Epithelium Flashcards
Epithelial tissue mainly arises from which 2 germ layers
-ectoderm
-endoderm
Purpose of Epithelia (3)
-cover exposed surfaces
-line internal tracts (ie. digestive, respiratory, urogenital)
-line cavities (ie. mouth, thoracic cavity, blood vessels, heart, etc)
Two main types of Epithelia
-Covering
-Glandular
Five characteristics of Epithelia
-cellularity (continuous layer of cells bound by cell junctions —> tight junctions, desmosomes, and gap junctions)
-Polarity (apical surface always faces external environment while basal surface is attached to the basement membrane)
-attachment
-avascularity (NO blood vessels; obtain nutrition by diffusion or absorption)
-regeneration (damaged/lost cells are replenished from Basal Stem Cells)
The apical surface (2)
-always faces the external environment/internal space
-can have cilia, microvilli, stereocilia
The basal surface is
Attached to the basement membrane
Four roles of Epithelia
-protection
-permeability
-sensation
-secretion
Epithelial types are classified according to
-arrangement (simple, stratified, pseudostratified)
-shape (squamous, cuboidal, columnar, transitional)
What are the 8 types of Epithelium
-simple squamous
-simple cuboidal
-simple columnar
-pseudostratified columnar
-stratified squamous
-stratified cuboidal
-stratified columnar (uncommon)
-Transitional (urinary only)
Simple Squamous (3), found in (4)
-flattened, polyhedral cells often with a bulging nucleus
-delicate
-allow for the exchange of gases, ions, and small molecules
FOUND IN:
-lung alveoli
-lining of body cavities
-heart
-blood vessels
Simple Cuboidal (2), found in (4)
-one layer with a central nuclei
-involved in secretion, absorption, and excretion
FOUND IN:
-glands
-ducts
-parts of the kidney tubules
-thyroid gland
Simple Columnar (4), found in (4)
-cells are taller than they are wide
-nuclei usually basal (ie. at the bottom)
-function in protection, absorption, and secretion
-often have a modified free surface (microvilli, cilia, stereocilia)
FOUND IN:
-lining of stomach
-intestines
-oviduct
-collecting ducts of kidneys
Pseudostratified Columnar (2), found in (2)
-tall principal cells and short pyramidal basal cells (ie. triangular)
-ALL cells rest on basement membrane BUT not all will reach the apical surface (ie. lumen)
FOUND IN:
-respiratory tract (contains cilia)
-epididymis (contains stereocilia)
Stratified Cuboidal (2), found in (3)
-2-3 layers of cuboidal/low columnar cells
-rare
FOUND IN:
-ducts of salivary glands
-sweat glands
-mammary glands
Stratified Columnar (3), found in (4)
-basal cells are more cuboidal
-apical cells are distinctly columnar
-rare
FOUND IN
-pharynx
-epiglottis
-urethra
-ducts of salivary glands
Transitional (4), found in (1)
-stratified
-various cell shapes
-surface layer may be binucleate (ie. two nuclei)
-high degree of stretch
FOUND IN
-urinary tract ONLY
Typically, simple epithelia is for ____ while stratified epithelium is for ____
-absorption / secretion
-protection
Stratified Squamous (3), found in (4)
-found in regions requiring mechanical protection from abrasion, pathogens, and chemicals
-basal cells multiply and move towards the surface becoming flattened (ie. ONLY the upper/apical surface is squamous)
-can be keratinized or non-keratinized
FOUND IN
-skin
-lining of mouth
-oesophagus
-anus
In stratified squamous, basal cells are ___ while the cells toward the surface are ___
-cuboidal
-squamous
Non-keratinised epithelium (2)
-stratified squamous
-kept moist by glandular sections (ex. Mouth)
Keratinised epithelium (4)
-stratified squamous
-forms where mechanical stress and dehydration are problems (ex. Skin)
-deposits keratin as cells mature, forming a tough acellular surface layer as the cells die
-four layers (stratum corneum, stratum granulosum, stratum spinosum, stratum germinativum)
Four layers of Keratinised Stratified Squamous Epithelium (from out to in):
-Stratum Corneum (Cornfied Layer): dead, keratinised cells
-Stratum Granulosum (Granular Layer): keratin granules form
-Stratum Spinosum (Prickle Cell Layer): contains desmosomes that hold the cells together
-Stratum Germinativum/Basale (Germinal/Basal Layer): near cells form
