Epithelial Tissues: Structure and Function Flashcards
what disease can have abnormal epithelial function? (4)
breast cancer, cystic fibrosis, cholera, atherosclerosis
breast cancer…
abnormal proliferation of epithelial cells (1 in 8 women)
cystic fibrosis…
defective epithelial chloride ion transport (1 in 2500 live births)
cholera…
enhanced activation of epithelial chloride ion transport in GI tract
atherosclerosis…
superficial injury to epithelial lining of blood vessels causing cardiovascular disease (40% of UK population will die as a result of associated complications with atherosclerosis)
what is epithelia? (2)
cells that cover or line all of the body surfaces, tubes and cavities and they form the interfaces between different physiological fluid compartments
interfaces… (5)
body tissue + environment = skin blood + tissues = blood vessel wall gut + tissues = gut wall air + blood = lungs, alveoli blood + brain = blood-brain barrier
what are the characteristics of epithelia? (3)
cells are in intimate contact and may be connected by tight junctions, epithelial cells are separated from underlying tissue by basement membrane (BM) and cells undergo rapid division to replace those continually lost from the surface
what are tumours developing from epithelial cells called?
carcinomas
what are the different shapes of the cells? (3)
columnar = apex next to lumen, base at basal part of cell
cuboidal
squamous
what colour are the cells stained? (2)
nucleus - blue, cytoplasm - pink
simple epithelia in cells… (2)
have one layer, all cells are in direct contact with lumen and BM
where are simple epithelia found? (3)
areas in the body where there is: diffusion, absorption, secretion
stratified epithelia in cells… (3)
multiple layers, have cells in contact with BM - basal, have cells in contact with lumen - apical
where are stratified epithelia found?
in sites where there is need for protection eg bladder, oesophagus, stomach
where are simple squamous cells found?
blood vessels
where are simple columnar cells found?
GI tract
where are simple cuboidal cells found?
kidney tubule
where are stratified squamous cells found?
skin
where are stratified cuboidal cells found?
reproductive system
where are pseudostratified columnar cells found?
respiratory
what are transitional cells?
layers of a mixture of different shapes of cells
where are transitional cells found?
bladder
what type of function have one layer of cells?
exchange, transported, ciliated
what shape are exchange cells?
squamous
what are features of exchange cells?
have pores between cells to allow passage of molecules
where are exchange cells found?
lung; blood vessels
what shape are transporting cells?
cuboidal or columnar
what are features of transporting cells?
tight junctions limit movement between cells
where are transporting cells found?
intestine; kidney
what shape are ciliated cells?
cuboidal or columnar
what are features of ciliated cells?
cilia move fluid across surface
where are ciliated cells found?
trachea; female reproductive tract
what type of function have many layers of cells?
protective, secretory
what shape are protective cells?
squamous on surface, polygonal in deeper layers
what are features of protective cells?
cells tightly connected by desmosomes
where are protective cells found?
skin, mouth
what shape are secretory cells?
columnar to polygonal
what are features of secretory cells?
extensive rough ER (proteins) or smooth ER (steroids)
features of single squamous epithelium… (5)
single layer of flattened cells cells are thin with central nucleus pavement-like appearance irregular shape no gaps between each other
what is the mesothelium?
single squamous epithelium lining body cavities (serous membranes)
what is endothelium?
single squamous epithelium lining blood vessels
what is the purpose of simple columnar epithelium in the lining of the small intestine? (2)
increase surface area for absorption
mucus secretion to lubricate gut contents
what are the 3 levels of folding to increase surface area?
- large folds - visible to naked eye
- microscopic villi - covered by a simple columnar epithelium
- microvilli - modifications to apical surface of the epithelial cells, visible only using electron microscopes
what are the 3 surface modifications of simple columnar epithelium?
- apical surface of each cell is covered by several hundreds of microvilli forming a brush border that mucus adheres to
- goblet cells with intensely staining mucus released to lubricate gut content
- BM that separates epithelial cells from underlying tissue
what stain is used to colour the mucus in the small intestine?
high power small intestine PAS stain for glycoprotein
what 3 cell types are in the pseudostratified columnar epithelium of the respiratory tract?
goblet cells, ciliated columnar cells, basal cell (rapid regeneration from below)
what is the name for flattened cells that are worn off and shed from the surface?
desquamation
why does stratified squamous epithelium line the oesophagus?
protects underlying tissue from abrasion
wet epithelium…
stratified squamous epithelium that is subject to abrasion but not dehydration eg vagina, anal canal, mouth
what is stratified squamous keratinised epithelium composed of? (low power)
starting at top -
epithelium, connective tissue, hair follicle, hypodermis adipose tissue, apocrine sweat gland
dry epithelium…
stratified squamous keratinised epithelium subject to abrasion that resists water loss eg skin
what is stratified squamous keratinised epithelium composed of? (high power)
starting at top -
dead squamous cells containing keratin undergoing desquamation, epithelial cell, basal cell undergoing mitosis, connective tissue containing capillaries, melanocyte
what do transitional epithelial cells in the bladder have that means they prevent leakage of urine into the tissues?
a high number of tight junctions
where is the baso-lateral membrane found?
on the sides of cells, between the apical and basal membranes
what is the purpose of actin in epithelial cell junctions?
anchors cell keeping it where it is supposed to be
what is a hemidesmosome?
a membrane protein that anchors the cell to the BM
what is trans-cellular transport?
movement is in one direction eg absorption or secretion
what is paracellular movement?
transport in and out of the cell in different directions simultaneously
what are the 2 major tight junction proteins?
claudins and occludins
how many sealing strands does a urinary bladder have?
8 with a resistance (how easy to pass to other side) of 7000 (omega.cm squared)
what are the roles of tight junctions? (3)
barriers, fences, gates
barriers…
separate one compartment from another
fences…
maintain the asymmetric distribution of lipids and proteins in the apical and basal membranes eg sodium and potassium transport
gates…
allow some molecules to flow more easily than others ie not open or closed, just selective
tight junctions in epithelial cell layers… (2)
create barriers between different cell compartments and allow the processes of absorption and secretion to create compartments with different molecular compositions
what does pseudostratified mean?
only one cell layer present although there appear to be many, all the cells make contact with the underlying basement membrane but not all cells within the epithelium reach the apical surface
epithelial tissue is avascular, what does this mean?
no blood supply, it diffuses through from the BM from capillaries in the underlying connective tissue
