Summary on Tissues

Summary

The study of tissues is known as histology. The four tissue types are epithelial, connective, muscle, and neural. Epithelial tissue includes epithelia and glands. Glands are secretory structures derived from epi-thelia. Epithelial tissue provides physical protection, absorbs, filters, excretes, provides sensation, produces specialized secretions, is permeable, and regenerates. Epithelia are classified on the basis of the number of cell layers and the shape of the cells. Epithelia may be labeled as squamous, cuboidal, columnar, transitional, or glandular.

Exocrine glands discharge secretions onto the body surface or into ducts. Endocrine glands secrete hormones into the blood circulation. Glands may release secretions by merocrine, apocrine, or holo-crine modes. Connective tissue is internal tissue that transports fluids and dissolved materials, cre-ates a structural framework, protects organs, stores fat, provides insulation, and defends against micro-organisms. Connective tissue contains specialized cells, a matrix of extracellular protein fibers, and a ground substance. Connective tissue cells include fibrocytes, mast cells, macrophages, lymphocytes, microphages, and melanocytes. Connective tissue fibers include collagenous, elastic, and reticular fibers. The categories of connective tissue are con-nective tissue proper, supporting connective tis-sues, and fluid connective tissues. Adipose tissue has cushioning functions and contains adipocytes. Areolar tissue binds skin to underlying organs and fills in spaces between muscles. Cartilage is tough, flexible connective tissue that supports, frames, and attaches to many tissues and bones. Types of ­cartilage include hyaline, elastic, and fibrocartilage. Bone is the most rigid type of connective tissue and establishes the body’s framework. Fluid connective tissue is of two types: blood or lymph.

Muscle tissue is specialized for contraction. The three types of muscle tissue are skeletal, cardiac, and smooth. Skeletal muscle is also known as striated voluntary muscle. Cardiac muscle tissue is found only in the heart. It is striated involuntary muscle, relying on pacemaker cells for regular contraction. Smooth muscle tissue, which is involuntary muscle tissue, is not striated. Neural tissue conducts electri-cal impulses, conveying information from one area of the body to another. Cells in the neural tissue are either neurons or neuroglia. Neurons transmit ­information as electrical impulses. Neuroglia helps to supply nutrients to neurons.

Tissue membranes may be serous, mucous, cuta-neous, or synovial. Serous membranes line cavities that lack openings to the outside of the body. Mucous membranes or mucosae line cavities that open to the outside of the body. The cutaneous membrane is the skin, covering the body surface. Synovial membranes are made up of loose connective tissues that form an incomplete lining within the cavities of syno-vial joints. Tissues are repaired by cell division and ­migration, with the repair process beginning with inflammation. As body tissues age, they are repaired more slowly. Connective tissues become more frag-ile, bones become brittle, and skin bruising occurs more easily.