Animal Body and Principles of RegulationName the 3 tissues in a developing embryoName the 4 primary tissues in adult vertebratesWhat is a tissue? A tissue is a group of cells with similar shape and function. What is an organ? What are some characteristics of epithelial cells? Give a few examples of tissue/ organs made of epithelial cellsWhat are the 2 classes of epithelial tissue? And how can epithelial cells be subdivided based on their shape? The 2 classes of epithelial tissue are simple and stratefied. Where simple is one layer thich and stratefied is multiple layers thick. These 2 classes can be further divided into three categories: squamous cells - flat; cubodial cells - cube shaped and columnar cells - cylindar shaped. What are some characteristics of conncetive tissue? Give examplesHow is epithelial tissue different from connective tissue? What is extracellular matrix made of? Who secretes it? The extracellular matrix is made up of protein fibers for example collagen and elastin and ground substance which includes proteins and polysacharides. This is secreted by fibroblasts cells.