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Flashcards in Epithelial Tissue & Cell Junctions Deck (69):

Epithelial Tissue Properties

1. Intercellular Space
2. Intercellular Junctions
3. Intermediate Filament: Keratin
4. Regenerate when injured
5. Avascular & Non-nervous
6. Basement Membrane
7. Exhibit Polarity
8. Metaplasia
9. Derived from all germ layers



Change in epithelial cell structure due to chronic condition


Skin derivation



Endothelium derivation



Lining of GI tract derivation



Lateral Domain

1. Zonula Occludens
2. Zonula Adherens
3. Macula Adherens
4. Nexus/Gap Junctions


Basal Domain

1. Basement Membrane
2. Focal Adhesions
3. Hemidesmosomes
4. Basal Membrane Infoldings


Apical Domain

1. Cilia
2. Microvilli
3. Stereocilia


Zonula Occludens

Paracellular route.
First from the top in Lateral Domain.
Includes JAM, occludin, claudin, ZO-1, ZO-2, ZO-3, and actin
Surrounds the entire perimeter of the cells

Intra-membranous sealing strands occlude the space between cells; confers epithelial tightness or leakiness; establishes functional domains in the plasma membrane



Form backbone; form extracellular aqueous channels for the paracellular passage of ions and other small molecules.



Maintain barrier between adjacent cells as well as barrier between apical and lateral domains.



Present in endothelial cells; mediates interactions between endothelial cells and monocyte adhesions.


Mutation in gene encoding claudin-14

Increased permeability of ZO in organ of Corti which decreases generation of action potentials causing hereditary deafness.


Cell Adhesion molecules

Cadherins- calcium dependent transmembrane proteins
Integrins- calcium independent transmembrane proteins


Zonula Adherens

Cell membranes separated by an intercellular space which is larger than zonula occludens.

Extends around the entire perimeter of the cell

Actin filaments are linked by alpha-actinin, vinculin, and catenin to E-cadherin (calcium dependent)

1. Mechanical Stability-cohesive function of cell groups
2. Regulate differentiation, migration, proliferation, morphogenesis (formation of tubes, embryonic folding, etc.), and survival of epithelial cells


Macula Adherens/Desmosomes

Think Stapling
Cell membranes separated by a wider intercellular space than ZA

Occurs at small discrete sites-spot welds

Link cytokeratin (intermediate) filaments to desmogleins & desmocollins

Linkage through plaque proteins (Desmoplakins & Plakoglobins)

1. Provide high tensile strength and resist shearing forces


Pemphigus Vulgaris

Autoantibodies against desmogleins causing painful flaccid blisters in oropharynx and skin

Effects people over 40 and results in dysfunctional desmosomes or macula adherens


Nexus/Gap Junctions

Important in tissues in which activity must be coordinated:
1. Epithelia engaged in fluid and electrolyte transport
2. Vascular and Intestinal Smooth Muscle
3. Heart Muscle


Nexus/Gap Junctions Features

1. Nutrients and signal molecules may be transported between cells without loss of material into the intercellular space.
2. Cell membranes of two adjoining cells are separated by an intercellular space bridged by connexon (individual unit of a gap junction)
3. Each connexon is formed by 6 Gap Junction Proteins Connexin
4. Connexons contain central pores that allow passage of molecules with molecular mass < 1500 Da


Tissues affected by mutation in genes encoding for connexin

1. Cardiac arrhythmias
2. Slower conduction of nerve impulses
3. Decreased peristalsis in the small intestine
4. Inefficient glycogenolysis
5. Congenital Deafness (Cx26)
6. Inherited Cataract (Cx46 & Cx50)


Lateral Plicae

1. Infoldings of lateral membrane
2. Localized Na+/K+ ATPase
3. Important in epithelia engaged in fluid and electrolyte transport (eg small intestine)



1. Heterotypic interactions
2. Interact with ECM molecules (such as collagens, laminin, and fibronectin) & with actin and intermediate filaments of the cell cytoskeleton
3. Regulate cell adhesion, control cell movement and shape, and participate in cell growth and differentiation

Calcium Independent!


Focal Adhesions

Create a dynamic link between the actin cytoskeleton and ECM.

1. Molecular basis for cell migration
2. Mechanosensitivity- sensing and transmitting signals from the extracellular environment into the interior of the


Intermediate Filament




1. Occurs in the cornea, the skin, and the mucosa of the oral cavity, esophagus, and vagina - epithelia subject to abrasion and mechanical shearing forces
2. Link intermediate filaments in cell to ECM
3. Intracellular Attachment Plaque-major proteins-Plectin, BP 230 (BPAG1), Erbin
4. Transmembrane Proteins belong to integrin family - a4B6 integrin, Collagen Type XVII, CD 151
5. Type XVII collagen (BPAG2, BP 180) - regulates expression and function of laminin-5


Dermo-Epidermal separation

Dermo-epithelial separation are antibodies against integrin causing blisters - think basal effect

Causes blisters that are less likely to erupt because they are deep


Bullous Pemphigoid

Autoantibodies against hemidesmosomal proteins BP230 and BP180

Causes widespread blistering with pruritus


Basement Membrane Staining

H&E stain does not show BM
PAS staining stains carbohydrates and shows BM


Basal Lamina vs. Basal Membrane

Basal Lamina includes lamina densa and lamina rara/lucida

Basal Membrane includes lamina densa, lamina rara/lucida, and reticular fibers

Clinically there really is no difference


Basement Membrane Zone

Important clinically as it contains:
1. Anchoring Plaque (Collagen type IV)
2. Anchoring Fibrils (Collagen type VII)- communicate with ECM and anchor cell


Basal Lamina Molecular Components and Functions

1. Collagen, Type IV: Insoluble structural support
2. Heparan Sulfate (Proteoglycan): Most common in basal lamina is perlecan. Confers electrostatic charge.
3. Laminin (Glycoprotein): Bridge between the cells & Type IV Collagen; Possess binding sites for different integrin receptors
4. Entactin/Nidogen (Glycoprotein): Bridge between two networks: Laminin and Type IV Collagen


Collagen in Basal Lamina

1. Type IV, major type: Insoluble structural support, forms scaffold
2. Type VII: Forms anchoring fibrils that link the basal lamina to the underlying reticular lamina


Basal Lamina Functions

1. Structural attachment-cells to adjacent CT

2. Compartmentalization-isolate the connective tissue from epithelia, nerve, and muscle tissues

3. Filtration- Movement of substances to and from the CT is regulated in part by the basal lamina, largely through ionic charges and integral spaces

4. Tissue Scaffolding-Serves as a guide or scaffold during regeneration

5. Serve as pathways for cellular migration but act as barriers against tumor cell invasion

6. Regulate cell shape, proliferation, differentiation, and motility as well as gene expression and apoptosis during morphogenesis, fetal development, and wound healing


Epidermolysis Bullosa Dystrophica

Type VII Collagen Gene Mutation
No anchoring fibrils- dermal-epidermal separation
Basement Membrane Zone separation
Results in scarring


Basal Infoldings

Invagination of the Cell Membrane-increase surface area
Numerous Mitochondria, Provide Substrate ATP
Contain Ion Pumps (Na+/K+ ATPase)
Predominate in cells involved in active transport- PCT, DCT, ducts of salivary glands
Shelf like cristae



Hair-like extensions of the apical plasma membrane- seen mostly in pseudostratified epithelium

Much taller than microvilli

9+2 arrangement



The internal core of microtubules in cilia


Basal body

Hold cilia in place in apical domain. A centriole-derived, microtubule organizing center (MTOC)


Cilia components

1. Axoneme
2. Basal body
3. Radial Spoke-connect peripheral to central microtubules
4. Nexin-between peripheral microtubules
5. Dynein arms-site of energy in cilia (ATPase)


Motile Cilia

1. The axoneme consists of 9 doublet microtubules uniformly spaced around 2 central microtubules. (9+2)

2. Nexin connects the 9 doublet microtubules. It keeps the doublets from moving away from each other independently.

3. Each doublet has short arms that consist of dynein ATPase, which splits ATP to provide energy.

4. These are inserted into basal body that consists of 9 triplet microtubules and no central microtubule (9+0).

5. Ciliary action results from bending of the doublets first in one direction and then in the other and is fuelled by dynein-catalyzed conversion of ATP to ADP.

6. Ciliary movement is frequently coordinated to permit a current of fluid or particulate matter to be propelled in one direction over the epithelial surface.

7. These form the core of flagella (eg tails of spermatozoa).


Primary Cilia

1. Non-motile; known as monocilia because each cell usually possesses only one.
2. Core of microtubules arranged in 9+0 pattern.
3. Important cellular-signaling devices; function as signal receptors sensing chemical, osmotic, light, and mechanical stimuli from external environment.


Mutations in genes ADPKD1 and ADPKD2

Affect development of primary cilia leading to polcystic kidney disease (PKD). The proteins encoded by these genes, polycystin-1 and polycystin-2, respectively, are essential in the formation of the calcium channels associated with primary cilia.


Nodal Cilia

1. Motile/Active rotational movement

2. Core of microtubules arranged in 9+0 pattern with motor proteins.

3. Observed in embryos - establish the left-right asymmetry of internal organs.


Kartagener's syndrome

Mutation in dynein causing absence of dynein

Nodal cilia defect
1. Dextrocardia
2. Situs inversus
3. Recurrent Respiratory Tract infections



Finger-like cytoplasmic projections

Found mostly in epithelia specialized for absorption

LM: striated or brush borders

The number and shape correlate with absorptive capacity


Actin microfilaments

Cytoplasmic core of microvillus which insert into the terminal web


Terminal Web

Specialization of actin cytoskeleton lying immediately beneath the cell surface.


Microvillus inclusion disease

Inclusion containing microvilli within apical cytoplasm of the cell

MYO5B gene mutation resulting in zero absorption

infantile diarrhea which is life threatening
life span is 3-20 years which does require a transplant
Total parenteral nutrition (TPN) needed



Act more like microvilli
unusually long, immotile microvilli
Epididymis - facilitate absorption
Inner Ear - Sensory Mechanoreceptors

Core - actin microfilaments


Epithelial Tissue Functions

1. Protect
2. Absorb
3. Secrete
4. Contract (Myoepithelial cells)
5. Sense (Olfactory)
6. Transport


Simple Squamous

1. Alveoli
2. Blood Vessels
3. Body Cavities
4. Cornea
5. Loop of Henle


Simple Cuboidal

1. Thyroid Gland
2. PCT
3. DCT
4. Ovary


Simple Columnar

1. GI Tract
2. Gall Bladder
3. Uterus
4. Uterine Tubes


Simple Pseudo-stratified

1. Respiratory Tract
2. Epididymis
3. Vas Deferens


Stratified Squamous

1. Epidermis of Skin

1. Oral Cavity
2. Pharynx
3. Esophagus
4. Anal Canal
5. Vagina


Stratified Cuboidal

1. Large Ducts of Exocrine Glands


Stratified Columnar

1. Male Urethra


Stratified Transitional

1. Ureter
2. Urinary Bladder


Glandular Epithelium Types

1. Exocrine (into duct)
2. Paracrine (local factors)
3. Endocrine (into blood stream directly)


Exocrine Gland Types

1. Multicellular
2. Unicellular- Goblet cells are only unicellular exocrine glands (Respiratory and GI tract)


Exocrine Glands Release Mechanisms

1. Merocrine- cells secrete in a common lumen and through the duct spread out (exocytosis)
2. Holocrine- Disintegrating cells with contents becoming the secretion
3. Apocrine- Pinching off of apical portion of secretory cell (mammary glands and sweat glands)


Exocrine Glands Type of Secretion

1. Serous cells are smaller, dark staining and more basophilic than mucus cells. They produce secretion which is thin, watery, and rich in enzymes (protein).

2. Mucus cells produce viscous and slimy secretions, rich in PAS +ve mucinogen (heavily glycosylated protein) granules. Mucins, outside the cell, are hydrated to form mucus.


Protein Secreting Cell

1. Perinuclear rER
2. Golgi Complex
3. Apical Secretory Granules

Secretion Examples:
1. Enzymes-gastric chief cells; pancreatic acinar cells
2. Albumin; hepatocytes
3. Hormones; chief cells: Parathyroid


Polypeptide (Hormone) Secreting Cell

1. Perinuclear rER
2. Golgi Complex
3. Basal (toward blood vessels) secretory granules

Secretion Examples:
1. Glucagon- a-cells, Pancreatic Islets
2. Insulin- B-cells, Pancreatic Islets
3. Gastrin- G-cells, Pancreatic Islet; Stomach; Small Intestine
4. Somatostatin- gamma-cells, Pancreatic Islet; Stomach; Small Intestine


Steroid Secreting Cell

1. sER
2. Lipid droplets
3. Mitochondria- tubular cristae instead of shelf-like

Secretion Example:
1. Testosterone- Leydig Cells, Testis
2. Estrogen- Follicular Cells, Ovary
3. Progesterone- Corpus Luteum, Ovary
4. Cortisone and Aldosterone- Adrenal Cortex


Epithelial Cell Highly Specialized for Absorption + Active Transport

Microvilli + numerous mitochondria in basal folds


Myoepithelial cells

Epithelial cells highly specialized for contraction
1. Finger-like processes that embrace an acinus or duct; contraction expels exocrine products.

2. Lie between the epithelial cells and their basal lamina.

3. Cytoplasm contains microfilaments, myosin, tropomyosin, and cytokeratin intermediate filaments.

4. Occur in lacrimal, salivary, mammary, and sweat glands.


Mucus Cells

1. Light-staining, Foamy Appearance (Mucus-containing Apical Vesicles)
2. PAS-positive
3. Predominantly Acidophilic Staining with H&E
4. A Large Supra-nuclear Golgi Complex
5. Nuclei and sparse RER in the Base

Secretion Examples:
1. Mucin- Goblet cells; Secretory Cells of Sublingual & Submandibular Salivary Glands


Serous Cells

Smaller, Darker-staining, and more basophilic than mucus-secreting cells

Secretion Example:
1. Enzymes- Pancreatic Acinar Cells; Secretory cells of Parotid Salivary Glands