The four tissue types
Every organ in the body is built from one or more of four tissue types — and recognizing which is which is the first move in any anatomy question.
Epithelial tissue
Epithelium covers surfaces, lines cavities, and forms glands. Its cells are tightly packed in continuous sheets with very little extracellular matrix between them.
Two structural flavors: squamous (flat, scale-like), cuboidal (cube-shaped), and columnar (tall). You can also specify layers — simple (one cell thick) or stratified (multiple layers). Skin is stratified squamous; the lining of the gut is simple columnar.
Connective tissue
Connective tissue is defined by what it doesn't have: tightly packed cells. Instead, cells sit far apart in a sea of extracellular matrix — fibers and ground substance that the cells secrete.
Loose connective tissue cushions organs. Dense connective tissue (tendons, ligaments) resists stretch. Cartilage and bone harden the matrix. Blood is also connective tissue — its matrix is plasma.
Muscle and nervous
Muscle tissue is specialized to contract. Three types: skeletal (striated, voluntary, attached to bones), cardiac (striated, involuntary, only in the heart), and smooth (non-striated, involuntary, in organs and vessels).
Nervous tissue is built from neurons and supporting glial cells. Neurons carry electrical signals; glia feed, insulate, and clean up. Most of the brain is glia.
Flashcard · Unit 1
Tightly packed cells in continuous sheets.
Check your understanding
Which tissue type is characterized by cells widely separated within a large extracellular matrix?