Epithelia Flashcards
What is the function of epithelia?
Protects, filters, secretes, absorbs and excretes
Where is epithelia found?
Covers body surface (e.g. skin) and hollow organs, cavities and ducts. It also forms the glands of the body
How are the cells of an epithelium held together?
by a variety of cell junctions
How can epithelia be arranged?
In continuous sheets as single or multiple layers
What are epithelia separated from and how are they separated? What does this make them?
Epithelia are separated from all other tissues (they are just above connective tissue)
They are separated by a basement membrane (BM)
This makes them avascular
What is the function of BM (besides separating epithelia from connective tissue?) Give a practical example of BM’s function
Supports the overlain epithelium, provides a surface along which epithelial cells migrate during growth and wound healing and acts as a physical barrier (e.g. with melanoma, if it is above BM then chance of survival is 95-100%, once it gets below it, e.g. into blood stream, survival drops quickly the deeper it is)
Epithelia are avascular, what does this mean? Do they have nerves? How do they get nutrients?
Epithelia cells don’t have any capillaries within cells, they do have nerves
Diffusion from vessels in connective tissue
What are cytoskeleton made of? What do they do within the cell?
Microfilaments (Actin): bundles beneath cell membrane and cytoplasm, gives cell strength, alters cell shape and ties cells together Intermediate filaments (Keratin): thicker than actin therefore gives cells more strength and helps move material through cytoplasm
What are the names of the different junctions?
Tight junctions, Adherens junction, Desmosome, Hemidesmosome, Gap junction
What are the three surface of a cell called? What are their relative locations to each other?
Apical (top exposed surface), lateral (side where the cells are touching each other) and basal (surface of contact with BM)
What is the function of the tight junction?
Maintains the cell polarity seperate from the neighbouring cells
How do the tight junctions keep the cells polarity seperate?
It is electrically tight (e.g. no ions can pass through gap in cell therefore control electrolyte balance on either side) and prevent migration of proteins between apical and basal surfaces surface
What else do tight junctions do other than create a ion barrier? what two proteins are particularly important in all of its roles?
Join cytoskeletons of adjacent cells together, Claudins and Occludins
What is the function of adherens junctions?
Holds two adjacent cells together by the microfilament (actin)
How do adherens junction perform their function?
Actin in the cell is attached onto plaque adhesion belts. These bond onto catenin (protein) through the cell membrane onto cadherins (another protein) which bridges the intercellular space connecting it to another cell via catenin–>plaque–>actin
What are the key proteins involved in tight junctions?
Claudins and Occludins
What is the function of the Desmosome? What forces does is this bonding good at resisting? Where can you find these bonds more often based on the forces it can resist?
Holds two adjacent cells together by the intermediate filaments (keratin) and is able to resist shearing forces so found a lot in muscles cells
How does the desmosome perform its function?
Similar to adherens junction, keratin is attached onto plaque in discrete connection points (stringy fibres attached onto discrete plaque pads instead of belt) which is then attached onto catenin which is joined through intercellular space by caderin etc.
What are the key proteins involved in the bonding of the cytoskeleton’s of neighbouring cells? What are their functions
Catenin (bind plaque onto cell membrane) and Cadherins (bind cell membranes together)
What is the function of gap junctions?
It is a communication channel between cells by allowing small molecules (e.g. Na+, K+, ATP, NADP and small bits of DNA) to pass through
What is the structure of a gap junction?
Connexins are imbedded in the plasma membrane and when the connexins from the other cell join it creates a hydrophilic channel
How many connexins and connexons are there per junction? What are connexons?
12 connexins = 2 connexons, 6 connexins per connexon = hemichannel
What is the function of hemidesmosome?
Connect the epithelia cell to the BM
How does hemidesmosome perform its function?
Discrete plaque pad connects onto keratin from the cytoskeleton . The plaque is attached onto the laminin through the cell membrane onto the BM by using integrin (in the place of cadherin)
What is the BM made of?
Basal lamina and Reticular lamina
What is Basal lamina made of and how is it made?
Made of collaged, laminin, other proteoglycans (FYI protein that is found widely in the connective tissue) and glycoproteins (FYI any protein which has a carbohydrate attached to it)
It is secreted by the epithelia cells
What is Reticular lamina made of and how is it made?
Contains fibrous proteins such as fibronectin and collagen
Produced by cells of underlying connective tissue, fibroblasts
Where is the BM found?
Between the epithelium and connective tissue
How is epithelia classified?
According got the arrangement of the cells in layers and the shape of the cells
What are the different arrangements of the cells? Explain their arrangement and function
Simple - single layer, secreting, absorption and filtration
Stratified - two or more layers, protective
Pseudostratified - non-regular arrangement of cells makes it appear as if cells are not all touching the BM (therefore multiple layers), however they all are, secretion
What are the different cell shapes? Describe them and their function
Squamous - flat and thin, diffusion
Cuboidal - about as tall as they are wide, secretion and absorption
Columnar - more tall than wide, secretion and absorption
Transitional - change shape from flat through cuboidal (e.g. allow for stretch), tissue that undergoes stress
Describe the simple squamous epithelium and and example of it in the body
Thin flat and irregular arrangement, it is a very delicate single cell layer used in filtration (kidney), diffusion (lung), secretion (serous membrane) or slippery surface needed
What are the subtypes of simple squamous layer? Where would they be found?
Mesothelium - inside cavities or organs and surrounding the heart
Endothelium - inside of hear and blood vessels
Describe the simple cuboidal epithelium and and example of it in the body
Single cell layer where height is the same as cell width, it is anywhere where there is secretion and absorption (e.g. pancreas ducts, lens surface)
Describe the simple columnar epithelium and and example of it in the body
Large volume of cytoplasm (so there can be more organelles in them) as they are tall and rectangular/hexagonal in shape with a nuclei often elongated, e.g. cilia or microvilli
What are the subtypes of simple columnar epithelium?
Non - ciliated simple columnar epithelium
Ciliated simple columnar epithelium
Describe the stratified squamous epithelium and and example of it in the body
Multiple layers of thin flat cells stacked onto of each other, are where mechanical/chemical stress is severe (e.g. skin, lining of mouth)
What are the two types of stratified squamous epithelium? What is the difference between them and where would you find them?
Keratinised: dead surface cells leave behind their keratin therefore stronger, e.g. skin
Non-keratinised: no dead cells left over for keratin deposition, e.g. oesophagus, mouth
What are the two types of pseudostratified epithelium?
What makes them different?
What different functions do they have?
Where would you find them?
Ciliated: have goblet cells in layers, secrete and move mucus e.g. upper respiratory tract
Non-ciliated: have NO goblet cells, absorb and protect e.g. larger ducts
What is a gland?
A single cell or a group of cells that secrete substance into ducts, onto a surface or into blood
What are the two types of glands? What are their functions?
Endocrine gland: secrete directly into blood by traversing interstitial fluid
Exocrine gland: Secrete into ducts that empty onto the surface covering/lining epithelium
Do all glands perform either endo or exocrine functions? Give an example
No, some glands perform both e.g. pancreas secretes into ducts and into the blood
What are the three characteristics of multicellular gland naming?
1 - structure of duct (e.g. branding/non-branching, simple/compound)
2 - structure of secretory area (e.g. shape)
3 - relationship between 1 and 2
What does a simple tubular gland describe?
Simple = single duct that does not divide on its way to the gland Tubular = straight tube to gland
What does a simple branched tubular gland describe?
Simple = single duct that does not divide on its way to the gland Branched = several secretory area share a duct Tubular = straight tube to gland
What does a simple branched alveolar gland describe?
Simple = single duct that does not divide on its way to the gland Branched = several secretory area share a duct Alveolar = forms a sac like pocket
What does a compound tubular gland describe?
Compound = multiple ducts leading onto gland Tubular = straight tube to gland
What does a compound tubuloalveolar gland describe?
Compound = multiple ducts leading onto gland Tubuloalveolar = where the secretory cells have both tubes (tubular) as sacs (alveolar)
