1. Cell attachment and connective tissue

What are the 3 primary functions of epithelial tissue?

Covering/lining/protection, absorption, and secretion.

What type of cells compose epithelial tissue?

Polyhedral cells that are strongly attached to one another.

Why are epithelial cells strongly attached to one another?

To form continuous cell sheets that coat or line surfaces.

Where does epithelial tissue occur in the body?

On outer surfaces, throughout the GI tract, and lining various organ surfaces

What structures can epithelial tissue form besides surface linings?

Glands and other secretory tissues.

Does epithelial tissue undergo mitosis?

Yes, epithelial tissue continually undergoes mitosis to replace lost or damaged cells.

Is epithelial tissue vascular or avascular?

avascular

How does epithelial tissue receive nutrients and oxygen if it is avascular?

diffusion from blood vessels in adjacent connective tissue.

What are the two major surfaces of epithelial tissue (POLARITY)?

apical surface and a basal surface.

What tissue generally anchors epithelial tissue?

Underlying connective tissue.

What is the primary function of the basement membrane?

anchor epithelial tissue to underlying connective tissue.

What is the basement membrane/basal lamina?

thin sheet of ECM that anchors epithelium to underlying connective tissue.

Which tissues make up the basement membrane?

Both epithelial tissue and connective tissue.

When would you call is basement membrane as opposed to basal lamina

used with light microscopy (BL is for electron microscopy) `

How are epithelial cells anchored to the basement membrane?

Via hemidesmosomes.

What are the 3 zones of the basement membrane?

Lamina lucida, lamina densa, and lamina fibroreticularis.

Which of the 3 zones of the basement membrane may be absent?

The lamina fibroreticularis.

What are the key components of the lamina lucida?

Laminin, entactin, and integrins on the epithelial cell side

What is the primary collagen found in the lamina densa?

Type IV collagen.

What are the key components of the lamina fibroreticularis?

Type III, V, and VII collagen.

What are microfilaments composed of?

Actin.

What are the two major functions of microfilaments?

Structural support and contractility.

How do microfilaments contribute to cell structure?

help maintain cell shape and form structures such as microvilli and filopodia.

How do microfilaments contribute to cellular contractility?

They form tracks for myosin, allowing contractile movement.

What are the main functions of intermediate filaments?

Structural support and anchoring.

Are intermediate filaments involved in cellular contraction?

no, non-contractile.

What intermediate filament is associated with cells of mesenchymal origin?

Vimentin

What intermediate filament is characteristic of epithelial cells?

Cytokeratin

What are microtubules composed of?

Tubulin

What is the role of microtubules in intracellular transport?

act as a “monorail system” for motor proteins such as kinesins.

Which motor protein is associated with microtubule-based intracellular transport?

Kinesin which runs along microtubules

Which motor protein is associated with the movement of cilia and flagella?

Dynein which runs along microtubules

What are two major structures that depend on microtubules for movement?

Cilia and flagella.

Overall what are the main compinents of the cytoskeleton

Microtubules, intermediate filaments, and microfilaments (actin).

What is another name for a tight junction?

Zonula occludens.

What type of interactions form tight junctions?

Homotypic interactions between transmembrane proteins on adjacent cells.

What is the main function of tight junctions?

restrict movement between cells by forming very narrow gaps.

How do tight junctions contribute to epithelial cell polarity?

maintain cell polarization by separating the apical and basal/lateral membrane domains.

What are the major transmembrane proteins found in tight junctions?

: Claudins, occludin, and JAM

Which cytoskeletal component do tight junctions bind to?

Actin microfilaments.

Besides controlling movement between cells, what other role do tight junctions have?

participate in cell signaling pathways.

What is another name for a cell-to-cell adhesive junction?

Zonula adherens.

What is the primary function of zonula adherens?

Holds adjacent cells together.

What proteins form the main adhesive complex in zonula adherens?

Cadherins on the outside + catenins on the inside.

Cadherins function

protein on the OUTSIDE of cell that participates in adhesive cell-cell junction

Catinins

proteins that link cadherins to the actin cytoskeleton inside the cell.

Special thing about cadherins

is that they require calcium ions for adhesion and stability.

What cytoskeletal element is associated with zonula adherens?

Actin filaments

Role of viniculin and actinin in cell-cell adhesive junctions

proteins that link cadherin-catinin complex to actin

Nectin role in cell-cell adhesive junctions

binds to afadin on the inside of cell

What is the primary function of focal adhesion junctions?

anchor cells to the ECM.

What transmembrane protein replaces cadherins in focal adhesions?

Integrins

What do integrins interact with in the ECM during focal adhesion?

ECM proteins such as collagen and fibronectin.

Which cytoskeletal component do focal adhesions attach to?

actin

Which proteins help connect focal adhesion complexes to actin?

Vinculin, α-actinin, and talin.

What is the primary function of desmosomes?

Cell-cell adhesion that helps resist shearing forces.

What are the specialized cadherins found in desmosomes?

Desmoglein and desmocollin.

What are the main intracellular proteins associated with desmosomes?

Desmoplakin, plakoglobin, and plakophilin.

What type of cytoskeletal filament do desmosomes attach to?

Intermediate filaments.

What type of interaction occurs between desmoglein and desmocollin?

A heterotypic interaction.

What is the primary function of hemidesmosomes?

Cell–ECM adhesion that helps resist shearing forces.

What transmembrane protein is found in hemidesmosomes?

Integrin

What does the intracellular side of a hemidesmosome contain?

An intracellular plaque that connects to intermediate filaments.

How do hemidesmosomes attach epithelial cells to the basal lamina?

Through integrin–laminin interactions and collagen XVII.

What is the primary function of gap junctions?

allow direct communication between adjacent cells through aqueous pores.

What are gap junction pores made of?

Connexins

How many connexins form one connexon?

6 connexins

What can pass through gap junctions?

Ions and small water-soluble molecules.

How do gap junctions help propagate electrical signals?

They allow ions to pass directly between adjacent cells.

Junctional complex

cluster of junctions along a cell-cell contact point including different types of junctions

Which junctions do NOT make up a junctional complex?

Hemidesmosomes

What is a terminal bar?

A group of junctional complexes that attach cells along their lateral surfaces (sheets sitting on top of eachother)

What are the 3 major components of connective tissue?

Cells, fibers, and ground substance.

From which embryonic germ layer are connective tissue cells derived?

Mesoderm.

What type of progenitor cells are found in connective tissue?

Multipotent mesenchymal progenitor cells.

Multipotent mesenchymal progenitor cells.

Stroma

What are the permanent connective tissue cells?

Fibroblasts, adipocytes, macrophages, and mast cells.

What are the transient connective tissue cells?

Plasma cells, lymphocytes, neutrophils, and eosinophils.

What is the main connective tissue cell responsible for ECM production?

fibroblast

What role does fibroblast motility play in connective tissue?

highly motile and migrate to areas where ECM production and tissue repair are needed.

Do fibroblasts typically form cell-cell connections?

rarely form cell-cell connections; an exception is the periodontal ligament.

What is a fibronexus?

A connection between actin, integrins, and fibronectin in the ECM.

What is the cytoskeletal component involved in the fibroblast fibronexus?

actin

What is the basic structural feature of collagen?

triple helix to provide tensile strength

Most abundant protein in the body

collagen

What amino acids are collagen particularly rich in?

proline and lysine for hydrogen bonding in triple helix

What is the major synthetic product of mesenchyme-derived cells?

collagen as a key extracellular matrix component

What is the primary collagen type in dentine?

Type I collagen, providing structure and strength.

What collagen types are found in dental pulp?

Type I and III collagen

What is the primary collagen type in cartilage?

Type II.

What type of collagen is found in the basement membrane?

Type IV.

What is the characteristic structure formed by Type IV collagen in the basement membrane?

A “chicken-wire” meshwork.

What produces the banded appearance of collagen fibrils?

The ¼ stagger of the microfibrils creates a banded structure.

Why is the staggered organization of collagen important in bone and dentin?

creates gap regions where mineral can be deposited.

What vitamin is essential for stable collagen assembly?

Vitamin C —>SCURVY

What happens to collagen when vitamin C is deficient?

proper hydroxylation is impaired —> less stability

What cell primarily produces elastin?

Fibroblasts in connective tissue.

What forms the scaffold for elastin fiber assembly?

Fibrillin-1 and fibrillin-2 form a microfibril scaffold to make sheets

What is the basic structure of a mature elastin fiber?

An elastin core supported by a glycoprotein microfibril scaffold.

What is the key molecular defect in Marfan syndrome?

mutation in fibrillin-1 (FBN1).