Cell Biology: Apical Cell Surface Structures

Apical Cell Surface Specializations

• Microvilli: Finger-like projections, stable and uniform.

• Microvilli core: Actin filaments with actin-binding proteins.

• Microvilli location: Small intestine and kidney tubules.

• Microvilli function: Increase surface area for absorption (20-30 times).

• Microvilli microscopy: Striations or brush border (light microscopy), detailed actin core (electron microscopy).

• Cilia: Highly motile, longer than microvilli.

• Cilia location: Upper respiratory tract and female genital tract.

• Cilia microscopy: Hair-like structures (light microscopy), basal body and shaft (electron microscopy).

• Cilia core: Microtubules (9 doublets+2 arrangement) with dynein arms for movement.

• Cilia function: Move fluids or particles along the surface.

• Flagella: Long, single, similar to cilia.

• Flagella core: Similar to cilia's axoneme structure.

• Flagella location: Sperm cells (form the tail).

• Flagella function: Facilitate cell movement.

Cellular Junctions

• Tight Junctions (Zonula Occludens):

• Location: Apical position in epithelial cells.

• Structure: Bands encircling cells; no intercellular space.

• Proteins: Claudin and occludin.

• Function: Prevent material flow between cells, form protective barrier (e.g., blood-brain barrier).

• Medical Significance: Defects can affect the blood-brain barrier, leading to neurological disorders.

• Adherent Junctions (Zonula Adherens):

• Location: Below tight junctions, encircling cells.

• Structure: Continuous band around cells connected to actin cytoskeleton.

• Proteins: Cadherins.

• Function: Strengthens and stabilizes tight junctions.

• Desmosomes (Macula Adherens):

• Location: Disk-shaped on adjacent cell surfaces.

• Structure: Spot-like, binds intermediate filaments.

• Proteins: Desmogleins, desmocollins (cadherin family).

• Function: Maintain cell integrity and cohesion.

• Medical significance: Autoimmune reactions can cause skin blistering.

• Hemidesmosomes:

• Location: Binds epithelial cells to basement membrane.

• Structure: Half of a desmosome.

• Proteins: Integrins.

• Function: Anchors cells to the basement membrane

• Gap Junctions (Nexuses):

• Location: Throughout cell membranes.

• Structure: Channels between adjacent cells, formed by connexins.

• Function: Allow rapid exchange of small molecules for cell coordination and communication.

Explore the fascinating world of apical cell surface specializations including microvilli, cilia, and flagella. This quiz covers their structures, functions, and locations within the body. Test your knowledge on how these structures contribute to cellular processes and movement.