Epithelial Cell Junctions and Bullous Pemphigoid Quiz

Epithelial Tissue Functions

• None of the following functions are NOT a function of epithelium: protection, absorption, filtration, secretion, and sensation.

Epithelial Tissue Structure

• Epithelial tissue is anchored to underlying connective tissue by hemidesmosomes.
• Epithelial cells are held together by desmosomes, which make them cohesive.
• The main characteristic of epithelial tissues is that they are composed of cells that are closely packed, with little intercellular space, and vary in shape and size.

Epithelial Cell Types

• Glandular epithelium contains cells specialized for secretion.
• Epithelial cells that demonstrate polarity are those that have different structures and functions at their apical and basal surfaces.

Basement Membrane

• The basement membrane is composed of a basal lamina and a reticular lamina.
• The basal lamina is a thin layer of extracellular matrix that separates epithelial cells from underlying connective tissue.
• The function of the basal lamina is to anchor epithelial cells to the underlying tissue and regulate the exchange of molecules.

Intercellular Junctions

• Intercellular junctions are structures that connect adjacent epithelial cells.
• The terms 'basal lamina' and 'basement membrane' are not interchangeable.
• Gap junctions allow ions and other small molecules to pass through to adjacent cells, facilitating communication.
• Tight junctions form a seal to prevent the flow of materials between epithelial cells.
• Adherens junctions provide adhesion between adjacent cells through cadherin and catenin proteins.
• Desmosomes are responsible for spot adhesion between cells.
• Hemidesmosomes attach epithelial cells to the basal lamina.

Epithelial Cell Specializations

• Microvilli are structures that increase the surface area for absorption or secretion in epithelial cells.
• Squamous epithelial cells are characterized by a width greater than height (flattened).
• Cilia are specialized apical structures responsible for the movement of fluid along the epithelial surface.
• Apocrine glands are characterized by the loss of a large amount of apical cytoplasm during secretion.
• Holocrine glands are characterized by the disintegration of secretory cells during secretion.
• Mucous cells produce mucins.
• Myoepithelial cells contain actin and can contract to squeeze out secretory product.

Epithelial Tissue Types

• Endothelial epithelium lines blood and lymphatic vessels.
• Mesothelial epithelium is found in the serous cavities (pleura, pericardium, peritoneum).
• Simple columnar epithelium is found in the small intestine.
• Stratified squamous epithelium covers areas where the skin is thin but needs protection.
• Exocrine glands retain a connection with the surface epithelium and secrete hormones through ducts.

Epithelial Diseases

• Pemphigus is a blistering disease caused by autoantibodies to desmoglein proteins, leading to loosening of spot desmosomes and fluid accumulation.