SSN Session

Epithelial TissueJennifer Chang (jtc2109)

Bram Welch-Horan (tbw5)October 11, 2005

Epithelium

What is epithelium?

• Covers exterior surfaces• Lines internal closed cavities and body tubes• Forms secretory portions of ducts and glands• Avascular tissue• High regeneration capacity

Polarized Cells

Apical: • faces the lumen or outside world• separated from the basolateral side by tight junctions

Basolateral:• Lateral:

• side that faces neighboring cell• forms functional continuum with basal side

• Basal: • adheres to extracellular connective tissue – basement membrane

Apical

Lateral

Lumen

Basal

The Apical RegionEpithelial Specializations:

Microvilli Stereocilia Cilia

small intestines epididymis fallopian tube

• Cytoplasmic processes that extend from cell surfaces

• Made of actin skeleton above intermediate filaments

• Increase area for absorption as in small intestine

• Insert into terminal web

Microvilli

terminal web

microvillus border

Small intestines

Stereocilia• Long microvilli (NOT CILIA!)• Non-motile

Epididymis

• Motile processes of microtubules that move synchronously

• Insert into basal bodies (1 cilium per 1 body)

• 9+2 microtubule arrangement

Cilia

cilia Basal bodies

Trachea

Fallopian tube

The Lateral RegionJunctional Complex (aka Terminal Bar) : site of specialized attachment of adjoining epithelial cells

terminal bar

terminal bar

microvillus border

terminal web

Bodian silver stain

3 Components (apical -> basal):

1. Zonula Occludens=Tight Junction•most apical•located around entire perimeter•diffusion barrier

2. Zonula Adherens •around entire perimeter•add to integrity of epithelial surface

3. Macula Adherens=Desmosome•occur at small discrete sites

Gap junctions•at small discrete sites•metabolic and electrical coupling

The Junctional Complex

Electron micrographs of the junctional complex

The Basal RegionBasement membrane1. Basal Lamina

• Secreted by epithelial cells• Barrier between epithelium and connective tissue• Collagen type IV, proteogylcans & glycoproteins (PAS +)

2. Reticular Lamina• Connective tissue below epithelium• Collagen type III

HemidesmosomesJunctions that anchors epithelial cells to basal lamina

basal lamina

PAS stain

Question 1. This structure is typically found in the

a) tracheab) kidneyc) epididymisd) small intestines

Question 2.Which of the following is FALSE regarding the structure at the pointer?

a) its permeability determines whether the epithelia is “tight or “leaky”b) it occurs at small discrete sitesc) it separates the apical surface from the basolateral surfaced) it is a component of the junctional complex

Question 3What type of collagen is found in the tissue at the pointer?

a) type IIb) type IIIc) type IVd) type VII

Types of Epithelial Cells

Epithelial Cell Types - Nomenclature

• Simple – 1 cell layer thick

• Stratified – 2 or more cell layers thick

• Squamous – cell width > height (i.e., flat)

• Cuboidal – width/depth/height ~same

• Columnar – cell height >> width

Simple Squamous Epithelium

• 1 cell layer thick

• function: exchange

• absorption, secretion, diffusion

• e.g. – blood vessels

• barrier function in CNS

Simple Cuboidal

• cuboidal shape (or pyramidal)• round, central nucleus• absorption / secretion, conduit• e.g. – small ducts of exocrine glands (pancreas), kidney tubules

Simple Columnar

• elongated cells w/ elongated nuclei

• height > width

• absorptive (e.g. small intestine) or secretory (e.g. gastric glands)

• other examples: -lining of colon, stomach, gall bladder

Stratified Epithelium

• 2 or more layers thick

• classified based on surface cells (can be squamous, cuboidal, or columnar)

• functions include: protection, barrier, resist abrasion

• Examples: epidermis, esophagus, larger exocrine ducts

What type of stratified epithelium is seen above?

Stratified Epithelium

What type of stratified epithelium is seen above?

Stratified Squamous Epithelium

• 2 or more layers thick

• classified based on surface cells (can be squamous, cuboidal, or columnar)

• functions include: protection, barrier, resist abrasion

• Examples: epidermis, esophagus, larger exocrine ducts

Pseudostratified Epithelium

All cells rest on basement membrane, but not all reach apical surface

-function: secretion, absorption, conduit-e.g., trachea, epididymis

Transitional Epithelium

Transitional Epithelium – “Urothelium"

• special stratified epithelium

• apical surface may appear “domed”

(empty) and flattened full)

• function: distensibility

• lines lower urinary tract

• i.e., ureters, bladder, proximal urethra

Question 4

What kind of epithelium lines the secretory alveoli of this exocrine gland?

a. Simple Columnar

b. Simple Cuboidal

c. Squamous

d. Transitional

Questions 5, 6

• 5. Select the one correct statement regarding the surface epithelium.• 6. The tissue or tissues that are specialized to provide a barrier to

luminal absorption are shown in:

Figure A Figure B

Lab 3, Slide 35 Lab 3, Slide 25

Question 7

This epithelial cell type is found in:

a. Bladder

b. Kidney tubules

c. Intestinal epithelium

d. Epidermis

Question 8

What type of epithelium is this?

a. Pseudostratified

b. Stratified Columnar

c. Stratified Squamous

d. Stratified Cuboidal