Cells of a similar type that are grouped together to perform a particular function are called tissues.
There are 4 main types of tissue in the human body: epithelial tissue, connective tissue, muscle tissue and nervous tissue.
Epithelial tissue is named based on the shape of the individual cells: squamous (flat), cuboidal (cube shaped) and columnar (tall, like a column)...
and named based on the number of layers of cells: simple (single layer) and stratified (multiple layers). So, a single layer of flat epithelial cells are called simple squamous.
Simple squamous cells form a thin layer and are usually found forming membranes in the body where diffusion or secretion is needed such as the air sacs of the lungs, serous membranes covering organs and the walls of capillaries.
Simple cuboidal cells are often found forming glands that secrete various substances.
simple columnar cells are found along the entire length of the digestive tract where they produce mucus.
Connective tissue is found throughout the body and can be classified into different types: bone, cartilage, dense connective tissue, loose connective tissue and blood.
All connective tissue consists of cells resting within an extracellular matrix composed of ground substance (water with dissolved compounds) and fibers produced by the cells (collagen, elastic fibers or reticular fibers).
Bone is composed of cells called osteocytes sitting in cavities known as lacunae together with calcium salts and collagen fibers.
Cartilage is similar to bone but not as rigid and the main cells within the cartilage matrix are called chondrocytes.
Muscle tissue is found throughout the body and is responsible for movement of the body, facial expressions, pumping of the heart and movement of food through the digestive system.
There are 3 main types of muscle tissue: skeletal muscle tissue, cardiac muscle tissue, and smooth muscle tissue.