Chapter 4 Lecture Notes PDF

Chapter 4: Introduction to Tissues I. Histology- study of normal structures of tissues A. All tissues share two basic components: 1. Discrete population of cells that are related in structure and function 2. Extracellular matrix (ECM) B....

Chapter 4: Introduction to Tissues I. Histology- study of normal structures of tissues A. All tissues share two basic components: 1. Discrete population of cells that are related in structure and function 2. Extracellular matrix (ECM) B. Four primary tissue types are defined by 1. Kind and number of cells 2. Amount and composition of ECM 3. Specific functions C. General features of four types 1. Epithelial a. structure: tightly packed sheets of cells with no visible ECM b. function: cover, line all body surfaces and cavities; form glands that manufacture secretions 2. Connective a. structure: ECM is a prominent feature for most with cells scattered throughout b. function: bind, support, protect, and allow for transportation of substances 3. Muscle a. structure: little ECM between elongated cells b. function: capable of generating force by contracting 4. Nervous a. structure: large neuron and unique ECM b. function: generating, sending, receiving messages II. The Extracellular Matrix- composed of substances in a liquid, thick gel, or solid that surround cells of a tissue A. Functions 1. Provides tissue with strength to resist tensile (stretching) and compressive forces 2. Directs cells to their proper positions within a tissue and holds those cells in place 3. Regulates development, mitotic activity, and survival of cells in a tissue B. ECM consist of two main components 1. Ground substance- makes up most of ECM and consists of extracellular fluid (ECF or interstitial fluid) a. components include water, nutrients, ions, and three families of macromolecules: 1. Glycosaminoglycans (GAGs) - “traps” water in ECM; helps ECM to resist compression 2. Proteoglycans- helps make ECM firmer, more solid, and resistant to compression; form barrier to diffusion of substances through ECM; protect underlying tissue from invading microorganisms 3. Cell-adhesion molecules (CAMs) –adhere cell to cell and cells to surroundings; hold everything in place within ECM 1  2. Protein fibers –embedded in ground substance; enormous tensile strength a. three protein fiber types are found within ECM: 1. Collagen fibers- form a white fibrous protein; resistant to tension and pressure 2. Elastic fibers –composed of elastin; allows fiber to stretch and return to resting length (called elasticity) 3. Reticular fibers –form a meshwork or scaffold that supports cells and ground substance of many tissues; form a weblike structure in organs like spleen that help trap foreign cells III. Cell Junctions– another way cells bind to one another where neighboring cell’s plasma membranes are linked by integral proteins A. Three major types of cell junctions are: 1. Tight junctions or occluding junctions a. hold cells closely together such that space between is impermeable to movement of macromolecules b. Example – found between cells in blood vessels 2. Desmosomes – composed of linking integral proteins a. allow for materials in extracellular fluid to pass through space between cells b. Increase strength of a tissue by holding cells together so mechanical stress is more evenly distributed c. Found in tissues subjected to a great deal of mechanical stress such as epithelia of skin 3. Gap junctions a. small pores formed by protein channels between adjacent cells that allow small substances to flow freely between each cell’s cytoplasm b. Found in between cells that communicate with electrical signals such as cardiac muscle cells Epithelial Tissues I. Epithelial tissues – found on every internal and external body surface A. Functions: barriers between body and external environment; line organs and fluid- filled cavities; protection; immune defenses; secretion; transport; sensation B. Components and Classification of Epithelia 1. Tightly packed cells linked together by tight junctions and desmosomes 2. Avascular (lack blood vessels and must obtain oxygen and nutrients by diffusion from deeper tissues); limits their thickness 3. ECM is found beneath cells in a thin basement membrane; has two components that “glue” epithelial tissue to underlying connective tissue; anchor underlying blood vessels in place; provide a barrier between epithelia and underlying tissues a. Basal lamina – ECM synthesized by epithelial cells; consists of collagen fibers and ground substance b. Reticular lamina – synthesized by underlying connective tissue; consists of reticular fibers and ground substance 2 II. Types A. Simple Squamous Epithelium- very thin single layer of cells 1. Adapted for rapid diffusion of substances like oxygen, carbon dioxide, fluids, and ions 2. Found in air sacs of lung, specific segments of kidney tubules, and lining blood vessels B. Simple Cuboidal Epithelium 1. Single layer of cube-shaped cells with large central nucleus 2. Thin enough for rapid substance diffusion 3. Found in segments of renal tubules, respiratory passages, ducts of many glands, and thyroid gland C. Simple Columnar Epithelium 1. Single layer of rectangular-shaped cells with nuclei located in basal portion of cell 2. Often has microvilli on apical plasma membrane or cilia 3. Found in small intestine, uterine tubes and segments of respiratory tract D. Pseudostratified Columnar Epithelium 1. Appears to be layered because nuclei are found at various heights, but only one cell-layer thick with basal plasma membranes firmly in contact with basement membrane 2. found in segments of respiratory tract and nasal cavity; ciliated E. Keratinized Stratified Squamous Epithelium 1. Apical cellular layers are dead; lack nuclei filled with protein keratin 2. Makes tissue tough and resistant to friction 3. Outer layers of skin F. Nonkeratinized Stratified Squamous Epithelium 1. Apical cellular layers retain nuclei; still alive 2. Found in regions subjected to mechanical stress where surface must remain moist 3. Mouth, throat, esophagus, anus, and vagina G. Stratified Cuboidal Epithelium 1. Rare in humans 2. Consists of two cell layers 3. Lines ducts of sweat glands H. Stratified Columnar Epithelium 1. Also rare in humans 2. consists of only a few layers; apical cell layer is columnar and basal cell layer is cuboidal 3. Found in male urethra, cornea of eye, and in ducts of certain glands like salivary glands I. Transitional Epithelium 1. Only found in urinary system 2. Basal cell layers are cuboidal while apical cell layers are dome-shaped when tissue is relaxed; ability of apical cells to flatten contributes to ability of urinary tissues to stretch III. Transport across simple epithelia occurs via one of two routes A. Paracellular transportation- where substances leak between cells 1. Limited due to tight junctions 3  B. Transcellular transportation- where a substance enters a cell by crossing plasma membrane, diffuses across cytosol and exits through plasma membrane on opposite side. IV. Glandular Epithelia A. Gland – structure of epithelial origin that synthesizes and secretes a product from designated secretory cells 1. Can be classified either by their shape or by how they release products 2. Products are released by two mechanisms: a. Endocrine glands secrete their products, usually hormones, directly into the bloodstream without the use of ducts 1. Allows products to have widespread systemic effects on distant cells in different areas of body b. Exocrine glands release products onto apical surfaces of epithelium located on external surface of body or lining a hollow organ that opens to outside of body 1. Products, secreted from gland through an epithelial-lined duct, have only local effects on cells in general vicinity 3. Goblet cells – most common unicellular exocrine gland; found in digestive and respiratory tracts; secrete mucus B. Exocrine glands have two methods for secreting products: 1. Merocrine secretion, used by majority of exocrine glands secretory cells a. package products in secretory vesicles for release by exocytosis into ducts 2. Holocrine secretion – used by sebaceous gland in skin to secrete sebum; a. secretory cells accumulate product in cytosol; only release product when cell ruptures and dies Connective Tissue I. Two basic groups that differ in their cell types and ECM components: A. Connective tissue proper (general connective tissue) B. Specialized connective tissue II. Connective tissue functions: A. Connecting and binding – anchor tissue layers in organs and link organs together B. Support – bone and cartilage support weight of the body C. Protection – bone tissue protects certain internal organs and cartilage and fat provide shock absorption; components of immune system are found throughout connective tissues D. Transport – blood is a fluid connective tissue that is main transport medium in body III. Connective Tissue Proper Cells A. Resident cells permanently inhabit tissue in which they are found 1. Fibroblasts – most common resident cell a. Make protein fibers and ground substance; continually produce collagen proteins 2. Adipocytes-fat cells 3. Mast cells -Largest resident cell a. Immune system cells release mediators (degranulate) when stimulated, causing inflammation 4  B. Migrant cells migrate into different areas of body depending on situation 1. Phagocytes – also immune system cells a. can ingest foreign substances, microorganisms, and dead or damaged cells by phagocytosis b. include macrophages (either resident or migrant) and neutrophils (migrant cells) IV. Types of Connective Tissue Proper A. Areolar tissue 1. Loose connective tissue mostly ground substance, with all three types of protein fibers, fibroblasts, and occasionally adipocytes, suspended in ground substance 2. Found beneath epithelium of skin, in membranes lining body cavities, and within walls of hollow organs 3. Contains and supports blood vessels vital to avascular epithelial tissues; houses immune system cells that protect body from microorganisms B. Dense Irregular Connective Tissue 1. Predominantly disorganized collagen bundles 2. Strong and resists tension in all three planes of movement 3. Found in high tension areas like dermis and surrounding organs and joints C. Dense Regular Connective Tissue 1. Predominantly organized into parallel collagen bundles; resistant to tension in one plane 2. Found in tendons and ligaments that are subject to tension in one plane of movement D. Dense Regular Elastic Connective Tissue 1. Mostly parallel-oriented elastic fibers with randomly oriented collagen fibers 2. Found in walls of organs that must stretch to perform their function, such as large blood vessels and certain ligaments E. Reticular Tissue 1. Composed mostly of reticular fibers produced by fibroblasts (reticular cells) 2. Forms bone marrow 3. Also found in lymph nodes and spleen; form weblike nets that trap old and foreign cells 4. Forms part of basement membrane that supports all epithelia and internal structure of liver and bone marrow F. Adipose Tissue 1. Consists of fat-storing adipocytes and surrounding fibroblasts and ECM 2. Functions include fat storage, insulation, shock absorption and protection V. Types of Specialized Connective Tissues A. Cartilage 1. Avascular tissue found in joints between bones, in ear, nose, and segments of respiratory tract 2. Tough, flexible tissue; absorbs shock and resists tension, compression, and shearing forces; ECM consists of collagen and elastic fibers, glycosaminoglycans, and proteoglycans 3. Populated with two cell types: a. Chondroblasts – immature cells that divide by mitosis and make most of ECM 5  b. Eventually surround themselves in small cavities (lacunae) in ECM to become mature, largely inactive chondrocytes 4. Three types: a. Hyaline Cartilage 1. Most abundant cartilage 2. ECM mostly ground substance made of small bundles of fine collagen 3. Found on ends of bones in joints (articular cartilage), linking sternum to ribs, framing sections of respiratory tract, and in nose 4. Most of fetal skeleton is hyaline cartilage b. Fibrocartilage 1. Filled with bundles of collagen fibers with little room for ground substance in ECM 2. Tissue has great tensile strength with some degree of elasticity 3. Found in between bones of fibrous joints; forms articular discs that improve fit of bones in joints c. Elastic Cartilage 1. Mostly elastic fibers in its ECM 2. Allows this tissue to vibrate 3. Found in a limited number of structures; external ear assists with detection of sound in air; larynx assists with production of sound B. Osseous tissue (bone) 1. Supports body; protects vital organs; provides attachments for muscles that allow for movement; stores calcium, and houses bone marrow (produces blood cells and stores fat) 2. ECM is composed of about 35% organic components consisting of collagen fibers and ground substance; remaining 65% of ECM is inorganic calcium phosphate crystals 3. Bone is a dynamic tissue capable of remodeling C. Blood 1. Unique connective tissue with a liquid ECM called plasma 2. Consists of mostly water, dissolved solutes, and proteins 3. Transports nutrients, gases, wastes and immune cells Muscle Tissues I. Muscle tissues A. Specialized for contraction B. Main component of muscle tissue is muscle cell or myocyte 1. Are excitable: II. Types A. Skeletal Muscle Tissue 1. Found mostly attached to skeleton a. produces body movement 2. Under voluntary control 3. Most skeletal muscle cells are long and striated; often called muscle fibers 6  B. Cardiac Muscle Tissue 1. Found only in heart; striated cells 2. Involuntary 3. Cells are short, branched, and usually have only one nucleus (uninucleate) 4. Intercalated disc – dark line separating individual cardiac muscle cells; contain gap junctions and modified tight junctions; allow heart muscle to contract as a unit C. Smooth Muscle Tissue 1. Involuntary cells with no striations 2. Found in walls of nearly every hollow organ, blood vessels, eyes, skin, and ducts of certain glands 3. Flattened cells with one centrally located ovoid nucleus 4. In most, neighboring cells are linked together by gap junctions Nervous Tissue I. Nervous tissue A. Makes up majority of brain, spinal cord, and nerves B. Composed of two main cell types and their surrounding ECM 1. Neurons – excitable cells capable of sending and receiving messages; no longer divide 2. Neuroglial cells – diverse group of smaller cells; variety of functions ultimately meant to support activity of neurons; able to divide by mitosis C. ECM is unique; made up of ground substance with unique proteoglycans not found in other tissues of body; contains very few protein fibers Membranes I. Membranes A. Thin sheets of one or more tissues that line a body surface or cavity B. Most consist of a superficial epithelial layer resting on a connective tissue layer; sometimes contains smooth muscle C. Functions: anchor organs in place, serve as barriers, function in immunity, and secrete various substances II. True Membranes A. Do not open to outside of body B. Two examples 1. Serous membranes or serosae – line pericardial, peritoneal, and pleural body cavities a. Consist of a mesothelium, associated basement membrane, and a layer of connective tissue; fold over themselves giving appearance of two layers b. mesothelial cells produce a thin, watery serous fluid; fills space between parietal and visceral layers; reduces friction created when organs (like heart or lungs) move within respective membranes 7  2. Synovial membranes – line cavities surrounding freely moveable joints like knee or shoulder; made up of two connective tissue layers without a layer of epithelial cells a. outer layer – usually composed of a mixture of loose and dense irregular connective tissue b. inner layer – synoviocytes (modified fibroblasts) secrete synovial fluid, a watery, slippery fluid; primarily functions to lubricate joint III. Membrane-like Structures A. Mucous Membranes (mucosae) 1. Line all body passages as components of walls of hollow organs that open to outside of body 2. Includes respiratory passages, mouth, nasal cavity, digestive tract, and male and female reproductive tracts 3. Contain glands with goblet cells; produce and secrete mucus a. serves several functions, primarily protection B. Cutaneous membrane – refers to skin; largest organ of body 1. Continuous protective surface that protects structures deep to it 8