CHAPTER FOUR
Tissue Level of Organization
Introduction to Tissues A. Histology=the study of tissues. B. Although studying tissues can be accomplished using a light microscope, studying cell parts often requires an electron microscope and the study of atoms and molecules can only be examined through special imaging techniques and experimental procedures. 4.1 Types of Tissues A. Despite the fact the body is composed of trillions of cells, there are only about 200 different cell types. These cells in turn produce only four principle tissue types: 1. Epithelial tissues=covers exposed surfaces; lines internal passageways; and produces glandular secretions. 2. Connective tissues=fills internal spaces; provides structural support, and stores energy 3. Muscle tissues=contracts to produce active movements 4. Nervous tissue=conducts electrical impulses; detects, interprets, and responds to stimuli B. Relative contribution of the four tissue types to the overall weight of the adult body. C. Embryonic origins: There are three types of embryonic tissues from which all adult tissues are derived. a. Endoderm=gives rise to the functional linings of the digestive and respiratory tracts as well as to the associated accessory glands and organs (i.e. liver, stomach, pancreas, etc.) b. Mesoderm= gives rise to the components of the skeletal, muscular, and circulatory systems Ectoderm= gives rise to the epidermis of skin and all of the components of the nervous system D. Tissue Membranes 1. Mucous Membranes=composed of epithelial tissues. These membranes line body cavities that open to the exterior environment such as those of the digestive tract, respiratory tract, or urogenital tract. In all cases, these are "wet" or moist membranes because of the secretion of mucous. The moisture helps reduce friction and in many cases, facilitates absorption or secretion activities. 2. Serous Membranes=consists of a mesothelium supported by areolar tissue. These are never exposed or connected to the exterior. Serous membranes secrete transudate, or serous fluid. There are three serous membranes that line the ventral body cavity: a. Pleura=lines the chest cavity and surrounds the lungs. b. Pericardium=lines the pericardial cavity and surrounds the heart c. Peritoneum=lines the peritoneal cavity and lines the surfaces of the visceral organs 3. Cutaneous Membranes=made of stratified squamous and areolar tissue reinforced by dense irregular connective tissue. In contrast to mucous and serous membranes, cutaneous membranes are dry, relatively thick, and waterproof. 4. Synovial Membranes=line mobile joint cavities but do not cover the opposing joint surfaces. Secretes synovial fluid. Although the covering of the synovial membrane is often called an epithelium, it differs from true epithelia in four respects: it develops within a connective tissue. no basal lamina is present, gaps of up to 1 mm may separate adjacent cells, and the synovial fluid and capillaries in the underlying connective tissue are continuously exchanging fluid and solutes. 4.2 Epithelial Tissues A. Functions of Epithelial Tissues 1. Epithelia provide physical protection. Epithelial tissues protect exposed and internal surfaces from abrasion, dehydration, and destruction by chemical or biological agents. 2. Epithelia control permeability. Any substance that enters or leaves the body has to cross an epithelial tiss