2.8 Epithelial cells and tissues Flashcards
What is a tissue
A group of cells whose type architecture and organisation are vital to its function
composed of cells, extra cellular matrix and fluid
What is an extracellular matrix
material formed by cells that are insoluble and extracellular
generally made of fibrillar protiens (elastin, fibrilin, collagens 1-3) that are in a hydrated ‘gel’ of proteoglycans
connective tissue is loosely organised, whereas bones and tendons are highly organised
What are the 5 main cell types
1) connective tissue
2) contractile tissue
3) haematopoetic cells
4) neural cells
5) epithelial cells
What are examples of connective tissue cells
fibroblasts (many tissues)
chondrocytes ( in cartilage )
osteocytes (in bones )
what are contractile tissues
cardiac muscles, skeletal muscle, smooth muscle
what are haematopoetic cells
blood cells
tissue resident immune cells
bone marrow cells
what constitutes neural cells
neurons and glial cells
what constitutes epithelial cells
-cells forming continuous layers
layers line surfaces and separate tissue compartments
What are epithelial cancers called
carcinomas
what are mesenchymal (connective tissue and muscle) cancers called
sarcomas
what are haematopoeitic cancers called
leukemias (if of bone marrow)
lymphomas (from lymphocytes )
what are neural cell cancers calls
neuroblastomas
gliomas
describe epithelial cells (3)
- make organised and stable cell- cell junctions and form continous and cohesive layers
- line internal and external body surfaces and tissue parts
- cell-cell junctions are v important to maintaining epithelial layers
What are the 3 ways that epithelial cells can by classified by
squamous - ‘plate like’
columnar
cuboidal
What is single layered epithelium called
simple epithelium
what is multi layered epithelium called
stratified epithelium
give 3 examples of squamous epithelial cells in the body
1) lining alveolus
2) lining internal cavities ( mesothelium )
3) endothelium lining blood vessels
where are cuboidal epithelia often found
lining found in ducts (eg collecting ducts of kidney )
Where are columnar cells found
surfaces involved in absorption or secretion
eg enterocytes lining guts
What are the 2 types of stratified squamous epithelial cells found
1) keratinising
2) non keratinising
What are keratinising stratified squamous epithelial cells and where are they found
squamous epithelial cells that produce keratin and so become thicker and die
They become thicker and more protective and stronger
They lose their nuclei and organelles
Not visible under a light microscope
eg epidermis (skin epithelium)
What are no keratinising cells and where are they found
do not undergo keratinisation
found in epithelium of oesophagus, mouth, anus, cervix and vagina
What is the point of keratinisation
form thick layers that protect underlying tissue from physical and chemical insults
(eg provides protection against cold, abrasion, solvents )
What are pseudo stratified epithelia and where are they located
They look like they are stratified but on closer inspection the apical cells have contact with the basal lamina
name the 4 cell-cell junctions from top to bottom
tight junction - seeling cells at apex like a belt
Adherens junction - ‘master junction ‘ that controls formation of all of the other junctions
desmosomes - spot junctions that form mechanically tough junctions between cells
gap junction - a channel forming junction forming pores between cells
What are the characteristics of transporting epithelia
- many mitochondria along the basal membrane
- basal membrane has infoldings for active transport
- apical membrane has ion channels for passive transport
what are some characteristics of absorptive epithelia using examples
eg. enterocytes (absorptive intestinal cells ) and and kidney proximal tubule cells
intestinal epithelial cells have villi which have microvilli to increase SA (microvilli are plasma membrane projections of villi)
- secretory cells (goblet cells secreting mucus present)
- carriers transporting nutrients on microvillous brush border
How are secretory epithelia often arranged
in tubules and glands
What are the 2 main types of secretion and define them
exocrine - into a duct or lumen
endocrine - into the bloodstream
Describe the arrangement of an exocrine secretory epithelium
1) it will be transporting AWAY from the basal membrane and capillary
2) its secretory vesicles and golgi apparatus will be at the apical part
3) nucleus and rough ER part will be at the basal part
Describe the arrangement of an endocrine secretory epithelium
1) will be transporting into the blood stream
2) so will be pointing TOWARDS the basal membrane and capillary
3) secretory vesicles and golgi will be towards the basal membrane
4) nucleus and rough ER will be at the apical membrane
What are the 2 ways in which you can classify secretory epithelial cells
stimulative - already has the secretory vesicles but only fuses with plasma membrane to release their contents ( fight and flight response meaning adrenaline is released from the adrenal medulla )
constitutive - as soon as secretory vesicles are formed, they fuse with the plasma membrane (hepatocytes making plasma proteins)
How are intestinal absorptive cells replaced
by crypt stem cells to replace cells lost from the villius tip
What can go wrong with the replacement mechanism for absorptive epithelia in the intestinal cells
- intestinal crypt cells can be inhibited from proliferating by chemotherapy
- leads to flattening of intestinal mucosa
- loss of finger like villi projections
What can produce hyperproliferation of the epidermis
papillomavirus
Why does hyperproliferation of the epidermis happen
increased production of epithelial cells outnumbers the number lost
- cells accumulate
- increased thickening and hardening
