Histology: Types of Tissues PDF

HISTOLOGY TYPES OF TISSUES A. A tissue is a group of similar cells that usually have a similar embryological origin and are specialized for a particular function. The science that deals with the study of tissues is called histology. B. Depending on their function and structure, the various t...

HISTOLOGY TYPES OF TISSUES A. A tissue is a group of similar cells that usually have a similar embryological origin and are specialized for a particular function. The science that deals with the study of tissues is called histology. B. Depending on their function and structure, the various tissues of the body are classified into four principal types: epithelial, connective, muscular, and nervous. 1. Epithelial tissue covers body surfaces and lines hollow organs, body cavities, and ducts. 2. Connective tissue protects and supports the body and its organs, binds organs together, stores energy reserves as fat and carries the components in the blood. 3. Muscle tissue is responsible for movement. 4. Nervous tissue initiates and transmits action potentials (nerve impulses) that help coordinate body activities. I. EPITHELIAL TISSUES A. General Features of Epithelia 1. Epithelium (epithelial tissue) is covering and lining tissue. a. Epithelium consists mostly of closely packed cells with little extracellular material. b. Epithelial cells are arranged in sheets, in either single or multiple layers. c. An epithelial cell has an apical (free) surface and a basal (bottom) surface attached to a basement membrane. d. Many cell junctions are present, providing secure attachments among the cells. e. Epithelia are avascular; exchange of materials between epithelium and adjacent connective tissue is by diffusion. f. Epithelia adhere firmly to nearby connective tissue via a thin extracellular layer, the basement membrane. g. Epithelia have a nerve supply. h. Epithelia have a high capacity for regeneration (high mitotic rate). 2. Functions of epithelia include protection, filtration, secretion, absorption, and excretion. B. Covering and Lining Epithelium 1. The arrangement of covering and lining epithelium reflects its location and function. 2. Layers are arranged as simple (one layer), stratified (several layers), and pseudostratified (one layer that appears as several). 3. Cell shapes include; squamous (flat), cuboidal (cube-like), columnar (rectangular), and transitional (variable). 4. Covering and lining epithelia may be classified as a combination of arrangement of layers and shape of the cells. The name of the specific type of stratified epithelium depends on the shape of the surface cells. a. Simple squamous epithelium consists of a single layer of flat cells. 1) It is adapted for diffusion and filtration and is found in lungs and kidneys and in serous membranes, 2) It is found in parts of the body that are subject to little wear and tear. 3) It forms the Endothelium that lines the heart and blood vessels. 4) It forms the Mesothelium that lines the thoracic and abdominopelvic cavities and covers the organs within them. b. Simple cuboidal epithelium consists of a single layer of cube-shaped cells. 1) It is adapted for; a) secretion - the production and release by cells of a fluid that may contain a variety of substances, such as mucus, perspiration, or enzymes and b) absorption - the intake of fluids or other substances by cells. 2) It is found lining some glandular ducts. c. Simple columnar nonciliated epithelium consists of a single layer of nonciliated rectangular cells. 1) It functions in secretion of mucus and in absorption. 2) It lines most of the gastrointestinal tract, where specialized cells containing microvilli perform absorption and goblet cells secrete mucus. d. Simple columnar ciliated epithelium consists of a single layer of ciliated rectangular cells. 1) It moves fluids or particles along a passageway by ciliary action. 2) It is found in a few portions of the upper respiratory tract, uterine tubes and uterus. e. Stratified squamous epithelium consists of several layers of cells in which the top layer of cells is flat and performs a protective function. 1) A keratinized variety forms the outer layer of skin; Keratin is a protein that is waterproof, resistant to friction, and helps repel bacteria. 2) A nonkeratinized variety lines the mouth, esophagus, part of the epiglottis, and vagina, and covers the tongue. f. Stratified cuboidal epithelium consists of several layers of cells in which the top layer is cube-shaped. 1) It functions in protection. 2) It is found in ducts of adult sweat glands and parts of the male urethra. g. Stratified columnar epithelium consists of several layers of cells in which the top layer is rectangular. 1) It functions to protect and secretion. 2) It is found in portions of the male urethra and large excretory ducts of some glands. h. Transitional epithelium consists of several layers of cells whose appearance is variable.  1) It is capable of stretching and thus permits distention of an organ. 2) It lines the urinary bladder and portions of ureters and the urethra. i. Pseudostratified columnar epithelium has only one layer but gives the appearance of many. 1) It functions in secretion and movement of mucus by ciliary action. 2) It lines larger excretory ducts of many large glands, part of the male urethra, and the auditory (Eustachian) tubes. The ciliated variety with goblet cells (secreting mucous) lines most of the upper respiratory tract. II. CONNECTIVE TISSUE A. General Features of Connective Tissue A. Connective tissue is the most abundant tissue in the body. b. Connective tissue consists of three basic elements: cells, ground substance, and fibers (the latter two of which combine to form the matrix with relatively few cells). c. Unlike epithelia, connective tissues do not occur on free surfaces. d. Except for cartilage, connective tissue has a nerve supply. e. Unlike epithelium, connective tissue is highly vascular (except for cartilage and tendons). f. The matrix of a connective tissue, which may be fluid, semifluid, gelatinous, flbrous, or calcified, is usually secreted by the connective tissue cells and adjacent cells and determines the tissue's qualities. B. Connective Tissue Cells a. Immature cells have names which end in -blast (ex. - osteoblast) while mature cells have names which end in -cyte (ex. - osteocyte). b. Most mature cells have reduced capacity for cell division and matrix formation and are mostly involved in maintaining the matrix. The advantage of these cells is their reduced energy requirements. 2. Types of cells found in various connective tissues include; a. fibroblasts (which secrete fibers and matrix), b. macrophages (which develop from monocytes and are phagocytic), c. plasma cells (which develop into antibody-producing B Lymphocytes, or B cells), d. mast cells (which are abundant alongside blood vessels and produce histamine), e. adipocytes (or fat cells, which store energy in the form of fat), and f. white blood cells (or leukocytes). C. Connective Tissue Matrix 1. The ground substance and fibers, deposited in the space between the cells, comprise the matrix of connective tissue. a. Substances found in the ground substance include; 1) hyaluronic acid, 2) chondroitin sulfate,  3) dermatan sulfate, and 4) keratan sulfate. b. The function of ground substance is that it supports, binds, provides a medium for the exchange of materials between the blood and cells, and is active in influencing cell functions. 2. Fibers a. Fibers in the matrix provide strength and support for tissues. b. Three types of fibers are embedded in the matrix between cells of connective tissues. 1) Collagen fibers, composed of the protein collagen, are very tough and resistant to stretching, yet allow some flexibility in tissue; they are found in bone, cartilage, tendons, and ligaments. 2) Elastic fibers, composed of the protein elastin, provide strength and stretching capacity and are found in skin, blood vessels, and lungs. 3) Reticular fibers, consisting of collagen and glycoprotein, provide support in the walls of blood vessels and form a strong, supporting network around fat cells, nerve fibers, and skeletal and smooth muscle cells. They help form the basement membranes and the framework (stroma) of many soft organs such as the spleen and lymph nodes. D. Mature Connective Tissue 1. Mature connective tissue exists in the newborn and does not change after birth. It is subdivided into several kinds: 1) connective tissue proper, Subtypes include loose fibrous connective tissue and dense fibrous connective tissue. 2.) cartilage 3.) bone, and 3) blood. 2. In loose connective tissue, the fibers are loosely woven and there are many cells. a. Areolar connective tissue consists of all three types of fibers, several types of cells, and a semifluid ground substance. 1) It is found in the subcutaneous layer and mucous membranes and around blood vessels, nerves, and body organs. 2) It functions in lending strength, elasticity, and support. b. Adipose tissue consists of adipocytes, specialized for storage of triglycerides (fat). 1) It is found in the subcutaneous layer, around organs, and in the yellow marrow of long bones. 2) It functions in that it a) reduces heat loss through the skin, b) serves as an energy reserve, c) supports and protects  c. Reticular connective tissue consists of fine interlacing reticular fibers and reticular cells. 1) It is found in the liver, spleen, and Lymph nodes. 2) It forms the stroma of organs and binds together smooth muscle tissue cells. 3. Dense connective tissue contains more numerous and thicker fibers but considerably fewer cells than loose connective tissue. a. Dense regular connective tissue consists of dense, regularly arranged bundles of collagen fibers and fibroblasts. 1) It forms tendons, ligaments, and aponeuroses (flat tendons). 2) It provides strong attachments between various structures. b. Dense irregular connective tissue consists of dense, randomly arranged collagen fibers and a few fibroblasts. 1) It is found in fasciae (broad sheets), dermis of the skin, periosteum (around bone), perichondrium (around cartilage), joint capsules, membrane capsules around organs, and heart valves. 2) It functions in providing strength. c. Elastic connective tissue consists of elastic fibers and fibroblasts. 1) It is found in the lungs, walls of arteries, trachea, bronchial tubes and the true vocal cords. 2) It allows stretching of various organs. 4. Cartilage has a jellylike matrix (chondroitin sulfate) containing collagenous and elastic fibers and chondrocytes. a. Unlike other connective tissues, cartilage has no blood vessels or nerves. b. The strength of cartilage is due to its collagen fibers while its resilience is due to the presence of chondroitin sulfate. c. Chondrocytes occur within spaces called lacunae in the matrix. d. There are three major types of cartilage. 1) Hyaline cartilage is the most abundant type of cartilage and has fine collagen fibers embedded in a gel-type matrix. a) It is found in the embryonic skeleton, at the ends of bones, in the nose, and in respiratory structures. b) It is flexible, allows movement at joints, and provides support. 2) Fibrocartilage contains bundles of collagen in its matrix. a) It is found in the pubic symphysis (joint between the pubic bones), intervertebral discs (between the vertebrae), and menisci of the knee. b) It functions in support and fusion. 3) Elastic cartilage contains a threadlike network of elastic fibers within the matrix. a) It is found in the epiglottis, auditory (Eustachian) tubes, and external ear. b) It gives support and maintains shape. 5. Bone (osseous tissue) consists of a matrix containing mineral salts and collagenous flbers and cells called osteocytes.  a. Calcium salts are responsible for bone's hardness and collagen fibers for its great strength. b. It functions in that it supports, protects, helps provide movement, stores minerals, and houses blood-forming tissue. 6. Blood (vascular tissue) consists of a liquid matrix called plasma and formed elements. a. Formed elements include erythrocytes, leukocytes, and thrombocytes. b. Blood is involved in transport, phagocytosis, allergic reactions, immunity, and clotting. III. MUSCLE TISSUE A. Muscle tissue consists of fibers (cells) that are modified for contraction and thus provide motion, maintenance of posture, and heat production. B. It is subdivided into three types. 1. Skeletal muscle tissue is attached to bones. The cells are striated (banded - due to the organization of the protein filaments), multinucleated, cylindrical shaped and voluntary. 2. Cardiac muscle tissue forms most of the heart wall. The cells are striated, uni- nucleated, branched and is usually involuntary and it pumps blood to all parts of the body. 3. Smooth muscle tissue is found in the walls of hollow internal structures (blood vessels and viscera). The cells are nonstriated, uninucleated, spindle shaped and is usually involuntary. It provides motion (e.g., constriction of blood vessels and airways, propulsion of foods through the gastrointestinal tract, and contraction of the urinary bladder and gallbladder). IV. NERVOUS TISSUE A. The nervous system is composed of only two principal kinds of cells: 1. neurons (nerve cells), and 2. neuroglia (protective and supporting cells). B. Most neurons consist of a cell body and two types of processes called dendrites and axons. C. Neurons are: 1. sensitive to stimuli, 2. convert stimuli into nerve impulses, and 3. conduct nerve impulses to other neurons, muscle fibers, or glands.