SSN Session Epithelial Tissue Jennifer 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 Region Epithelial Specializations: MicrovilliStereocilia Cilia small intestinesepididymis 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 Region Junctional Complex (aka Terminal Bar) : site of specialized attachment of adjoining epithelial cells 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 Region Basement membrane 1.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 Hemidesmosomes Junctions that anchors epithelial cells to basal lamina basal lamina PAS stain

Question 1. This structure is typically found in the a) trachea b) kidney c) epididymis d) 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 sites c)it separates the apical surface from the basolateral surface d)it is a component of the junctional complex

Question 3 What type of collagen is found in the tissue at the pointer? a)type II b)type III c)type IV d)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