Chapter 4

 Tissue: group of cells that are similar in structure and function  Histology: study of tissues Types of Tissues: 1. Epithelium (covering) 2. Connective (support) 3. Muscle (movement) 4. Nervous (control)

Part I: Epithelial Tissue

Epithelial Tissue  “epithe” = laid on, covering  Structure: 1. Covering and lining epithelium 2. Glandular epithelium  Function:  Protection  Absorption  Filtration  Secretion

Skin Properties 1. Polarity  Apical surface = exposed free surface or edge (some with microvilli, cilia)  Basal surface = lower, attached surface 2. Specialized contacts  Fits close together to form continuous sheets

Skin Properties Continued 3. Supported by connective tissue  Rests on basement membrane 4. No blood supply (avascular)  Rely on diffusion and underlying connective tissue for food/O 2 5. Regeneration – Replace lost cells

How Skin is Classified  Two names = (# cell layers) + (shape of cells)  Cell Layers: simple or stratified (based on number of layers STRATIFIED FOR INTEGUMENTARY  Shapes: squamous, cuboidal, or columnar

Simple Epithelium  Absorption, secretion, filtration  Very thin

Simple Epithelium

Stratified Epithelium  2+ layers, more durable  Main function = protect

Glandular Epithelium  Gland: make and secrete a particular product  2 Types:  Endocrine gland: produce hormones secreted into tissue fluid or bloodstream  Exocrine gland: secrete products into ducts  onto body surfaces or body cavities  Eg. mucous, sweat, oil, saliva, bile

Exocrine Glands UnicellularMulticellular  Mucus cells or goblet cells  Duct structure

Hair  The basic component of human hair and nails is keratin.  Hair on the head protects the scalp from the sun and provides insulation from the cold.  Hairs in the nostrils, external ear canals, and around the eyes (in the form of eyelashes) prevent dirt and other particles from entering the body.  Hair is produced by cells at the base of structures called hair follicles, which are tubel-ike pockets of epidermal cells that extend into the dermis.  Individual hairs are actually large columns of cells that have filled with keratin and then died.  Rapid cell growth at the base of the hair follicle causes the hair to grow longer.  Hair follicles are in close contact with sebaceous glands. The oily secretions of these glands help hairs stay soft and flexible.

Nails  Nails grow from an area of rapidly dividing cells known as nail roots, which are located near the tips of the fingers and toes.  During cell division, the cells of the nail root fill with keratin and produce a tough, platelike nail that protects the tips of the fingers and toes.  Nails grow at an average rate of 3 mm per month, with fingernails growing about four times faster than toenails.