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Ch. 4 Tissues

by: Simone Notetaker
Simone Notetaker


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Anatomy and Physiology
Dr. Carpenter
Class Notes
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This 15 page Class Notes was uploaded by Simone Notetaker on Saturday September 17, 2016. The Class Notes belongs to 0516 at Cleveland Institute of Medical Massage taught by Dr. Carpenter in Fall 2016. Since its upload, it has received 8 views. For similar materials see Anatomy and Physiology in Medical massage therapy at Cleveland Institute of Medical Massage.


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Date Created: 09/17/16
4.1 Types of Tissues -All of the cells of the body can be classified into about 20 different cell types ▯ -Tissues: a group of similar cells, usually with a common embryonic origin, that functions together to carry out specialized activities  Epithelial tissue: covers body surfaces; lines body cavities, hollow organs, and ducts (tubes); and forms glands  Connective tissue: protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity  Muscular tissue: generates the physical force needed to make body structures move  Nervous tissue: detects changes inside and outside the body and initiates and transmits nerve impulses a that coordinate body activities to help maintain homeostasis ▯ -Histology: the science that deals with the study of tissues ▯ -Pathologist: a physician who specializes in laboratory studies of cells and tissues to help other physicians make accurate diagnoses  they examine tissues for any changes that might indicate disease ▯ ▯ ▯ -Cell junctions: epithelial cells and some muscle and nerve cells are tightly joined into functional units by points of contact between plasma membrane  Tight junctions: consist of weblike strands of transmembrane proteins that fuse the outer surfaces of adjacent plasma membranes together. Cells of epithelial tissues that line the stomach, intestines, and urinary bladder have many tight junctions to retard the passage of substances between cells and prevent the contents of these organs from leaking into the blood of surrounding tissues.  Adherens junctions: contain plaque, a dense layer of proteins on the inside of the plasma membrane that attaches to both membrane proteins and to microfilaments of the cytoskeleton. In epithelial cells, adherens junctions often form extensive zones called adhesion belts because they encircle the cell similar to the way a belt encircles your waist. Adherens junctions help epithelial surfaces resist separation during various contractile activities (ex: food moves through the intestines)  Desmosomes: contain plaque and have transmembrane glycoproteins that extends into the intercellular space between adjacent cell membranes and attach cells to one another. (Unlike adherens junctions) The plaque of desmosomes attaches to intermediate filaments. The intermediate filaments extends from desmosomes on one side of the cell across the cytosol to desmosomes on the opposite side of the cell-this structural arrangement contributes to the stability of the cells and tissue. These junctions are common among the cells that make up the outermost layer of the skin, and the cardiac muscle cells. Desmosomes prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction.  Hemidesmosomes: On the insides of the plasma membrane, intermediate filaments attach to the plaque. On the outside of the plasma membrane, the transmembrane glycoproteins in the extracellular space attach to the basement membrane. Hemidesmosomes anchor cells not to each other but to the basement membrane. Gap junctions: connexons (tiny fluid-filled tunnels) connect neighboring cells. The plasma membrane is separated by a very narrow intercellular gap. Through the connexons, ions and small molecules can diffuse from the cytosol of one cell to another. The transfer of nutrients and wastes, takes place through gap junctions in avascular tissues (ex: the lens and cornea of the eye.) Gap junctions also allow the cells in a tissue to communicate with one another; gap junctions enable nerve or muscle impulses to spread rapidly among cells. ▯ -Supplied with nerves ▯ -Epithelial tissue may be divided into two types (1) covering and lining epithelium and (2) glandular epithelium  covering and lining epithelium: forms the outer covering of the skin and the outer covering of some internal organs. It also lines the inside of body cavities; blood vessels; ducts; and the interiors of the respiratory, digestive, urinary, and reproductive systems. (It makes up, with nervous tissue, the parts of the sense organs for hearing, vision, and touch)  glandular epithelium: makes up the secreting portion of the glands (ex: sweat glands) ▯ -General features of epithelial tissue  Consists largely/entirely of closely packed cells with little extracellular material between them, and the cells are arranged in continuous sheets, in either single or multiple layers  An apical (free) surface, which is exposed to a body cavity, lining of an internal organ, or the exterior of the body; lateral surfaces, which face adjacent cells on either side; and a basal surface, which is attached to a basement membrane. The term apical layer refers to the most superficial layer of cells; basal layer refers to the deepest layer of cells. The basement membrane is a thin extracellular structure composed of two layers, the basal lamina and the reticular lamina. It is located between the epithelium and the underlying connective tissue layer and helps bind and support the epithelium. Basal lamina: epithelial tissues; reticular lamina: connective tissues  Epithelia are avascular (without blood vessels); the vessels that supply nutrients to and remove wastes from epithelia are located in adjacent connective tissues. The exchange of materials between epithelium and connective tissue occurs by diffusion  Epithelia have a nerve supply  Epithlium goes through wear, tear, and injury; it has a high capacity for renewal by cell division ▯ (a) Arrangement of cells in layers: the cells of covering and lining epithelia are arranged in one or more layers depending on the functions the epithelium performs  simple epithlium: a single layer of cells that functions in diffusion, osmosis, filtration, secretion, and absorption. Secretion: the production and release of substances such as mucus, sweat, or enzymes. Absorption: the intake of fluids or other substances such as digested food from the intestinal tract  Pseudostratified epithelium: appears to have multiple layers of cells because the cell nuclei lie at different levels and not all cells reach the apical surface. Cells that do extend to the apical surface may contain cilia; others (goblet cells) secrete mucus.  Stratified epithelium: (stratum: layer) consists of more than one layer of cells that protect underlying tissues in locations where there is considerable wear and tear ▯ (b) Cell shapes  Squamous cells: thin, this allows for the rapid passage of substances through them  Cuboidal: nearly as tall as wide, shaped like cubes; may have microvilli at their apical surface and function in either secretion or absorption  Columnar: taller than width (columns); protect underlying tissues. Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption  Transitional: change shape, from flat to cuboidal and back (ex: bladder) ▯ ▯ (a) simple epithelium ▯ simple squamous epithelium ▯ simple cuboidal epithelium ▯ simple columnar epithelium (nonciliated and ciliated) ▯ pseudostratified columnar epithelium (nonciliated and ciliated) ▯ (b) stratified ▯ stratified squamous epithelium (keratinized and nonkeratinized) ▯ stratified cuboidal epithelium ▯ stratified columnar epithelium ▯ transitional epithelium ▯ ▯ -Covering and Lining Epithelium: covers or lines various parts of the body, is classified according to the arrangement of cells into layers and the shape of the cells. ▯ (a) Simple epithelium  Simple Squamous Epithelium: consists of a single layer of flat cells that resembles a tiled floor when viewed from its apical surface. The nucleus is centrally located. SSE is so thin that the flattened nucleus makes a bulge in the cell; there is very little cytoplasm. SSE is found in parts of the body where filtration (kidneys) or diffusion (lungs) are priority processes; NOT found in body areas subjected to wear and tear. -Endothelium: SSE that lines the heart, blood vessels, and lymphatic vessels. -Mesothelium: forms the epithelial layer of serous membranes (peritoneum, pleura, pericardium)  Simple Cuboidal epithelium: SCE found in organs like the thyroid gland and kidneys; performs the functions of secretion and absorption. Cells that are strictly cuboidal could not form small tubes  Simple Columnar Epithelium: SCE appear like columns with oval nuclei near the base of the cells. Exists in two forms: nonciliated SCE and ciliated SCE. Columnar epithelium functions in secretion and absorption; the larger columnar cells contain more organelles and are capable of a higher level of secretion and absorption than cuboidal cells o Nonciliated SCE: contains absorptive cells and goblet cells. Mucus accumulates, in the goblet cell, in the upper portion of the cell, causing the area to bulge. The whole cell then resembles a goblet cell (or wine glass.) Secreted mucus is a lubricant for the linigs of the digestive, respiratory, reproductive, and most of the urinary tracts. Mucus also helps to trap dust entering the repiratory tract, and it prevents destruction of the stomach lining by acid secreted by the stomach.  Absorptive cells: columnar epithelial cells with microvilli.  Microvilli: microscopic finger-like projections that increase the surface area of the plasma membrane; increase the rate of absorption for the absorptive cell.  Goblet cells: modified columnar cells that secrete mucus (a slightly sticky fluid) at their apical surfaces. o Ciliated SCE: contains cells with cilia at their apical surface. (ex: upper respiratory tract; mucus secreted by the goblet cells forms a film over the respiratory surface that traps inhaled foreign particles. The cilia wave in unison and move the mucus and etc. toward the throat to be coughed up, swallowed, or spat.) Cilia also help move oocytes.  Pseudostratified Columnar Epithelium: appears to have several layers because the nuclei of the cells are at various levels. All the cells are attached to the basement membrane in a single layer, but some cells do not extend to the apical surface. o Ciliated PCE: contains cells that extend to the surface and either secrete mucus (goblet cells) or bear cilia. The secreted mucus traps foreign particles and the cilia sweep it away o Nonciliated PCE: contains cells without cilia and also lacks goblet cells and functions in absorption and protection. ▯ (b) Stratified Epithelium: contains two or more layers of cells and therefore is useful for protection of underlying tissues in areas where there is considerable wear and tear. Some cells of stratified epithelia also produce secretions.  Stratified Squamous Epithelium: Apical layer: flat; Deep layers: cells vary from cuboidal to columnar. The deepest cells continually undergo cell division; when new cells grow, the cells of the basal layer are pushed toward the surface. As the cells move farther from the deeper layers and from their blood supply in the underlying connective tissue, they become dehydrated, shrunken, and harder. At the apical layer the cells lose their cell junctions are “sloughed” off, and are replaced as new cells continually emerge from the basal cells. SSE forms the first line of defense against microbes. o Keratinized SSE: Develops a tough layer of keratin in the apical layer and also several layers deep.  Keratin: a tough protein that helps protect and waterproof the skin and protect underlying tissues from microbes, heat, and chemicals. o Nonkerantinized SSE: contains living cells as evidenced by the nuclei at the free surface. (ex: lining of the mouth; it does not contain keratin in the apical layer and remains moist)  Stratified Cuboidal Epithelium: (fairly rare) sometimes consists of more than two layers of cells. Cells in the apical layer are cuboidal; its mainly protective; in some locations it also functions in secretion and absorption.  Stratified Columnar Epithelium: (uncommon) usually the layer/layers near the basement membrane consist of shortened, irregularly shaped cells; only the apical layer of cells is columnar in form. Functions in protection and secretion.  Transitional Epithelium: varies in appearance depending on whether the organ it lines is unstretched or stretched; somewhat constant state of transition. Unstretched TE looks similar to stratified cuboidal epithelium, except that the cells in the apical layer tend to be large and rounded (dome shaped); as the cells are stretched, they become flatter, giving the appearance of stratified squamous epithelium. Because of its elasticity, TE lines hollow structures that are subjected to expansion from within (ex: urinary bladder). It allows organs to stretch to hold a variable amount of fluid without rupturing. ▯ -Glandular Epithelium: Function: secretion; is accomplished by glandular cells that often lie in clusters deep to the covering and lining epithelium. A gland may consist of a single cell or a group of cells that secrete substances into ducts (tubes), onto a surface, or into the blood. All glands are either exocrine or endocrine.  Endocrine glands: secretions enter the interstitial fluid and then diffuse directly into the bloodstream without flowing through a duct. These secretions, hormones, regulate many metabolic and physiological activities to maintain homeostasis. (ex: pituitary, thyroid, and adrenal glands)  Exocrine glands: secrete their products into ducts that empty onto the surface of a covering and lining epithelium epithelium such as the skin surface (lumen) of a hollow organ. Secretions include mucus, sweat, oil, earwax, saliva, and digestive enzymes. Glands include sudoriferous (sweat) glands-produce sweat to lower body temp. and salivary glands which secrete saliva. o Unicellular glands: are single-celled. Goblet cells are important unicellular exocrine glands that secrete mucus directly onto the apical surface of a lining epithelium. o Multicellular glands: most glands are MG; composed of many cells that form a distinctive microscopic structure or macroscopic organ. (ex: sudoriferous, sebaceous (oil), and salivary glands) o Merocrine glands: (Eccrine glands) The secretions are synthesized on ribosomes attached to rough ER; processed, sorted, and packaged by the Golgi complex; and released from the cell in secretory vesicles by exocytosis. Most glands of the body are Merocrine glands (ex: salivary and pancreas glands) o Apocrine glands: accumulate their secretory product at the apical surface of the secreting cell; then that portion of the cell pinches off from the rest of the cell to release the secretion, the remaining part of the cell repairs itself and repeats the process. o Holocrine glands: accumulate a secretory product in their cytosol. As the secretory cell matures, it ruptures and becomes the secretory product. The sloughed off cell is replaced by a new cell. (ex: sebaceous gland of the skin) ▯ ▯ Papanicolaou test: (Pap smear) ▯ involves collection and microscopic ▯ exami-Connective tissue: is the most abundant and widely distributed tissue in the body.ed off the apical layer of a tissue  Function: binds together, supports, and strengthens other body tissues; protects and insulates internal organs; compartmentalizes structures such as skeletal muscles; is the major transport system within the body (blood is a fluid connective tissue); is the major site of stored energy reserves (adipose (fat) tissue), & is the main site of immune responses. ▯ -Connective tissue consists of two basic elements: cells and extracellular matrix. ▯ -Extracellular matrix: is the material between its widely spaced cells; it consists of protein fibers and ground substance (the material between the cells and the fibers); the extracellular matrix is usually secreted by the connective tissue cells and determines the tissue’s qualities ▯ -General features of connective tissue  (unlike epithelia) do not usually occur on body surfaces  (unlike epithelia) are usually highly vascular (they have a rich blood supply)  Cartilage is avascular  Tendons and ligaments have a scanty blood supply  (like epithelia) are supplied with nerves ▯ -Fibroblasts: are large, flat cells with branching processes. Present in nearly all connective tissues (usually the most numerous cell type). They migrate through the connective tissue, secreting the various fibers and ground substance of the extracellular matrix ▯ -Macrophages: develop from monocytes (a white blood cell). Macrophages have an irregular shape with short branching projections and are capable of engulfing bacteria and cellular debris by phagocytosis ▯ -Plasma cells: small cells that develop from a type of white blood cell (B lymphocyte.) They secrete antibodies: proteins that attack or neutralize foreign substances in the body. Important part of the immune response. ▯ -Mast cells: abundant by the blood vessels that supply connective tissue. They produce histamine: a chemical that dilates small blood vessels as part of the inflammatory response (the body’s reaction to injury or infection). They can also kill bacteria. ▯ -Adipocytes: (adipose/fat cells) connective tissue cells that store triglycerides (fats). They are found below the skin and around organs. (ex: heart and kidneys) ▯ -Neutrophils gather at infection sites; Eosinophils migrate to sites of parasitic invasion and allergic responses ▯ -Connective Tissue Extracellular Matrix  -Ground substance: the component of a connective tissue between the cells and fibers, supports cells, binds them together, and provides a medium through which substances are exchanged between the blood and cells. o Plays a role in how tissues develop, migrate, proliferate, and change shape, and how they carry out their metabolic functions. o Contains water and large organic molecules (ex: polysaccharides and proteins) o Hyaluronic acid: a viscous, slippery substance that binds cell together, lubricates joints, and helps maintain the shape of the eyeballs (also plays a role in helping phagocytes migrate through connective tissue during development and would repair) o Hyaluronidase: can be produced by white blood cells, sperm cells, and some bacteria; is an enzyme that breaks apart hyaluronic acid and causes the ground substance of connective tissue to become watery. The ability to produce hyaluronidase enables white blood cells to move through connective tissues to reach sites of infection and enables sperm cells to penetrate the ovum during fertilization-also accounts for how bacteria spread through connective tissues o Chondroitin sulfate: (polysaccharide) provides support and adhesiveness in connective tissues in bone, cartilage, skin, and blood vessels. o Glucosamine: (protein) polysaccharide molecule  Fibers: in the extracellular matrix strengthen and support connective tissues; there are 3 different types (collagen fibers, elastic fibers, and reticular fibers) o Collagen fibers: are very strong, resist pulling forces, but are NOT stiff-this promotes tissue flexibility. The parallel bundles provide support. Tropocollagen molecules form collagen fibrils and then through hydrogen bonding, fibrils are organized into larger collagen fibers. Is the most abundant protein in the body; represents about 25% of total protein. Found in most types of connective tissues (ex: bone, cartilage, tendons, and ligaments). Hydrogen bonding gives collagen fibers and molecules their strength; if muscle activity is greatly decreased or increased, collagen molecules bind together and collagen fibers increase, creating “tightness” o Elastic fibers: (smaller than collagen fibers) branch together to form a network within a tissue. Consists of of molecules of a protein called elastin surrounded by fibrillin (glycoprotein)- this is essential to the stability of an elastic fiber. Can be stretched up to 1.5 times their size and return to their normal size (elasticity). Plentiful in skin, blood vessel walls, and lung tissue o Reticular fibers: (consist of: collagen fibrils and a coating of glycoprotein) provide support in the walls of blood vessels and form branching networks around fat cells, nerve fibers, and skeletal and smooth muscles. Produced by: fibroblasts; much thinner than collagen fibers. Provide: support, strength, and also form the stroma: supporting framework of many soft organs (ex: spleen and lymph nodes) Reticular fibers also help form the basement membrane o ▯ Marfan syndrome: an inherited disorder caused by a defective fibrillin gene- ▯resulting in abnormal development of elastic fibers. Tissues rich in elastic fibers are ▯ malformed or weakened (ex: ligament that suspends the eyelid, walls of the large ▯ arteries). These people tend to be tall with long limbs. A common symptom is blurred vision, and weakening of the aorta which can suddenly burst. ▯ ▯ ▯ ▯ ▯ -Classification of Connective Tissues ▯ I. Embryonic connective tissue a. mesenchyme b. mucous connective tissue ▯ II. Mature connective tissue a. loose connective tissue -areoular connective tissue -adipose tissue -reticular connective tissue b. dense connective tissue -dense regular connective tissue -dense irregular connective tissue -elastic connective tissue c. cartilage -hyaline cartilage -fibrocartilage -elastic cartilage d. bone tissue e. liquid connective tissue -blood tissue -lymph -Embryonic connective tissue: present primarily in the embryo and fetus  Mesenchyme: (the tissue from which all other connective tissues eventually arise) is composed of irregulary shaped cells, a semifluid ground substance, and delicate reticular fibers. ARE present throughout life and are the stem cells from which all connective tissues continue to form.  Mucous connective tissue (wharton’s jelly) found mainly in the umbilical cord of the fetus; is a form of mesenchyme; contains widely scattered fibroblasts (a more viscous, jelly-like ground substance) and collagen fibers ▯ -Mature connective tissue: present in the newborn. Its cells arise from mesenchyme.  Loose connective tissue: are loosely arrange among the many cells. The different types of loose connective tissue are areolar connective tissue, adipose tissue, and reticular connective tissue. o Areolar connective tissue: (one of the most widely distributed connective tissues in the body) it contains several kinds of cells including: fibroblasts, macrophages, plasma cells, mast cells, adipocytes, and a few white blood cells. All 3 types of fibers (collagen, elastic, reticular) are arranged randomly thoughout the tissue. “packing material” of the body because it is found in and around nearly every structure of the body. Combined with adipose tissue, ACE forms the subcutaneous layer: the layer of tissue that attaches the skin to underlying tissues and organs o Adipose tissue: a loose connective tissue in which adipocytes are specialized for storage of triglycerides (fats). Because the cell fills with a single, large triglyceride droplet, the cytoplasm and nucleus are pushed to the periphery of the cell. Adipose tissue is found wherever areolar connective tissue is located. Is a good insulator-reduces heat loss through the skin; is a major energy reserve and generally supports and protects various organs.  As the amount of adipose tissue increase with weight gain, new blood vessels form. Ex: an obese person has many more miles of blood vessels than does a lean person, this can cause high blood pressure o Reticular connective tissue: consists of fine interlacing reticular fibers and reticular cells, cells that are connected to each other and form a network. RCE forms the stroma (supporting framework) of certain organs, helps bind together smooth muscle cells, and filters worn out blood cells and bacteria  Dense connective tissue: contains more numerous, thicker, and denser fibers (more closely packed) but fewer cells than loose connective tissue. There are 3 types: dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue. o Dense regular connective tissue: bundles of collagen fibers are arranged regularly in parallel patterns that provide the tissue with great strength. Fibroblasts (produce the fibers and ground substance) appear in row between the fibers. (ex: tendons and most ligaments)  Predominant collagen fibers are not living (since they were secreted by fibroblasts); damaged tendons and ligaments are therefore slow to heal o Dense irregular connective tissue: contains collagen fibers that are packed more closely together than in loose connective tissue and are usually irregularly arranged. Found in parts of the body where pulling forces are exerted in various directions. Usually occurs in sheets (ex: dermis of the skin, heart valves, periosteum (covering around bone)) o Elastic connective tissue: has a yellowish color; fibroblasts are present in the spaces between the fibers. ECT is strong and can recoil to its original shape after being stretched ▯ -Cartilage: consists of a dense network of collagen fibers or elastic fibers firmly embedded in chondroitin sulfate ( a rubbery component of the ground substance); cartilage can endure considerably more stress than loose and dense connective tissues; the strength of cartilage is due to its collagen fibers, and its resilience is due to chondroitin sulfate. The surface of most cartilage is surrounded by perichondrium. Cartilage has NO blood vessels or nerves EXCEPT in the perichondrium. It heals slowly because it has no blood supply. The 3 types of cartilage are hyaline cartilage, fibrocartilage, and elastic cartilage ▯ -chondrocytes: (the cells of mature cartilage) occur singly or in groups within spaces in the extracellular matrix-called lacunae ▯ -perichondrium: a membrane of dense irregular connective tissue  Hyaline cartilage: contains a resilient gel as its ground substance and appears in the body as a bluish white, shiny substance. Most hyaline cartilage is surrounded by a perichondrium-except for the articular cartilage in joints and at the epiphyseal plates (the regions where bones lengthen as a person grows). The MOST abundant cartilage in the body-it affords flexibility and support; at joints, reduces friction and absorbs shocks. The WEAKEST of the 3 types of cartilage  Fibrocartilage: chondrocytes are scattered among clearly visible bundles of collagen fibers within the extracellular matrix; lacks a perichondrium; combines strength and rigidity and is the STRONGEST of the three types of cartilage (ex: located in the discs between vertebrae).  Elastic cartilage: chondrocytes are located within a threadlike network of elastic fibers within the extracellular matrix. A perichondrium is present; provides strength and elasticity and maintains the shape of certain structures (ex: external ear) ▯ -Bone tissue: bone tissue: supports soft tissues, protects delicate structures, and works with skeletal muscles to generate movement. Bone stores calcium and phosphorus; stores red bone marrow; and a storage for triglycerides ▯ -Liquid connective tissue  Blood tissue: (blood) is a connective tissue with a liquid extracellular matrix (blood plasma: a pale yellow fluid that consists mostly of water with a wide variety of dissolved substances; nutrients, wastes, enzymes, hormones, respiratory gases, and ions). Suspended in the plasma are red blood cells, white blood cells, and platelets. o Red blood cells: transport oxygen to body cells and help remove carbon dioxide from them o White blood cells: are involved in phagocytosis, immunity, and allergic reactions o Platelets: participate in blood clotting ▯ -Lymph: is fluid that flows in lymphatic vessels. It is a connective tissue that consists of several types of cells in a clear extracellular matrix similar to blood plasma but with much less protein ▯ ▯ -Connective tissues: diverse and dynamic  the protein, collagen, makes up the bulk of connective tissues structures and is the most abundant protein in the body  when hyaline is added to the ground substance it becomes a form of cartilage; connective tissue becomes bone when mineral salts become involved  Interstitial fluid consists of blood plasma, nutrients, and hormones that have moved out of the blood stream by diffusion; the ground substance of connective tissue is produced by fibroblasts  Protein combines with carbohydrates to form molecules called mucopholysaccharides; when the mucopolysaccharides are small, the resulting gound substance is somewhat watery; when the mucopolysaccharides are larger and more numerous, the ground substance is more viscous and resembles gelatin.  Collagen fibers are predominant in tendons, ligaments, aponeurosis, the dermis of the skin, bone, blood vessels, the framework (stroma) of virtually all visceral organs, and fasciae  Collagen fibers are strong and flexible  Connective tissue fibers (manufactured by fibroblasts) are not living matter  Fibroblasts are able to move from one part of the body to another and then producing the fibers and ground substance that is appropriate to the tissue at any given time  Fibroblasts are key in healing  The process of forming scar tissue (fibrosis) occurs when dead or damaged cells are replaced by the connective tissue stroma of that organ  Collagen is formed by fibroblasts ▯ ▯ -Membranes: are flat sheets of pliable tissue that cover or line apart of the body. ▯ -Epithelial membrane: the combination of an epithelial layer and an underlying connective tissue layer ▯ -The principal epithelial membranes of the body are mucous membranes, serous membranes, and the cutaneous membrane (skin) ▯ -Membranes: are flat sheets of pliable tissue that cover or line apart of the body. ▯ -Epithelial membrane: the combination of an epithelial layer and an underlying connective tissue layer ▯ -The principal epithelial membranes of the body are mucous membranes, serous membranes, and the cutaneous membrane (skin) ▯ -Mucous membranes: (mucosa) lines a body cavity that opens directly to the exterior. Mucous membranes line the entire digestive, respiratory, and reproductive systems, and much of the urinary systems. The epithelial layer of a mucous membrane secretes mucus, which prevents the cavities from drying out. The connective tissue layer (areolar connective tissue) helps bind the epithelium to the underlying structures. It also provides the epithelium with oxygen and nutrients and removes wastes by its blood vessels ▯ -Serous membranes: lines a body cavity that does not open directly to the exterior, and it also covers the organs that lie within the cavity. Serous membranes consist of two parts: a parietal layer and a visceral layer  Parietal layer: is the part attached to the cavity wall  Visceral layer: is the part that covers and attaches to the organs insides these cavities o each layer consists of areolar connective tissue sandwhiched between two sheets of mesothelium  mesothelium: (a simple squamous epithelium) it secretes serous fluid (a watery lubricating fluid that allows organs to glide easily over one another or to slide against the walls of cavities) ▯ -Pleura: the serous membrane lining the thoracic cavity and covering the lungs ▯ -Pericardium: the serous membrane lining the heart cavity and covering the heart ▯ -Peritoneum: the serous membrane lining the abdominal cavity and covering the abdominal organs ▯ -Synovial membranes: line the cavities of most joints; composed of areolar connective tissue and adipose tissue with collagen fibers; they do not have an epithelial layer. Synovial membranes contain cells (synoviocytes) that secrete synovial fluid: this fluid lubricates the ends of bones as they move at joints, nourishes the cartilage covering the bones, and removes microbes and debris from the joint cavity. ▯ ▯ -Muscular tissue: consists of elongated cells called muscle fibers that are highly specialized to generate force; as a result MT produces motion, maintains posture, and generates heat, and offers protection. There are 3 types of muscular tissues: skeletal, cardiac, and smooth  Skeletal muscle tissue: named for its location-it is usually attached to the bones of the skeleton  Cardiac muscle tissue: forms the bulk of the wall of the heart  Smooth muscle tissue: located in the walls of hollow internal structures such as blood vessels, airways to the lungs, the stomach, intestines, gallbladder, and urinary bladder ▯ ▯ ▯ -Nervous tissue: consists of only two principal types of cells: neurons and neuroglia  Neurons: (nerve cells) are sensitive to various stimuli. They convert stimuli into nerve impulses and conduct these impulses to other neurons, to muscle fibers, or to glands.  Neuroglia: do not generate or conduct nerve impulses  ▯ -Tissue repair is the process that replaces worn-out, damaged, or dead cells. New cells originate by cell division from the stroma (the supporting connective tissue) or from the parenchyma (cells that constitute the functioning part of the tissue or organ. Stem cells (immature, undifferentiated cells) divide to replace lost or damaged cells; ex: stem cells reside in protected locations in the epithelia of the skin and gastrointestinal tract to replenish cells sloughed from the apical layer. Nervous tissue has the poorest capacity for renewal. If parenchymal cells accomplish the repair, tissue regeneration is possible, and a near perfect reconstruction of the injured tissue may occur; if fibroblasts of the stroma are active in the repair, the replacement tissue is a new connective tissue. Fibrosis (the fibroblasts synthesize collagen and other matrix materials that aggregate to form scar tissue) because scar tissue is not specialized to perform the functions of the parenchymal tissue, the original function of the tissue or organ is impaired. ▯ ▯ -Glucose is the most abundant sugar in the body; and plays a role in aging. Glucose is added to proteins inside and outside cells, forming irreversible cross-links between adjacent protein molecules. With advancing age, more cross-links form, which contributes to the stiffening and loss of elasticity that occur in aging tissues. Collagen fibers, responsible for the strength of tendons, increase in number and change in quality with aging. Elastin (responsible for the elasticity of blood vessels and skin) thickens, fragments, and acquires a greater affinity for calcium with age; changes that may also be associated with the development of atherosclerosis (the deposition of fatty materials in arterial walls)  Excess adiposity: as people age skeletal muscles atrophy; adipose tissue tends to grow. Muscle tissue does not turn into fat tissue (fat tissue is specialized for energy storage). Adiposity can cause hypertension: high blood pressure, poor blood sugar regulation, heart disease, certain cancers, gallstones, arthritis, and back aches ▯


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All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.