Histology- Epithelia Flashcards by Sara Waheed

Epithelia is categorised by

The number of layers of cells within them

The shapes of the cells

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Simple Epithelia

Epithelia with a single layer of cells on a basement membrane

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Stratified (compound) epithelia

Two or more layers of cells on a basement membrane

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Pseudo- stratified epithelia

Look as if they have more than one layer of cells but they don’t actually

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Cell junctions

Used by epithelial cells to hold onto their neighbours

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Basement membrane

Important part of epithelial but not visible using light microscopy using H&E staining

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Epithelia

Epithelia comprise a cohesive sheet of cells, with one or more layers, resting on a basement membrane.

-Found on edges of us-

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Epithelia forms barriers for

Protection – e.g. skin

Absorption – e.g. gut

Secretion – e.g. pancreas

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Simple squamous epithelium

Single layer of flattened plate-like cells on a basement membrane

Parallel oval nuclei (1 per cell)- Nucleus is the thickest part of the cel

Lines inside of blood vessels (endothelium), outside of lungs (mesothelium) and abdominal organs (peritoneum)

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Simple squamous epithelium inside a blood vessel

Endothelium

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Simple squamous epithelium lining the chest cavity and abdominal cavity

Peritoneum membrane

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Simple squamous epithelium outside of lungs in alveoli- form the barrier between the blood and the air

Useful for this function as the cytoplasm is very thin

Mesothelium

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Simple cuboidal epithelium

Single layer of cells with similar height and width on a basement membrane

Central spherical nuclei (1 per cell)

Line kidney tubules, small ducts

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Simple cuboidal epithelium

Single layer of cells with similar height and width on a basement membrane

Central spherical nuclei (1 per cell)

Line kidney tubules, small ducts

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Simple columnar epithelium

Single layer of cells taller than they are wide, on a basement membrane

Line the stomach, intestines and uterus

May or may not have cilia or microvilli

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Cillia on surface of columnar epithelium

Move material across the surface of the epithelium

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Microvilli on columnar epithelium

Increase surface area for absorption

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Microvilli

Microscopic projections on luminal surface of absorptive cells

Increase surface area to allow absorption of water and nutrients to take place

Intestinal brush border

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Cilia- longer than microvilli

Microscopic motile projections on luminal surface of cells

Contain contractile proteins that allows these to rhythmically beat.

The coordinated movement of cilia wafts whatever materials is on its surface of the epithelium across it all in the same direction

Cillia found…

Respiratory tract

Reproductive tract

Features of stratified epithelia

Protective function

Many layers of cells

Continually being worn down, worn-away cells replaced from below

Location of stratified epithelia

Found at sites subject to abrasive forces (frictional forces)

E.g.
mouth involves eating, speaking
Vagina and cervix
Oesophagus

Where do cells start their life?

Resting against the basement membrane (so near the basement membrane they are quite immature)

How do cells move up from the basement membrane?

As the cells develop they are pushed up by new cells forming underneath them towards the surface of the epithelium where there is a continuous loss of cells

So there is continuous replenishment of the epithelium from the basement membrane upwards

What does keratin do?

Helps to waterproof the epithelium Helps to ensure that when we are in a hot environment all the body does not just pass out through the skin in an uncontrolled way. Found on skin

Stratified squamous non-keratinising epithelium in the OESOPHAGUS

Cells start their lives at the bottom, from the basement membrane and as they mature they flatten out and become squames

Stratified squamous non-keratinising epithelium in the VAGINA

The epithelial cells tend to accumulate glycogen at various points in the menstrual cycle, giving the cytoplasm the pale appearance

Stratified squamous non- keratinising epithelium

Multiple layer of cells on a basement membrane Mature surface layers are plate-like squames Lines the mouth, oropharynx, oesophagus, vagina

Stratified squamous keratinising epithelium

Multiple layer of cells on a basement membrane Mature surface layers are plate-like squames Waterproof layer of keratin Skin

On the basement membrane of the keratinising epithelium lies…

Cells from the basement membrane and as they mature they flatten out and become squames As the cells mature they accumulate the protein keratin within the cytoplasm

As keratin accumulates in the cytoplasm of the cells,

The cells die, leaving dead flat plates of keratin

Pseudostratified epithelium

Single layer of cells of variable height, mimicking multiple layers on a basement membrane All cells in contact with basement membrane Nuclei are at different heights within the cells, closer t or further away from the basement membrane Lines the conducting airways- have Cillia

Urothelium is specialised stratified epithelium

Breaks the rules – looks stratified, probably is stratified, but: Surface layer of umbrella cells Cells between umbrella cels appear 3-7 layers this and this layer is pseudostratified Sometimes called transitional epithelium Lines the collection part of the urinary tract: bladder, ureters and renal pelvis

Basement membrane

Always present – usually cannot see it in H&E stained sections Infer presence – difference between epithelium and underlying connective tissue

We can stain the basement membrane using

PAS- periodic acid shift Stains membrane magenta

What is the basement membrane made of?

Composed of several extra-cellular proteins including Collagen IV and Fibronectin

Function of basement membrane

Essential for the proper functioning and survival of the epithelium If basement membrane is removed the epithelium is going to fall apart

Epithelial junctions- Occluding (tight) junctions

-Band-like fusions between cells that are impervious to most molecules (don’t let fluid pass through) -Prevent diffusion between cells

Epithelial junctions- Desmosomes (Anchoring/Adherent junctions)

Plaques that form physical joins between cells and connect the cytoskeletons of adjacent cells Spread forces across several cells so mechanical laid is spread across multiple epithelial cells Prominent in the skin due to skin being exposed to large forces Above the basement layer

Epithelial junctions- Gap (aka communicating) junctions

Electrical junctions that permit the transfer of small molecules Electrically couple adjacent cells

A gland secretes by shedding individual cells. What type of secretion is this?

Holocrine

Which 2 proteins are principally involved in the generation of ciliary movement?

Tubulin and dynein

Hemidesmosomes

Helps with the adhesion of the epithelial cells to the basement membrane

Types of tissue

Epithelia Supporting tissues Muscle

Epithelia

one or more layers of cells that line a body cavity protection, absorption, secretion

Supporting tissues

structure and protection cartilage, bones, tendons and blood

Muscle

Smooth Skeletal Heart