BIO 201 Chapter 4: Epithelial Tissue

_ tissue

epithelial

_ tissue

connective

epithelial tissue

• consists of cells arranged in continuous sheets, in either single or multiple layers (cell rich)

• little intercellular space between cells (matrix)

• avascular (lacks blood vessels)

surface epithelium

• covers or lines a surface

• forms outer covering of skin and some internal organs

• inner lining of blood vessels, ducts, body cavities, and the respiratory, digestive, urinary and reproductive systems

glandular epithelium

• makes up secreting portion of glands

• thyroid, adrenal, sweat and digestive glands

apical surface

• faces body surface, body cavity, lumen (interior) of internal organ, or tubular duct that receives cell secretions

• may contain cilia or microvilli

• most superficial layer of cells in multicellular epithelia

lateral surface

• face adjacent cells on either side

• contain tight junctions, adhering junctions, desmosomes and/or gap junctions

basal surface

• opposite the apical surface

• deepest layer of cells in multilayered epithelia

• adhere to extracellular materials such as the basement membrane

basement membrane

• composed of basal lamina and reticular lamina

• forms a surface on which epithelial cells migrate during growth or wound healing

• restrict passage of larger molecules between epithelium and connective tissue

• participate in filtration of blood in the kidneys

basal lamina

• thin layer

• secreted by epithelial cells

• contains laminin (adhere to integrins in hemidesmosomes, attaching epithelial cells to basement membrane) and collagen

reticular lamina

• close to connective tissue

• contains collagen produced by fibroblasts (connective tissue cells)

Simple epithelium

single layer of cells that functions in diffusion, osmosis, filtration, secretion, or absorption

Pseudostratified epithelium

• appears to have multiple layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface

• actually a simple epithelium because all its cells rest on the basement membrane

• May contain cilia or secrete mucus

Stratified epithelium

two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear

Squamous

thin, which allows for the rapid passage of substances through them

Cuboidal

• as tall as they are wide and are shaped like cubes or hexagons.

• may have microvilli at their apical surface and function in either secretion or absorption

Columnar

• much taller than they are wide, like columns, and protect underlying tissues.

• Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption

Transitional

change shape, from squamous to cuboidal and back, as organs of the urinary system such as the urinary bladder stretch (distend) to a larger size and then collapse to a smaller size

Simple squamous epithelium

• a single layer of flat cells that resembles a tiled floor when viewed from apical surface; centrally located nucleus that is flattened and oval or spherical in shape

• Location: lining of lungs (mesothelium), blood and lymphatic vessels (endothelium)

• Function: filtration (such as blood filtration in kidneys) or diffusion (such as diffusion of oxygen into blood vessels of lungs)

Simple cuboidal epithelium

• single layer of cube-shaped cells; round, centrally located nucleus

• Location: surface of ovary, lens and retina of eye, lines kidney tubules, secreting portion and smaller ducts of many glands

• Function: Secretion and absorption

Nonciliated simple columnar epithelium

• single layer of nonciliated columnlike cells with oval nuclei near base of cells

• contains columnar epithelial cells with microvilli at apical surface and mucus-secreting goblet cells

• Location: digestive canal, gallbladder, ducts of many glands

• Function: Secretion and absorption; helps prevent destruction of stomach lining by acidic gastric juice secreted by stomach; lubricates linings of digestive, respiratory and reproductive tracts

Ciliated simple columnar epithelium

• single layer of ciliated columnlike cells with oval nuclei near base of cells and goblet cells interspersed

• Location: bronchioles of respiratory tract, uterine tubes, uterus, sinuses, spinal cord, and ventricles of brain

• Function: cilia move mucus and foreign molecules toward throat and move oocytes from ovaries into uterus in the Fallopian tubes

Nonciliated pseudostratified columnar epithelium

• Appears layered because nuclei are at various levels, some cells do not extend to apical surface

• Lacks cilia and goblet cells

• Location: lines epidermis, larger ducts of many glands, parts of male urethra

• Function: absorption and secretion

Ciliated pseudostratified columnar epithelium

• Appears layered because nuclei are at various levels, some cells do not extend to apical surface

• Some cells extend to apical surface and secrete mucus or have cilia

• Location: Lining of airways

• Function: secrete mucus to trap foreign particles, cilia sweep mucus away for elimination

Stratified squamous epithelium

• As basal cells move toward apical surface, they become dehydrated and though, eventually dying and sloughing off to be replaced by new cells

• Can be keratinized or nonkeratinized

Nonkeratinized stratified squamous epithelium

• Does not contain large amounts of keratin

• Constantly moistened by mucus from salivary and mucous glands

• Surface cells are shed before they die

• Location: lines wet surfaces (ex. inside mouth)

• Function: Protection against abrasion, water loss, ultraviolet radiation, and foreign invasion

Keratinized stratified squamous epithelium

• Tough layer of keratin in apical layer and several layers deep

• Relative amount of keratin increases in cells as they move away from nutritive blood supply and organelles die

• Location: skin

• Function: Protection against abrasion, water loss, ultraviolet radiation, and foreign invasion

Stratified cuboidal epithelium

• Two or more layers of cells, cubical apical cells

• Location: ducts of sweat and esophageal glands, male urethra

• Function: protection, secretion, absorption

Stratified columnar epithelium

• Basal layers consist of shortened, irregular cells

• Location: lines part of urethra; large excretory ducts of some glands, such as esophageal glands; small areas in anal mucous membrane; part of conjunctiva of eye

• Function: protection and secretion

Transitional epithelium

• AKA urothelium

• Looks like stratified cuboidal epithelium in relaxed state and stratified squamous epithelium in filled state

• Location: unique to bladder, ureters and urethra

• Function: allows stretching of urinary organs while maintaining protective lining

Pap smear

• involves collection and microscopic examination of epithelial cells that have been scraped off the apical layer of a tissue

• commonly examines nonkeratinized stratified squamous epithelial cells

• mainly performed to detect early signs of cancer

Gland

Specialized epithelial cell or cells that secrete substances; may be exocrine or endocrine

Endocrine gland

• secretes hormones into bloodstream without flowing through duct

• Location: pituitary gland, pineal gland, thyroid and parathyroid glands, adrenal glands, pancreas, ovaries, testes, thymus

• Function: regulate metabolic and physiological activities to maintain homeostasis

Exocrine gland

• secreted products are release into ducts that empty onto an epithelium that lines a surface (ex. skin, organ lumen)

• Location: sweat, oil and earwax glands; salivary glands; pancreas

• Function: produce substances such as sweat to help lower body temperature, oil, earwax, saliva, or digestive enzymes

Unicellular glands

single-celled glands (ex. goblet cells)

Multicellular glands

multi-celled glands; most exocrine glands

Simple gland

a gland with a duct that does not branch

Compound gland

a gland with a duct that branches

Acinar gland

a gland with rounded secretory portions

Tubular gland

a gland with tubular secretory parts

Tubuloacinar glands

glands with both tubular and round secretory parts

Simple tubular

Example: glands in the large intestine

Simple branched tubular

Example: gastric glands

Simple coiled tubular

Example: sweat glands

Simple acinar

Example: glands of spongy urethra

Simple branched acinar

Example: glands of spongy urethra

Compound tubular

Example: glands of spongy urethra

Compound acinar

Example: glands of spongy urethra

Compound tubuloacinar

Example: acinar glands of the pancreas

Merocrine glands

release substances via exocytosis using secretory vesicles generated at rough ER and then Golgi complex

Apocrine glands

• Product builds up apical surface then releases

• Portion of cell is pinched off via exocytosis

• Cell repairs to repeat process

Holocrine glands

• product builds up in cytosol

• as cell matures, it ruptures and releases product

• the cell is then replaced with a new cell