L28: Epithelial tissue

Question 1

Common properties of epithelium

Answer 1

1. Derived from ectoderm
2. Contain cytokeratin as intermediate filament
3. Lateral junctional structures (form an intact sheet over a surface)
4. Rest on BM
5. Supported by CT
6. No intercellular matrix
7. Avascular

Question 2

Functions of epithelium

Answer 2

PASTS

1. Protection: epidermis
2. Absorption: GI epithelium
3. Secretion: Endocrine and exocrine glands
4. Transport: kidney tubules
5. Sensory: Olfactory and retinal epithelium

Question 3

Basement membrane and its 5 components

Answer 3

Basal lamina (from epithelial cells) + Reticular lamina (from CT)

Five components:

1. Nidogen
2. Perlecan
3. Laminin
4. Collagen type IV
5. Integrin

Question 4

Classification of epithelial cells:

1. Number of cell layers
2. Shape
3. Presence or absence of keratinised layer
4. Specialised epithelium

Answer 4

1. Simple / Stratified
2. Squamous / Cuboidal / Columnar
3. Non-keratinised (moist) / Keratinised (dry)
4. • Respiratory epithelium (ciliated pseudostratified columnar epithelium with goblet cell)
     - Transitional epithelium (bladder: from cuboidal to squamous)
     - Glandular epithelium (exocrine, endocrine)
     - Mesothelium (simple squamous epithelium)
     - Endothelium (simple squamous epithelium)

Question 5

Examples of:
Simple squamous
Simple cuboidal
Simple columnar

Answer 5

Simple squamous: Lung alveoli

Simple cuboidal: kidney tubules

Simple columnar: Intestinal epithelium

Question 6

Examples of:
Stratified squamous
Stratified cuboidal
Stratified columnar

Answer 6

Stratified squamous: skin (keratinised), esophagus (non-keratinised)

Stratified cuboidal: Sweat gland

Stratified columnar: Ducts of exocrine glands

Question 7

Apical specialisation of epithelial cells

Answer 7

1. Microvilli (Actin: absorption)
2. Stereocilia (long microvilli)
3. Cilia (Microtubules: movement of fluid)
4. Flagella (movement of spermatozoa)

Question 8

Lateral specialisations of epithelial cells

Answer 8

1. Tight junction / Zonula occluden: prevent passage of fluid between epithelial cells
2. Adhering junction / Zonula adherens: actin filament, adhesion
3. Gap junction (communication): communication
4. Desmosome: intermediate filament

Question 9

Basal specialisations of epithelial cells

Answer 9

1. Anchoring junction
   - Hemidesmosome (intermediate)
   - focal adhesions (integrin and actin)
2. Adhesion to basal lamina (Collagen type VII)
3. Basal membrane infolding (kidney tubular cells)

Question 10

Exocrine vs endocrine glands

Answer 10

Exocrine glands: with duct, excrete to external surface

Endocrine glands: hormone, ductless, secrete to blood capillary

Question 11

Single cell gland vs multicellular gland

Answer 11

Single cell gland: Goblet cell (in tracheal and intestinal epithelium)

Multicellular gland: Mucous (thick, GI), Serous (watery, pancreas), Mixed (salivary)

Question 12

Mode of secretion of glands

Answer 12

MAH

1. Merocrine (secretory vesicle, exocytosis without significant loss of cytoplasm): sweat gland
2. Apocrine (loss of a portion of apical cytoplasm): mammary gland
3. Holocrine (lysis of whole cell, mature cell die and become secretory product): sebaceous gland

Question 13

Shapes and ducts of glands

Answer 13

Shape: Tubular vs Acinar

Ducts: unbranched (simple), branched (compound)

Question 14

Mucosa vs Serosa

Answer 14

Mucosa:

• Mucous membrane + CT (lamina propria) + mucularis mucose
• line cavities connecting outside
• mucinous, thick and slimy (rich in proteoglycan)

Serosa:

• Mesothelium + CT
• Peritoneal, Pericardial, Pleural
• watery (rich in protein, basophilic)