Epithelia, Cell Division and Polarity Flashcards
What are the three types of epithelial tissue and what do they cover?
-Mesothelium - lines organs, body cavities, blood vessels and ducts
-endothelium - lines inner surface lining of blood and lymphatic vessels
-glandular epithelium - forms glands
What are the general features if epithelial tissue?
-closely packed cells with very little extra cellular matrix
-continuous sheets
-have different surfaces : apical surface, lateral surface facing adjacent cells, basal surface attached to the basal lamina
Give some features of the epithelial tissue structure and their functions
-they have cytoskeleton linked anchoring junctions, these bind epithelial cells tones higher and to the basal lamina
-gap junctions allow molecules to pass from cell to cell
-its polarised hence leak proof to create tight junctions. This allows the epithelial to form barriers to separate biological compartments and so regulate homeostasis by controlling the ion and solute transport
Give the general features of epithelial cells
-avascular
-supplied by nerves
-they have a high capacity for renewal
What epithelial tissues are an exception for the general feature of a high capacity for renewal?
Corneal endothelium and retinal pigment epithelium
What are the 6 types of epithelial tissue?
Simple:
-squamous
-cuboidal
-columnar
Stratified
-squamous
-cuboidal
-pseudo(stratified)
-columnar
Transitional: multiple layers of epithelial cells which look cuboidal when they contact and squamous when they expand
Give examples of simple squamous cells and give the functions
Examples: linings of the peritoneal, pleural and pericardial cavities, glomerulus of the kidney, alveoli of lungs and lymphatic vessels
Functions: filtration, diffusion, osmosis and secretion
Give examples and the functions of simple cuboidal
Examples: anterior surface of the crystalline lens, retinal pigment epithelium, surface of ovary, lining of kidney tubes, lining of smaller ducts of many glands such as thyroid
Function: secretion and absorption
Give examples and the functions of simple columnar
Examples: there’s
non ciliated = lining of the gastrointestinal tract, lining of ducts of many gland
ciliated = lining of upper respiratory tract, uterine tubes and uterus
Function: secretion, absorption and moving substances
Give examples and the functions of pseudostratified
Examples: the ciliated epithelium of the trachea of the upper respiratory tract, larger ducts of glands such as the pseudostratified columnar epithelium in the stereocilia of the epididymis
Functions: ciliated= secretion and movement of mucus, non ciliated= absorption and protection
Give examples and the functions of stratified squamous
Examples: epidermis (most keratin), linings of the mouth, oesophagus and vagina (medium keratin), corneal epithelium and tounge epithelium (non - keratinised)
Function: protection
Give examples and the functions of stratified columnar
Examples: parts of urethra, large excretory ducts of some glands, gland in oesophaghs, makes up the conjunctiva
Function: protection, secretion
Give examples and the functions of stratified cuboidal
Examples: ducts of sweat glands, glands in oesophagus, male urethra
Function: protection, sometimes secretion or absorption
Give examples and the functions of stratified transitional
Examples: the transitional epithelium of the urinary passages urothelium, lining of urinary bladder and portions of urethra and ureters
Function: permits distension
What are the types of glandular epithelium
- Endocrine glands: they produce hormones and secretes them into the blood
- exocrine glands: secrete sweat, oil, earwax, saliva and digestive enzymes into ducts
What is cell adhesion for?
-to organise cells into tissues to allow them to be held by cell-cell and cell-extra cellular matrix adhesions
-to spread mechanical stress across a tissue
-to allow for the cell division of mammalian cells
What are the 5 types of cell junctions
Tight junctions
Adherents junctions
Desmosomes
Gap junctions
Hemidesmosomes
What two proteins span through the extra cellular space in tight junctions?
Claudins and occludins
What proteins are bound on the inner cystosolic side of the cells in tight junctions and what is bound to those proteins
Zona occludins, actin filaments
What do tight junctions do?
They act as a diffusion barrier and block the transport of ions and different types of molecules between the cells
What surface do tight junctions connect the cells?
At the apical surface
Where are you likely to find tight junctions?
-blood brain barrier and blood retina barrier
-gastrointestinal tract
What proteins span across adherence junctions and what molecule is between the proteins?
E - Cadherins which bind with each other via the calcium ion hence cadherins are calcium dependant proteins
Which proteins is on the inner cytosolic side of a cell in adherens junctions? Give it in order going in to out
Vinculin, catenin, actin filaments
What is the function of adherence junctions?
They withstand shearing and abrasive forces to allow for stretch
What surface of cells do adherence junctions connect to in comparison to tight junctions
They’re are more basal than the tight junctions
Give examples where adherence junctions are found
-urinary tract
-respiratory tract
-blood vessels
-the skin
What are desmosomes made out of
Cadherins being desmoglein and desmocolin with calcium between them, Desmoplakin bound to the cytosolic part of the membrane and then intermediate filaments on the most cytosolic side that contain keratin
What are desmosomes for?
High tensile stress
Give examples where you might find desmosomes
Cardiac tissue- cells are held by intercollated disks which consist of the desmosomes and gap junctions
Skin- to bind the epidermal cells to each other
What are hemidesmosomes?
They are the connection of the cell to the basal lamina
What does the basal lamina consist of?
Fibronectin, laminin and collagen
What is the protein that spans through the cell and connects it to the basal lamina?
The integrin and this has intermediate filaments mainly made of keratin attached to it
What do hemidesmosomes do?
They form the basement membrane via the connection between the basal lamina and the epithelium above it
Where are hemidesmosomes found? Give an example
In epithelial tissue for example the skin
What’s a good video to watch on cell junctions?
YouTube, cell junctions by ninja nerds
What proteins make up gap junctions?
2 Connexons. Each connexon is made up of 6 connincs
What do gap junctions do?
Allow for cell-cell communications by allowing for ion transfer such as Na+ and Ca2+ as well as transfer molecules such as cAMP- useful in cells that get excited
Where are gap junctions most useful in?
Cardiac tissue’s intercollated disks
Smooth muscle tissue such as the GIT
Neurons
Which intercellular junctions provide cells with ability to transfer small signalling molecules from one cell to another?
gap junctions
which intercellular junctions are the closest to the apical surface of epithelial cells?
occluding junctions
which of the following proteins serve as transmembrane linker proteins in adhering junctions?
cadherins and integrins
in which adhering intercellular junctions are the intermediate filaments of the cytoskeleton linked with the transmembrane linker protein via the intracellular attachment proteins?
spot desmosomes
give 4 things that happen as a result of depletion of extracellular calcium
-intercellular binding through zonula adherens and macula adherens is broken
-calcium dissociates from cadherins molecules
-binding between cadherin dimers is disrupted
-intercellular binding via belt desmosomes is disrupted
which intercellular junctions are responsible for providing blood-retina barrier?
zonula occludens
how many helical subunits does a connexin have?
4
