Epithelium

Question 1

What are the most important (of many) functions of epithelia?

Answer 1

Physical protection and selective transport (diffusion, absorption, secretion)

Question 2

Describe the basic structure of epithelia.

Answer 2

(1) Continuous sheetw w/ either one or multiple layers; (2) Different types of cell juctions = different physical strenth and cell communication; (3) Basement membrane lies beneath epithelium, separating it from underlying tissue; (4) Diffusion of nutrients (since no blood vessels pentrate basement membrane); (5) Polarized: apical surface faces external environment & basal surface faces basement membrane

Question 3

What are 3 criteria by which to histologically classify epithelia?

Answer 3

(1) Number of cell layers (2) Shape of Cells (3) Surface Specializations

Question 4

Describe histological classification of epithelia based on number of cell layers.

Answer 4

Simple = 1, Stratified = 2, Pseudostratified = simple but appears stratified

Question 5

Describe histological classification of epithelia based on shape of cells.

Answer 5

Squamous = flattened, Cuboidal = as tall as wide, Columnar = taller than wide, Transitional = stratified epithelium w/ cuboidal and squamous; Note: Stratified epithelia named after shape of most superficial layer

Question 6

What are transitional epithelia specialized to do?

Answer 6

Deal with stretch and serve as barrier against toxicity

Question 7

What are epithelial surface specializations? Where they found?

Answer 7

Allow epithelia to act as selective pemeability barrier; All 3 epithelial surfaces = Apical, Lateral, & Basal

Question 8

What are common apical specializations? Define/Describe and give examples of each.

Answer 8

(1) Microvilli - small processes increase surface area, E.g. Intestinal brush border & proximal convolute tubule of kidney (2) Stereocilia - long, non-motile microvilli, E.g., epididymis & ductus deferens (3) Cilia - motile processes, E.g., respiratory tract & female reproductive tract

Question 9

What are common lateral specializations? Define/Describe and give examples of each, where possible.

Answer 9

(1) Tight junctions (zonula occludens) - block movement of extracellular molecules between adjacent cells, maintain polarity, proteins: claudins and occludins, E.g. columnar epithelial gut lining; (2) Adhering junctions (zonula adherens) - provide strength to epithelium by linking actin cytoskeletons of adjacent cells, beneath zonula occludens, form continuous contractile bind around each cell, transmembrane proteins: cadhedrins bind actin; (3) Desmosomes (macula adherens) - deep to adhering junctions, transmembrane proteins: cadherins but bind intermediate filaments not actin E.g., abundant in stratified epithelia exposed to stress; (4) Gap junctions - allow passage of small molecules & nutrients between adjacent cells, transmembrane proteins: connexin –> connexons –> gap junctions

Question 10

What is a junctional complex? What is its significance? How is it visualized?

Answer 10

Combo of zonula occludens, zonula adherens, and macula adherens; divides plasma membrane into apical and basolateral surfaces; EM necessary to see individual components, Light microscope shows terminal bar

Question 11

What are common basal specializations? Define and describe each.

Answer 11

(1) Basement membrane - thin, non-cellular layer between epithelium & connective tissue, components: collagenous & non-collagenous glycoproteins & proteoglycans, structural support & selective barrier (2) Hemidesmosomes - variant of intracellular desmosomes and anchor to basement membrane, transmembrane proteins: integrins (bind extracellular lamins in basement membrane)

Question 12

Where are leaky versus impermeable epithelia found?

Answer 12

Leaky - blood vessels, alveoli, & kidneys to allow nutrients to move; Impermeable - GI tract

Question 13

What are some ways to histologically distinguish simple squamous epithelia? Give an example.

Answer 13

Continuous surface of irregularly shaped, flat cells w/ bulges in area around nuclei; E.g., - blood vessel enodthelium

Question 14

What is endothelium?

Answer 14

Squamous epithelium lining of blood and lymphatic compartments

Question 15

What are some ways to histologically distinguish simple cuboidal epithelia? Give examples.

Answer 15

As tall as wide, clear basal versus apical sides, E.g., Glands/glandular ducts (salivary, pancreatic, & bile ducts plus kidney tubules)

Question 16

What are some ways to histologically distinguish simple columnar epithelia? Give an example.

Answer 16

Taller than wide, honeycomb-like arrangement, nuclei typically at same level, nuclei elongated and polarized to either base, center, or apex, E.g. - gallbladder - absorbing water to concentrate bile

Question 17

What are some ways to histologically distinguish pseudostratified columnar epithelia? Give an example.

Answer 17

Simple columnar but so packed that can trace origin to basement membrane, E.g., Respiratory airways w/ cilia

Question 18

What are some ways to histologically distinguish stratified squamous epithelia? What is this epithelia particularly good for?

Answer 18

2 or more layers, look cuboidal/columnar at base and squamous at apex/superficial side, condensation and loss of nuclei as cells move from basal layer (site of mitosis); Withstand abrasion since superficial layer can be sloughed off without compromising underlying tissue

Question 19

What is keratin? Where is it found?

Answer 19

Fibrous structural protein; found in human skin

Question 20

What is an important consideration for the way transitional epithelia appears? Give examples.

Answer 20

Thickness depends on state of distention of an organ; E.g., - renal pelvis, ureter, bladder

Question 21

Where are stereocilia found? What do they do there? What do they contain?

Answer 21

Male reproductive tract; facilitate absorption in epidymis and ductus deferns; contain actin filaments

Question 22

Compare microvilli and cilia structure.

Answer 22

Microvilli = dense, parallel array of actin filament, Cilia = 9+2 arrangement of microtubules

Question 23

What is another name for the basement membrane? Is it more or less thick than plasma membrane? What is it made of? What connects it with epithelial cells? How is it visualized?

Answer 23

Basal lamina; Much More - it is 30-60 nm, while plasma membrane is 10 nm; Collagenous and non-collageonous glycoproteins and proteoglycans; Integrins on basal surface of epithelial cells interact with proteins on basement membrane; Silver stain or Periodic acid-Schiff

Question 24

What is the normal type and function of epithelia in esophagus? What occurs in the pathologic phenomenon of Barrett’s Esophagus?

Answer 24

Stratified squamous - protect against mechanical damage; Barrett’s Esophagus: Gastro-esophageal reflux disease (GERD) –> metaplastic change to columnar, secretory epithelium (like duodenum/small intestine) to help protect against acid, may be precursor to esophageal cancer

Question 25

What is the normal type of epithelia in cervix? What occurs in the pathologic phenomenon of Cervical Intraepithelial Neoplasia (CIN), including its 3 stages?

Answer 25

Stratified Squamous; Loss of controlled growth, CNI I - mild dysplasia & nuclear angulation & vacuolization, CN II - more severe & widespread dysplasia, variation in cell and nuclei size (even though superficial layers may appear normal), CN III - changes in cell and nuclear size plus abnormal mitoses in all epithelial layers