecolumnarepithelial cells

(c) Diagram: Simple columnar

Photomicrograph: Simple columnarepithelium of the small intestine (575×).

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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

Figure 3.18d Types of epithelia and their common locations in the body.

(d) Diagram: Pseudostratified(ciliated) columnar

Photomicrograph: Pseudostratifiedciliated columnar epithelium lining thehuman trachea (560×).

Basementmembrane

Basementmembrane

Pseudo-stratifiedepitheliallayer

Pseudo-stratifiedepithelial layer

Cilia

Connectivetissue

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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

Figure 3.18e Types of epithelia and their common locations in the body.

Basementmembrane

BasementmembraneConnectivetissue

Stratifiedsquamousepithelium

Stratifiedsquamousepithelium

(e) Diagram: Stratified squamousPhotomicrograph: Stratified squamousepithelium lining of the esophagus (140×).

Nuclei

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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

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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

Figure 3.18f Types of epithelia and their common locations in the body.

Basementmembrane

Basementmembrane

Connectivetissue

Transi-tionalepithelium

Transitionalepithelium

(f) Diagram: TransitionalPhotomicrograph: Transitional epithelium lining ofthe bladder, relaxed state (270×); surface rounded cellsflatten and elongate when the bladder fills with urine.

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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

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Glandular Epithelium

• Two major gland types– Endocrine gland• Ductless; secretions diffuse into blood vessels• All secretions are hormones• Examples include thyroid, adrenals, and pituitary

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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