Epithelial Tissues Flashcards
What are epithelial tissues?
A diverse group of tissues that provides structural and functional barrier between biological compartments
What are the 2 major types of epithelial tissue?
- Surface
- Glandular
What is surface epithelial tissue?
- Covers or lines the body surfaces, tubes and cavities
- Forms boundaries between different environments
What is glandular epithelial tissue?
- Primarily involved in secretion
- Exocrine glands
- Endocrine glands
What are the characteristics of epithelial tissue?
- Continuous sheets of cells tightly bound together
- Supported by a basement membrane
- Epithelial cells are POLARISED:
- Structurally and functionally distinct cell surfaces
- Basal surface attached to (or facing towards) BM
- Apical surface not attached to cells (free)
- Form structural and functional barrier
What are the functions of epithelial tissue?
- Physical protection
- Diffusion
- Absorption
- Secretion
Where in the body does epithelial tissues act as physical protection?
- Skin and oral cavity
Where in the body does epithelial tissues use diffusion?
- Transfer of gases, nutrients and waste between blood and surrounding surfaces
Where in the body does epithelial tissues use absorption?
- Nutrients from GIT
Where in the body does epithelial tissues use secretion?
- Sweat
- Mucus
- Enzymes
What are the 3 main criterial of epithelial tissue that is related to their function?
- Number of layers
- Cell shape
- Specialisations
What are SIMPLE epithelia?
- One layer of cells
- Diffusion/absorption/ secretion
What are STRATIFIED epithelia?
- Two or more layers
- Physical protection against mechanical stress
What are PSEUDOSTRATIFIED epithelia?
- Single layer of cells that appear stratified
- Nuclei are at different heights and not all cells reach apical surface
What is a squamous cell?
- Cells are flat
- Width greater than height
What is a cuboidal cell?
- Cells appear square
What is a columnar cell?
- Height is greater than width
What is a transitional cell?
Changes shape to accommodate stretching
What are microvilli?
- Tiny projections of the plasma membrane
- Increase apical surface area
- Good for absorption
What are cilia?
- Long motile projections that beat rhythmically
What is keratin?
- Confers mechanical strength
- Good for physical protection
What is the function and location of simple squamous cells?
Function - lines surfaces involved in passive diffusion
Location - Lungs (gases), capillaries (fluids)
What is the function and location of simple cuboidal cells?
Function - Lines small ducts and tubules
Location - Collecting tubules of kidneys, Small ducts of salivary glands
What is the function and location of simple columnar cells?
Function - Lines absorptive surfaces
Location - Small intestine (note presence of microvilli)
What is the function and location of ciliated simple columnar cells?
Function - Ciliary action facilitates transport of ovum from ovary to uterus
Location - Female reproductive tract
What is the function and location of pseudostratified columnar ciliated cells?
Function - Ciliary action propel surface layer of mucus containing trapped particles towards pharynx
Location - Airways of respiratory tract
What are goblet cells and what do they secrete?
- Modified columnar epithelial cells
- Synthesise and secrete mucus
Where are goblet cells located?
Scattered through simple columnar epitheliums
- Respiratory
- Gastrointestinal
What does the number of cells in stratified epithelia relate to?
The level of physical stress
What are stratified epithelia named after?
The shape of the cells at the apical surface
How do stratified epithelial cells mature?
From basal layer from continuously dividing stem cells
Stratifies epithelia cells gradually migrate to the surface and shed. What in the name of these shedded cells?
Anucleate squames - a thin cell lacking a nucleus
What is the function and location of stratified squamous cells?
Function -
- Protection
- Non-keratinised (moist)
- Keratinised
Location -
- Soft mucosal tissues in oral cavity, pharynx
- Epidermis, gingival tissues
What is the function and location of stratified cuboidal cells?
Function - secretory
Location - Secretory ducts of exocrine glands, such as salivary
What is the function and location of stratified columnar cells?
Function - secretory and protective
Location - Male urethra and lining some glands
What is the function and location of transitional cells?
Function - Allows for expansion and stretch
Location - Bladder
What is the function of keratin?
Enhances resistance to physical stress
- Epithelial cells accumulate keratin filaments as they mature
- Formation of tough, non-living surface layer
What is a carcinoma?
- Malignant tumour arising from epithelial tissue
- Subclassified by tissue of origin
- Squamous cell carcinoma resembles stratified squamous epithelium
- Adenocarcinomas originate/ resemble glands
What is epithelial dysplasia?
- A disorder of differentiation of epithelial cells which may regress, remain stable or progress to invasive carcinoma
- Can invade and destroy adjacent tissues
