Basic Cell Types Flashcards
What are the four basic tissue types?
Epithelial tissue
Supporting tissue
Muscular tissue
Nervous tissue
What are epithelial tissues?
A diverse group of tissues including surface epithelia and solid organs
What exactly do surface epithelium cover?
All body surfaces, cavities and tubes and are therefore the interface between different compartments
What is the function of surface epithelium?
Containment, selective diffusion, absorption, secretion and physical protection
What is cytokeratin and what is it involved in?
Cytokeratin is present in all epithelial cells as an intermediate filament and allows for recognition by immunohistochemistry
All epithelium are supported by a…
basement membrane
What does the basement membrane do?
Separates the epithelium from the underlying supporting tissue
Blood vessels never cross epithelial basement membranes so how do epithelial cells obtain their needs?
They are dependent on diffusion of nutrients and oxygen from connective tissue for survial
Epithelial cells are polarised, what does this mean?
One side faces the basement membrane and one side is towards the surface
What is the side of the epithelial cell that faces the BM called and what is the side of the epithelial cell that faces the surface called?
The basal surface and the apical surface
Epithelial cells are classified according to three morphological characteristics, what are these?
- Number of cell layers
- Shape of component cells
- Presence of surface specialisations
When epithelial cells are classified according to the number of cell layers, what does this mean?
They can either be simple which means they consist of one layer or they can be stratified which means they are multilayered
When epithelial cells are classified according to the shape of the component cells what does this mean?
Based on appearance at right angles to the epithelial surface. They can be squamous, cuboidal or columnar - simple epithelia. In stratified the surface shape determines the name
When epithelial cells are classified according to the presence of surface specialisations what does this mean?
It means the presence of specialisations such as cilia / keratin
There are different types of simple epithelia, list them.
- Simple squamous epithelium
- Simple cuboidal epithelium
- Simple columnar
- Pseudostratified columnar ciliated epithelium
Describe the structure of simple squamous epithelium
Flattened, irregular shaped cells forming a continuous surface often called pavemented epithelium
Where are simple squamous epithelium found and why?
Found as lining surfaces involved in diffusion of gases .g. lungs or fluids e.g. blood capillaries
Sometimes simple squamous epithelial cells are difficult to recognise because they are too flattened. How do they sometimes show up under the microscope?
They can only be recognised by the nucleus which bulges into the lumen
What are simple cuboidal epithelial cells?
They are the intermediate between simple squamous and simple columnar
Describe the nucleus in a simple cuboidal cell.
Round and located in the centre of the cell
Where are simple cuboidal epithelium cells found and what functions do they play? Give an example
Line small ducts and may have excretory, secretory or absorptive functions, e.g. collecting tubules of kidney
The cell borders in simple cuboidal cells are often indistinct so how would you be able to recognise these cells under a microscope?
The nuclei gives a clue to the cell shape, the nucleus is round and located in the centre of the cell
Describe simple columnar epithelial cells
They are like cuboidal cells but they are taller
Describe the nucleus in a simple columnar epithelial cell
They are elongated and may be located towards the base, apex or centre of the cytoplasm
Where are simple columnar epithelial cells found and give examples?
On absorptive surfaces e.g. small intestine, gall bladder (absorbs water)
or play a secretory role, e.g. the stomach
Explain why the pseudostratified columnar ciliated epithelium are considered to be a true simple epithelium
All the cells rest on the basement membrane. The nuclei are all at different levels giving the appearance of different cell layers.
Where are pseudostratified columnar ciliated epithelium found?
Confined to airways so known as respiratory epithelium.
The pseudostratified columnar ciliated epithelium have cilia on them which propel the mucus to the pharynx, what is the term applied to this?
Mucociliary escalator
What are stratified epithelia?
Defined as epithelia consisting of two or more layers
What is the main function of stratified epithelia?
Mainly a protective function
Why are stratified epithelia poorly suited for absorption and secretion?
Due to the thickness of all the cell layers
What is the classification of stratified epithelium based on?
Cell shape and structure
What are the three types of stratified epithelium mentioned on the lecture slides?
- Stratified squamous epithelium
- Stratified cuboidal epithelium
- Transitional epithelium (urothelium)
Describe stratified squamous epithelium
Flattened cells at the top (surface) and cuboidal cells at the base (basement membrane)
Which type of stratified squamous epithelium constitute the epithelium of the skin?
Keratinising stratified squamous epithelium
How are keratinising stratified squamous epithelium specialised for their function?
Specialised to withstand constant abrasion and desiccation due to touch non living surface layer composed of keratin wrapped in plasma membrane
What happens to the nucleus of the epithelium of stratified squamous epithelium as they mature?
The nuclei are eventually lost
Describe the structure of stratified cuboidal epithelium
Thin stratified epithelium usually two or three layers of cuboidal cells only
Where are stratified cuboidal epithelium cells found?
Lining of larger excretory ducts of exocrine glands, e.g. salivary glands
The stratified cuboidal epithelium is more robust than simple epithelium. Also, they are not involved in any significant
secretory or absorptive activity
Where are transitional epithelium found?
Only in the urinary tract in mammals
Why are transitional epithelium only found in the urinary tract?
Because they are highly specialised to accommodate stretch and the toxicity of urine
What are the features of transitional epithelium like?
Intermediate between stratified squamous epithelium and stratified cuboidal epithelium
Describe the structure of transitional epithelium found in the urinary tract when stretched and relaxed.
When relaxed, they are rounded and large (u - like an umbrella lol) when stretched the surface layers and intermediate layers are extremely flattened
List three membrane specialisations of epithelia
- Cilia
- Microvilli
- Goblet cells
What are cilia?
Motile structures that project from the luminal surface of epithelial cells
Where are cilia mostly found?
In the female reproductive tract and the respiratory tract
Cilia may be how many micrometres long and a cell may have up to how many cilia?
10 micrometres, and a cell may have up to 300 cilia
Are cilia easily seen via light microscopy?
Yasss!
What are microvilli?
Minute fingerlike projections of the luminal plasma membrane found in epithelia that are specialised for absorption
Up to how many times can microvilli increase the surface area?
x30 times
Can cilia be resolved by a light microscope?
No and they appear as a brush border
Give an example of where microvilli are found
The small intestine
What are goblet cells?
Modified columnar epithelial cells that synthesise and secrete mucus
Where are goblet cells found?
Scattered amongst many simple epithelia particularly the GI and respiratory tract
What is PAS staining?
A staining method used to detect polysaccharides such as mucosubstances - glycoproteins, glycolipids
What colour do goblet cells stain with PAS staining?
Bright pink
Why do goblet cells stain bright pink with PAS staining?
Due to the secretions of mucus
Epithelium that is primarily involved in secretory purposes is arranged into…
glands
What are glands?
Invaginations of the epithelial surface which proliferate into the underlying connective tissue
All glands have a continous basal rate of secretion which is then modulated by…
nervous and hormonal influences
What are exocrine glands?
Glands that release their contents onto an epithelial surface either directly or via a duct
Where are exocrine glands found?
Vary from microscopic swear glands of the skin to large solid organs such as the liver
The exocrine glands are divided and classified according to two traits what are these?
The secretory component and the duct system
The secretory component of a gland may be
tubular or acinar, coiled or branched
The duct system of an exocrine gland may be
branched (compound) or unbranched (simple)
Where are simple tubular glands found?
In the large intestine
Describe a simple tubular gland
A single straight tubular lumen into which the secretory products are discharged - the secretory cells line the entire duct
Give an example of a simple coiled tubular gland
Sweat glands are the only type of example
Describe a simple coiled tubular gland
Tightly coiled in 3d so different portions are seen in each plane of section
Where are simple branched tubular glands found?
Mainly in the stomach, mucus secreting glands
Describe a simple branched tubular gland
Several tubular secretory portions which converge onto a single unbranched duct
What are endocrine glands?
Glands that have lost their connection to the epithelial surface during development and release secretions directly into the blood
Give an example of an endocrine gland
The thyroid gland
What are secretions from endocrine glands mainly controlled by?
Metabolic factors such as glucose, secretion of other hormones and/or the nervous system
Describe what endocrine glands look like
Contain clusters of secretory cells, each with their own basement membrane, surrounded by a rich network of blood vessels
Where do endocrine glands release their secretions such as hormones?
Into the intercellular spaces from where they diffuse rapidly into the blood
