Epithelial tissue

Question 1

What are the types of epithelium?

Answer 1

Covering
Glandular

Question 2

What is covering epithelium?

Answer 2

Lines cavities and cover surfaces
A continuous layer of cells which line externals surfaces e.g. skin
Internal - lines tracts e.g. reproductive, respiratory and digestive tracts.

Question 3

What is glandular epithelium?

Answer 3

Secretory epithelial cells.
Arises from covering epithelium, forms when covering epithelium invaginates.

Question 4

What is the differentiation of epithelial cells?

Answer 4

Differentiate into secretory cells, can maintain contact with covering or lose it.
Exocrine glands maintain contact via duct - have secretion of product into lumen of the gland, which then rises up and covers the surface of the covering epithelium.
Endocrine glands lose contact with covering epithelium, secrete products into bloodstream.

Question 5

How do epithelial cells join?

Answer 5

Cell to cell contact between each epithelial cell via cell junctions.
These can form a continuous sheet, which sits on the basement membrane.

Question 6

What are the sides of the basement membrane?

Answer 6

Side next to basement membrane is basal.
Side that is exposed (forms lumen), is the luminal surface or apical surface.

Question 7

What is the basement membrane?

Answer 7

Extracellular matrix scaffold which epithelial cells adhere to - provides structural support to epithelial cells.
Forms a barrier to connect epithelium above to tissues below, only lets water and small molecules through.

Question 8

What is the basal lamina?

Answer 8

It can be the basement membrane, but is actually part of the basement membrane.
Made from connective tissue below and some from epithelial cells above.

Question 9

How is the basement membrane observed?

Answer 9

Basement membrane not seen by H&E, but can be made visible by PAS stain - stains carbohydrates.
Or electron microscopy.

Question 10

What is simple epithelial tissue?

Answer 10

One cell thick
see image

Question 11

What is stratified epithelium?

Answer 11

Multiple layers of cells.
image

Question 12

How are epithelial cells classified through layers?

Answer 12

Simple or stratified

Question 13

How are epithelial tissues classified through shape?

Answer 13

Cuboidal
Columnar
Squamous

Question 14

What is cuboidal epithelium?

Answer 14

Round, cube shaped
image

Question 15

What is columnar epithelium?

Answer 15

Taller than wider
Nuclei is towards the basal surface.
image

Question 16

What is squamous epithelium?

Answer 16

Flattened cells
image

Question 17

How are epithelial tissues classified through specialisations?

Answer 17

Cilia or keratinisation (keratin on apical surface)

Question 18

What is the name order of epithelial tissue?

Answer 18

Specialisation, number, shape, Epithelium
Can have various shapes of cells but it is classified by the most superficial and uppermost cell seen.

Question 19

What are the applications of stratified epithelium?

Answer 19

Stratified - Presence of many layers gives functional advantage of protection.
Found in areas where you find abrasion - anal canal, oesophagus and skin - in contact with external environment.

Question 20

What are the applications of simple epithelium?

Answer 20

Simple line ducts and tubes and is in areas with secretory or absorptive functions.
e.g. found in digestive tract - easier to absorb nutrients through one layer of cells than many.

Question 21

What is the application of cuboidal epithelium?

Answer 21

Secretory or absorptive functions - collecting ducts at kidneys, salivary glands, but not where there is physical abrasion or stress.

Question 22

What is the application of columnar epithelium?

Answer 22

Columnar - highly absorptive areas - digestive tract, stomach, small intestine, large, and in the ducts of many glands.

Question 23

What is the application of squamous epithelium?

Answer 23

Squamous - highly specialised, flat, little metabolic activity.
Involved in diffusion of material - found in capillaries, or alveoli, or lining surfaces not in contact with exterior environment.

Question 24

What are the applications of cilia?

Answer 24

Cilia on apical surface, motile and help to waft and move cell debris over top of epithelial tissue.
Found in respiratory tract - clear mucus and protect your lungs.

Question 25

What do ciliated epithelium look like?

Answer 25

ciliated simple columnar epithelium found in fallopian tubes image

Question 26

What is the application of keratinised epithelium?

Answer 26

Keratinisation - excessive production of keratin, found on skin - waterproofs and strong, flexible outer coating, protection.

Question 27

What does keratinised epithelium look like?

Answer 27

Keratinised stratified squamous epithelium on skin. Various shapes of cells but it is classified squamous as it is the most superficial and uppermost cell seen. image

Question 28

What is pseudostratified epithelium?

Answer 28

Each cell is sat on the basement membrane so is a simple epithelium, but the nuclei are at different levels, so appears stratified. image e.g. ciliated pseudostratified columnar epithelium, found in the respiratory tract.

Question 29

What is transitional epithelium?

Answer 29

Found in the ureter and bladder. When the bladder is empty, see umbrella-shaped cells. When bladder is full, the superficial cells flatten and allows lots of stretch, transition to a more squamous cell shape.

Question 30

What is cell polarity?

Answer 30

The asymmetrical organisation of cellular context to allow functional difference at different poles of the cell.

Question 31

What is the apical side?

Answer 31

Or luminal. Has keratinisation, cilia, microvilli. This is because it is the side in contact with the lumen.

Question 32

What is the basal surface?

Answer 32

Has specialised cell junctions which help to anchor the base to the basement membrane. Epithelium tissues receive nutrients from connective tissue below and receive nervous innervation.

Question 33

What are tight junctions?

Answer 33

Tight junction / occluding junction - is very important for setting up differences between basal and apical surfaces. So the apical cell surface can have relevant receptors and enable epithelium to be selective in which nutrients it takes up into epithelial cells. Also prevent paracellular diffusion.

Question 34

What is the lateral side?

Answer 34

Has specialised cell junctions which help connect the epithelial cells to neighbouring cells and help the cells form coherent epithelial layer.

Question 35

What is paracellular diffusion?

Answer 35

Diffusion of nutrients between lumen and tissues beneath, and between the cells rather than through the cell. Tight junctions prevents leakage into surrounding tissue.

Question 36

What are zonular adhesions?

Answer 36

Or adheren junctions Tightly bind adjacent cells together, and anchor sites for cytoskeleton within epithelial cells. This ensures epithelium is cohesive and can withstand movement.

Question 37

What are gap junctions?

Answer 37

Or communicating junctions - formed by a ring of proteins which forms a channel where small ions can be directly transferred between cells, forms a functional bridge.

Question 38

What are macular adherins?

Answer 38

Desmosomes - connect cytoskeleton together. Macular means they are dotted around the cell, not banded. These also rivet the cytoskeleton of neigbouring cells together.

Question 39

What are hemidesmosomes?

Answer 39

Like desmosomes but only interact with extracellular matrix, adhere cells to basement membrane.

Question 40

What is the structure of cilia compared to microvilli?

Answer 40

Made from microtubules, 10um, motile, present only in respiratory and reproductive tracts. Microvilli - made from actin, 1um, less motile, more widespread - mainly in kidney and digestive tract.

Question 41

What is the order of cell junctions?

Answer 41

Tight junction Adhering junction Desmosome

Question 42

What is keratin?

Answer 42

A cytoskeletal protein. At the top, cells die and leave behind keratin which acts as a protective, impermeable to water, layer.

Question 43

What are secretory epithelial cells?

Answer 43

Scattered - goblet cells, found in respiratory epithelium. Have many secretory granules Do not stain well as produces mucus.

Question 44

What is glandular epithelia?

Answer 44

Specialised epithelial tissue secreting a particular protein, lipid or carbohydrate. Can be endocrine - produce hormones or exocrine e.g. salivary glands, the pancreas is both. Glands can be straight or coiled or branched.