Epithelial Tissue🖐🏻 Flashcards
What are the 4 main tissues in the body?
-Muscle
-Connective
-Epithelium
-Nervous
What structural arrangement do epithelial tissues have?
Diverse Structural Arrangement depending on the location and the function of the tissue.
What functional features are common to ALL epithelial tissues?
-They are LINING tissues;
Line and cover all of our internal and external body surfaces.
Line all internal tubules and cavities e.g. in digestive system, cardiovascular system and respiratory system.
-They have a barrier function;
All Substances entering and leaving our body pass through epithelium.
Continuous boundary between different environments
Give examples of how ‘all substances entering and leaving our body pass through epithelium’ in epithelial tissue’s barrier function?
Digestive System;
-Once the food we consume is broken down by our digestive system, in order for our cells to access and use these nutrients and minerals, they must first be absorbed across the epithelium that lines our intestine and then enters our blood.
Respiratory System;
-In our lungs, O2 and CO2 must pass across the epithelial lining of our lungs and into blood or vice versa.
-In order for all these nutrients and oxygen to be utilised by our cells, must be able to cross through the epithelial lining of our blood vessels to reach our cells. Or vice versa
Expand on this role in epithelial tissue’s barrier function; ‘Forms a continuous boundary between different environments’
- In particular, they form a barrier to microbial invasion
- This is evident and important in sites such as our oral cavity and our gut.
- Both of these sites are heavily colonised by microbes and the only barrier to prevent these microbes gaining entry into our internal organs are the epithelial tissues that line these sites.
How are ALL epithelia arranged?
As continuous sheets of tightly bound cells
What is the structure (continuous sheets of tightly bound cells) of all epithelia important for?
-Enabling the tissues to perform the barrier function
What structures permeate epithelial tissue layers?
NO STRUCTURES permeate epithelial tissue, including blood vessels (avascular)
Why do no structures permeate epithelial tissue?
Because if there was, it would have a negative impact on the barrier function of these tissues, it would weaken the tissue layer.
What do the continuous sheets of tightly bound cells of epithelia provide?
- Protection against microbial Invasion so they cannot gain access to underlying tissues.
-Opportunity to regulate movement of substances from one bodily compartment to another.
What is the term given to the cells of Epithelial Tissue?
Polarised
What does polarised mean?
Refers to the fact that each of the different surfaces of the epithelial cell has different features or functions
What is the apical Surface of Epithelial Tissue?
Adjacent to or facing the lumen/ external surface. The side of the cells that faces towards or is the top layer of the cell.
What is the basal Surface of epithelial Tissue?
Adjacent to or facing the interior surface. (The bottom surface)
What is the Lateral Surface of Epithelial Tissue and what are they like in ET?
-Lateral- Sides
-Lateral surfaces are in direct contact with one another and are tightly adhered to each other.
The Lateral Sides of epithelial cells being tightly bound together ensures what?
Microbes and other substances cannot pass through gaps between cells and must pass through the cells to gain access to underlying tissues.
What feature of epithelial tissue in particular supports the ‘barrier function’?
The lateral surfaces of epithelial cells being tightly adhered to each other.
What do tight junctions do?
-Create an impermeable seal between adjacent cells- so there’s no space between the cell membranes of the two adjacent cells
-Prevents water passage and passage of other microbes/ substances.
What do tight junctions do?
-Create an impermeable seal between adjacent cells- so there’s no space between the cell membranes of the two adjacent cells
-Prevents water passage and passage of other microbes/ substances.
What are desmosomes and what do they do?
-Strong Junctions
-Composed of a variety of different protein molecules that can connect the cell membranes of adjacent cells to the cytoskeleton.
-Provide Strength to the tissue
-Ensures epithelial tissues can stretch and maintain contact
What are desmosomes and what do they do?
-Strong Junctions
-Composed of a variety of different protein molecules that can connect the cell membranes of adjacent cells to the cytoskeleton.
-Provide Strength to the tissue
-Ensures epithelial tissues can stretch and maintain contact
What are cell junctions and name two present in epithelial tissue?
-A class of cellular structures consisting of protein complexes that provide contact/adhesion between neighbouring cells and tissues.
-Desmosomes and tight Junctions
Recap the Structural Features common to all epithelial Tissues
-Continuous sheets of cells
-Cells are bound together (via cell junctions)
-Cells are polarised
Recap the functional features common to all epithelial tissues
-Cover and line all internal and external surfaces
-Form a barrier
Name 4 functions of SPECIFIC epithelial tissues and the location of these tissues
-Physical protection from mechanical abrasion
Skin and oral cavity
-Diffusion of gases, nutrients and waste between blood and surrounding tissues
Lungs, blood capillaries
-Absorption of nutrients
Gastrointestinal tract/renal tubules
-Secretion of sweat, mucus, enzymes, hormones
Glands and ducts
How are epithelial tissues Classified?
According to their structure
In what 3 ways can epithelial structure differ?
- Shape of Cells
- Number of Cell Layers
- Apical Specialisations
What are the 3 typical cell shapes that compose epithelial tissues and what do they look like?
-Squamous- thin, flat, scale like- width>height
-Cuboidal- roughly same width and height, resemble cube
-Columnar- taller than width, resemble column
What will the shape of the cells that make up the epithelial tissue reflect on?
The functional activity of that tissue
What functions will squamous- shaped cells facilitate?
-Passive Diffusion of substances through epithelial layer.
Where are squamous shaped cells most typically to be found? Give examples
In tissues where passive diffusion is the main function of that tissue.
Examples include;
-Lungs
-Lining of blood vessels
What cell shape(s) is/are the most metabolically active?
So these/ this cell(s) what?
-Columnar and cuboidal cells are more metabolically active compared to squamous cells
-These cells will contain more cellular organelles to reflect the additional cellular functions that these cells perform
Cuboidal and Columnar shaped cells will compose epithelial tissues that are involved in what functions?
-Absorption
-Secretion
What name is given to epithelial tissue composed of a single layer of cells?
SIMPLE epithelium
What is the name given ti epithelial tissue composed of two or more layers of cells?
STRATIFIED epithelium
Classification of epithelial Tissues by shape and number of layers table:
Insert table
What 2 types of epithelia do not conform with the typical classification system?
-Pseudostratified - layer numbers
-Transitional - Shape
Describe Pseudostratified Epithelia
-Columnar as the cell shapes do resemble columnar shaped epithelia.
- Whereas in true columnar Epithelium, all the nuclei are located towards the basal layer of the tissue, but in pseudo stratified E.T the nuclei are all at different heights.
-At first glance it can look like its made up of more than one cell layer but is only a single layer, hence the name ‘pseudostratified’
What is the specialised Structure of Pseudostratified epithelia?
-Cilia at apical surface
-Pseudostratified epithelia always has cilia on its apical surface
Describe Transitional Epithelia.
-Stratified
-Cells within epithelia are not all one shape
What does transitional epithelia support?
Organs where stretch and recoil are important such as;
-Bladder
What does transitional epithelia support?
Organs where stretch and recoil are important such as;
-Bladder
Name 3 apical specialisations of epithelial tissues and their function
Microvilli
Cilia
Keratin
Name 3 apical specialisations of epithelial tissues and their function
Microvilli
Cilia
Keratin
what are microvilli and what do they do? (apical specialisation)
-Small, fingerlike projections that extend into the lumen of the tissue
-Dramatically increase surface area of the apical surface of the epithelium so helps our bodies reabsorb things like nutrients
What tissues are microvilli likely to be found?
Tissues in which the function of that tissue is involved in absorption
e.g. gastrointestinal tract- absorption of nutrients
portions of the renal tubule
What are cilia and what do they do? (apical specialisation)
-Long hair like projections
-beat rhythmically and help move particulate matter across apical surface of epithelium.
In what tissues are cilia likely to be found?
-In tissues where mucous secretions will be important for protecting the tissue
-Cilia will beat rhythmically to move mucous across the surface of the tissue
What is keratin and what does it do? (apical specialisations)
- a strong interlinked protein
-composes our hair and nails
What is keratin and what does it do? (apical specialisations)
- a strong interlinked protein
-composes our hair and nails
What tissue/ epithelia is certain likely to be found?
Epithelia where the function of that tissue is to provide protection and is also involves in water proofing
What tissue/ epithelia is certain likely to be found?
Epithelia where the function of that tissue is to provide protection and is also involves in water proofing
What function does SIMPLE SQUAMOUS epithelia support?
Lines surfaces involved in Passive Diffusion
e.g. -Movement of gases in lungs
- Movement of nutrients, water, gases etc from our blood vessels into cells
Why does simple squamous epithelium support passive diffusion?
- Because this tissue/ cell layer is very thin
- No energy is required in passive diffusion, substances can simply move down a concentration gradient from an area of high concentration to an area of low concentration.
- Provides barrier between compartments but is thin enough to allow passive diffusion of substances.
Give 2 locations of Simple Epithelia
-Lungs (Alveoli)
-Capillaries (Endothelium)
*endothelium refers to simple squamous epithelium that lines our blood vessels and all over our cardiovascular system.
What is the function of SIMPLE CUBOIDAL epithelium?
Why are cuboidal and columnar cells larger than squamous cells
-Because they are more metabolically active, so the larger size is to support the active functions they perform.
-Absorption and secretion are examples of active functions where energy is required
Give 2 locations where you would find SIMPLE CUBOIDAL epithelia
-Renal Tubules
-Small ducts of salivary glands
What is the function of SIMPLE COLUMNAR epithelium?
Why are the cells that make up this so large?
-Lines absorptive surfaces such as in the small intestine.
-Microvilli on surface help facilitate absorption of nutrients
Large as they are HIGHLY metabolically active
Give one location of where you would find Simple Columnar epithelium? Expand on their function in this location
-Small Intestine
-In the gut these cells need to facilitate active absorption of the nutrients
-also provide a physical barrier to invasion of microbes
*Tissue needs to balance these 2 functions by providing protection against microbial invasion whilst being thin enough to allow the absorption of nutrients .
Give one location of where you would find Simple Columnar epithelium? Expand on their function in this location
-Small Intestine
-In the gut these cells need to facilitate active absorption of the nutrients
-also provide a physical barrier to invasion of microbes
*Tissue needs to balance these 2 functions by providing protection against microbial invasion whilst being thin enough to allow the absorption of nutrients .
What is ciliated simple columnar epithelium?
Single layer of columnar cells with cilia on the apical surface.
What is the function of Ciliated Simple Columnar and where would you find it?
-Ciliary action facilitates movement e.g. transport of ovum from ovary to uterus
-Located in the female reproductive tract.
What is The function of Pseudostratified Epithelia?
-Lines respiratory surfaces
-Rhythmic movement of cilia propel surface layer of mucus containing trapped particles towards pharynx
How can you distinguish between pseudostratified columnar ciliated epithelium and simple columnar ciliated?
By the position of the nuclei- all at different heights in pseudostratified epithelia where as they’re all towards the basal surface of the cell.
Where would you find Pseudostratified columnar ciliated epithelia?
-Airways of respiratory system
(respiratory epithelium)
Why do some cells of ciliated simple columnar tissues not have cilia on their apical surface?
- They are specialised types of simple columnar cells called goblet cells
What are goblet cells?
-Modified columnar epithelial cells packed full of mucin granules.
-Do not have cilia on their apical surface
What is the function of goblet cells?
-Synthesise and secrete mucus
What is the function of goblet cells?
-Synthesise and secrete mucus
Describe the location of goblet cells?
-Scattered throughout simple columnar epithelium
can also be found in;
-Respiratory
-Gastrointestinal Tract
Although rare, where stratified epithelia found, their role is primarily what?
Secretion
Location and function of stratified cuboidal epithelia?
Location;
-Rare but found in some secretory ducts and glands
Function;
-Secretory
Location and Function of stratified columnar epithelia?
Location;
-Rare
-Male urethra and lining of tissue
Function;
-Secretory and Protective
What is the most common form of stratified epithelia?
Stratified Squamous Epithelia
What is the function of stratified squamous epithelia?
Protection from mechanical abrasion
What is the function of stratified squamous epithelia?
Protection from mechanical abrasion
What is stratified squamous epithelia named after
After the shape of the cells at the apical surface, some cells towards then basal layer are cuboidal in shape
What is stratified squamous epithelia named after
After the shape of the cells at the apical surface, some cells towards then basal layer are cuboidal in shape
What are the cells doing In stratified squamous epithelia?
Continuously dividing
Cells in stratified squamous epithelia are continuously dividing, but where are they dividing and maturing from?
From the basal layer, so mature from basal layer from continuously dividing stem cells
What does stratified squamous epithelium shed?
Anucleate Squames
Describe the process of how stratified squamous epithelia sheds anucleate squames?
-The cells are forced to move towards the surface as new dividing cells are formed by division underneath
-As they are pushed towards the surface they become flatter and flatter and eventually die at the surface
-These dead cells are shed and are known as anucleate squares
Give examples of where you would find stratified squamous epithelium
-Epidermis of skin
-Oral Cavity
What 2 classifications can stratified squamous epithelia be?
Keratinised or non-keratinised
Where do you find the keratin layer of epithelia?
On the apical Surface of the epithelium
Where do you find the keratin layer of epithelia?
On the apical Surface of the epithelium
What will be at the surface of
A) Keratinised
B)Non- Keratinised epithelium
A) Keratin
B) Dead/ Flattened Squames
All epithelia contain keratin proteins, so are all epithelial tissues classed as keratinised?
No- the type of keratin in tissues classified as keratinised epithelia will form at the apical
Explain how epithelia forms at the apical surface of epithelial tissues?
-As the epithelial cells migrate towards the surface and become more mature, they begin to cross-link accumulating keratin filaments.
-Resulting in the very tough non living keratin layer on the surface of the tissues
What does the keratin layer of stratified squamous epithelia provide?
Enhanced resistance to physical stress and waterproofing for the tissue
What does transitional epithelial tissue allow?
Expansion and Stretch
What does transitional epithelial tissue allow?
Expansion and Stretch
How to transitional epithelial cells appear when;
A) Stretched
B)Relaxed
A- Flat
B-Taller
How to transitional epithelial cells appear when;
A) Stretched
B)Relaxed
A- Flat
B-Taller
In what organ would you find transitional Epithelium? and why?
Bladder- as this transitional cell structure allows the bladder to stretch when full and then recoil when empty
In what organ would you find transitional Epithelium? and why?
Bladder- as this transitional cell structure allows the bladder to stretch when full and then recoil when empty
Why does Ulceration arise?
Due to a break in the continuity of epithelium
Give examples of diseases that cause ulceration
Herpetic/ Gingival Stomatitis
Trauma
Describe Herpetic/Gingival Stomatitis
-Infection caused by herpes simplex virus
-Common in young children but can also occur in adults
-Characterised by small pale vesicles on palette and gingiva
-Infection
What is the cancer of the epithelial lining of the mouth called?
Oral Squamous Cell Carcinoma
What is Oral Squamous Cell Carcinoma?
Cancer of the epithelial lining of the mouth
How would you test a lesion in the mouth for oral squamous cell carcinoma?
-Referral of patient
-Lesion would be sampled
-Specimen would be sent off to histopathology unit for examination
How would you test a lesion in the mouth for oral squamous cell carcinoma?
-Referral of patient
-Lesion would be sampled
-Specimen would be sent off to histopathology unit for examination
Describe the formation of Oral Squamous Cell Carcinoma
-Dysplastic Epithelial Cells proliferate in an uncontrolled manner
-They destroy and invade adjacent Tissues
