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The Tissue Level of Organization Tissues A group of similar cells that function together to perform a specific function Cell Junctions Cellular Junctions connect adjacent cells mechanically at the cell membranes or through cytoskeletal elements within and between cells. Tight Junctions • Web-like strands of transmembrane proteins – Fuse cells together – Seal off passageways between adjacent cells • Common in epithelial tissues of the stomach, intestines, and urinary bladder • Help to retard the passage of substances between cells and leaking into the blood or surrounding tissues Adherens Junctions • Resist separation of cells during contractile activities • Structural components – Transmembrane glycoproteins called cadherins insert into the plaque and join cells – Located inside of the plasma membrane attached to both membrane proteins and microfilaments of the cytoskeleton – In epithelial cells, adhesion belts encircle the cell Desmosomes • Contain plaque and cadherins that extends into the intercellular space to attach adjacent cells together – Desmosome plaque attaches to intermediate filaments that contain protein keratin – Prevent epidermal cells from separating under tension and cardiac muscles cells from pulling apart during contraction Hemidesmosomes • Resemble half of a desmosome – Do not link adjacent cells but anchor cells to the basement membrane – Contains transmembrane glycoprotein integrin – Integrins attach to intermediate filaments and the protein laminin present in the basement membrane Gap Junctions • Connect neighboring cells via tiny fluid-filled tunnels called connexons – Plasma membranes of gap junctions are separated by a very narrow intercellular gap (space) • Communication of cells within a tissue • Ions, nutrients, waste, chemical and electrical signals travel through the connexons from one cell to another 4 Basic Tissues • Epithelial Tissue – covers surfaces because cells are in contact – lines hollow organs, cavities and ducts – forms glands when cells sink under the surface • Connective Tissue – material found between cells – supports and binds structures together – stores energy as fat – provides immunity to disease • Muscle Tissue – cells shorten in length producing movement • Nerve Tissue – cells that conduct electrical signals – detects changes inside and outside the body – responds with nerve impulses Epithelial Tissue General Features: • Closely packed cells forming continuous sheets • Cells sit on basement membrane • Apical (upper) free surface • • • • Avascular - nutrients diffuse in from underlying connective tissue Good nerve supply Rapid cell division Covering / lining versus glandular types Basic Functions: - protection - secretion - absorption - filtration Types of Epithelium • Covering and lining epithelium – epidermis of skin – lining of blood vessels and ducts – lining respiratory, reproductive, urinary & GI tract • Glandular epithelium – secreting portion of glands – thyroid, adrenal, and sweat glands Basement Membrane • Two Layers – Basal lamina – Reticular lamina • Holds cells to connective tissue • Guide for cell migration during development Classification of Epithelium • Classified by arrangement of cells into layers – simple – stratified – pseudostratified • Classified by shape of surface cells – – – – squamous cuboidal columnar transitional • Epithelium Naming epithelia according to shape Flat, wide “paving stone” cells Cells as tall as they are wide Cells taller than they are wide • Epithelium Naming epithelia according to arrangement One layer. All cells in contact with basement membrane Appears to have layers, but in reality all cells go from the apex to the base Two or more layers. Only basal layer in contact with basement membrane Epithelial Tissues 1. Simple Epithelium a. Squamous b. Cuboidal c. Columnar 2. Stratified Epithelium a. Squamous b. Cuboidal c. Columnar 3. Pseudostratified columnar 4. Transitional 5. Glandular Simple Squamous Epithelium • composed of a single layer of flat cells found: – In the air sacs of lungs – In the lining of blood vessels, the heart, and lymphatic vessels – In all capillaries, including those of the kidney – As the major part of a serous membrane Simple Squamous Epithelium Simple squamous Side view Glomerular capsules of the kidney Simple Cuboidal Epithelium • composed of a single layer of cube shaped cells. – It is often found lining the tubules of the kidneys and many other glands. Simple Cuboidal Epithelium Simple Columnar Epithelium • forms a single layer of column-like cells, ± cilia, ± microvilli, ± mucous (goblet cells). – Goblet cells are simple columnar cells that have differentiated to acquire the ability to secrete mucous. Simple Columnar Epithelium Simple columnar Digestive tract Simple Columnar Epithelium Simple columnar Digestive tract Pseudostratified Columnar Epithelium • appears to have layers, due to nuclei which are at various depths. All cells are attached to the basement membrane in a single layer, but some do not extend to the apical surface. – Ciliated tissue has goblet cells that secrete mucous. Pseudostratified Columnar Epithelium Pseudostratified ciliated columnar Trachea Pseudostratified Columnar Epithelium Pseudostratified columnar Stratified Squamous Epithelium • has an apical surface that is made up of squamous (flat) cells. – The other layers have different shapes, but the name is based on the apical layer. – The many layers are ideal for protection against strong friction forces. Stratified Squamous Epithelium Stratified squamous Epidermis of the skin Stratified Cuboidal Epithelium Stratified Columnar Epithelium Transitional Epithelium • The cells change shape depending on the state of stretch in the tissue. – The apical “dome cells” of the top layer (seen here in relaxation) are an identifiable feature and signify an empty bladder . – In a full bladder, the cells are flattened. Transitional Epithelium Transitional Urinary bladder Epithelium Stratified squamous epithelium is a prominent feature of the outer layers of the skin. Simple squamous makes up epithelial membranes and lines the blood vessels. Columnar is common in the digestive tract. Pseudostratified ciliated columnar is characteristic of the upper respiratory tract. Transitional is found in the bladder. Cuboidal lines ducts and sweat glands. Copyright © John Wiley & Sons, Inc. All rights reserved. Glandular Epithelium • Derived from epithelial cells that sank below the surface during development • Exocrine glands – cells that secrete---sweat, ear wax, saliva, digestive enzymes onto free surface of epithelial layer – connected to the surface by tubes (ducts) – unicellular glands or multicellular glands • Endocrine glands – secrete hormones into the bloodstream – hormones help maintain homeostasis Methods of Glandular Secretion cells release their products by exocytosis: - saliva - digestive - enzymes - sweat upper part of cell pinches off - sweat - milk whole cells die & rupture to release their products - oil gland Connective Tissue General Features: • • • • • Cells rarely touch due to extracellular matrix Matrix(fibers & ground substance secreted by cells Consistency varies from liquid, gel to solid Does not occur on free surface Good nerve & blood supply except cartilage & tendons Basic Functions: - support to body organs - storage - protection - binds body parts together Connective Tissue 1. Ground substance: interstitial fluid, cell adhesion proteins, proteoglycans 2. Fibers: Collagen, Elastin, Reticular 3. Cells: - blast mast cells - cyte macrophages - clast blood cells Connective Tissue 1. Loose connective tissue 3. Cartilage a. Areolar connective tissue a. Hyaline cartilage b. Adipose tissue b. Fibrocartilage c. Reticular connective tissue c. Elastic cartilage 4. Bone Tissue 2. Dense connective tissue 5. Blood tissue a. Dense regular connective tissue (ligaments + tendons) b. Dense irregular connective tissue (dermis of skin) c. Elastic connective tissue (arteries, bronchial tubes) Loose Connective Tissue – Areolar Connective Tissue is the most widely distributed in the body. It contains several types of cells and all three fiber types. • It is used to attach skin and underlying tissues, and as a packing between glands, muscles, and nerves. Areolar Connective Tissue Areolar (4x) fibroblasts; macrophages; mast cells stretchable; loosely arranged fibroelastic tissue packages organs supports capillaries Loose Connective Tissue – Adipose tissue is located in the subcutaneous layer deep to the skin and around organs and joints. • It reduces heat loss and serves as padding and as an energy source. Adipose Tissue Adipose (10x) fat containing cells; act as packing around and between organs Loose Connective Tissue – Reticular connective tissue is a network of interlacing reticular fibers and cells. • It forms a scaffolding used by cells of lymphoid tissues such as the spleen and lymph nodes. Reticular Connective Tissue Reticular framework; spleen Dense Connective Tissue – Dense regular Connective Tissue comprise tendons, ligaments, and other strong attachments where the need for strength along one axis is mandatory (a muscle pulling on a bone). Dense Regular Connective Tissue Dense regular tendons Dense Connective Tissue – Dense Irregular Connective Tissue consists predominantly of fibroblasts and collagen fibers randomly arranged. • It provides strength when forces are pulling from many different directions. Dense Irregular Connective Tissue Dense irregular dermis of the skin Dense Connective Tissue – Elastic Connective Tissue consists predominantly of fibroblasts and freely branching elastic fibers. • It allows stretching of certain tissues like the elastic arteries (the aorta). Elastic Connective Tissue Elastic Cartilage • Cartilage is a tissue with poor blood supply that grows slowly. When injured or inflamed, repair is slow. – Hyaline cartilage is the most abundant type of cartilage; it covers the ends of long bones and parts of the ribs, nose, trachea, bronchi, and larynx. • It provides a smooth surface for joint movement. Hyaline Cartilage Hyaline cartilage (10x) precursor of skeleton; articular surface; trachea; tip of nose perichondrium chondrocytes chondroblasts Cartilage – Fibrocartilage, with its thick bundles of collagen fibers, is a very strong, tough cartilage. • Fibrocartilage discs in the intervertebral spaces and the knee joints support the huge loads up and down the long axis of the body. Fibrocartilage Fibrocartilage (40x) dense and resistant to stretching; vertebral discs; pubic symphysis Cartilage – Elastic cartilage consists of chondrocytes located in a threadlike network of elastic fibers. • It makes up the malleable part of the external ear and the epiglottis. Elastic Cartilage Elastic cartilage (4x) flexible; predominance of elastic fibers; external ear; epiglottis; larynx Bone Tissue • a connective tissue with a calcified intracellular matrix. In the right circumstances, the chondrocytes of cartilage are capable of turning into the osteocytes that make up bone tissue. Bone Tissue Compact Bone (10x) matrix- inorganic salts (calcium phosphate and calcium carbonate) Blood Blood red blood cells eosinophil (red arrow) neutrophil (yellow arrow) Blood Blood Muscle Tissue • Cells that shorten • Provide us with motion, posture and heat • Types of muscle – skeletal muscle – cardiac muscle – smooth muscle Skeletal Muscle • Cells are long cylinders with many peripheral nuclei • Visible light and dark banding (looks striated) • Voluntary or conscious control Skeletal Muscle Skeletal (40x) Cardiac Muscle • Cells are branched cylinders with one central nuclei • Involuntary and striated • Attached to and communicate with each other by intercalated discs and desmosomes Cardiac Muscle Smooth Muscle • Spindle shaped cells with a single central nuclei • Walls of hollow organs (blood vessels, GI tract, bladder) • Involuntary and nonstriated Smooth Muscle Smooth (10x) Nervous Tissue • • Cell types -- nerve cells and neuroglial (supporting) cells Nerve cell structure – nucleus & long cell processes conduct nerve signals • dendrite --- signal travels towards the cell body • axon ---- signal travels away from cell body Tissue Repair • Inflammation: protect damaged area and bring in supplies for repair • Fibrosis: replacement with stromal connective tissue cells, scar formation (fibroblasts) • Regeneration: replacement with original cell types (parenchymal cells) – some cell types can divide (liver & endothelium) – some tissues contain stem cells that can divide • bone marrow, epithelium of gut & skin – some cell types can not divide & are not replaced • muscle and nervous tissue