There are four basic tissue types: epithelial, connective, muscle, and nervous tissue. Tissues combine to form organs, which are made of groups of tissues working together for a common function. Epithelial tissue forms sheets that cover surfaces or line cavities. Connective tissue connects and supports other tissues and includes bone, cartilage, fat, and blood. Muscle tissue includes three types: smooth, skeletal, and cardiac. Nervous tissue includes the brain, spinal cord, and nerves.