Epithelial Tissues Flashcards
Define Epithelial Tissue
Epithelia cover and line internal and external surfaces of the body, forming barriers between other tissues of the body and the internal and external environments
What does this barrier act as
a defense barrier for underlying tissue and a surface where exchanges (secretion, absorption, excretion) can occur
List the features common to all types of epithelial tissue
a. totally cellular; i.e., no connective (support) tissue fibres holding the cells together; integrity depends on cell junctions.
b. no blood vessels (avascular)
c. stem cells lie within the epithelium (self-regenerating)
d. separated from underlying tissues by a basal lamina
e. always supported by an underlying layer of connective tissue (for mechanical support) containing blood vessels (for metabolic support). Epithelia can be divided into 2 main types: simple (single layer of cells) and stratified (multiple layers of cells).
How is the epithelial lining arranged?
- Apical Surface
- Epithelial cell
- Basal lamina (thin connective tissue called basement membrane)
- Connective tissue
What are the different types of cell junctions
- tight junction = act as a barrier- selective permeability of solute particles through neighbouring cells
- Desmosomes and hemidesmosomes which act as anchors to provide strength. D= cell to cell adherance. H= anchoring, structures that allow attachment of cell to basal surface.
- Gap junctions allow communication (movement between cells): like pores that allow transportation of solute particules between different cells
How do we classify Epithelia?
- Simple (single layer of cells)
2. Stratified (multi layer)
Name the types of simple epithelia
- Squamous - flat
- Cuboidal - cubes: height and width of cell is equal and centrally located nucleus
- Columnar- height longer than width
- Pseudostratified- single layer of cells but diff shape:. nuclei appear in different location. False multi layered appearance
Name the types of stratified epithelia
- Squamous - 3 subgroups
a) Keratinised stratified squamous epithelium (skin)
b) Parakeratotic stratified squamous
c) Stratified Squamous - Transitional (change shape according to environment or function. dedicated to excretory system. Ability to change shape according to function
Characteristics of simple squamous
> single layer
flattened cells with large surface area
thin
Hardly any cytoplasm (thin), nucleus buldges
irregular cell margins- no distinctive shape
Function of simple squamous
- thin so idea for rapid transport (lungs)
- Smooth surface = low friction covering on internal organs that move against each other/ body walls
Where is Simple Squmous epithelial found which gives it a different name?
entire circulations (blood vessels and heart) system is lined: endothelial cells
Characteristics of simple cuboidal epithelial
- Single Layer
- Cell height and Width are the same
- Nucleus is centrally placed
Example of where simple cuboidal is found
lining the secretory part of an exocrine gland.
OR
In thyroid gland, lining secretory unit of individual follicles containing the thyroid hormone
what is a common fact for simple cuboidal and squmous?
they are restricted to internal protected surfaces as only a single layer of cells
Characteristics of simple columnar
- Height larger than width
- Elongated nuclei arranged in ordered layer towards the base of the cell
- contain more cytoplasm than simple cuboilad or squmous
Function of simple columnar and e.g.
- Absorption: lining of small intestine
- Secretion: lining of small intestine
- moving material over the surface of epithelium: cilia in airways
Why does Simple Columnar epithelium have higher cellular activity
Contain more cytoplasm
characteristics of Pseudostratified Columnar epithelium
- Nuclei at different levels
- All cells still make contact with the basal lamina
- cilia on top to filter/ trap unwanted particles: line airways
Characteristics of Stratified squamous epithelium
- Multiple layers
- basal layer cells roughly cuboidal, upper layer is squmous
- Tightly packed which is maintained by desmosomes between cells
- Rete pegs allow attachment to underlying connective tissue
Function of Stratified Squamous
line oral cavity and oesophagus as thick layer provides defence against mechanical damage
Characteristics of Keratinised Stratified Squmous Epithelium
- cuboidal to squmous shape
- accumulate granules of keratohyalin which stain dark blue with H&E
- In superficial layer all cellular detail is lost- layers of red-staining keratin
Function of Keratinised stratified squamous epithelium
forms the epidermis as keratin is physically strong, chemically inert and semi-waterproof. This protects from mechanical and chemical damage and dessication
Characteristics of Parakeratotic Stratified Squamous epithelium
- Similar to stratified squamous but superficial layer of cells shows CELLULAR detail AND KERATINISATION
Function of PArakeratotic stratified Squamous Epithelium
Protects against coarse ingesta, allowing absorption of useful products of fermentation (e.g. VFA) in runimant stomach.
