Chapter 4: Histology - Part 1

Tissues

a group of structurally and functionally related cells, surrounded by the extracellular matrix

Extracellular matrix

liquid component (water, nutrients, ions, macromolecules) and protein fibers (collagen, elastic, and reticular fibers)

Integral proteins

link neighboring cell’s plasma membranes

Cell junction

ways neighboring cells bind to one another (tight junction, desmosomes, gap junction)

Tight junction

hold cells closely together, integral proteins of adjacent cell’s plasma membranes are locked together, forming a seal around apical perimeter of cell

Desmosomes

strongly hold cells together but allow materials in extracellular fluid to pass through space between cells (tissues subjected to great mechanical stress-epithelia of skin)

Gap junctions

channels between adjacent cells that allow small substances to move from one cell to another (cells that communicate with electrical signals-cardiac muscle cells)

Pemphigus vulgaris

autoimmune disease that attacks desmosomes

Types of tissues

epithelial, connective, muscle, nervous tissues

Epithelial tissues (epithelia)

cover and line all body surfaces (outside wall of organs, inner lining of hallow organs, walls of body cavities, skin) and cavities, constantly injured cell type

Classifying epithelia

depends on number of cell layers and cell shape

Simple epithelium

1 layer of cells

Stratified epithelium

multiple layers of cells

Squamous epithelium

flattened, irregularly shaped cells

Cuboidal epithelium

cube-shaped cells

Columnar epithelium

column-shaped cells

Transitional epithelium

Apical cells dome-shaped when relaxed and flattened when stretched

Functions of epithelium

protection (skin), secretion (glands), absorption (small intestines), sensory (taste buds), filtration (glomerulous)

Characteristics of epithelia

attached to a basement membrane, composed of closely packed cells held together by intercellular junctions, avascular (no blood vessels), innervated (contains neurons), high rate of regeneration

Basement membrane

an acellular structure produced by both epithelial and underlying connective tissue cells

Basal surface

the side of epithelial cells that touches the basement membrane

Apical surface

the side of epithelial cells that doesn’t touch the basement membrane