The Appearance & Classification of Epithelial Tissues ! Flashcards
What is histology?
Study of tissues
How do we study tissues in a lab?
Get a tissue biopsy
Fixation- using a chemical fixative or using liquid nitrogen to freeze it
Dissection- very thin layer so light can pass through
Stain- to highlight structures within cell
Visualisation- light microscopes used most commonly. Electron could be used to see components in detail
Why do we fixate the tissue and what are the 2 methods?
Fixing tissue prevents degradation and helps maintain architecture
Two methods: chemical vs physical
Different fixation for different microscopy e.g. electron microscopy uses osmium tetroxide
How and why do you embed and section tissue?
Embedding and sectioning- embeddiing tissue in wax or plastic resin enabling us to cut very thin sections of tissue using microtome (cutting tool)
Why do we stain tissue?
We stain bc tissues are colourless
able to see different areas of the tissue more easily due to the contrast
What the different types of stains and what do the stain?
Most common stain used is Haematoxylin (H&E) - basic dye
and Eosin- acidic dye
Therefore Haemotoxylin binds to acidic parts of the cell and eosin binds to basic parts of the cell
Other stains:
Masson’s trichrome - for connective tissue
Elastic Van Gieson- stains elastic fibres black
What are some examples of specific stains?
Specific stains- stains for particular proteins
Immunohistochemistry- using an antibody to detect for a specific protein
Immunocytochemistry- different cells attached to fluorescent cell markers
Name the microscopes you can use to view tissue
light microscope- visible light passes through the specimen
confocal microscope- uses light from a laser to excite a specimen within a narrow plane of focus (detect proteins using filters)
SEM- beam of electrons is produced at the top of the microscope by an electron gun. It follows a vertical path through the microscope, which is held within a vacuum.
TEM- electrons travel through a vacuum. Electromagnetic lenses used to focus the electrons into a thin beam which is directed through the specimen
What are the 4 basic classifications of tissues?
1) Muscle- specialised contractile tissue responsible for movement
2) Nervous tissue - responsible for transmitting electrical signals around the body
3) Connective tissue- highly prevalent, has supportive role
4) Epithelial tissue- form sheets of cells
What is epithelium?
Epithelium means “upon nipple”
Epi- upon
Epithelial cells are found UPON body- skin, lining vessels, lining all your tracts
What are the 2 types of epithelium?
Covering: lines cavities ad cover surfaces
Glandular: secretory epithelia cells- formed when cells invaginate inwards that allow secretion
What is the structure of epithelial tissue?
Cells form cell to cell junctions and adhere to a basement membrane
The side of the cell is refered to as the basal
What is the basement membrane?
Basement membrane is a specialised connective tissue that forms a scaffold on which the cells can attach to
Also forms barrier to prevent paracellular transport of materials between outer environment and the tissue
What is the basement membrane made out of?
Basement membrane is made of the basal lamina and reticular lamina
Basal lamina is a part of the basement membrane and is secreted by the epithelial cells.
H&E will not allow us to see these components therefore Peiodic acid- Schiff (PAS) stain would need to be used
What is the first part of the nomenclature of epithelial tissue?
1) Number of layers
Simple = one cell thick, usually found in areas that have secretory or absorbatory functions e.g. GI tract
Stratified/ compound = multiple layers, more suited for protection e.g skin, oral and anal cavity
What is the second part of the nomenclature of epithelial tissue?
2) Shape of the cells
Cuboidal- round, cube shaped
Involved in secretory and absorptive functions
Columnar- taller than wider
Found in the GI tract and gull bladder
Squamous- flat
Specialised for absorption as they have a thin barrier to allow for fast exchange of materials. Found in lungs, capillaries etc
What is the third part of the nomenclature of epithelial tissue?
3) Specialisations?
E.g. cilia- small hair like structures of the surface of cells
Keratin- skeletal protein that becomes extracellular when produced in high levels at the surface of the skin
Micro villi not mentioned when naming epithelial tissue bc they are so prevalent in epithelial cells
In cells with keratin, when naming it, you look at the top layer of cells and identify what it is
What is microvilli?
○ small membrane projections on apical border
○ contains cores of actin filaments
○ function to increase epithelial cells’ apical SA for absorption
○ They tend to be found in absorptive surfaces (GI system)
What is stereocilia?
○ Long and branched microvilli
○ non-motile
○ increase SA for diffusion of molecules in and out of the cells in epididymis and ductus cells (tissues of male reproductive tract)
What is cilia?
○ highly motile large projections with core of microtubules (9 + 2 arrangement)
○ Surrounded by the cell membrane
○ rapidly move forwards and backwards using ATP
○ The often waft mucous, (secreted by the goblet cells) forming the muco-ciliary escalator.
What are the layers of keratinisation?
○ The further cells get away from the basal membrane the harder it is for them to get their support (nutrients) resulting in their death
○ Keratinized epithelium, is composed of numerous layers of dead squamous cells which are specially structured (by further secretions) to be waterproof and reduce evaporation from underlying tissues. This protects the underlying tissue.
What are goblet cells?
○ specialised columnar epithelial cells
○ synthesise & secrete mucus
○ found in respiratory & GI tracts
- mucus traps particulates & bacteria so they can be swallowed and be destroyed by the acid in the stomach
- Mucous helps prevents acid attack on the cells of the GI tract
- Mucous reduces friction between surfaces
What is the order for naming epithelial tissue?
Name order- Specialisation, number, shape “ epithelium”
What are the exceptions of classifications?
Pseudostratified epithelium- cells look like they are on top of each other when in fact they’re all adhered to the basement membrane. Found in the respiratory tract
Transitional epithelium- stratified epithelium which changes shape of cells depending on the environment.
Found in urinary system- also referred to as urothelium.
Can turn into squamous cells when the bladder is full allowing stretching to occur when the bladder is full
