Structural organisation in animals (epithelial)

Till epithelial tissues

squamous

flattened cells with irregular boundaries

location of squamous

walls of endothelium, walls of bowman capsule, loop of henles, alveoli of lungs

function of squamous

forming a diffusion boundary

cuboidal

cube like cells

location of cuboidal

ducts of glands, germinal epithelium, tubular parts of nephrons

function of cuboidal

absorption, secretion

columnar

tall, slender cells, nuclei at base, free surface may have microvilli

location of columnar

lining of stomach and intestines

function of columnar

absorption, secretion

ciliated

if cuboidal and columnar calls have microvilli

function of ciliated

to move particles or mucus in a specific direction

location of ciliated

inner surface of hollow organs like bronchioles and fallopian tubes.

glandular

specialised columnar or cuboidal cells for secretion

types of glandular

unicellular (goblet cells of alimentary canal), multicellular (salivary gland)

classification of glandular on the basis of the mode of pouring of their secretions

endocrine, exocrine

Exocrine glands

products are released through ducts or tubes

endocrine glands

Their products called hormones are secreted directly into the fluid bathing the gland

Compound epithelium

a limited role in secretion and absorption

compound epithelium function

provide protection against chemical and mechanical stresses.

types of compound epithelium

stratified, transitional

stratified

deepest layer stratum germinativum made of columnar cells, morphology of superficial layer varies with different stratified epithelia

stratified cuboidal

lines inner surfaces of larger salivary and pancreatic ducts

types of stratified squamous

keratinized, non keratinized

stratified keratinized squamous

cover dry surfaces of skin, heavy deposit of insoluble protein keratin on dead superficial cells, highly resistant to mechanical abrasion

stratified non keratinized squamous

covers moist surfaces like oesophagus, pharynx, buccal cavity. cannot prevent water loss, moderate protection against abrasion

transitional

thinner and more stretchable than stratified, lines inner surface of ureters and urinary bladder