Tissue: The Living Fabric 4 P A R T A Tissue: The Living Fabric

Groups of cells similar in structure and function Tissues Groups of cells similar in structure and function Histology studies the four tissue types of the human body: Epithelial Covers organs and the body Lines cavities Connective Binds (holds) the body together Protection, insulation, transportation

Muscle Contracts (shortens) to move the body or substances inside the body Nerve Sends electrical signals to control the body

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Epithelial Tissue Found on the surface of the body Covers the organ wall Lines the body cavities Found in the glands

Epithelial functions: Forms boundaries Protection Absorption: allows materials in Filtration: regulates what goes in or out Excretion: removes wastes Secretion: release something useful Sensory reception: changes shape

Epithelial Tissue: special characteristics 1. Special contacts – it tightly fits close together to form continuous sheets 2. Polarity – it has two surfaces... A top & a bottom. Apical (top) is free and basal (bottom) is attached to something 3. Supported by connective tissue 4. Avascular but innervated – contains no blood vessels (avascular) but supplied by nerve fibers (innervated) 5. Regenerative – rapidly replaces lost cells by mitosis… (grows easily)

Classification of epithelium Epithelial tissue is classified by cell shape and by how many layers of cells there are

Classification of Epithelia: number of layers Simple 1 layer stratified Two or more layers Figure 4.1a

Classification of Epithelia: cell shape Squamous Flattened, scalelike Cuboidal boxlike Columnar Tall, rectangular or column shaped Stopped 2nd Figure 4.1b

Epithelia: Glandular A gland is one or more cells that makes and secretes an aqueous (water based) fluid Classified by: Site of product release – endocrine or exocrine number of cells forming the gland

Ductless glands that produce hormones Endocrine Glands Ductless glands that produce hormones Chemical messengers carried by the blood Secretions include amino acids, proteins, and steroids

Exocrine Glands More numerous than endocrine glands Secrete their products onto body surfaces (skin) or into body cavities Must use ducts Examples include mucous, sweat, oil, and salivary glands