Epithelial tissue (epithelium)

Epithelial tissue (epithelium)

is a sheet of cells that covers body surfaces or cavities that forms boundaries between different

Two main forms of epithelial tissue (epithelium)

Covering/lining epithelia and Glandular epithelia

Covering/lining epithelia

A form of epithelial tissue, on external and internal surfaces

Covering and lining epithelia example

skin

Glandular epithelia

A form of epithelial tissue, secretory tissue in glands

Glandular epithelia example

salivary glands

Epithelial tissue's main functions

protection, absorption, filtration, excretion, secretion, and sensory reception

Five distinguishing characteristics of epithelial tissue

Polarity, Specialized contacts, Supported by connective tissues, Avascular, but innervated and Regeneration

Polarity characteristic

Cells have a top and bottom

Apical surface characteristic

The surface borders open space, and the upper free side is exposed to surface or cavity

basal lamina

an adhesive sheet that holds basal surface of epithelial cells to underlying cells

Specialized contacts characteristic

bind adjacent epithelial cells together (tight and desosome junctions)

(characteristic) Epithelial tissue is supported by

connective tissues

Reticular lamina

Deep to basal lamina and consists of network of collagen fibers

Basement membrane

Basal and reticular lamina reinforce epithelial sheets, resisting stretching and tearing.

Avascular, but innervated characteristic

No blood vessels are found in epithelial tissue

Regeneration characteristic

the natural process where cells are replaced or repaired, restoring damaged or lost tissue

Two classifications of epithelia

First name indicates cell layers, second name indicates cell shape.

Simple epithelia

a single layer thick of epithelia found where rapid diffusion is priority

Simple epithelia functions

Involved in absorption, secretion, or filtration processes

Stratified epithelial tissue

two or more layers thick of epithelia and involved in protection (example: skin)

Stratified epithelial tissue function

Protection for durablity

Squamous epithelia

Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm

Cuboidal epithelia

box-like, cube

Columnar epithelia

tall, column-like

Two special simple squamous epithelia are based on locations

Mesothelium and Endothelium

Endothelium

lining of lymphatic vessels, blood vessels, and heart

Mesothelium

serous membranes in the ventral body cavity

Pseudostratified columnar epithelium

Tissue appears multi-layered but is single-layered simple epithelium.

Keratinized cells

cells, specifically keratinocytes, that are filled with the protein keratin

Transitional epithelium

The ability of cells to change shape when stretched allows for more storage space

Gland

One or more cells that makes and secretes an aqueous fluid

secretion

aqueous fluid secerted from glands

2 sites of product release of glands

Endocrine and Exocrine

Endocrine glands

Ductless gland that internally secrets (example: hormones) (exocytosis)

Exocrine glands

externally secreting onto body surfaces (example: sweat)