Epithelial tissue Flashcards
What is epithelia?
Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body, and line the internal surfaces
What is the exterior epithelial lining?
Skin
What kind of epithelium is skin?
Keratinised, stratified, squamous
Is skin living or dead?
Outermost layer is dead, living underneath
Give 3 interior epithelial surfaces that open to the exterior
- Gastrointestinal
- Respiratory tract
- Genitourinary tract
Where does the GI tract start and end?
Mouth to anus
Where does the respiratory tract start and end?
Nasal cavity to alveoli
Give 5 epithelial surfaces that don’t open to the exterior
- Pericardial sac
- Pleural sacs
- Peritoneum
- Blood vessels
- Lymphatic vessels
What is the pericardial sac?
Sac that contains heart
What is the pleural sac?
Very thin sac that contains the lungs
What does the peritoneum contain?
Most of the gut contents
What do the blood vessels constitute?
The entire cardiovascular system
What is the epithelium a derivative of?
The 3 germ layers of the embryo
Describe the structure of the trilaminar embryonic disc
3 layers with motor cord in middle
What are the 3 layers in the trilaminar disc?
NAME?
What epithelium is derived from the ectoderm?
- Epidermis of skin
- Corneal epithelium of skin
What epithelium is derived from the mesoderm?
NAME?
What epithelium is derived from the ectoderm?
NAME?
What are the two main classifications of epithelia?
NAME?
What is meant by simple epithelium?
One cell layer thick
What is meant by stratified/compound?
More than 1 cell layer thick
What does all epithelium have?
A basal surface on the basement membrane
What is the basement membrane?
A thin, flexible, acellular layer that lies between epithelial cells and subtending connective tissue
What is meant by acellular?
Not made up of cells
What is the part of the basement membrane closest to the epithelium
Basal lamina
What lies down the basement membrane?
Epithelial cells
How is the thickness of the basement membrane augmented?
By variably thick layer of reticular fibrils, elaborated by type III connective tissue
what are reticular fibrils?
Type III collagen
What is the purpose of the basement membrane?
- Serves as a strong, flexible layer to which the epithelial cells adhere.
- Cellular and molecular filter
What is basement membrane made up of?
Not cells, just fibre type connective tissue
How is the basement membrane clinically relevant in cancer?
The degree to which the malignant cells permeate the basement membrane is highly relevant to prognosis- better prognosis if the neoplasm is not through the basement membrane
Describe the structure of simple squamous epithelium
NAME?
What is endothelium?
Simple squamous lining of all vascular elements (arterial, venous, capillary and lymphatics)
What is the function of endothelium?
- Exchange gases and nutrients
- Allow certain blood cells to enter tissues
- Regulate platelet coagulation
Where is simple squamous epithelium located?
- Lining of blood and lymph vessels
- Lining of body cavities- pericardium, pleura, peritoneum
- Pulmonary alveoli
- Bowman’s capsule and Loop of Henle in kidney
- Inner and middle ear
What is simple squamous epithelium called when it’s lining body cavities?
Mesothelium
What are the functions of simple squamous epithelium?
NAME?
Where does simple squamous epithelium have a lubricating function?
NAME?
Where does simple squamous epithelium have a gas exchange function?
Pulmonary alveoli
Where does the simple squamous epithelium have a barrier role?
In the Bowman’s capsule
Where does the simple squamous have a role in active transport by pinocytosis?
Mesothelium and endothelium
What shape are the cells of simple cuboidal epithelium?
Polygonal, but the cells are about as high as they are wide
Where is simple cuboidal epithelium found?
NAME?
Are all ducts lined with simple cuboidal epithelium?
No, depends on location and size
What is the surface of the ovary called?
Germinal epithelium
What are the functions of simple cuboidal epithelium?
- Absorption and conduit
- Absorption and secretion
- Barrier/covering
- Hormone synthesis, storage and metabolism
Where does simple cuboidal epithelium have a absorption and conduit function?
Exocrine glands
Where doessimple cuboidal epithelium have an absorption and secretion function?
Kidney tubules
Where doessimple cuboidal epithelium have a barrier function?
Ovary
Where doessimple cuboidal epithelium have a hormonal function?
Thyroid
What shape are simple columnar epithelium?
Taller than they are wide
How can simple columnar epithelium sometimes appear under microscopes due to the cut?
Stratified
What features can simple columnar epithelium found?
NAME?
What is the purpose of simple columnar with microvilli?
Increase the surface area
Where are junctional complexes?
In apical portion of adjoining cells
What is a junctional complex?
A particularly tight junction
What is the purpose of junctional complexes?
Prevents gut contents penetrating between cells and gaining access to the body
What is the advantage of junctional complexes?
They give very tight control of what goes into the body
What does occludin do?
Binds adjacent plasma membranes tightly together is apical portions of some epithelia
Can membrane proteins bypass the junctional complex?
No
What are junctional complexes also known as?
Zonula occludens
What does the zonula occludens allow the cell to do?
Restrict certain proteins to apical (free) surface, and restrict others to the lateral and basal surface.
What does the junctional complex separate?
The luminal space from the intercellular space
Describe the passage of fluid from the intestinal lumen
Intestinal lumen → cell → intercellular space → basement membrane → connective tissue
What are villi?
Projections into the small intestine
What are villi lined by?
Simple columnar epithelium with microvilli
What is the purpose of the villi?
Increase SA
What do villus do?
Absorb nutrients from the small intestine
What cells do simple columnar often have?
Goblet cells
Where do goblet cells run from?
Basement membrane → surface
What do goblet cells do?
Produce mucus
Where is simple columnar epithelium found?
- Stomach and gastric glands
- Small intestine and colon
- Gall bladder
- Large ducts of some exocrine cells
- Oviducts
- Uterus
- Ductuli efferents of testis
What are the functions of simple columnar epithelium?
- Absorption
- Secretion
- Lubrication
- Transport
Where doessimple columnar epithelium have an absorption function?
- Small intestine and colon
- Gall bladder
Where doessimple columnar epithelium have a secretion function?
- Stomach lining
- Gastric glands
- Small intestine
- Colon
Where doessimple columnar epithelium have a lubrication function?
NAME?
Where doessimple columnar epithelium have a transport function?
Oviduct
Why is pseudostratified epithelium so named?
Because it looks like its stratified, but simple because every cell makes contact with the basement membrane
What happens to nuclei inpseudostratified epithelium?
They end up in different places
How does the basement membrane differ inpseudostratified epithelium?
It is thicker
What features canpseudostratified epithelium have?
- Can have cilia and stereocilia
- Can contain goblet cells
Where doespseudostratified epithelium have cilia?
Trachea
Where doespseudostratified epithelium have stereocilia?
Testes
Where ispseudostratified epithelium found?
- Lining of nasal cavity, trachea and bronchi
- Epididymis and ductus deferens
- Auditory tubes and part of lymphatic cavity
- Lacrimal sac
- Large excretory ducts
What are functions ofpseudostratified epithelium?
- Secretion and conduit
- Absorption
- Mucus secretion
- Particle trapping and removal
Where doespseudostratified epithelium have a secretion and conduit function?
NAME?
Where doespseudostratified epithelium have an absorption function?
Epididymis
Where doespseudostratified epithelium have a particle trapping and removal function?
Respiratory tract
In stratified epithelium, what is the name based on?
The outermost cell- next to the lumen
In stratified epithelium, which cell is attached to the basement membrane?
Only basal cell layer
What kind of epithelium is found in the vagina?
Stratified squamous non-keratinized epithelium
What are vagina cells rich in?
Glycogen
Why is it important that vagina cells are rich in glycogen?
Substrate for numerous lactobacilli, which produce lactic acid, maintaining a low vaginal pH
What do the vaginal cells cause in absence of hormonal stimulation?
Atrophy
What kind of epithelium is found in the oesophagus?
Stratified squamous non-keratinised epithelium
What is the role of the epithelium in the oesophagus?
Protects from abrasion
How is the oesophagus need protection from abrasion?
When eating, the outer cells slough off, but are replaced by mitosis, which is occurring in the basal layer, with cells differentiate as they move upwards.
What epithelium lines epiglottis?
NAME?
What does the epiglottis do?
Stops food going into lungs on swallowing, and then springs back to allow for breathing
What is the epiglottis adapted for?
Protection against abrasion
What epithelium is on the outermost layer of the eye?
Stratified squamous
What is the epithelium on the outermost layer of the eye adapted for?
To withstand the constant abrasion of opening and closing the eye
In what locations is stratified squamous epithelium found?
- Oral cavity
- Oesophagus
- Larynx
- Vagina
- Part of anal canal
- Surface of cornea
- Inner surface of eyelid
What are the functions of stratified squamous epithelium?
NAME?
What is special about keratinised stratified squamous epithelium?
Outermost cells are dead and have lost their nuclei
What doeskeratinised stratified squamous epithelium line?
Skin
Where is the epidermis thicker?
Sole of foot and palms of hands
What is often true of the margin between connective tissue and epidermis?
It’s quite convoluted
What is meant by the border being convoluted?
Dermal papilla go up
What is the purpose of the convoluted border?
The skin doesn’t slide off as easily, so less likely to blister
Where iskeratinised stratified squamous epithelium located?
NAME?
When does the oral cavity begin to keratinise?
If someone mouth breaths a lot
What is the function ofkeratinised stratified squamous epithelium?
- Protection against abrasion and physical trauma
- Prevents water loss
- Prevents ingress of microbes
- Shields against UV light damage
How is the skin protected from UV damage?
Melanosomes in the skin line up on the outer surface of the nuclei, to try and protect the DNA from UV damage
Describe transitional epithelium
Surface cells can vary in shape, from columnar/cuboidal to flattened. It looks different depending on wether or not its stretched
What is transitional epithelium adapted to do?
Stretch
Why is transitional epithelium adapted to stretch?
Because it lines the urinary system, and so needs to allow for extension of the bladder
How can transitional epithelium often be recognised on micrographs?
By slightly bowed appearance of outermost cells in stretched state
Where is transitional epithelium found?
NAME?
What is the function of transitional epithelium?
NAME?
Is a epithelial cells rate of renewal variable or constant?
Pretty constant
What does the turnover rate for each epithelial cell type depend on?
- Location
- Function
When is the renewal time frame for epithelium not constant?
When injury leads to acceleration
What is the time frame for renewal of epidermis?
From cell division in basal layer to being sloughed off, ~28 days
What happens to a epidermis cell in its lifetime?
Differentiation, migration to exterior, keratinisation and death
How often are cells lining the small intestine replaced?
Every 4-6 cells
What replaces cells in the lining of the small intestine?
Regenerative cells in the base of crypts
What happens to some epithelial cells once adulthood is reached?
They cease to be renewed
What can happen to cells that cease to be renewed once they reach adulthood?
The triggering of cell proliferation
What does cell proliferation do?
Replace lost cells
Why might cells be lost?
NAME?
Give 2 epithelial cells that have different types of surface specialisation?
NAME?
What are microvilli?
Cytoplasmic apical extensions
What is the purpose of microvilli?
They increase the SA for selective absorption of intestinal contents
What do microvilli have inside them?
Little actin threads going into them
What is the purpose of the actin threads?
Give them shape
What are stereocilia?
Very long microvilli
Where are sterocilia found?
Extending from surface of epididymal
