Epithelial cells and tissues Flashcards
Define tissues
- A group of cells whose type, organisation and architecture and integral to its function
- Made up of cells, extracellular matrix and fluid
What is the extracellular matrix?
- Cell deposited material forming part of the extracellular environment
- Generally composed fibrillar (reticular) proteins ie collagen, elastin) embedded in a hydrated gel (proteoglycans or ground substance)
What two ways can extracellular matrix be organised and give examples of each
poorly organised - loose connective tissue
highly organised - tendon, bone, basal lamina
What are the five main cell types and give examples of each
- Connective tissue cells - fibroblasts (many tissues), chondrocytes (cartilage), osteocytes (bone)
- Contractile tissues - (skeletal muscle, cardiac muscle, smooth muscle)
- Haematopoietic cells - blood cells, tissue-resident immune cells and cells of bone marrow from which blood cells are derived
- Neural cells - nervous system cells; neurones (carry electrical signals) and glial cells (support cells)
- Epithelial cells - form continuous layers, these layers line surfaces and separate tissue compartments and have a variety of other functions
What type of cancerous tumours do epithelial cells have?
Carcinomas
What type of cancerous tumours do mesenchymal cells have?
Mesenchymal (connective tissue and muscle) cancers are sarcomas
What type of cancerous tumours do neural cells have?
neuroblastomas (from neurones) or gliomas (from glial cells)
What type of cancerous tumours do haematopoietic cells have?
leukaemia’s (from bone marrow cells) or lymphomas (from lymphocytes)
How is the epithelial cells organised and where are they found?
Make stable cell-cell junctions to form continuous cohesive layers
Line external and internal body surfaces
Cell-cell junctions are key to the formation and maintenance of epithelial layers
What are the three different shapes of epithelial cells?
Squamous - flattened, plate shapes
Columnar - arranged in columns
Cuboidal - cube-like
What are the three different shapes of epithelial cells?
Squamous - flattened, plate shapes
Columnar - arranged in columns
Cuboidal - cube-like
In what two ways are epithelial cells layered?
Single layer - simple epithelium
Multi-layer - stratified epithelium
Where is simple squamous epithelium found? How is it useful?
Lung alveolar sac Epithelium mesothelium (lining major body cavities) endothelium lining blood vessels and other blood spaces
Thin epithelium that allows for gas exchange
Where is simple columnar epithelium found? How is it useful?
Typical of surfaces involved in absorption and secretion of molecules
ie enterocytes lining the gut - involved in the take up of digested products
Where is simple cuboidal epithelium found?
Typical of the linings found in ducts
ie those lining the kidney ducts
Explain the two different types of stratified squamous epithelium
Keratinising -
epithelial cells that produce keratin causing them to die and become thicker, stronger protective structures (skin epithelium-epidermis)
These cells lose their cellular organelles and nuclei
Non-keratinising -
don’t undergo keratinisation and thus retain their nuclei and organelles (mouth, oesophagus, cervix epithelium)
What is pseudo stratified epithelium? Where is it found?
Epithelium appears to be multilayered
However surface cells have contact with basal lamina
Airway (trachea and bronchi) epithelium and various ducts in repro and urinary tracts
What is epithelial polarity?
Different regions of cell-surface being different from one another, with discretely organised cellular contents
Allowing secretion to only occur in one direction and absorption to occur either apically or basolaterally
Why must the pumps, channels and secretory machinery of transporting epithelium be polarised?
If not polarised they can be present in all parts of the cell membrane meaning they are pumping ions both apically and basolaterally so the directional flow is not occurring
Also important for secretion to ensure the direction of secretion is towards the intended target (ie to prevent digestive enzymes secreted going towards the basal aspect)
Name the four different types of junctions between cells
Tight. junction
Adherens junction
Desmosomes
Gap junction
What is the role of tight junctions and adherens junctions
Tight junction - seals gaps between cells
Adherens junction - Controls formation of other junctions- master junction
What is the role of desmosomes and gap junctions?
Desmosomes - spot junctions that form mechanically tough junctions between cells and restrict mechanical stresses
Gap junction - Form pores between cells that allow cells to exchange and share materials
These communicating junctions allow cells to form communities and to synchronise a number of activities
What features of transporting epithelium make it suitable to its function?
Plasma membrane contains high conc of ion transporters
Mitochondria lie close to the basal lamina to provide ATP required for active transport at these membranes
Because active transport is mainly confined to the basal membranes, ion and water transport will have directionality - infoldings increase the SA for pumping of these ions
Where are absorptive epithelial cells found?
Brush border membrane - absorptive intestinal cells on the villi surface of small intestine
What is the function of absorptive epithelial cells?
They contain large amounts of active transporters and channels for uptake of nutrients from the lumen of the gut
As concentration of nutrients increase in cytoplasm of these cells, it diffuses down concentration gradient into basal interstitial space to be collected in capillaries and distributed into circulation
What secretory epithelium cells are dispersed in the small intestine?
Goblet cells - mucous secreting
Describe the 2 main types of secretion by secretory epithelium
Exocrine (into duct or lumen)
Endocrine (into bloodstream)
How are exocrine secretory cells adapted for their function?
Secretory granules in apical cytoplasm as secretion will occur through the apical plasma membrane
How are endocrine secretory cells adapted for their function?
Secretory granules found along the basal aspect of the epithelium - contents can be released straight into the blood
What is constitutive secretion?
secretory vesicles, as they are formed, move directly to the plasma membrane and release their contents
What is stimulated secretion?
Secretory vesicles stored in cytoplasm that fuse with plasma membrane and only release contents when stimulated ie pancreatic acinar cells releasing their digestive enzymes when food enters the duodenum
Give two examples of epithelial proliferation
- Cells in intestinal crypts replacing cells lost from the tips of intestinal villi
- Cells of the basal layer of stratified squamous epithelia dividing replace cells lost from the surface
How might chemotherapy treatments be responsible for gastro-intestinal disturbances?
Inhibition of intestinal crypt cells results in loss of the finger like intestinal villi and flattening of the intestinal mucosa.
Cell loss from the villus tips continues as normal, but the failure to produce new cells to replace the lost cells results in a loss of tissue and the villi shorten.
How are epithelial cells in the epidermis replaced?
Surface cells are constantly being lost and are replaced by new cells being formed in the basal layer which migrate up while undergoing a programme of differentiation that eventually leads them to flattening out and keratinising
Each layer replaces the one above as layers are lost from the surface
What is the epidermis?
Keratinising stratified squamous epithelium of our body surface - is the outermost layer of skin on your body.
What happens during hyperproliferation of epithelial cells?
results in increased cell numbers and a thickening of cell layers, this is in response to repeated or constant pressure
If the increase in cell production is greater than cell loss from the surface, cells will accumulate creating an increased thick hard layer ie pressure and abrasion to areas can lead to local proliferation leading to hard skin or corns
What induces hyper proliferation of epithelial cells?
nfectious agents such as papilloma virus can also induce hyperproliferation. They do this by hijacking the cellular machinery of stratified squamous epithelia and inducing increased cell proliferation, which results in a surface growth eg a wart
