The human body contains about 100 trillion different cell, Some are bone and blood cells. Others include muscle, epithelial, and nerve cells. When similar cells group together to perform the same task, they are called tisue. Epithclial cells, for example, group together to form cpithelial tissue. This tissue lines and protects your nose, throat, windpipe, and digestive tract. You also know this tissue as skin which protects your body Other tissues include blood tissue, muscle tissue, and nerve tissue.