Tissues Student Learning Objectives: Distinguish between the different varieties of tissue: epithelium, connective tissue, muscle, and nervous tissue. Types of tissues: Epithelium: Simple Simple squamous epi. Simple cuboidal epi. Simple columnar epi. Stratitified Stratified squamous epi. Transitional epi. Pseudostratified Pseudostratified columnar epi. Muscle: Skeletal Cardiac Smooth Connective Tissue: Soft Areolar connective tissue Adipose connective tissue Dense collagenous con. tissue Support Cartilage Bone Fluid Blood Lymph Nervous Tissue Introduction Cells are the basic building blocks of the living organism, however, for multicellular organisms, like the human, the cells join forces as tissues. Tissues are formed from groups of cells of the same type and that have a similar function. These tissues serve as the basic construction material for organs. In this exercise, we will look at some of the primary tissues that form our body. Epithelial Tissues Epithelial tissues are surface tissues and lack a direct blood supply. They must rely on the adjacent connective tissues to supply them with nutrients. The cells are tightly packed together, with little space between cells. A simple epithelium will be very thin because the tissue is composed of a single layer of cells. This picture shows an example of simple cuboidal epithelium (between the two arrows). There is a single row of square cells in this type of epithelium. This type of epithelium can be found in the kidneys and certain glands.
There are several types of simple epithelium in the body. Simple squamous epithelium has a single layer of very flat cells. Simple squamous epithelium is used in a number of places in the body where separation is needed between two areas, but movement of materials across the epithelium is essential. The lungs, kidneys, and blood capillaries use this type of epithelium. Simple columnar epithelium is composed of a single layer of tall rectangular cells. This type of epithelium is found in the digestive system. Stratified epithelia are very thick, and may have many layers. Stratified epithelium is used in places were protection is needed. Multiple layers are much more difficult to invade than a single layer is. Stratified squamous epithelium forms the covering of the skin. Transitional epithelium forms the lining of the urinary bladder.
Pseudostratified epithelium is a single layer of tissue cells that gives a false appearance of multiple layers. Pseudostratified columnar epithelium lines the large airways. Connective Tissues Connective tissues are underlying tissues that are generally covered with epithelium. These tissues look much different than the epithelium because there are large spaces between the individual cells of the tissue. This space is filled with a material known as matrix. Matrix is composed of a ground substance and fibers. The ground substance varies from liquid to gelatinous to crystalline, depending upon the type of connective tissue. The fibers can include collagen, elastic, or reticular varieties. Soft connective tissue varieties have a rubbery texture. Areolar connective tissue and adipose connective tissue are very commonly found in the body. These connective tissues are often associated with the epithelia and are involved in supply the epithelial tissues with nutrients. Adipose connective tissue is also known as fat. Dense collagenous connective tissue is composed of numerous collagen fibers. Collagen is very strong, but not stretchy, so this type of connective tissue is what is used to form the tendons and ligaments that hold the skeleton and musculoskeletal systems together.
Support connective tissues have a firm texture. Cartilage forms the flexible parts of the skeleton. The ground substance is gelatinous, giving this tissue a firm, yet elastic, consistency. Cartilage forms the external parts of the nose and ear, as well as, parts of the airways and the intervertebral discs of the spine. Bone uses a crystalline ground substance and, therefore, has a very rigid texture. Bone tissue forms the majority of the skeleton, providing support and protection of the other body structures. The fluid connective tissues are different from the others because they do not have the same type of matrix. The fluid connective tissues include blood and lymph. Muscle Muscle is the only tissue which is capable of producing movement. The cells of muscle tissue are closely packed together, as you saw with epithelial tissue. There are three varieties of muscle. Skeletal muscle forms the muscles that are attached to the skeleton and is involved in moving the body around in its environment. The cells are striated (i.e. striped), very large, and multinucleated (i.e. have more than one nucleus). This is the only type of muscle that can be voluntarily controlled. Cardiac muscle forms the walls of the heart. This muscle is also striated, but the cells are branched and have a single nucleus. Cells are connected to one another by the intercalated discs. This type of muscle is capable of autorhymicity (i.e. self-stimulating contractions).
Smooth muscle is found in the muscular walls of most other organs. The cells of this tissue are not striated and are quite small. Nervous Tissue The final type of basic tissue is nervous tissue. Nervous tissue is composed of special cells, the neurons, which are capable of sending electrical messages. The neurons are very large cells with fibrous extensions that connect to body cells and other neurons. Neurons control many of the actions of body cells. The remaining cells in nervous tissue cells are collectively known as neuroglia. These support cells help protect the neurons and assist the neurons in doing their job.