Four Tissue Types Epithelial- cover exposed surfaces, and line internal passageways Connective Tissue- Provide structural support, transport materials, store energy

Tissue Types (cont.) Muscle Tissue- perform specific movements Neural Tissue- carries info. from one part of the body to another using electrical impulses

Epithelial Tissue Epithelia- are layers of cells that cover internal and external structures Ex. Skin, and lines digestive tract Glands- secretory structures Produce secretions, ex. Sweat glands

Characteristics of Epithelial Cellularity- cells closely bound together Polarity- uneven distribution of membrane and organelle distribution In the skin organelles are closer to inside of body than outside

Characteristics of Epithelial Attachment- epithelial cell is bound by a basement membrane Avascularity- do not contain blood vessels Regeneration- continuously replaced

Functions of Epithelial Tissue Physical Protection Control Permeability Provide Sensation- contain lots of sensory nerves Produce specialized secretions- referred to as gland cells

Specializations of Epithelial Cells Ciliated Epithelium- line respiratory tract and move mucus out of lungs

Types of Epithelia Appear thin, flat and irregular Simple Squamous- one layer of cells, very thin and fragile, line internal passageways, and found where secretions and absorptions occur Ex. Lungs for gas exchange

Stratified Squamous Epithelium Several layers of cells like a stack of plywood sheets Found in areas of mechanical stress and chemical stress Ex. Surface of skin, mouth, and esophagus

Simple Cuboidal Appear Square w/ nuclei in the center of the cell Provides limited protection and occurs where secretion and absorption take place Ex. Pancreas, salivary glands this tissue secretes enzymes and buffers, and the kidney

Simple Columnar Appear Rectangular, and nuclei are crowded toward the bottom of the cell Found where absorption and secretions take place to help protect against chemical stresses Ex. Stomach and small intestine

Glandular Epithelium Endocrine- released into interstitial fluid and blood Secretions called hormones Exocrine- discharged onto skin or other epithelial surface Enzymes into digestive tract, perspiration onto skin, tears, saliva etc. Use ducts (passageways)