Cell Surface Specializations and Junctions

This set of vocabulary flashcards covers cellular anatomy, specifically apical and baso-lateral surface specializations, types of cell junctions (occluding, anchoring, and communicating), and the components of the basal and basement membranes.

Microvilli

Tiny projections from the apical membrane covered by cell coat, with a core of actin filaments fixed basally to the terminal web.

Occluding junctions

A type of cell junction that acts as a barrier with no space between cells.

Anchoring junctions

Junctions that provide mechanical attachment of cells to their neighbors or to the ECM through specialized transmembrane proteins called CAMs.

Communicating junctions

Junctions that permit the movement of ions between cells.

Homotypic CAMs

Cell adhesion molecules involved in cell to cell junctions.

Heterotypic CAMs

Cell adhesion molecules involved in cell to matrix junctions.

Occludin

The transmembrane protein found in occluding junctions, supported by actin filaments.

Zonula occludens

A type of tight junction that forms a complete belt around the whole circumference of the cell, such as in the columnar cells of the intestine.

Fascia occludens

Patches of occluding junctions, for example, those found in blood capillaries.

Macula occludens

A rare, spot-like occluding junction.

Adherens junctions

A type of anchoring junction located basal to the zonula occludens with an intercellular space of $20\,nm$ where actin filaments attach to cadherins.

Cadherins

The Cell Adhesion Molecules (CAMs) specifically associated with anchoring junctions.

Desmosomes

A spot-like anchoring junction and the third part of junctional complexes, characterized by an intercellular space of $30\,nm$ and keratin intermediate filaments attached to desmoglein.

Focal adhesions

Spot-like junctions that anchor cells to the ECM using integrin transmembrane proteins to connect actin filaments to fibronectin.

Hemidesmosomes

Spot-like junctions that anchor cells to the basal lamina using integrin to connect intermediate filaments to laminin.

Junctional complexes

A characteristic arrangement of junctions in epithelial cells consisting of (from top to bottom): zonula occludens, zonula adherens, and desmosomes.

Gap junction (Nexus)

A communicating junction with a narrow intercellular space of $2\,nm$ formed by the transmembrane protein connexin; it is not part of the junctional complex.

Connexin

The transmembrane protein that forms cylindrical channels in gap junctions between two cells.

Lateral Interdigitation

Finger-like projections that interlock adjacent cells together.

Basal membrane infoldings

Deep invaginations of the basal cell membrane that form compartments for mitochondria, typical of ion-transporting cells.

Basal lamina

An extracellular supportive layer visible only by EM, comprised of the lamina lucida and lamina densa.

Lamina lucida

An electron-lucent layer of the basal lamina present towards the cell basal membrane, formed of laminin glycoprotein and the transmembrane protein integrin.

Lumina densa

An electron-dense layer of the basal lamina present towards the underlying connective tissue, formed of glycoprotein, GAGs, and $Collagen\,IV$.

Lamina fibro-reticularis

A layer formed by connective tissue lying between the basal lamina and underlying tissue, containing $Collagen\,I$ and $Collagen\,III$.

Anchoring fibers

Fibers made of $Collagen\,VII$ that join the lamina fibro-reticularis to the basal lamina.

Basement membrane

The PAS +ve layer seen by LM underneath epithelium, resulting from the glycoprotein content of the lamina lucida and lamina densa.