Intro to Epithelium

Question 1

Tight junctions (zonula occlundes)

Answer 1

• Block movement of extracellular molecules between adjacent cells
• Maintain cell membrane polarity
• Made of claudins and occludins

Question 2

Apical domain membrane specializations

Answer 2

• Microvilli
• Stereocilia
• Cilia

Question 3

Apical junction complex

Answer 3

Tight junctions + Adherens junctions + Desmosomes = segmented membrane

Question 4

Stereocilia

Answer 4

• Long, thin, non-motile microvilli
• Found in male reproductive tract (epididymis and ductus deferens)

Question 5

Keratinized/cornified

Answer 5

with protective layers of dead cells and keratin

Question 6

Lateral membrane

Answer 6

Faces side (another epithelial cell)

Question 7

Gap junctions

Answer 7

• Pore between two membranes allowing passage of small molecules and nutrients
• Made of connexin proteins that form connexons => multiple connexons from two cells align to form gap junction

Question 8

Pseudostratified epithelium

Answer 8

Structure: 1 layer (all cells touch basement membrane) but looks like multiple as nuclei aren’t aligned

Examples:

• large airways (trachea)
• epididymis

Question 9

Simple columnar epithelium

Answer 9

Structure: 1 layer, rectangular cells

Examples:

• small intestine
• terminal/small airways of respiratory system (bronchioles)

Question 10

Microvilli

Answer 10

• small processes that project from surface to increase SA (great for absorption)
• found at intestinal brush border and PCT of kidney

Question 11

Adherens junctions (zonula adherens)

Answer 11

• link actin cytoskeletons of adjacent cells => epithelial strength
• form continuous contractile band around cells
• made of transmembrane cadherins; cytoplasmic tails bind anchor proteins in an intracellular plaque

Question 12

Desmosomes (macula adherens)

Answer 12

• beneath adherens junctions
• in stratified epithelia exposed to stress
• made of transmembrane cadherins; cytoplasmic portion binds IFs not actin

Question 13

Where is epithelium found?

Answer 13

• covers/lines free surfaces of the body
• interface between different biological compartments

Question 14

Stratified squamous epithelium (keratinized)

Answer 14

Structure:

• multiple layers: more cuboid => flat => dry, protective layer of dead cells and keratin

Example: skin

Question 15

Stratified

Answer 15

more than one layer of cells

Question 16

Transitional epithelium

Answer 16

• Changes structure depending on stretch/relaxation
• Found in the bladder
• Relaxed: 5-6 layers, top layer very cuboid
• Stretched: 2-4 layers, top layer very flat

Question 17

Apical membrane

Answer 17

Faces lumen (inside of tube like structure)

Question 18

Cubiodal

Answer 18

square cells

Question 19

Squamous

Answer 19

flat cells

Question 20

Basal membrane

Answer 20

Faces underlying connective tissue

Question 21

3 characteristics that describe different kinds of epithelium

Answer 21

1. Number of cell layers - simple - stratified - pseudostratified 2. Cell shape - squamous - cubiodal - columnar 3. Keratinization - keratinized/cornified - non-keratinized/non-cornified

Question 22

Pseudostratified

Answer 22

one layer of cells (all cells touch basement membrane) but looks like more than one because nuclei are not aligned

Question 23

Simple cuboidal epithelium

Answer 23

Structure: 1 layer, square cells

Examples:

• renal tubules
• thyroid follicles
• glandular tissue

Question 24

Simple squamous epithelium

Answer 24

Structure: single layer, flat cells

Examples:

• parietal layer of Bowman’s capsule
• lining of blood vessels (endothelium)
• lining of body cavities (mesothelium)
• lung alveolar walls

Question 25

Hemidesmosome

Answer 25

- Anchor cell to basement membrane - Attachemnt site for keratin IFs - Transmembrane integrins bind extracellular lamins (type IV collagen) in basement membrane

Question 26

Defining characteristics of all epithelium

Answer 26

- anchored to basement membrane (which rests on underlying connective tissue) - avascular: relies on diffusion of nutrients and gases from vasculature in adjacent connective tissue - tightly connected at lateral surface via specialized junctional complexes

Question 27

Columnar

Answer 27

rectangular cells

Question 28

Stratified squamous epithelium (non-keratinized)

Answer 28

Structure: - multiple layers: more square towards basement membrane =\> more flat - all cells have nuclei Examples: - esophagus - oral cavity - vagina - anal cavity

Question 29

Cilia

Answer 29

- Actively motile with complex inner structure - Found in lining of respiratory tract and female reproductive tract

Question 30

Basal domain

Answer 30

- 30-60nm non-cellular membrane between epithelium and connective tissues - Made of collagenous and non-collagenous glycoproteins and proteoglycans - Gives structural support and is a selective barrier to/from supporting tissue

Question 31

Junctional complexes of the lateral domain

Answer 31

- tight junctions (zona occludens) - adherens junctions (zonula adherenes) - desmosomes (macula adherens) - gap junctions