Epithelial Histology

Question 1

What is the epithelium [1]

Answer 1

Cell-dense layer that covers internal and external bodily surfaces

Question 2

Describe the general order of structures of the epithelial lining, starting with the epithelial cells themselves [2]

Answer 2

Epithelial cells → basal epithelial cells (if stratified) → basal membrane (separates epithelial cells from connective tissue) → lamina propria (often contain glands/vessels)

All of them together = mucosa

Question 3

List 4 structural features of squamous epithelial cells [4]

Answer 3

Cells are flat and fish-scale like
Nuclei are disk-shaped
Nuclei are centrally located
Cytoplasm is sparse

Question 4

Describe and explain the main function of stratified squamous epithelial cells (mention where they are mainly found) [2]

Answer 4

Protection because they are more than one layer of single-cells which makes them thick. Found in areas where there is friction/abrasion

Question 5

Compare, by describing and explaining, the metabolic activity of basal/apical epithelial cells [2]

Answer 5

Basal epithelial cells are metabolically active whereas apical epithelial cells are metabolically dead

Question 6

Describe and explain the main function of simplified squamous epithelial cells:
- Explain presence of these cells in 4 areas of the body
[2]

Answer 6

Single layered flat cells that are responsible for secretion and absorption (rapid transport)

Transport: STRUCTURE that allows this = thin shape
Exchange of CO2/O2 in air of alveoli within lungs and surrounding capillaries
Filtration of blood within the kidney glomeruli

Secretion: STRUCTURE that allows this = smooth and secrete lubricating substances, reducing friction between cavity/organ & epithelium
Lining of pericardial sac

Question 7

Describe and explain the main function of stratified squamous epithelial cells:
- Give 6 examples of where these cells might be present
[2]

Answer 7

Stratified so layered thus thick = allows it to be protective + withstand friction

Examples:
- Anal canal
- Eesophagus
- Pharynx
- Vagina
- Mouth
- Tounge

Question 8

List 4 structural features of cuboidal epithelial cells [4]

Answer 8

Large nuclei
Centralised nuclei
Spherical nuclei
Cube like cells = tall as they are wide

Question 9

Where in the body would you expect simple cuboidal and stratified cuboidal epithelia to be present? [2]

Answer 9

Simple = small glands
Stratified = larger glands

Simple cuboidal = ducts/areas of small glands
Stratified = salivary, sweat, mammary

Question 10

List 4 structural features of columnar epithelial cells [4]

Answer 10

Elongated columnar shape,
elongated nuclei,
associated with other cells, e.g., goblet cells (oval & non-ciliated) = mucus secreting cells,
ciliated or smooth

Question 11

Describe the structure and funtion [with location] of stratified columnar epithelial cells [3]

Answer 11

• Multilayered rectangular columnar cells, only basal layer anchored to basal membrane
• Specialised for secretion and protection
• Rare = seen in male urethra, conjunctiva of eye + some glands

Question 12

Describe the structure and funtion [with location] of pseudostratified columnar epithelial cells [3]

Answer 12

• Single layer of rectangular columnar cells that appear multilayered but are only a single layer as all the cells are anchored to the basal membrane
• Primary function = secretion and protection
• Seen in the repiratory tract, with oval & non-ciliated goblet cells (mucus-secreting) along with ciliated cells = defence

Question 13

Describe the structure and funtion [with location] of simple columnar epithelial cells [3]

Answer 13

• Single layer of rectangular columnar cells
• Primary function = secretion and absorption, seen in small intestine (digestive tract)

Question 14

Describe the appeareance of stereocilia and their function [2]

Answer 14

projections that act as mechanoreceptors, sense fluid movement and convert to electrical impulse, detect changes in hearing/balance

appear as irregular filament border

Question 15

Describe the appeareance of microvilli and their function [2]

Answer 15

actin-based finger like projections on the apical (lumen-side) surface that, increase SA of mucosa = increased absorption/digestion

solid border of filaments

Question 16

Describe the appeareance of cilia and their function [2]

Answer 16

motile actin-based hair like projections, facilitate fluid movement across epithelium, thicker border then microvilli

Question 17

Compare the location of stereocilia, microvilli and keratinization [2]

Answer 17

Kertanisation - nails, dorsal tongue, stratum corneum
Cilia - inner ear
MV - small intestine

Question 18

What are keratin proteins and their function [2]

Answer 18

intermediate filaments that give structure to epithelial cells = tough/fibrous proteins
- Allows epithelium to resist abrasion

Question 19

Describe all the type of simple exocrine glands and their related epithelial cells [5]

Answer 19

Simple tubular - straight secretory portion = single duct, simple columnar
Simple coiled tubular - coiled portion = single duct, simple/stratified cuboidal
Simple branched tubular - straight portions = single duct, simple columnar
Simple alveolar - saclike secretory portion = single duct, simple columnar/cuboidal

Question 20

Describe all the type of compound exocrine glands and their related epithelial cells [3]

Answer 20

Compound tubular - straight sec portion = branched duct, simple columnar
Compound alveolar - sac sec portion = branched duct, simple cuboidal or secretory granules of pyramidal cells
Compound tubuloalveolar - straigt & saclike = branched duct, simple columnar/cuboidal & stratified columnar

Question 21

Compare endocrine and exocrine glands [2]

Answer 21

Endocrine = secrete into bloodstream
Exocrine = secrete onto a duct which empties into surface, i.e., epithelial surface

Question 22

List the two epithelial membranes and their directions [2]

Answer 22

apical - faces external world
basolateral - bathed by interstitial fluid

Question 23

Describe the structure of tight junction [2]

Answer 23

Tight junctions (zonula occludans), like zip lock bags, use claudin and occludin proteins that are associated with cytoplasmic proteins, CT proteins allow linkage to adherens + actin cytoskeleton
TJs = encircle the cell + completely fill the space

Question 24

Describe the function of tight junction [2]

Answer 24

1. create a barrier for movement of water/solutes in paracellular pathway (between lumen/interstitial fluid)
2. they create a prevent migration of transport proteins between apical/basolateral membranes

Question 25

Describe the structure and function of adherens junction, mention their appearence [2]

Answer 25

Adheren junctions, like velcro, link the actin filaments in adjacent epithelial cells via cadherin proteins + intracellular proteins, FUNCTION = hold adjacent cells together Appearance = bands (zonula adherens) that encircle cell or discrete attachments (adhesion plaques)

Question 26

Describe the structure and function of desmosomes, mention their appearence [2]

Answer 26

Desmosomes, link the intermediate keratin filaments in adjacent cells via cadherin proteins Create an anchor between cells, cadherin within the cell binds to the attachment plaques which are connected to the keratin intermediate filaments FUNCTION = strong cell-cell adhesion, required when cells undergo mechanical stress, e.g., cardiac muscle and epithelia

Question 27

What are hemidesmosomes [1]

Answer 27

Hemidesmosomes, use same method as desmosomes but link the epithelial cell to basement membrane

Question 28

Describe the structure and function of gap junctions, mention their appearence [2]

Answer 28

Gap junctions, use 6 connexin proteins to form one connexon which joins connexon in adjacent cell, forms channel which can be open/closed FUNCTION = allows passage of water soluble, small molecules and ions, thus establishing a path for flow of electrical current Appearance = found when cells need to function in group = cardiac myocytes/smooth muscle