Introduction to Tissues Tissues are groups and layers

Introduction to Tissues • Tissues are groups and layers of similar cells specialized to carry on a particular function. • There are 4 major types of tissues: • Epithelial Tissue • Form protective coverings and function in absorption and secretion • Connective Tissue • Supports soft body parts and bind structures together • Muscle Tissue • Produce body movements • Nervous Tissue • Conduct impulses that help control and coordinate body activities

Tissue Components • There are two general parts of a tissue: • Cells: must be similar cells and have a common function • Extracellular matrix: the nonliving portion of tissue that varies in composition between tissue types and can be solid or liquid

Epithelial Tissues-Location • Found throughout the body • Covers organs • Forms the lining of body cavities (nasal, oral, etc) • Lines hollow organs (bladder, stomach, etc) • It always has a free surface (exposed to the outside of the body or to an open internal space) • The opposite surface is anchored to connective tissue by a nonliving layer called the basement membrane (the extracellular matrix of epithelial tissue)

Epithelial Tissues-Characteristics • Lack blood vessels • Nutrients diffuse to epithelium from underlying connective tissues • Divide readily • Injured epithelium heals rapidly • (ex: the cells that line the stomach and intestines are continually damaged and replaced) • Tightly packed • Very little extracellular matrix between the cells of epithelial tissue • This allows them to form effective protective barriers (epidermis, lining of the mouth, etc)

Epithelial Tissues-Functions • Protection-orifices, skin, organ linings, etc • Secretion-endocrine glands (pancreas, ovaries, etc) • Absorption-line the intestines • Excretion-sebaceous glands, mammary glands

Epithelial Tissues-Classification • Epithelial tissues are classified based on the shape and number of layers of cells. • There are three shapes: • 1) Squamous-thin, flattened cells • 2) Cuboidal-cube shaped cells • 3) Columnar-tall, elongated cells • There are two varieties: • 1) Simple-composed of one layer • 2) Stratified-composed of multiple layers