Epithelial Tissue

Covering and lining epithelia - forms outer covering and inner lining

Glandular epithelia - forms the secretory portion of glands

Endocrine glands

Exocrine glands

Secrete directly into blood, usually via traversing interstitial fluid

e.g. pituitary gland

Secrete into ducts that empty onto the surface of a covering or lining epithelium

e.g sweat and salivary glands

Single cell glands

Some glands such as the pancreas are mixed secreting into ducts and directly into the blood

individual secretory cells called mucous cells - secrete mucin; apical cytoplasm is filled with (large) secretory vesicles that look clear/foamy in a light micrograph

Multicellular glands

Simple glands - single duct that does not divide on its way to the gland cells

Simple tubular - glandular cells form straight tubes e.g. intestinal glands

Simple coiled tubular - glandular cells form coiled tubes e.g. merocrine sweat glands

Simple branched tubular - glandular cells form tubes and several secretory areas share a common duct e.g. gastric glands

Simple alveolar (acinar) - glandular cells from sac-like pockets e.g. embryonic stage in development of simple branched glands

Simple branched alveolar - glandular cells form sac-like pockets and share a common duct e.g. sebaceous (oil) glands

Compound glands - duct divides one or more times on its way to gland cells

Compound tubular - glandular cells form tubes e.g. mucous glands in mouth

Compound alveolar (acinar) - glandular cells form sac-like pockets e.g. mammary glands

Compound tubuloalveolar - secretory cells form both tubes and sacs e.g. salivary glands and pancreas

Simple epithelium - single layer of cells all in contact with basement membrane; secretion, absorption, filtration

Simple squamous - flat and thin; irregular like jigsaw; most delicate epithelium; filtration (kidney), diffusion (lung), secretion (serous membranes)

Stratified epithelium - two or more layers of cells

Simple cuboidal - cells about as tall as they are wide; cuboidal/hexagonal boxes; secretion and absorption

Endothelium lining blood vessels

Mesothelium lines pericardial, pleural and peritoneal cavities

Lines kidney tubules and ducts of glands

Simple columnar - rectangular, nuclei often elongated; more cytoplasm = more organelles

Ciliated - have cilia and goblet cells; assist motility of mucus, foreign objects oocytes

Stratified squamous - located where mechanical/chemical stresses are severe; microbe protection;

Non-ciliated - have microvilli on apical surface, which increases the surface area for absorption

Line gastrointestinal tract from stomach to anus

Line parts of the upper respiratory tract, Fallopian tubes and brain ventricles

Apical layer only determines the subtype

Keratinised - apical cells are packed with keratin, making surface tough and waterproof e.g. skin

Non-keratinised - no keratin in apical cells; protect from abrasion, defense from microbes, require secretions e.g. lining of mouth and oesophagus

Stratified cuboidal - ducts of adult sweat glands, oesphageal glands, male urerhtra

Stratified columnar - rare; part of conjunctiva of the eye

Stratified transitional - bladder

Pseduostratified epithelium - appears to have multiple layers as judged by positions of nuclei but all cells in contact with basement membrane and no all reach apical surface

Pseduostratified columnar - two main sub-types

Ciliated - goblet cells secrete mucus and cilia move it; lines airways of most of the upper respiratory tract

Non-ciliated - no goblet cells so functions in absorption and protection; larger ducts of sweat glands

Basement Membrane

All epithelia overlay a basement membrane composed of two parts

Reticular lamina - produced by cells of underlying connective tissue, known as fibroblasts

Functions

Provides a surface along which epithelial cells migrate during growth and wound healing

Acts as a physical barrier

Supports overlying epithelium

The basement membrane is thus found between the epithelium and connective tissue

Basal lamina - secreted by basal layer of epithelial cells

Cell Junctions

Lateral junctions

Basal junction

Hemidesmosome

Connects epithelia to basement membrane

Integrin linker protein binds to laminin in the basement membrane and keratin intermediate filament in cytoplasm

Adherens junctions

Gap junctions

Tight junctions

Desmosome

Transmembrane glycoprotein cadherin links to intermediate filaments containing keratin in adjacent cells

6 connexin molecules form connexons that connect neighbouring cells

Narrow intercellular gap - small molecules/ions diffuse through - allow cell communication and nerve impulses to spread

Cadherins span gap/space between cells; catenins link cadherins to actin in microfilaments in cell cytoplasm

Electrically tight; transmembrane proteins fuse adjacent plasma membranes together - claudins and occludins