Tissue is any group of cells of similar structure that perform a common function. They also have a nonliving material between the cells called the extracellular matrix which we will discuss in detail later.
There are 4 basic tissue types:
Epithelial (covering)
Connective (support)
Muscle (movement)
Nervous (control) tissue
Epithelial tissue covers a body surface or lines a body cavity and is present on almost all glands.
Functions of Epithelia
Protection of underlying tissues
Sensory reception via nerve endings/receptors
Diffusion (movement of molecules down their concentration gradients)
Absorption (taking molecules into cells)
Note role of Microvilli in pic above (to absorb)
Secretion (releasing molecules from cells)
Ion transport (moving charged ions across the tissue)
Filtration (removal of molecules from fluid)
Forms slippery surfaces (production of mucus)
Note role of Cilia in pic above (to propel)
Special characteristics of Epithelia
High Cellularity (cells separated by minimal amounts of ECM)
Specialized contacts (cells joined by special junctions)
Polarity (Apical surface differs from basal surface)
Supported by layer of connective tissue (includes a basement membrane)
Avascular (has no blood vessels) but innervated (has nerves). It receives nutrients from underlying connective tissue where capillaries lie.
Regeneration (lost cells are quickly replaced by mitosis)
How to Classify Epithelia
First name of tissue indicates number of cell layers
Simple—one layer of cells
Stratified—more than one layer of cells
Last name of tissue describes shape of cells
Squamous—cells are wider than tall (plate-like) – “squashed”
Cuboidal—cells are as wide as tall, like cubes
Columnar—cells are taller than they are wide, like columns
Use this Table of Contents to go to the next article
