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TISSUE: THE LIVING FABRIC

TISSUE: THE LIVING FABRIC. INTRODUCTION TO TISSUE. Tissues are groups of cells that are similar in structure and function (tissue=woven) There are four primary tissues types: Epithelial: covering Connective: support Nervous: control Muscular: movement Histology: study of tissues.

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TISSUE: THE LIVING FABRIC

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  1. TISSUE: THE LIVING FABRIC

  2. INTRODUCTION TO TISSUE • Tissues are groups of cells that are similar in structure and function (tissue=woven) • There are four primary tissues types: • Epithelial: covering • Connective: support • Nervous: control • Muscular: movement • Histology: study of tissues

  3. EPITHELIAL TISSUE • Epithelium (plural: epithelia) • Sheet of cells that covers a body surface or lines a body cavity (epithe=laid on, covering) • Occurs in the body as: • 1. Covering and lining epithelium: • Forms the outer layer of the skin, dips into and lines the open cavities of the cardiovascular, digestive, and respiratory systems, and covers the walls and organs of the closed ventral body cavity • 2. Glandular epithelium: • Fashions the glands of the body

  4. EPITHELIAL TISSUE • In its role as an interface tissue, epithelium accomplishes many functions, including: • 1. Protection • 2. Absorption • 3. Filtration • 4. Excretion • 5. Secretion • 6. Sensory Reception

  5. Special Characteristics of Epithelium • Has many characteristics that distinguish them from other tissue types: • 1. Cellularity: • Composed of closely packed cells with little extracellular material between • 2. Specialized contacts: • Adjacent epithelial cells are bound together to form continuous sheets by specialized contacts such as desmosomes and tight junctions • 3. Polarity: • Exhibits polarity by having an apical surface (upper free surface exposed to the body exterior or the cavity of an internal organ)) and a lower attached basal surface • All epithelia exhibit polarity, meaning that cell regions near the apical surface differ from those near the basal surface in both structure and function • Example: • Some apical surfaces have villi while the basal surface acts as a filter determining which molecules will be allowed to enter the epithelium • 4. Supported by connective tissue: • Supported by the underlying connective tissue (reticular lamina) containing collagen fibers • 5. Innervated but avascular: • Nourished by substances diffusing from blood vessels in the underlying connective tissue • 6. Has a high regeneration capacity: • Replace lost cells rapidly by cell division

  6. Classification of Epithelia • Each epithelial tissue is given two names: • The first name indicates the number of layers present: • Simple (one): • Composed of a single cell layer • Typically found where absorption and filtration occur and a thin epithelial barrier is desirable • Stratified (more than one): • Consist of two or more cell layers stacked one on top of the other • Common in high-abrasion areas where protection is important, such as the skin surface and the lining of the mouth • The second name describes the shape of the cells

  7. Classification of Epithelia

  8. Classification of Epithelia • All epithelial cells have six (somewhat irregular) sides • Apical surface view of an epithelial sheet looks like a honeycomb • This polyhedral shape allows the cells to be closely packed • Cells vary in height • Three common shapes of epithelial cells: nucleus will be the same shape • 1. Squamous cells are: flattened and scalelike (squam=scale) • 2. Cuboidal cells are: boxlike • Approximately as tall as they are wide • 3. Columnar cells are: tall and column shaped

  9. Classification of Epithelia

  10. Classification of Epithelia • Simple epithelia are easy to classify by cell shape because all cells in the layer usually have the same shape • Stratified epithelia: • Cell shapes usually differ among the different cell layers • Named according the shape of the cells in the apical layer

  11. Simple Epithelia • Concerned with absorption, secretion, and filtration • Consist of a single layer and are usually very thin • Protection is not one of their specialties

  12. Simple Squamous Epithelium

  13. Simple Cuboidal Epithelium

  14. Simple Columnar Epithelium

  15. Pseudostratied Columnar Epithelium

  16. Stratified Epithelia • Contains two or more cell layers • Main function is protection • Regenerate from below: • The basal cells divide and push apically to replace the older surface cells • Consequently more durable than the simple epithelia • Stratified squamous epithelium is composed of several layers with the cells on the free surface being squamous-shaped and the underlying cells being cuboidal or columnar in shape • Transitional epithelium forms the lining of the hollow organs of the urinary system that stretch as they fill

  17. Stratified Squamous Eputhelium

  18. Stratified Cuboidal Epithelium • Rare • Found mostly in the ducts of some of the larger glands • Sweat glands • Mammary glands

  19. Stratified Columnar Epithelium • Found in limited distribution with small amounts in the pharynx, male urethra, and lining some glandular ducts • Only its apical layer of cells is columnar

  20. Transitional Epithelium

  21. Glandular Epithelia • A gland consists of one or more cells that make and secrete (export) a particular product: • This product, called a secretion, is an aqueous (water-based) fluid that usually contains proteins • Some release lipid-rich or steroid-rich secretion • Secretion is an active process: • Glandular cells obtain needed substances from the blood and transform them chemically into a product that is then discharged from the cell • Notice: the term secretion can refer to BOTH the gland’s product and the process of making and releasing that product

  22. Glandular Epithelia • Classified as to: • Where they release their products: • Endocrine: internally secreting • Exocrine: externally secreting • Relative cell numbers making up the gland: • Unicellular: one-celled • Scattered within epithelial sheets • Multicellular: many-celled • Form by invagination (inward growth) or evagination (outward growth) from an epithelial sheet

  23. Endocrine Glands • Ductless glands • Produce hormones: regulatory chemicals that they secrete by exocytosis directly into the extracellular space • From there the hormones enter the blood or lymphatic fluid and travel to specific target organs • Each hormone prompts its target organ(s) to respond in some characteristic way • Most are complex multicellular organs • Some are individual hormone-producing cells in organs (intestines/brain)

  24. Exocrine Glands • More numerous than endocrine glands • Secrete their products onto body surfaces (skin) or into body cavities: • Unicellular glands directly (exocytosis) • Multicellular glands via an epithelial-walled duct that transports the secretion to the epithelial surface • Mucous, sweat, oil, salivary glands • Liver, (bile), pancreas (digestive enzymes)

  25. Unicellular Exocrine Glands • Only important example of a unicellular (one-celled) gland is the goblet cell • Shaped like a goblet (drinking glass with a stem) • (d): Sprinkled in the epithelial linings of the intestinal and respiratory tracts amid columnar cells with other functions • In humans produce mucin: complex glycoprotein that dissolves in water when secreted • Once dissolved, mucin forms mucus, a slimy coating that both protects and lubricates surfaces

  26. Pseudostratified Columnar EpitheliumUnicellular Exocrine Glands (Goblet Cells)

  27. Multicellular Exocrine Glands • Two basic parts: • An epithelium-derived duct • Secretory unit consisting of secretory cells (acini) • In all BUT the simplest glands, supportive connective tissue surrounds the secretory unit and supplies it with blood vessels and nerve fibers, and forms a fibrous capsule that extends into the gland proper and divides the gland into lobes

  28. Multicellular Exocrine GlandsStructural Classification • On the basis of their duct structures • Simple: • Unbranched duct

  29. EXOCRINE GLANDS

  30. Multicellular Exocrine GlandsStructural Classification • Compound: • Branched duct • Compond: mulitple branched ducts • Further classified by their secretory units: • Tubular: if the secretory cells form tubes • Alveolar: if the secretory cells form small, flask-like sacs (alveolus=small hollow cavity) • Tubuloalveolar: if they have BOTH types of secretory units (tubes and alveolar) • NOTE: acinar is used interchangeably with alveolar

  31. EXOCRINE GLANDS

  32. Multicellular Exocrine GlandsFunctional Classification • Modes of Secretion: • Merocrine Glands: • Secrete their products by exocytosis as produced • Secretory cells are not altered in any way • Examples: • Sweat glands • Pancreas • Salivary glands

  33. Merocrine Gland

  34. Multicellular Exocrine GlandsFunctional Classification • Modes of Secretion: • Holocrine Glands: • Accumulate their products within them until they rupture • They are replaced by the division of underlying cells • Secretion includes the synthesized product plus dead cell fragments (holo=all) • Examples: • Sebaceous (oil) glands

  35. Holocrine Gland

  36. Multicellular Exocrine GlandsFunctional Classification • Modes of Secretion: • Apocrine Glands: • Present in all animals but questionable in humans • Accumulated their products just beneath the free surface • Eventually, the apex of the cell pinches off (apo=from off), releasing the secretory granules and a small amount of cytoplasm • Example: controversy in humans • Some believe mammary glands are apocrine while others say merocrine

  37. Connective Tissue • Found everywhere in the body • It is the most abundant and widely distributed of the primary tissues • Amounts vary in particular organs • Example: • Skin is primarily connective tissue • Brain has very little connective tissue • Four main classes and several subclasses: • 1. Connective tissue proper: • Includes fat and fibrous tissue of ligaments • 2. Cartilage • 3. Bone tissue • 4. Blood

  38. CONNECTIVE TISSUE • Does more than just connect body parts • It has many forms and functions • Major functions include: • Binding and support • Protection • Insulation • Transportation

  39. Common Characteristics of Connective Tissue • 1. Common origin: All connective tissue arises from an embryonic tissue called mesenchyme • 2. Degrees of vascularity: Connective tissue ranges from avascular (cartilage) to poorly vascularized (dense connective tissue) to highly vascularized • 3. Extracellular matrix: Connective tissue is composed mainly of nonliving extracellular matrix that separates the cells of the tissue • Enables connective tissue to withstand physical trauma

  40. Connective Tissue Origins

  41. EMBRYONIC CONNECTIVE TISSUE

  42. Structural Elements of Connective Tissue • Three main elements: • Ground substance: extracellular matrix • Fibers: extracellular matrix • Cells • Properties of the cells and the composition and arrangement of extracellular matrix elements vary tremendously • Resulting in an amazing diversity of connective tissues • Matrix can be delicate and fragile (soft packing around an organ) to rope-like (tendons and ligaments)

  43. Structural Elements of Connective Tissue • Even though there are diverse types they still have a common plan: • Prototype (model) used is areolar connective tissue • All other subclasses are simply variants of this common tissue type

  44. AREOLAR CONNECTIVE TISSUE

  45. Ground Substance • Unstructured material that fills the space between the cells and contains the fibers • Composed of: • Interstitial (tissue) fluid • Cell adhesion proteins: serves as connective tissue glue that allows connective tissue cells to attach themselves to matrix material • Fibronectin • Laminin • Proteoglycans: • Consist of a protein core to which glycosaminoglycans are attached • Strandlike GAGs ( chondroitin sulfate, keratan sulfate, hyaluronic acid) are large, negatively charged polysaccharides that stick out from the core protein like the fibers of a bottle brush • Intertwine and trap water, forming a substance that varies from a fluid to a viscous gel

  46. PROTEOGLYCAN

  47. Ground Substance • Holds large amounts of fluid and functions as a molecular sieve, or medium, through which nutrients and other dissolved substances can diffuse between the blood capillaries and the cells • Fibers embedded make it less pliable and impede diffusion somewhat

  48. AREOLAR CONNECTIVE TISSUE

  49. Fibers • Fibers of the connective tissue provide support • Three types of fibers are found in connective tissue matrix: • Collagen • Elastic • Reticular

  50. AREOLAR CONNECTIVE TISSUE

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