Chapter 4: The Tissue Level of Organization Study Guide

Chapter 4: The Tissue Level of Organization Study Guide 1. Define the term “tissue,” and classify the tissues of the body into four major types. • Tissue-a group of cells that usually have a common origin in an embryo and function together to carry out specialized activities. The structure and properties of a specific tissue are influenced by factors such as the nature of the extracellular material that surrounds the tissue cells and the connections between the cells that compose the tissue. • TISSUES HAVE A COMMON ORIGIN AND FUNCTION TOGETHER TO CARRY OUT SPECIALIZED ACTIVITIES • epithelial tissue-cover body surfaces and line hollow organs, body cavities, and ducts; they also form glands. This tissue allows the body to interact with both its internal and external environments. • connective tissue-protect and support the body and its organs. Various types of connective tissues bind organs together, store energy reserves as fat, and help provide the body with immunity to disease-causing organisms. • muscular tissue-are composed of cells specialized for contraction and generation of force. In the process, muscular tissues generate heat that warms the body. • nervous tissue- detects change in a variety of conditions inside and outside the body and responds by generating electrical signals called nerve action potentials (nerve impulses) that activate muscular contractions and glandular secretions. 2. Describe the structure and functions of the five principal types of cell junctions. • cell junction-are contact points between the plasma membrane of tissue cells. • tight junction-consist of weblike strands of transmembrane proteins that fuse together the outer surfaces of adjacent plasma membranes to seal off passageways between adjacent cells. Cells of epithelial tissues that line the stomach, intestines and urinary bladder have many tight junctions. They inhibit the passage of substances between cells and prevent the contents of these organs from leaking into the blood or surrounding tissues. TIGHT JUNCTIONS CONSIST OF WEBLIKE STRANDS AND TRANSMEMBRANE PROTEINS THAT FUSE TOGETHER PLASMA MEMBRANES • adherens junction-a dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and to microfilaments of the cytoskeleton. • ADHERENS JUNCTIONS ARE DENSE LAYERS OF PROTEINS ON THE INSIDE OF THE PLASMA MEMBRANE THAT ADHERES MEMBRANE PROTEINS AND MICROFILAMENTS • Transmembrane glycoproteins called cadherins join the cells. Each cadherin inserts into the plaque from the opposite side of the plasma membrane, partially crosses the intercellular space (the space between the cells) and connects to cadherins of an adjacent cell. In epithelial cells, adherins 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, as when food moves through the intestines. • CADHERINS ARE TRANSMEMRANE GLYCOPROTEINS THAT JOIN THE CELLS, THEY OFTEN FORM EXTENSIVE ZONES CALLED ADHESION BELTS • Desmosome-Like adherens, desmosomes contain plaque and have transmembrane glycoproteins (cadherins) that extend into the intercellular space between adjacent cell membranes and attach cells to one another. Unlike adherens junctions, the plaque of desmosomes does not attach to microfilaments. Instead, a desmosome plaque attaches to elements of the cytoskeleton known as intermediate filaments, which consists of the protein keratin. The intermediate filaments extend from desmosomes on one side of the cell across the cystol to desmosomes on the opposite side of the cell. This structural arrangement contributes to the stability of the cells and tissue. These spot-weld-like junctions are common among the cells that make up the epidermis (the outermost layer of the skin) and among cardiac muscle cells in the heart. Desmosomes prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contractions • A DESMOSOME IS LIKE ADHERENS AS IT HAS PLAQUE AND TRANSMEMBRANE GLYCOPROTEINS CALLED CADHERINS THAT ATTACH THE CELLS, BUT INSTEAD, THE PLAQUE ATTACHING TO INTERMEDIATE FILAMENTS INSTEAD OF MICROFILAMENTS • INTERMEDIATE FILAMENTS CONTAIN THE PROTEIN KERATIN • DESMOSOMES HAVE TRANSMEMBRANE GLYCOPROTEINS CALLED CADHERINS • Hemidesmosome-resemble desosomes but they do not link adjacent cells. Name arises cuz they look like half a desosome. The transmembrane glycoproteins are integrins rather than cadherins. On the inside of the plasma membrane, integrins attach to intermediate filaments made of the protein keratin. On the outside of the plasma membrane, the integrins attach to the protein laminin, which is present in the basement membrane. Thus, hemidesmosomes anchor cells not to each other but to the basement membrane. • HEMIDESMOSOMES ARE LIKE DESMOSOMES BUT THEY DO NOT LINK ADJACENT CELLS – THEY LOOK LIKE HALF A DESMOSOME • THE TRANSMEMBRANE GLYCOPROTEINS ARE CALLED INTEGRINS, RATHER THAN CADHERINS • HEMIDESMOSOMES HAVE TRANSMEMBRANE GLYCOPROTEINS CALLED INTEGRINS • • gap junction-membrane proteins called connexions from tiny fluid-filled tunnels called connexions that connect neighboring cells. The plasma membranes of gap junctions are not fused together as in tight junctions, but are separated by a very narrow intercellular gap (space). Through the connexions, ions and small molecules can diffuse from the cystol of one cell to another, but the passage of large molecules such as vital intracellular proteins is prevented. The transfer of nutrients, and perhaps wastes, takes place through gap junctions in avascular tissues such as the lens of the cornea of the eye. They allow the cells in a tissue to communicate with one another. In a developing embryo, some of the chemical and electrical signals that regulate growth and cell differentiation travel via gap junctions. They also enable nerve or muscle impulses to spread rapidly among cells, a process that is crucial for the normal operation of some parts of the nervous system and for the contraction of muscle in the heart, gastrointestinal tract, and uterus. • GAP JUNCTIONS ARE MEMBRAINE PROTEINS CALLED CONNEXIONS • THE PLASMA MEMBRANES OF GAP JUNCTIONS ARE NOT FUSED TOGETHER, THEY HAVE A GAP (DUH), WHERE NUTRIENTS CAN BE TRANSFERRED IN AVASCULAR TISSUE, AND WHICH ALLOWS TISSUES TO COMMUNICATE 3. Describe the general features of epithelial tissue. • epithelial tissue or epithelium-consists of cells arranged in continuous sheets, in either single or multiple Epithelial tissues form coverings and linings throughout the body. They are rarely covered by another tissue, so they always have a free surface. They are avascular- without blood vessels and rely on adjacent connective tissue to bring nutrients and remove wastes by diffusion. Most important roles are: protection, filtration, secretion, absorption, and excretion. • EPITHELIAL TISSUE OR EPITHELIUM CONSISTS OF CELLS ARRANGED IN CONTINUOUS SHEETS, EITHER SINGLE OR MULTIPLE LAYERS, THEY ALWAYS HAVE A FREE SURFACE, MEANING THEY AREN’T COVERED BY ANY OTHER TISSUES • THEY ARE AVASCULAR • THEY FUNCTION IN PROTECTION, FILTRATION, SECRETION, ABSORPTION, AND EXCRETION • Divided into 2 types • 1. Covering and lining epithelium (forms the outer covering of the skin and some internal organs. Also forms the inner lining of blood vessels, ducts and body cavities and the interior of the respiratory, digestive, urinary and reproductive systems. • 2. Glandular epithelium makes up the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands. -3 major functions: 1. THEY ARE Selective barriers that limit or aid the transfer of substances into and out of the body. 2. Secretory surfaces that release products produced by the cell onto their free surfaces; and 3. Protective surfaces that resist the abrasive influences of the environment. • basement membrane-a thin extracellular layer that commonly consists of two layers, the basal lamina and reticular lamina. THE BASEMENT MEMBRANE CONSISTS OF THE BASAL LAMINA, WHICH IS DIRECTLY UNDER THE EPITHELIAL CELLS, AND THE RETICULAR LAMINA, WHICH IS UNDERNEATH THE BASAL LAMINA AND CLOSER TO THE CONNECTIVE TISSUES • The basal lamina is closer to- and secreted by- the epithelial cells. It contains proteins such as laminin and collagen , as well as glycoproteins and proteoglycans. The laminin molecules in the basal lamina adhere to integrins in hemidesmosomes and thus attach epithelial cells to the basement membrane. THE BASAL LAMINA IS CLOSER TO EPITHELIAL CELLS – IT ATTACHES EPITHELIAL CELLS TO THE BASEMENT MEMBRANE • The reticular lamina is closer to the underlying connective tissue and contains proteins such as collagen produced by connective tissue cells called fibroblasts. In addition to attaching to and supporting the overlying epithelial tissue, basement membranes have other functions. They form a surface along which epithelial cells migrate during growth or would healing, restrict passage of larger molecules between epithelium and connective tissue, and participate in filtration of blood in the kidneys. THE RETICULAR LAMINA IS CLOSER TO THE UNDERLYING CONNECTIVE TISSUES AND CONTAINS COLLAGEN PRODUCED BY FIBROBLASTS – THEY HELP TO FILTER BLOOD IN KIDNEYS 4. Describe the structure, location, and function of each of the types of epithelium listed below. • simple epithelium-a single layer of cells that functions in diffusion, osmosis, filtration, secretion and absorption. SIMPLE EPITHELIUM IS A SINGLE LAYER OF CELLS THAT FUNCTION IN DIFFUSION, OSMOSIS, FILTRATION, SECRETION AND ABSORPTION – IT’S THE TOP LAYER OF OUR SKIN! • 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, but it is actually a simple epithelium because all its cells rest on the basement membrane. Cells that do extend to the apical surfaces may contain cilia; others (goblet cells) secrete mucus. PSEUDOSTRATIFIED EPITHELIUM LOOKS AS THOUGH IT HAS MULTIPLE LAYERS BECAUSE THE NUCLEI LIE AT DIFFERENT LEVELS – BUT IT IS ACTUALLY SIMPLY EPITHELIUM • Stratified epithelium- consists of two or more layers of cells that protect underlying tissues in locations where there is considerable wear and tear. STRATIFIED EPITHELIUM HAS TWO OR MORE LAYERS AND IS FOUND IN LAYERS WHERE THERE IS MORE WEAR AND TEAR • Squamous cells- are thin, which allows for the rapid passage of substances through them SQUAMOUS CELLS ARE THIN WHICH ALLOWS FOR RAPID PASSAGE OF SUBSTANCES • Cuboidal cells- are as tall as they are wide. Shaped like cubes or hexagons. May have microvilli at their apical surface and function in either secretion or absorption. CUBOIDAL CELLS ARE SHAPED LIKE CUBES AND FUNCTION IN EXCRETION OR ABSORPTION • Columnar cells- are much taller than they are wide, like columns and protect underlying issues. Their apical surfaces may have cilia or microvilli and they often are specialized for secretion and absorption. COLUMNAR CELLS ARE SHAPED LIKE TALL COLUMNS – THEY PROTECT UNDERLYING TISSUES AND ALSO FUNCTION IN EXCRETION AND ABSORPTION • Transitional cells- change shape, from squamous to cuboidal and back, as organs such as the urinary bladder stretch (distend) to a larger size and then collapse into a smaller size. TRANSITIONAL CELLS CHANGE SHAPE FROM SQUAMUS (FLAT) TO CUBOIDAL (CUBE) AND BACK IN ORGANS LIKE THE BLADDER THAT STRETCH AND COLLAPSE • simple squamous epithelium • simple cuboidal epithelium • simple columnar epithelium • pseudostratified columnar epithelium • stratified epithelium • stratified squamous epithelium • stratified cuboidal epithelium • stratified columnar epithelium • transitional epithelium • covering and lining epithelium-forms the outer covering of the skin and some internal organs. It also forms the inner lining of blood vessels, ducts and body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems. 5. Define the term “gland,” and distinguish between exocrine and endocrine glands. • glandular epithelium-function is secretion, which is accomplished by glandular cells that often lie in clusters deep to the covering and lining epithelium. • Gland-may consist of a single cell or group of cells that secrete substances into ducts (tubes), onto a surface, or into the blood. All glands are classified as either endocrine or exocrine • endocrine gland-secretions of endocrine glands called hormones enter the interstitial fluid and then diffuse directly into the bloodstream without flowing through the duct. They have far reaching effects because they are distributed throughout the body by the bloodstream. • IN ENDOCRINE GLANDS, SECRETIONS CALLED HORMONES ENTER THE INTERSTITIAL FLUID AND DIFFUSE DIRECTLY INTO THE BLOODSTREAM WITHOUT FLOWING THROUGH A DUCT • exocrine gland-secrete their pdoucts into ducts that empty onto the surface of a covering and lining epithelium such as the skin surface or the lumen of a hollow organ. The secretions of exocrine glands have limited effects and some of them would be harmful if they entered the bloodstream. Some glands of thebody like the pancreas, ovaries, and testes are mixed glands that contain both endocrine and exocrine tissue. • IN EXOCRINE GLANDS, SECRETIONS DO ENTER DUCTS THAT ENTER ON THE SURFACE OF A COVERING AND LINING EPITHELIUM LIKE THE SKIN SURFACE • structural classification -endocrine glands are classified as unicellular or multicellular. -Unicellular glands- single-celled glands. Goblet cells are important unicellular exocrine glands that secrete mucus directly onto the apical surface of the lining epithelium. -Most are multicellular glands-composed of many cells that form a distinctive microscopic structure or macroscopic organ. Ex: sudoriferous (sweat), sebaceous(oil) and salivary glands. They are categorized according to 2 criteria: 1. Whether their ducts are branched or unbranched and 2. The shape of the secretory portions of the gland. - If the duct of the gland does not branch, it is a simple gland. - If the duct branches, it is a compound gland COMPOUND GLANDS ARE BRANCHED -Glands with tubular secretory parts are tubular glands TUBULAR GLANDS HAVE TUBULAR SECRETORY PARTS -Those with rounded secretory portions are acinar glands, also called alveolar glands ACINAR GLANDS HAVE ROUNDED SECRETORY PORTIONS -Tubuloacinar glands- have both tubular and more rounded secretory parts. TUBULOACINAR GLANDS ARE BOTH TUBULAR AND ROUNDED 1. Simple glands: A. Simple tubular- tubular secretory part is straight and attaches to a single unbranched duct (s in large intestines) B. Simple branched tubular- tubular secretory part is branched and attaches to a single unbranched duct. (ex. Gastric glands) C. Simple coiled tubular-tubular secretory part is coiled and attaches to a single unbranched duct. (ex. Sweat glands) D. Simple acinar- secretory portion is rounded and attaches to a single unbranched duct (ex. Glands of the penile urethra) E. Simple branched acinar- rounded secretory part is branched and attaches to a single unbranched duct (ex. Sebaceous glands) 2. Compound glands A. Compound tubular- secretory portion is tubular and attaches to a branched duct. (Ex: bulbourethral (Cowpers) gland) B. Compound acinar- secretory portion is rounded and attaches to a branched duct. (ex. Mammary glands) C. Compound tubuloacinar-secretory portion is both tubular and rounded and attaches to a branched duct. (ex. Acinar glands of the pancreas) • functional classification-based on how their secretions are released. Each of these secretory processes begins with the endoplasmic reticulum and Golgi complex working together to form intracellular secretory vesicles that contain the secretory product. – merocrine gland-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 via exocytosis. Most exocrine glands of the body are merocrine glands. (Ex. Salivary glands and pancreas) • MEROCRINE GLANDS’ SECRETIONS ARE SYNTHESIZED ON RIBOSOMES ATTACHED TO ROUGH ER • MOST EXORCRINE GLANDS ON THE BODY ARE MEROCRINE, LIKE SALIVARY GLANDS AND THE PANCREAS • – apocrine gland-accumulate their secretory product at the apical surface of the secreting cell. Then, that portion of the cell pinches off by exocytosis from the rest of the cell to release the secretion. The remaining part of the cell repairs itself and repeats the process. This is the mechanism of secretion of milk fats in the mammary glands. Sweat glands of the skin, named apocrine sweat glands after this mode of secretion, actually undergo merocrine secretion. • APOCRINE GLANDS – holocrine gland-accumulate a secretory product in their cystol. As the secretory cell matures, it ruptures and becomes the secretory product. Because the cell ruptures in this mode of secretion, the secretion contains large amounts of lipids from the plasma membrane and intracellular mambranes. The sloughed off cell is replaced by a new cell (ex. Sebaceous gland of the skin) 6. Describe the general components of connective tissue: cells, ground substance and fibres. • connective tissue-one of the most abundant, and widely distributed tissues in the body. They bind together, support and strengthen other body tissues; protect and insulate internal organs; compartmentalize structures such as skeletal muscles; serve as the major transport system within the body (blood, a fluid connective tissue); are the primary locations of stored energy reserves (adipose, or fat, tissue); and are the main source of immune response. • Consist of 2 basic elements: extracellular matrix and cells. Connective tissues do not usually occur on body surfaces (unlike epithelial tissues) and connective tissues, like epithelial tissues, are supplied with nerves. Except for cartilage, • extracellular matrix-is the material located between its widely spaced cells. Consists of protein fibers and ground substance, the material between the cells and the fibres. Extracellular fibres are secreted by connective tissue cells and account for many of the functional properties of the tissue in addition to controlling the surrounding watery environment via specific proteoglycan molecules. The structure of the extracellular matrix determines much of the tissues qualities. For instance, in cartilage, the extracellular matrix is firm but pliable. The extracellular matrix of bone, by contrast is hard and flexible. • connective tissue cells-embryonic cells called mesenchymal cells give rise to the cells of connective tissues. 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 chondroblasts in cartilage, and osteoblasts in bone. Blast cells retain the capacity for cell division and secrete the extracellular matrix that is characteristic of the tissue. Mature cells have reduced capacities for cell division and extracellular matrix formation are mostly involved in monitoring and maintaining the extracellular matrix. • Fibroblast- large, flat cells with branching processes. Present in all the general connective tissues, and usually are the most numerous. They migrate through the connective tissues, secreting the