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 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 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
What are the 3 different sides to a cell?
Apical side (apex/luminal)- cellular specialisations: keratinisation, cilia, microvilli etc
Basal side- anchors to basement membrane
Allows cells to receive nutrients- epithelium is avascular (receives nutrients through diffusion not through the blood stream)
Allows cells to receive nervous innervation
Lateral/ intercellular sides- connecting epithelial cells together via cell to cell junctions
what is the lamina propria and where is it located?
The lamina propria is a layer of connective tissue.
It provides nutrition to epithelium and binds it to underlying tissue.
The area of contact between the epithelium and lamina propria is increased due to the presence of small evaginations called papillae.
Papillae tether the skin to the body.
Epithelial cells are separated from the lamina propria by a sheet of extracellular material called the basal lamina (subsection of basal membrane).
what is mucosa and what are the 3 elements its made up of?
built from 3 elements:
epithelium
basement membrane
lamina propria i.e connective tissue
What the tight junctions?
Tight junctions form a continuous band around each cell just below the apical surface. They prevent the passage of molecules and ions through the space between the plasma membranes of adjacent cells, so materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue.
What are Adherens junctions?
provide strong mechanical attachments between adjacent cells.
What are desmosomes?
They form spot junctions that rivet cells together.
What are hemidesmosomes?
modified desmosomes found at basal surface of the cell. Join the basal surface of the cell to the underlying basement membrane.
What are gap junctions?
Each gap junction contains many channels known as connexons. Connexons (protein) line up physically connecting the two cells by having half of each connexon in either cell. There is a hydrophilic pore in the connexon allowing the passage of ions from the cytoplasm of one cell to another.
