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Types of tissue

epithelial tissue, connective tissue, muscular tissue, and nervous tissue

Epithelial tissue

sheets of densely packed cells (can be single layer or multiple layer); there is little extracellular "stuff"; the tissue is avascular (without blood vessels); supported by basement membrane; the tissue is highly mitotic; it combines with nervous tissue to form special organs (olfactory membrane, hearing, vision, touch, taste); divided into covering and lining epithelium, and glandular epithelium

Connective tissue

the most abundant and widely destributed tissue in the human body; composed of a matrix and cells; has lots of extracellular "stuff"; the matrix is composed of fibers and ground substance; not found on surfaces; has a rich blood supply (ecept for cartilage and tendons); generally contains nerves (except for cartilage and bone)

Muscular tissue

generates the physical force needed to make body structures move and gnerates body heat

Nervous tissue

detects changes in a variety of conditions inside and outside teh body and responds by generating action potentials (nerve impulses) that activate muscular contractions and glandular secretions

Cell junctions

contact points between the plasma membranes of tissue tells; we consider tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions

Tight junctions

consists of weblike strands of transmemebrane proteins that fuse the outer surfaces of adjacent plasma membranes together to seal off passageways between adjacent cells; found in cells of epithelial tissues that line the stomach, intestines, and urinary bladder

Adherens junctions

contain plaque, a dense layer of proteins on teh inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of teh cytoskeleton

Cadherins

transmembrane glycoproteins that join cells in adherens junctions; each inserts into the plaque from the opposite side of teh plasma membrane, partially crosses teh intercellular space (the space between cells), and connects to cadherins of an adjacent cell

Desmosomes

contain plaque and have transmembrane glycoproteins (cadherins) that extend into the intercellular space between adjacent cell membranes and attach cells to one another; the plaque attaches to elements of the cytoskeleton known as intermediate filaments that consists of the protein keratin; the intermediate filaments extend from desmosomes on one side of the cell across the cytosol to desmosomes on the opposite side of the cell

Hemidesmosomes

resemble desmosomes but they do not link adjacent cells; the transmemebrane glycoproteins are integrins rather than cadherins; on the inside of the plasma membrane, integrins attach to intermediate filaments made of the protein keratine; on the outside of the plasma membrane, the integrins attach to the protein laminin, which is presnet in teh basement membrane

Gap junctions

membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighboring cells; the plasma membranes are not fused together as in tight junctions but are separated by a very narrow intercellular gap (space); though the connexons, ions and small molecules can diffuse from teh cytosol of one cell to another

Basement membrane

a thin extracellular layer that commonly consists of two layers, the basal lamina (is closer to and secreted by the epithelial cells), and the reticular lamina

Covering and lining epithelium

forms the outer covering of the skin and some internal organs; also forms the inner lining of blood vessles, ducts, and body cavities, and teh interior of the respiratory, digestive, urinary and reproductive system; classified by arrangement of cells (layers), and cell shape

Glandular epithelium

makes up the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands; there are two types endocrine and exocrine

Simple epithelium

a single layer of cells that functions in duffusion, osmosis, filtration, secretion, or absorption

Secretion

the production and release of substances such as mucus, sweat, or enzymes

Absorption

the intake of fluids or other substances such as food from teh intestinal tract

Pseudostratified epithelium

appears to have multiple layers of cells because the cell nuclei lie at different levels and not all cells reach teh apical surface; cells that do extend to teh apical surface may contain cilia; others (goblet cells) secrete mucus

Stratified epithelium

consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear

Squamous cells

are arranged like floor tiles and are thing, which allows for the rapid passage of substances

Cuboidal cells

are as tall as they are wide and are shaped like cubes or hexagons; they may have microvili at their apical surface and function in either secretion or absorption

Columnar cells

are much taller than they are wide, like columns, and protect underlying tissues; their apical surfaces may have cilia or microvili, and they often are specialized for secretion and absorption

Transitional cells

change shape, from flat to cuboidal and back, as organs such as the urinary bladder stretch to a larger size and tehn collapse to a smaller size

Simple squamous epithelium

single layers of flat cells; centrally located nucleus; function in filtration, diffusion, osmosis, and secretion in serous membranes

Simple cuboidal epithelium

single layer of cube-shaped cells; centrally located nucleus; function in secretion and absorption

Nonciliated simple columnar epithelium

single layer of nonciliated column-like cells with nuclei near base of cells; contains goblet cells and cells with microvilli in some locations; function in secretion and absorption

Ciliated simple columnar epithelium

single layer of ciliated column-like cells with nuclei near base; contains goblet cells in some locations; moves mucus and other substances by ciliary action

Pseudostratified columnar epithelium

not a true stratified tissue; nuclei of cells are at different levels; all cells are attached to basement membrane, but not all reach teh apical surface; function in secretion and movement of mucus by ciliary action (ciliated cells); absorption and protection (nonciliated cells)

Stratified squamous epithelium

several layers of cells; cubouidal to columnar shape in deep layers; squamous cells form teh apical layer and several layers deep to it; cells from teh basal laeyr replace surface cells as they are lost; function in protection

Stratified cuboidal epithelium

tow or more layers of cells in which the cells in teh apical layer are cube-shaped; function in protection and some secretion and absorption

Stratified columnar epithelium

several layers of irregularly shaped cells; only the apical layer has columnar cells; function in protection and secretion

Transitional epithelium

appearance is variable (transitional); shape of cells in apical layer ranges from squamous (when stretched) to cuboidal (when relaxed); it permits distension

Endocrine gland

secretory products (hormones) diffuse into blood after passing through interstitial fluid; produce hormones that regulate various body activities

Exocrine gland

produces substances into ducts, that empty onto body surfaces or inside body cavities; produce substances such as sweat, oil, earwax, saliva, or digestive enzymes

Structural classification of exocrine glands

they are classified as unicellular or multicellular glands

Functional classification of exocrine glands

the classification is based on how their secretions are released: merocrine (produce secretion in vesicle), apocrine (part of the cell is pinched off), holocrine (whole cell is secreted)

Merocrine glands

secretions are synthesized on ribosomes attached to rough ER; processed, sorted, and packaged by the Golgi complex; and released from teh cell in secretory vesicles via exocytosis; mox exocrine glands of the body are this; examples include salivary glands and pancreas

Apocrine glands

accumulate their secretory product at the apical surface of teh 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 teh process; mammary glands use this mechanism of secretion

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; one example is a sebaceous gland of the skin

Extracellular matrix

the material located between connective tissue's widely spaced cells; this is usually secreted by the connective tissue cells and determines the tissue's qualities; consists of protein fibers and ground substance ( the material between teh cells and the fibers, can be fluid, semifluid, gelatinous, fibrous, or calcified)

Connective tissue cells origin

mesodermal embryonic cells called mesenchymal cells give rise to the cells of connective tissue

Connective tissue nomenclature

each major type of connective tissue contains an immature class of cells with a name ending in -blast, which means "to bud or sprout" (these immature cells are called fibroblasts in loose and dense connective tissue, condroblasts in cartilage, and osteoblasts in bone); blast cells retain the capacity for cell division and secrete teh extracellular matrix that is characteristic of the tissue; in cartilage and bone, once the extracellular matrix is produced, the immature cells differentiate into mature cells with names ending in -cyte, namely chondrocytes and osteocytes; mature cells have reduced capacities for cell division and extracellular matrix formation and are mostly involved in maintaining the matrix

Types of connective tissue cells

fibroblasts, adipocytes, mast cells, white blood cells, macrophages, and plasma cells

Fibroblasts

large, flat cells with branching processes; they are present in several connective tissues, and usually are the most numerous; they migrate through the connective tissue, secreting the fibers and certain components of the ground substance of the extracellular matrix

Adipocytes (adipose cells)

also called fat cells, are connective tissue cells that store triglycerides; they are found deep to the skin and around organs such as the heart and kidneys

Mast cells

are abundant alongside the blood vessels that supply connective tissue; they produce histamine, a chemical that dilates small blood vessels as part of teh inflammatory response, teh body's reaction to injury or infection; in addition, researchers have recently discovered that these cells can bind to, ingest, and kill bacteria

White blood cells

are not found in significant numbers in normal connective tissue; however, in response to certain condidtions they migrate from bood into connective tissues

Macrophages

have an irregular shape with short branching projections and are capable of engulfing bacteria and cellular debris by phagocytosis

Plasma cells

secrete antibodies, proteins that attack or neutralize foreign substances in the body; thus, they are an important part of the body's immune response

Ground substance

the component of a connective tissue between teh cells and fibers; it may be fluid, semifluid, gelatinous, or calcified; it supports cells, binds them together, stores water, and provides a medium through which substances are exchanged between the blood and cells; it plays an active role in how tissues develop, migrate, proliferate, and change shape, and in how they carry out their metabolic functions

Connective tissue fibers

three types are embedded in the extracellular matrix between cells: collagen fibers, elastic fibers, and reticular fibers; they function to strenghten and support connective tissues

Collagen fibers

are very strong and resist pulling forces, but they are not stiff, which allows tissue flexibility; they often occur in parallel bundles, which adds great strenght to the tissue; they consist of the collagen fiber, which is the most abundant protein in the body; found in most types of connective tissue, especially bone, cartilage, tendons, and ligaments

Elastic fibers

are smaller in diameter than collagen fibers; branch and join together to form a network within a tissue; consists of molecules of the protein elastin surrounded by a glycoprotein named fibrillin, wiht adds strenght and stability; because of their unique molecular structure, they are strong but can be stretched up to 150% of their relaxed lenght without breaking; equally important, they have the ability to return to their origianal shape after being stretched; these are plentiful in skin, blood vessel walls, and lung tissue

Reticular fibers

consist of collagen arranged in fine bundles with a coating of glycoprotein; provide support in teh walls of blood vessels and form a network around the cells in some tissues, such as areolar connective tissue, adipose tissue, and smooth muscle tissue; they provide support and strenght; they are plentiful in reticular connective tissue, which forms the stroma or supporting framework of many soft organs,such as the spleen and lymph nodes; these fibers also help form the basement membrane

Classification of connective tissue

embryonic connective tissue (mesenchyme and mucous connective tissue), and mature connective tissue (loose connective tissue, dense connective tissue, cartilage, bone tissue, and liquid connective tissue); loose connective tissue is further divided into areolar connective tissue, adipose tissue, and reticular connective tissue; dense connective tissue is divided into dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue; cartilage is divided into hyaline cartilage, fibrocartilage, and elastic cartilage; liquid connective tissue is divided into blood tissue and lymph

Mesenchyme

(embryonic connective tissue) the tissue from which almost all other connective tissues eventually arise

Mucous connective tissue

(embryonic connective tissue) found mainly in the umbmilical cord of the fetus; a form of mesenchyme that contains widely scattered fibroblasts, a more viscous jellylike ground substance, and collagen fibers

Types of embryonic connective tissue

mesenchyme and mucous connective tissue

Types of mature connective tissue

loose connective tissue, dense connective tissue, cartilage, bone tissue, and liquid connective tissue

Loose connective tissue

the fibers of this tissue are loosely arranged between cells; the different types are areolar connective tissue, adipose tissue, and reticular connective tissue

Areolar connective tissue

consists of fibers (collagen, elastic and reticular) and several kinds of cells (fibroblasts, macrophages, plasma cells, adipocytes, and mast cells) embedded in a semifluid ground substance; located in teh subcutaneous layer deep to skin, papillary (superficial) region of dermis of skin, lamina propria of mucous membrnaes, and around blood vessels, nerves nad body organs; function in strenght, elasticity, and support

Adipose tissue

consists of adipocytes, cells specialized to store triglycerides as a large centrally located droplet; nucleus and cytoplasm are peripherally located; the tissue is found in teh subcutaneous layer deep to the skin, aroudn heart and kidney, yellow bone marrow, and padding around joints and behind eyeball in eye socket; function: reduces heat loss through skin, serves as an energy reserve, supports, and protects; in newborns, brown adipose tissue generates considerable heat that helps maintain proper body temperature

Reticular connective tissue

a network of interlacing reticular fibers and reticular cells; located in the stroma (supporting framework) of liver, spleen, lympht nodes, also found in red bone marrow, which gives rise to blood cells, found in the reticular lamina of the basement membrane, and aroudn blood vessels and muscles; function: form stroma of organs, binds together smooth muscle tissue cells, filters and removes worn-out blood cells in teh spleen and microbes in the lymph nodes

Dense connective tissue

contains more numerous, thicker, and denser fibers, but considerably fewer cells that loose connective tissue; there are three types: dense regular connective tissue, dense irregular connective tissue, and elastic connective tissue

Dense regular connective tissue

extracellular matrix looks shiny white; consists mainly of collagen fibers regularly arranged in bundles; fribroblasts present in rows between bundles; location: forms tendons (attach muscle to bone), most ligaments (attach bone to bone), and aponeuroses (sheetlike tendons that attach muscle to muscle or muscle to bone); fucntion: provides strong attachment between various structures

Dense irregular connective tissue

consists predominantly of collagen fibers randomly arranged and a few fibroblasts; location: fasciae (tissue beneath skin and around muscles and other organs), reticular (deeper) region of dermis of skin, periosteum of bone, prechondrium of cartilage, joint capsules, membrane capsules around various organs (kidneys, liver, testes, lymph nodes), pericardium of the heart, and heart valves; function: provides strenght

Elastic connective tissue

consists predominantly of elastic fibers; fibroblasts are present in spaces between fibers; location:lung tissue, walls of elastic arteries, trachea, bronchial tubes, true vocal cords, suspensory ligament of penis, and some ligaments between vertebrae; function: allows stretching of various organs

Cartilage

consists of a dense network of collagen fibers or elastic fibers firmly embedded in chondroitin sulfate, a gel-like componetn of the ground substance; can endure considerably more stress than loose and dense connective tissues; its strenght is due to its collagen fibers, adn its resilience is due to chondroitin sulfate; the mature cells of this tissue are called chondrocytes, which occur singly or in groups within spaces called lacunae in teh extracellular matrix; a covering of dense irregular connective tissue called the perichondrium surrounds the surface of most cartilage; cartilage has no blood vessels or nerves, excepts in teh perichondrium; there are 3 types: hyaline cartilage, fibrocartilage, and elastic cartilage

Perichondrium

a covering of dense irregular connective tisue that surrounds the surface of most cartilage; is composed of 2 layers: an outer fibrous layer that conssits of collagen fibers, blood vessels, adn fibroblasts, and an inner cellular layer that consists of cells involved in the growth of cartilage

Elastic cartilage

conssits of chondrocytes located in a threadlike network of elastic fibers within the extracellular matrix; location: lid on top of larynx, part of external ear, and auditory tubes; function: gives support and maintains shape

Hyaline cartilage

conssits of a bluish-white, shiny ground substance with thin, fibe collagen fibers and many chondrocytes; most abundance type of cartilage; location; ends of long bones, anterior ends of reibs, nose, parts of larynx, trachea, bronchi, bronchial rubes, and embyronic and fetal skeleton; function: provides smooth surfaces for movement at joints, as well as flexibility and support

Fibrocartilage

consists of chondrocytes scattered among thick bundles of collagen fibers within teh extracellular matrix; location: pubic symphysis, intervertebral discs, menisci (cartilage pads) of knee, and portions of tendons that insert into cartilage; function: support and fusion

Compact bone

consists of osteons (harvesian systems) that contain lamellae, lacunae, osteocytes, canaliculi, and central (harvesian) canals; location: make up the various parts of bones of the body; function: support, protection, storage; houses blood-forming tissue; serves as levers that act with muscle tissue to enable movement

Blood

consists of blood plasma and formed elements; red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes); location: within blood blood vessels (arteries, arterioles, capillaries, and veins) and within the chambers of the heart; function: red blood cells transport oxygen and some carbon dioxide; white blood cells carry on phagocytosis and are involved in allergic reactions and immune system responses; platelets are essential for the clotting of blood

Spongy bone

lacks osteons; it consists of columns of bone called trabeculae, which contain lamellae, osteocytes, lacunae, and canaliculi; spaces between trabeculae are filled with red bone marrow

Lymph

the extracellular fluid that flows in lymphatic vessels; it is a connective tissue that conssits of several types of cells in a clear extracellular matrix that is similar to blood plasma but which much less protein

Lamellae

concentric rings of extracellular matrix that consist of mineral salts (mostly calcium and phosphates), which give bone its hardness, andn collagen fibers, which give bone its strenght; are responsible for the compact nature of this type of bone tissue

Lacunae

small spaces between lamellae that contain mature bone cells called osteocytes

Canaliculi

projecting from the lacunae; networks of minute canals containing the processes of osteocytes; they provide routes for nutrients to reach osteocytes and for wastes to leave them

Central (harvesian) canal

contains blood vessels and nerves

Membrane

the combination of epithelial cells and under-lying connective tissue; there are 3 principle types: mucous membrane, serous membrane, synovial membrane

Mucous membrane

lines a body cavity that opens directly to the exterior; line the entire digestive, respiratory, reproductive tracts, and much of the urinary tract; consists of a lining layer of epithelium and an underlying layer of connective tissue

Epithelial layer of mucous membrane

a barrier that microbes and other pathogens have difficulty penetrating; usually tight junctions connect the cells, so materials cannot leak in between them; goblet cells and other cells of the of the layer secrete mucus, and this prevents cavities from drying out; this layer also secretes some of the enzymes needed for digestion and is the site of food and fluid absorption in teh gastrointestinal tract

Connective tissue layer of mucous membrane

areolar connective tissue; supports the epithelim, binds it to the underlying structures, and alows some flexibility of the membrane; also holds blood vessels in place and affords some protection for underlying structures; oxygen and nutrients diffuse from here to the epithelium covering it; carbon dioxide and wastes diffuse in teh opposite direction

Serous membrane

lines a body cavity that does not open directly to the exterior, and it covers the organs that lie within the cavity; consists of a thin layer of areolar connective tissue and simple squamous epithelium; produces serous fluid; consists of a parietal layer and a visceral layer

Serous fluid

a watery lubricant tha allows organs to glide easily over one another or to slide against the walls of cavities

Parietal layer

the layer attached to and lining the cavity wall

Visceral layer

the layer that covers and adheres to the organs within the cavity

Specialized serous membrane

pleura (lungs), pericardium (heart), peritoneum (abdominal cavity)

Synovial membrane

line the cavities of freely movable joints; they line structures that do not open to the exterior; they lack an epithelium and are therefore not epithelial membranes; composed of areolar connective tissue, some adipose tissue, and elastic fibers; secretes synovial fluid

Synovial fluid

lubricates and nourishes the cartilage covering the bones at movable joints and contains macrophages that remove microbes and debris from the joint cavity

Skeletal muscle tissue

long, cylindrical, striated fibers with many peripherally located nuclei; voluntary control; location: usually attached to bones by tendons; function: motion, posture, heat production, and protection

Cardiac muscle tissue

branched striated fibers with one or two centrally located nuclei; contains intercalated discs; involuntary control; location: heart wall; function: pumps blood to all parts of the body

Smooth muscle tissue

spindle-shaped (thickest in middle and tapering at both ends), nonstriated fibers with one centryally located nucleus; involuntary control; location: iris of eyes, walls of hollow internal structures such as blood vessels, airways to the lungs, stomach, intestines, gallbladder, urinary bladder, and uterus; function: motion (constriction of blood vessels and airways, propulsion of foods through gastrointestinal tract, contraction of urinary bladder and gallbladder)

Nervous tissue

composed of two types of cells: neurons and neuroglia cells

Neuron

are sensitive to various stimuli; they convert stimuli into electrical signals called action potentials (nerve impulses) and conduct these action potentials to other neurons, to muscle tissue, or to glands; most conssits of three basic parts: a cell body, dendrites, and axons

Neuroglia cells

they do not generate or conduct nerve impulses, but they have many important supportive functions

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