Ch4 Epithelial and connective tissue.docx - Chapter 4 –...

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Unformatted text preview: Chapter 4 – Epithelial and Connective Tissue Reading Outline Introduction A tissue is a group of similar cells and extracellular products that perform a common function The extracellular matrix of different tissues varies in structure and function – Generally composed of water, protein fibers, dissolved molecules – Composition, volume and consistency is different across tissues Four types of tissue in the body: Epithelial tissue Connective tissue Muscle tissue Nervous tissue Epithelial Tissue Epithelial tissue lines every body surface and all body cavities Organs are lined on the outside and inside by epithelial tissue The majority of glands are derived from epithelial tissue Epithelial tissue possesses little to no extracellular matrix Characteristics of Epithelial Tissue All epithelia are: cellular, polar, attached to a basement membrane, avascular, richly innervated, and regenerative Cellularity: Composed almost entirely of cells - little extracellular matrix Cells are bound together by several types of intercellular junctions Polarity: Epithelial cells have an apical surface and a basal surface Apical surface is exposed Basal surface is attached to connective tissue underneath it Attachment: Basal surface attaches to basement membrane - molecules produced by both epithelial and neighboring connective tissues Avascularity: Epithelial tissues lack blood vessels Innervation: Epithelia are richly innervated to detect changes in environment (externally or internally) High regeneration capacity: Because exposed apical surface is frequently damaged, epithelial cells are quickly replaced Functions of Epithelial Tissue Physical protection: Defend against dehydration and abrasion, as well as physical, chemical, and biological agents Selective permeability: Regulate passage of molecules in or out of certain regions of the body Secretion: Secrete substances for use in the body (e.g., hormone) or for elimination from the body (e.g., sweat) Sensation: Possess nerve endings that can detect light, taste, sound, smell, and hearing Specialized Structures of Epithelial Tissue The basement membrane is a specialized structure of epithelium Found between epithelium and underlying connective tissue Provides physical support and anchoring of epithelial tissue Acts as a barrier regulating passage of large molecules between epithelium and connective tissue Classification of Epithelial Tissue Many different types of epithelial tissue Classified according to two criteria: Number of layers of cells Shape of the cells Classification by Number of Cell Layers Simple epithelium: Consists of a single layer of cells Stratified epithelium: Consist of two or more layers of cells All cells have an apical surface and attach to the basement membrane Not all cells have an apical surface nor do all cells attach to the basement membrane Pseudostratified epithelium: Appears to have multiple layers, but all cells attach to the basement membrane A subtype of simple epithelium Classification by Cell Shape Squamous: Flat, wide, and somewhat irregular in shape Cuboidal: About the same size on all sides; nucleus is usually centrally located Columnar: Taller than they are wide; nucleus is oval and located in basal region of the cell Types of Epithelia Simple Squamous Epithelium Single layer of flat cells Allows for rapid exchange Example: amnion around embryo Simple Cuboidal Epithelium Single layer of boxy cells Allows for absorption, secretion Example: kidney tubules Nonciliated Simple Columnar Epithelium Ciliated Simple Columnar Epithelium Single layer of tall, narrow, ciliated cells Allow for secretion, movement of material across free surface Example: uterine tube Pseudostratified Columnar Epithelium Single layer of narrow cells with varying heights - Some examples are ciliated Protection; ciliated form secretes mucin, moves mucus Example: respiratory tract lining Stratified Squamous Epithelium • Multiple layers, apical cells are flat • Apical cells may or may not be keratinized Keratinized Stratified Squamous Epithelium Multiple layers of cells Apical cells are dead, flat Superficial layers of cells contain tough, protective keratin Function: protection Example: epidermis of skin Nonkeratinized Stratified Squamous Epithelium Multiple layers of cells Flat, apical cells are alive and moist Function: protection Example: lining of vagina Stratified Cuboidal Epithelium Multiple layers of cells, apical cells are boxy Protection and secretion Example: lining of sweat gland duct Stratified Columnar Epithelium Multiple layers of cells, apical cells are elongated Protection and secretion Example: part of male urethra Transitional Epithelium Multiple layers, apical cell shape varies depending on degree of stretch Can distend or recoil depending on how stretched it is Lining of urinary tract Glands Individual cells or multicellular organs Perform a secretory function Produce mucin, hormones, enzymes, waste products Glands fall into two categories: Endocrine glands do not possess ducts; secrete directly into interstitial fluid or bloodstream Exocrine glands possess ducts and their cells secrete products into their ducts Structure of Exocrine Glands Goblet cells are unicellular exocrine glands Multicellular exocrine glands are often enclosed in a fibrous capsule Inside the capsule, the gland is divided into lobes A connective tissue stroma supports and organizes the gland Microscopic lobules contain secretory acini and ducts Classification of Exocrine Glands Gland secretion types are serous, mucous, or mixed Serous glands produce watery fluids (such as sweat) Mucous glands secrete mucin Mixed glands produce a mixture of watery and mucoid secretions (e.g. salivary glands under oral cavity) • Types of secretion mechanisms Merocrine: secrete products from vesicles via exocytosis Holocrine: cell accumulates product, then disintegrates Apocrine: product stored in apical part of cell that pinches off Connective Tissue Connective tissue is the most diverse, abundant, widely distributed, and structurally varied of the four main tissue types It is the “glue” of the body Includes blood, tendons, ligaments, fat, bones, cartilage Characteristics of Connective Tissue Cells: Different cells in different types of connective tissue Examples include fibroblasts, osteocytes, and adipocytes Protein fibers: Elastic fibers, collagen, reticular fibers Ground substance: A mixture of proteins and carbohydrates with variable amounts of salts and water Protein fibers and ground substance comprise the extracellular matrix Functions of Connective Tissue Physical protection Support and structural framework Binding of structures Storage Transport Immune protection Classification of Connective Tissue Types present after birth can be classified into three broad categories: Connective tissue proper Supporting connective tissue Fluid connective tissue Connective Tissue Proper Connective tissue proper includes multiple subtypes Subtypes vary in number and types of cell and in properties of extracellular matrix There are two groups of cells in connective tissue proper: Resident cells: Include fibroblasts, adipocytes, fixed macrophages, and mesenchymal cells Wandering cells: Include mast cells, plasma cells, free macrophages, and other leukocytes Protein Fibers of Connective Tissue Proper Three types of fibers produced by cells and secreted into the extracellular matrix: collagen fibers, elastic fibers, reticular fibers Collagen fibers: long, strong, flexible cables Collagen is the most abundant protein in human body Called “white fibers” (e.g. in tendons and ligaments) Elastic fibers: Thinner than collagen, stretch easily, branch, and rejoin Allow structures such as blood vessels to stretch and relax Reticular fibers: Thinner than collagen fibers; form a branching, woven framework Found in organs with abundant spaces such as liver, lymph nodes, and spleen Ground Substance of Connective Tissue Proper A combination of proteins and carbohydrates Texture is usually gelatinous Additional content such as water and salts can result in a texture anywhere from semifluid (adipose) to hard (bone) Categories of Connective Tissue Proper Connective tissue proper is classified into two categories: Loose connective tissue: Serves as the body’s packing material, found in spaces around organs • Types include areolar, adipose, and reticular Dense connective tissue: Strong, has fibers (mostly collagen) packed tightly together • Types include dense regular, dense irregular, and elastic Supporting Connective Tissue Two types of supporting connective tissue: Cartilage Bone Cartilage Firm, gel-like extracellular matrix composed of protein and ground substance Cells are called chondrocytes Chondrocytes occupy small spaces enclosed by their extracellular matrix called lacunae Strong and resilient to provide support and withstand deformation Usually covered by perichondrium Dense irregular connective tissue and stem cells for cartilage growth Types of Cartilage There are three types of cartilage: Hyaline cartilage Fibrocartilage Elastic cartilage Bone Two-thirds of bone’s weight is inorganic (mostly calcium salts); one-third is organic (collagen and other proteins) Organic parts provide flexibility Inorganic parts provide compressional strength Periosteum: dense irregular connective tissue covering Mature bone cells are called osteocytes Two forms of bone: compact bone and spongy bone Compact bone is arranged in cylindrical osteons of concentric lamellae Spaces within spongy bone house hemopoietic cells that generate blood cells Fluid Connective Tissue Fluid connective tissue refers to blood and lymph ...
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