Epithelium and Histology

Simple Epithelium

layer of epithelium with only one row of cells

Stratified Epithelium

layer of epithelium with more than one row of cells

Pseudostratified Epithelium

layer of epithelium where every cell touches basement membrane but not every cell touches the apical surface

Squamous Cells

flattened and scale-like cell formation

Cuboidal Cells

cells that appear to be cubes

Columnar Cells

cells are formed in a cylinder

Cell in Glands

usually in a simple cuboidal conformation

Cells Lining Ducts

usually in a stratified cuboidal formation

Transitional Epithelium

usually included in hollow organs that stretch, cells near apical surface become pillowy compare to the others

Layering of Skin (functions)

protects against friction and injury, barrier to water, diseases, and toxins, lower layers help regenerate the upper layer

Apical Surface

side of cell that faces the lumen or external environment, contain microvilli, cilia, and sterocilia

Lateral Surface

side of cell that faces the sides of adjacent cells, includes tight junctions, adherens junctions, desmosomes, and gap junctions

Basal Surface

side of the cell that attaches to the basement membrane, basal lamina hemidesmosomes

Tight Junctions

seal the space between adjacent cells forming a barrier to diffusion

Adherens Junctions

ribbon-like structures that provide mechanical attachment between adjacent cells

Desmosomes

spot-like adhesions that provide resistance to mechanical stress

Gap Junctions

aqueous channels between the cytoplasm of adjacent cells that allow the passage of small molecules

Important Epithelium of the Skin

simple cuboidal, stratified squamous, keratinized stratified squamous, stratified cuboidal

Connective Tissue

provides structural and functional support to tissues, houses blood vessels, immune defense, protects organs, and stores fat

Loose Connective Tissue

supports epithelium and surrounds vessels and nerves of the dermis, not resistant to stress, contains loosely arranged collagen fibers, rich in fibroblasts and has an abundant ground substance

Dense Irregular Connective Tissue

consists primarily of collagen fibers, the predominant connective tissue in the skin, fewer fibroblasts, fibers orient in different directions to withstand stress

Dense Regular Connective Tissue

uniform collagen bundles forming ligaments and tendons

Cells of the Connect Tissue

fibrocytes, osteocytes, and chondrocytes; adipocytes; immune cells (lymphocytes, plasma cells, macrophages, mast cells etc.)

Fibers of the ECM

composed of proteins, specifically collagen, reticular fibers, and elastic fibers

Collagen Fibers

most abundant fiber in adults

Reticular Fibers

aka type III collagen, most abundant type in the embryo or fetus, also abundant in healing tissues, particularly prominent in lymphoid and hematopoietic tissues, needs special stain to be visualized on histology

Elastic Fibers

interwoven with collagen to allow tissues to stretch, arranged in branching pattern with elastin monomers cross-linked to form fibers

Ground Substance

important fluid in the ECM< composed of glycosaminoglycans (GAGs) and multiadhesice glycoproteins

Glycosaminoglycans (GAGs)

polysaccharides with long, inflexible linear chain of repeating disaccharides, mostly sulphated to give negative charge, hydrates and resists compressive forces, most attach to a core protein (except hyaluronan)

Hyaluronan

larges GAG, does not form PGs, but binds PGs to its surface, the aggregates with PGs provide excellent shock absorption

Multiadhesive Glycoproteins

serve to stabilize the ECM and link ECM to cell surfaces, laminins the most important, interact with receptors to cell membrane