Chapter Summary

Definition and Classification of Tissues

1. Tissues are aggregations of similar cells that perform specific functions. The study of tissues is called histology.
2. Cells are surrounded and bound together by an intercellular matrix, the composition of which varies from solid to liquid.
3. The four principal types of tissues are epithelial tissue, connective tissue, muscle tissue, and nervous tissue.

Epithelial Tissue

1. Epithelia are derived from all three germ layers and may be one or several layers thick. The lower surface of most membranous epithelia is supported by a basement membrane.
2. Simple epithelium consists of a single cell layer that varies in shape and surface characteristics. It is located where diffusion, filtration, and secretion occur.
3. Stratified epithelium consists of two or more layers of cells and is adapted for protection.
4. Transitional epithelium lines the urinary bladder, ureters, and parts of the urethra. The cells of transitional epithelium permit distension.
5. Body membranes are composed of thin layers of epithelial tissue that may be coupled with supporting connective tissue. The two basic types are mucous membranes and serous membranes.
6. Glandular epithelia are derived from developing epithelial tissue and function as secretory exocrine glands.

Connective Tissue

1. Connective tissues are derived from mesoderm and, with the exception of cartilage, are highly vascular.
2. Connective tissue contains fibroblasts, collagenous fibers, and elastic fibers within a flexible ground substance.
3. Cartilage provides a flexible framework for many organs. It consists of a semisolid matrix of chondrocytes and various fibers.
4. Bone tissue consists of osteocytes, collagenous fibers, and a durable matrix of mineral salts.
5. Blood consists of formed elements (erythrocytes, leukocytes, and thrombocytes) suspended in a fluid plasma matrix.

Muscle Tissue

1. Muscle tissues (smooth, cardiac, and skeletal) are responsible for the movement of materials through the body, the movement of one part of the body with respect to another, and for locomotion.
2. Fibers in muscle tissue are adapted to contract in response to stimuli.

Nervous Tissue

1. Neurons are the functional units of the nervous system. They respond to stimuli and conduct impulses to and from all body organs.
2. Neuroglia support and bind neurons. Some are phagocytic; others provide sustenance to neurons.