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group of cells that are similar in structure and perform a common or related function






enhances contrast


minor distortions that altered tissues contain

Epithelial Tissue

a sheet of cells that covers a body surface or lines a body cavity. Functions: protection, absorption, filtration, excretion, secretion, and sensory reception

epithelium (plural: epithelia), (epithe = laid on, covering)

(2 main types: Covering and Lining and Glandular Epithelium

Covering and Lining Epithelium

forms the outer layer of the skin, dips into and lines the open cavities of the cardiovascular, digestive, and respiratory systems, and covers the walls and organs of the closed ventral body cavity

Glandular Epithelium

fashions the glands of the body

Apical-Basal Surface

cells regions near the apical surface differ from those near the basal surface in both structure and function


finger like extensions of the plasma membrane

Special Charactersistics of Epithelium

2. Specialized Contacts (cell close together/cell sheets)
3. Supported by connective tissue
4. Avascular but innervarted
5. Regeneration


supplied by nerve fibers


contains no blood vessels

Basal Lamina

adjacent to basal surface, noncellular adhesive sheet consisting of glycoprotiens secreted by epithelial cells.

Functions: acts as a selective filter that determines which molecules diffusing from the underlying connective tissue are allowed to enter epithelium

Reticular Lamina

deep to the basal lamina, layer of extracellular materials (collagen fibers)

Basement Membrane

formed together by Basal and Reticular laminae

Functions: reinforces the epithelial sheet, helping it to resist stretching, and tearing forces

Classification of Epithelia

each epithelium is given two names the first indicates (1) how many cell layers and the second (2)describes the shape of the cell

Simple Epithelia

consists of a single layer of cells

locations: typically found where absorption, secretion, and filtration occur

Stratified Epithelia

composed of 2 or more layers of cells (if stratified, name according to top layer of cells)

locations: common in high abrasion areas, such as the skin surface and the lining of the mouth

(2) Cell Types

1. Squamous
2. Cuboidal
3. Columner


flat, disclike, nucleus in center, slight bump


cubelike, 6 sides, nucleus near the center (could be oval), little dimension


like a column, long linear cell, nucleus near the basal, never at top

Simple Squamous Epithelium

simplest of epithelia

Function: allows passage of materials by diffusion and filtration, in sites where protections is not important; secretes lubricating substances in serosae

Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity


simple squamous epithelia in body which reflects its location. Provides a slick, friction - reducing lining in lymphatic vessels and in hollow organs of the cardiovascular system


the epithelium found in serous membranes lining the ventral body cavity and covering its organs

Simple Cuboidal Epithelium

Function: secretion and absorption

Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface

Tip: Associate with kidney and salvary glands

Simple Columner Epithelium

layer may contain mucous-secreting unicellular glands (goblet cells)

Function: absorption; secretion of mucus, enzymes and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action

Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, etc

Pseudostratified Columner Epithelium

Description: single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucous-secreting cells and bear cilia (gives appearance that their are many different layers of cells)

Function: secretion, particularly of mucus; propulsion of mucus by ciliary action; known for absorption

Location: Nonciliated type in makes sperm carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Also asscociate with lungs

Stratified Squamous Epithelium

Description: thick memabrane composed of several cell layers; basal cells are cuboidal or columner and metablically active; in the keratinized type the surface cells are full of keratin and dead; basal cells are active in the mitosis and produce the cells of the more superficial layers

Function: protects underlying tissues in areas subjected to abrasion

Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane

Stratified Cuboidal Epithelium

Quite rare in body, Found in some sweat and mammary glands, Typically two cell layers thick

Stratified Columner Epithelium

Limited distribution in body, Small amounts in pharynx, male urethra, and lining some glandular ducts; Also occurs at transition areas between two other types of epithelia

Transitional Epithelium

Description: resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columner; surface cells dome shaped or squamous like, depending on degree of organ stretch

Function: stretches readily and permits distension of urinary organ by contained urine

Location: lines the ureters, urinary bladder, and part of the urethra


consists of one or more cells that make and secrete (export) a particular product. This product, called secretion, is an aqueous (water based) fluid that usually contains proteins

ex: some glands release a lipid or steroid rich secretion

Gland Classification

endocrine( internally secreting) or exocrine (externally screting) depending on where they release their product, and as unicellular (one celled) or multicellular (many celled) based on relative cell number making up the gland

Endocrine Glands

ductless glands that secrete hormones that travel through lymph or blood to target organs directly into blood and lymphatic system

Exocrine Glands

More numerous than endocrine glands, secrete products into ducts and secretion released onto the body surfaces (skin) or into body cavities to reduce friction

ex: mucous, sweat, oil, and salivary glands

Unicellular Exocrine Gland

The only important unicellular gland is the goblet cell. Unicellular glands are sprinkled into the epithelial linings of the intestinal and respiratory tracts amid columner cells with other functions


a complex glycoprotien that dissolves in water when secreted


comes to be after Mucin is dissolved; a slimy coating that both protects and lubricates surfaces

Multicellular Exocrine Glands

structually more complex, and have two basic parts: an epitheliumderived duct and a sensory unit (acinus) consisting of secretory cells

Classification: Duct Type (Simple : unbranched duct; Compound: branched ducts) and structure of their secretory units (tubular: secretory cells form tubes) (alveolar: secretory cells form small flasklike sacs) (tubuloalveolar: if they have both types of secretory units)

Modes of Secretion: Merocrine (products are secreted by exocytosis)[ex: pancreas, sweat, and salivary galnds] and Holocrine (Products are secreted by rupture of gland cells)[ex: sebaceous glands]

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