There are four types of tissue that make up the body and organs of human beings. But before enumerating them, let us define what is a body tissue: it is a cluster of cells, which are similar in origin, form, and structure, all of them specialized to perform the same function.
1) Epithelial tissue- The epithelium covers the body, lines organ cavities, and constitutes the inner walls of blood vessels. According to the shape of the cells: there are cuboidal and squamous epithelium. Cuboidal cells have the shape of a cube and form the kidney tubules, while squamous epithelial cells are flat and overlapping, constituting the walls of capillaries and arteries. When epithelial cells line organ cavities and blood vessel walls, it is called endothelium.
2) Connective tissue- It is a fibrous structure which connects and support internal organs and forms bone. It also constitutes the outer layer of blood vessels (tunica externa). The fibers are composed of a protein which is called collagen, performing supportive and protective functions. Remember, aside from cartilage, tendons and the eye sclera, bone, adipose cells, and blood are also different forms of connective tissue.
3) Muscle tissue- The cells that make it up are specialized for contraction, to move a body part, to narrow the lumen of arteries, or perform peristalsis. From the structure point of view, there are two types: striated and smooth muscle tissue. Skeletal and heart muscle have a striated structure, while smooth muscle form the middle layer of blood vessels as well as the digestive tract walls (stomach and intestines). Skeletal muscular tissue is voluntary (we can contract them at will), while smooth and heart muscle are involuntary.
4) Nervous tissue- It is formed by nerve cells (neurons), which are highly specialized cells for generating and transmitting electro-chemical impulses, regulating body functions. Their efferent impulses contract our muscles, while the afferent impulses send visual, auditory, olfactory, and tactile information to our brain, which is the hub of the nervous tissue.
