Epithelial tissue Flashcards
Function of epithelial tissues
- Covers body surfaces
- lines hollow organs
- forms the glands of the body
What are cell junctions
Cell junctions are connection points between the plasma membranes of adjacent cells.
There are namely 5 types: gap junction, adherens junction, desmosomes, hemidesmosomes, and tight junction.
Key functions of epithelial tissues
A group of similar cells that work together to cover body surfaces and line hollow organs, body cavities, and ducts; it also forms glands.
- selective barriers (limit or aid transfer)
- secretory (onto a free surface)
- protective (especially from abrasion)
What do each arrow point to
- Tight junction
- adherens junction
- Gap junction
- Desmosome
- Hemidesmosome
What is the apical surface
The edge surface of epithelial tissue facing the body surface, body cavity, lumen of an internal organ, or a tubular duct that receives cell secretions. They may contain cilia or microvilli
What is the lateral surface
The surface of an epithelial cells which face the adjacent cells on either side - these surfaces contain junctions (gap, desomosome, tight, adherens)
What is the basal surface
The deepest layer of epithelial cells facing the basement membrane - these may contain hemidesmosome junctions.
Cytoskeleton - Microfilaments
- bundles beneath cell membrane and cytoplasm; strength; alter shape; link cytoplasm to membrane; tie cells together; muscle contraction e.g actin
Cytoskeleton - Intermediate filaments
- strength; move materials through cytoplasm e.g keratin
How are epithelial cells arranged
Arranged into flat, continuous sheets and can be comprised of single or multiple layers
What is actin
A type of microfilament - protein bundles beneath cell membrane and cytoplasm that determine cell shape and structure and allow for muscle contraction
What is keratin
A type of intermediate filament - structural roles in the cytoplasm of cells, also allow movement of material within cytoplasm
Structure of tight junctions
Located near the apical surface
Strands of transmembrane proteins (claudins and occludins) link adjacent plasma membranes in a ‘sewing-like’ appearance
No gap is left
Function of tight junctions
Joins adjacent plasma membranes tightly together keeping cell polarity (ie electrically tight) by preventing migration of proteins between apical and basal surfaces
What cell junction is this
Tight junction
Where are tight junctions located
Stomach, intestines, and bladder
What are claudins and occludins?
Transmembrane proteins that form the tight junction
Structure of adherins junction
Located near the apical surface
Two plaques (patches of protein tissue) on each membrane linked together by transmembrane glycoproteins (cadherin) - belt-like appearance
What do the cadherins do in the adherens junction
Span the gap but links cell surface to Keratin
What do the catherins do in the adherens junction
Link the cadherins to Actin
Adherens junction prevents __ ____ from tensions forces like in contractions
Cell separation
What cell junction is this
Adherens junction
Structure of the desmosome junctions
A lateral wall and has plaques
What is the similarity between adherens and desmosome junctions
Both have plaques
What is the funciton of the desmosome junction
Resist shearing forces
What cell junction is this
Desmosome
What does keratin do in desmosome junction
Spans from one desmosome to another on other side of the cell - structural integrity
Where are desomosome junctions most commonly found
Skin epithelium and cardiac cells of the heart to prevent pulling apart
What is the structure of the gap junction
6 connexin protein molecules form a connexon or hemichannel.
2 hemichannels make up a gap junction
What is the function of the gap junction
Opens up a tunnel from one cell to another, and sends messages (irons, RNA etc.) and allows cell tissue communication. Also coordinated movement
What cell junction is this
Gap junction
How can gap junctions communicate
Open up a tunnel from one cell to another, send messages (ions, RNA etc)
What is the function of the hemidesmosome
- Connects epithelia to basement membrane.
- Links cellular basal intermediate filamentt (keratin) to basement membrane
What does integrin linker protein do in the hemidesmosome
Instead of cahderin, binds to the laminim in the BM and to Keratin (IF in cytoplasm)
True of false: not all epithelia overlay a basement mebrane
False, All epithelia overlay (2 parts)
True of false: not all epithelia overlay a basement mebrane
False, All epithelia overlay (2 parts)
What are the two parts of the basement membrane
- Basal lamina
- Reticular lamina
BM
What is the basal lamina secreted by and what does this contain
Secreted by epithelia cells contaning collage, laminim, other proteoglycans and glycoproteins etc.
What is the reticular lamina produced by and what does the RL produce
Cells of underlying connective tissue known as fibroblasts.
Produces fibrous proteins such as fibronectin, collagen etc
Where is the basement membrane found
Between epithelium and connective tissue
Epithelia are avascular, what does this mean
They contain nerves but do not contain blood vessels
How does exchange of nutrients and wastes take place by in the BM
Diffusion from vessles in the connective tissue
Functions of the basement membrane
- Supports overlying epithelium
- provides surface along which epithelial cells migrate during growth and wound healing
- acts as physical barrier
- participation in filtration of substances in kidney
What are the two types of epithelial tissue
Covering and lining, and glandular
What does covering and lining epithelia form
- form outer covering of the skin and some internal organs
- form inner lining of blood vessles, ducts, and body cavities, and the interior of the respiratory, digestive, urinary and reproductive systems.
What is the function of the glandular epithelium
Constitute the secretory portion of glands.
What do simple epithelia do
Single layer for secretion, absorption and filtration
Function of stratified epithelia
Protective
Pseudostratified epithelia
Not all reach apical surface but all cells are in contact with the BM
What does squamous shape help
Flat and thin shape helps allow passage by diffusion
What does cuboidal shape allow
Tall and thin as they are wide (for secretion and absorption)
What does columnar shape do
Tall and wide; for secretion and absorption
What is transitional epithelium and what is its funciton
A stratified epithelium which cells change shape from cuboidal to flate depending on organ shape; allow stretch e.g urinary bladder
What epithelial cell is this
Simple squamous
What is the most delicate epithelium
Simple squamous
Regards to their funciton
Where is simple squamous epithelium
Where filtration (kidney); diffusion (lung); secretion where slippery surface needed (e.g outer layer of serous membrane)
Appearance of simple squamous
Thin, flat somewhat irregular cells like fried eggs
What are the two specialised subtypes of simple squamous epithelium
- Mesothelium: lines pericardial, pleural, peritoneal cavities
- Endothelium: lines inside of heart, blood and lymphatic vessels
What are location examples of simple squamous
- Bowman’s capsule of kidney
- cardiovascular and lymphatic systems
- inside eye
- alveoli of lungs
- visceral cavity linings
- inside blood vessels
- inside heart
What does serous membrane (serosa) in simple squamous line/found
Lines the body cavity and viscera
Features/function of simple cuboidal epithelium
Where there is secretion and absorption
Location examples of sumple cuboidal epithelium
- Pancreas ducts
- parts of kidney tubules
- anterior surface of lens
- pigmented epithelium at posterior of retina
- secretory part of some glands like thyroid
What do each 5 parts of the microvili labelled
- microvolli
- cytoplasm
- nucleus
- basal lamina
- loose connective tissue
What epithelial tissue is this, and label all four sectinons on the right
- simple cuboidal epithelium
- nucleus of simple cuboidal cell
- lumen of duct
- connective tissue
Features of simple columnar epithelium
More cytoplasm so more organelles
Two major subtypes of simple columnar epithelium
- non ciliated
- ciliated
What epithelial tissue is this
Non ciliated simple columnar epithelium
What epithelial tissue is this
Ciliated columnar epithelium
What are goblet cells
Modified colunar cell: full of mucous, sit in intestinal wall, squirts mucous for lubrication in large instestine for faeces.
Location examples and functions of of non-ciliated columnar epithelium
Lines gut mucosa from stomach to anus; ducts of many glands’ gall bladder
Function: secretion and lubrication (goblet); and absorption
Does only one or both ciliated and non-ciliated simple columnar epithelium have goblet cells
Both have goblet cells
Locatione examples of simple columnar epithelium
- Bronchioles
- uterine fallopian tubes
- sinuses
- central canal of spinal cord
- ventricles of brain
Function of simple columnar epithelium
Synchronous movement assists motility of mucus and foreign objects or oocytes
Located where
Featurs of stratified squamous epithelium
- Where mechanical or chemical stresses are severe - some severe places contain keratin which makes surface tough and waterproof)
- all forms protect against microbes
Two subtypes of stratified squamous epithelium
Keratinised and non-keratinised
Location example(s) of keratinised stratified squamous epithelium
Skin
Location examples of non-keratinised epithelium
Mouth, throat, tongue, esophagus, and vagina
What epithelia tissue is this
Non-keratinised epithlium
Function of non-keratinised stratified squamous epithelium
- Protection from abrasion, defence from microbes, require secretions from glands
What epithelial tissue is this
Keratinised simple squamous epithelium
Specialised subtypes of columnar epithelium
Ciliated and non
Does both or only one of either ciliated and non-ciliated columnar epithelium have goblet cells
Non-ciliated none but ciliated does
Examples of locations of ciliated pseudostratified columnar epithelium and function
Located most of upper airways
Secrete mucus and move it
Examples of locations of non-ciliated pseudostratified columnar epithelium and function
Located: larger ducts of glands, epididymus, part of male urethra
Function: absorption and protection
