Tissue Level of Organization - Human Biology PDF

Dr Radhika G Bhardwaj, AIU BIO 320 Objectives 2  The Invention of Stains and Dyes Van Leeuwenhoek The first person to use a histological stain to color specimens (he used saffron!). Joseph von Gerlach...

Dr Radhika G Bhardwaj, AIU BIO 320 Objectives 2  The Invention of Stains and Dyes Van Leeuwenhoek The first person to use a histological stain to color specimens (he used saffron!). Joseph von Gerlach Introduced carmine mixed with gelatin as a histological stain. 7  1. Epithelial tissue Refers to the sheets of cells that cover exterior surfaces of the body, line internal cavities and passageways, and form certain glands. 8  1. Epithelial tissue Functions of the epithelial tissue: Epithelial tissues provide the body’s first line of protection from physical, chemical,and biological wear and tear. The cells of an epithelium act as gatekeepers of the body controlling permeability and allowing selective transfer of materials across a physical barrier. All substances that enter the body must cross an epithelium. 9  2. Connective tissue Binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. 12  2. Connective tissue Functions of the connective tissue: ❖Support and connect other tissues. ❖Protection. ❖Specialized cells in connective tissue defend the body from microorganisms that enter the body. ❖Transport of fluid, nutrients, waste, and chemical messengers is ensured by specialized fluid connective tissues, such as blood and lymph. ❖Adipose cells store surplus energy in the form of fat and contribute to the thermal insulation of the body. 13  3. Muscle tissue Excitable tissue that responds to stimulation and contracts to provide movement. Three major types: 1. Skeletal muscle 2. Smooth muscle 3. Cardiac muscle 14  Skeletal muscles Cardiac muscles Smooth muscles most of them move form most of the lack striations bones of the skeleton heart wall Which muscle type is striated? Which is voluntary? 15  4. Nervous tissue Excitable tissue that allows the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body.  4. Nervous tissue Functions of the Nervous tissue: Neurons propagate information via electrochemical impulses, called action potentials, which are biochemically linked to the release of chemical signals. Neuroglia play an essential role in supporting neurons and modulating their information propagation. Comparison of (a) skeletal muscle to (b) cardiac and (c) smooth muscle as seen with light microscopy (top panels) and in schematic form (bottom panels). Both skeletal and cardiac muscle have a striated appearance. Cardiac and smooth muscle cells generally have a single nucleus, but skeletal muscle fibers are multinucleated. MEMBRANE JUNCTIONS or CELL JUNCTIONS Three types of specialized membrane junctions: (a) desmosome; (b) tight junction; (c) electron micrograph of two intestinal epithelial cells joined by a tight junction near the apical (luminal) surface and a desmosome below the tight junction; and (d) gap junction  The tight junction, forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them. Unlike the desmosome, which is limited to a disk-shaped area of the membrane, the tight junction occurs in a band around the entire circumference of the cell. Most epithelial cells are joined by tight junctions near their apical surfaces. For example, epithelial cells line the inner surface of the small intestine, where they come in contact with the digestion products in the cavity (or lumen) of the intestine Desmosomes consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm. Desmosomes are characterized by accumulations of protein known as “dense plaques” along the cytoplasmic surface of the plasma membrane. These proteins serve as anchoring points for cadherins. Cadherins are proteins that extend from the cell into the extracellular space, where they link up and bind with cadherins from an adjacent cell.  The gap junction, consists of protein channels linking the cytosols of adjacent cells A variety of cell types possess gap junctions, including the muscle cells of the heart, where they have a very important function in the transmission of electrical activity between the cells Bing Videos  Types of Smooth Muscle Many smooth muscles can be placed, however, into one of two groups, based on the electrical characteristics of their plasma membrane: single-unit smooth muscles and multiunit smooth muscles. Innervation of single-unit smooth muscle is often restricted to only a few cells in the tissue. Electrical activity is conducted from cell to cell throughout the tissue by way of the gap junctions between the cells.  Single-Unit Smooth Muscle The muscle cells in single unit smooth muscle undergo synchronous activity, both electrical and mechanical; that is, the whole muscle tissue responds to stimulation as a single unit. This occurs because each muscle cell is linked to adjacent fibers by gap junctions, which allow action potentials occurring in one cell to propagate to other cells by local currents. Therefore, electrical activity occurring anywhere within a group of single-unit smooth muscle cells can be conducted to all the other connected cells  Multiunit Smooth Muscle Multiunit smooth muscles have no or few gap junctions. Each cell responds independently, and the muscle tissue behaves as multiple units.  Cardiac muscle combines properties of both skeletal and smooth muscle. Adjacent cells are joined end to end at structures called intercalated disks, within which are desmosomes that hold the cells together and to which the myofibrils are attached. Also found within the intercalated disks are gap junctions similar to those found in single-unit smooth muscle (a) Light micrograph. b) Cardiac muscle cells and intercalated disks