Characteristics of the Epithelia

Question 1

Does the epithelial layer have blood vessels?

Answer 1

No, the epithelium is avascular (devoid of blood vessels)

Question 2

What are the two pathways in which transport can occur between epithelial cells?

Answer 2

1. Paracellular pathways- between cells
2. Transcellular pathways- through the cells

Question 3

3 domains of polarity of epithelial cells

Answer 3

1. Apical
2. Basal
3. Lateral

Question 4

Apical side (epithelial cells

Answer 4

• Directed to the lumen or the external surface
• Can have modifications:
  1. Cilia- motile cytoplasmic processes
  Eg. Respiratory epithelium
  2. Stereocilia- microvilli of unusual length. Eg. Inner ear, testis
  3. Microvilli- cytoplasmic processes that extend from cell surface. Eg. Small intestinal epithelium

Question 5

Basal side (epithelial cells)

Answer 5

• Basement membrane- contains basal lamina/lamina densa, and lamina lucida
• Contain secretions (eg. Proteoglycans, collagen) from the epithelial cells

**Note: Basal lamina is the structural attachment site for overlying epithelial cells and underlying connective tissues

Question 6

Lateral side (epithelial cells)

Answer 6

• Makes connections to the adjacent/neighbouring cells, and communicates with them
• Various types of junctions are present:
  1. Tight junctions (barrier function)
  2. Anchoring junctions (mechanical stability)
  3. Communicating junctions (direct communication between cells)

Question 7

What kind of epithelium is Epidermis?

Answer 7

Stratified squamous epithelium (can be with or without keratin)

Question 8

Layers of the epidermis

Answer 8

1. Stratum basale
2. Stratum spinosum (prickle cell layer)
3. Stratum granulosum
4. Stratum lucidum
5. Stratum corneum

Question 9

Stratum basale

Answer 9

• A single layer of cuboidal cells on basement membrane (stem cells)
• Divides the epidermis and the dermis

Question 10

Stratum spinosum (prickle cell layer)

Answer 10

5-10 layers of polyhedral keratinocytes flattened towards the surface (also called prickle cells)

Question 11

Stratum granulosum

Answer 11

3-5 layers of flattened keratinocytes filled with keratohyaline granules. Actively producing keratin

Question 12

Stratum lucidum

Answer 12

• A very thin layer containing extremely flattened and tightly packed keratinocytes filled with keratin filaments
• Nuclei beginning to be eliminated

Question 13

Stratum corneum

Answer 13

• Layer of dead, nonnucleated cells. Cells are constantly being sloughed off
• If keratinocytes produce keratin, then the surface is called keratinized and will have wavy/string appearance

Question 14

Epitheloid Tissue

Answer 14

Tissues that appear epithelial, make contact with adjacent cells, but are devoid of the characteristic free surface

Eg. Endocrine organs- develop from typical epithelia, but lost its connection to a surface during development

Eg. Pancreatic islet cells, Leydig cells in testis, anterior pituitary, adrenal parenchyma- specialized epithelial cells but no longer on the surface

Question 15

Why is epithelia so important?

Answer 15

1. Secretion- ex. columnar epithelium of the gastric glands
2. Absorption- ex. columnar epithelium of the small intestine
3. Transport – ex. respiratory and olfactory epithelia
4. Protection- ex. stratified squamous epithelium of the skin (epidermis)
5. Receptor- ex. epithelia of the tongue (taste buds), nasal mucosa (smell)

Question 16

Mesothelium

Answer 16

The epithelium that lines the pleura, peritoneum, and pericardium

Question 17

Goblet Cells

Answer 17

Secrete mucin and create a protective mucus layer