98 terms

The Tissue Level of Organization

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
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
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
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
the production and release of substances such as mucus, sweat, or enzymes
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
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
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
(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
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
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
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
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
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
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
small spaces between lamellae that contain mature bone cells called osteocytes
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
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
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