TISSUES

1. TISSUES

2. STRUCTURAL ORGANIZATION • Life is characterized by hierarchical orders of organization • Atoms • Molecules • Organelles • Cells • Tissues • Organs • Organ systems • Organism • (Population) • (Community) • (Ecosystem)

3. STRUCTURAL ORGANIZATION • The cell is the lowest level of organization that can live independently as an organism Amoeba Paramecium

4. STRUCTURAL ORGANIZATION • In multicellular organisms, specialized cells are grouped into tissues • A tissue is a group of cells similar in structure and performing a common function • Organs are comprised of combinations of various tissues • Organ systems include multiple organs working together

5. INTERCELLULAR JUNCTIONS • Neighboring cells within a multicellular organism often adhere, interact, and communicate through intracellular junctions • Tight junctions • Desmosomes • Gap junctions

6. TIGHT JUNCTIONS • Integral membrane proteins of adjacent cells fuse together • Membranes of adjacent cells are fused • Form continuous belts around cells • Impermeable barrier • Some tight junctions are somewhat leaky • “Not-so-tight junctions”

7. DESMOSOMES • Anchoring junctions • Rivets keeping adjacent cells from separating • Composition • Button-like plaque on cytoplasmic face of membrane • Thin linker protein filaments interdigitate • Desmosomes on opposite sides of the same cell connected through intermediate filaments

8. GAP JUNCTIONS • Communicating junction connecting cytoplasm of adjacent cells • Composition • Transmembrane proteins form “connexons” • Hollow tubes • Connexons of adjacent cells fuse • Chemical substances travel through these channels • Different connexons have different specificities

9. TISSUE TYPES Four major tissue types • Epithelial tissue • Connective tissue • Muscle tissue • Nervous tissue

10. EPITHELIAL TISSUE • Sheets of cells covering body surfaces or lining body cavities • Form boundaries between different environments • e.g., Epidermis of skin separates inside and outside of body • e.g., Epithelium lining urinary bladder separates underlying cells from urine

11. EPITHELIAL TISSUE • Many diverse functions • Protection • Absorption • Filtration • Excretion • Secretion • Sensory reception

12. EPITHELIUM CHARACTERISTICS • Cellularity • Little extracellular material • Specialized contacts • Tight junctions & desmosomes • Polarity • Basal and apical surfaces • Supported by connective tissue • Avascular • Nourished from below • Innervated • Regeneration • Rapid cell division at basal surface

13. CLASSIFICATION OF EPITHELIA Cell layers • Simple epithelia • Single cell layer • Facilitates absorption and filtration • Stratified epithelia • Two or more cell layers • Common in high-abrasion areas • e.g., Skin surface, mouth

14. CLASSIFICATION OF EPITHELIA Cell shape • All epithelia have six sides • Cells vary in height • Three common shapes • Squamous cells • Cuboidal cells • Columnar cells • Shape of nucleus conforms to shape of cell

15. CLASSIFICATION OF EPITHELIA Cell layers & cell shape • Two names • First name indicates cell layers • Second name indicates cell shape • e.g., Simple squamous epithelium • e.g., Stratified cuboidal epithelium

16. SIMPLE SQUAMOUS EPITHELIUM • Flattened • Sparse cytoplasm • Resemble tiled floor from top • Resemble fried egg from side • Thin and permeable • Found where exchange is important • e.g., Filtration in kidneys • e.g., Rapid diffusion in lungs, capillaries

17. SIMPLE SQUAMOUS EPITHELIUM • Two have special names reflecting their location • Endothelium • Inner lining of the heart, blood vessels, and lymphatic vessels • Capillaries are exclusively endothelium • Mesothelium • Found in serous membranes lining the ventral body cavity and covering its organs

18. SIMPLE CUBOIDAL EPITHELIUM • Forms the walls of the smallest ducts of glands and of many kidney tubules

19. SIMPLE COLUMNAR EPITHELIUM • Mainly associated with absorption & secretion • Lines digestive tract (stomach  rectum) • Microvilli on apical surface of absorptive cells • Mucus-secreting goblet cells • May possess cilia

20. PSEUDOSTRATIFIED COLUMNAR EPITHELIUM • Single layer of cells • All cells rest on basement membrane • Cells vary in height • Only tallest cells reach free (apical) surface • Gives false appearance of multiple layers • Secretes or absorbs substances • May possess cilia • May possess goblet cells

21. STRATIFIED EPITHELIA • Possess two or more cell layers • Regenerate from below • Basal cells divide and push apically (“upward”) • More durable than simple epithelia • Protection is major role

22. STRATIFIED SQUAMOUS EPITHELIUM • Most widespread of stratified epithelia • Found in areas subjected to wear and tear • External part of skin, extending into body openings directly continuous with skin • Free surface cells are squamous • Cells in deeper layers are cuboidal or columnar

23. STRATIFIED SQUAMOUS EPITHELIUM • Free surface (apical) cells less viable • Avascular  fewer nutrients further from blood • Outer layer of skin is keratinized • Cells filled with resinous protein keratin • Protective role

24. STRATIFIED CUBOIDAL OR COLUMNAR EPITHELIUM • Both are rather rare in the body • Cuboidal • Present in ducts of some larger glands • e.g., Sweat glands, mammary glands • Typically two layers of cuboidal cells • Columnar • Only apical layer is columnar • Limited distribution • e.g., Pharynx, ♂ urethra, line some glandular ducts • Also present at transition areas or junctions between two other types of epithelia

25. TRANSITIONAL EPITHELIUM • Forms lining of hollow urinary organs • Bladder and ureters • Basal layer cuboidal or columnar • Apical cells vary in appearance • Appearance depends on degree of distension • ~6 cell layers when empty • Thins to ~3 layers when distended with urine • Allows more urine to be stored or transported

26. GLANDULAR EPITHELIA • A gland consists of one or more cells that produce and secrete a product (secretion) • Secretion: verb and noun • Endocrine vs. exocrine • Unicellular vs. multicellular

27. ENDOCRINE GLANDS • “Ductless glands” • (Ducts are eventually lost) • Produce hormones • Secreted directly into extracellular space via exocytosis • Many (but not all) are epithelial derivatives • More information in their own chapter

28. EXOCRINE GLANDS • More numerous than endocrine glands • Secrete into body cavities or onto body surfaces • (i.e., Not into extracellular space) • Unicellular glands via exocytosis • Multicellular glands via ducts • Diverse • e.g., Mucous, sweat, oil, and salivary glands, etc.

29. EXOCRINE GLANDS Unicellular Gland: Goblet cell • Shaped like a goblet • Present in columnar epithelia of intestinal and respiratory tracts • Produce mucin • Mucin + water  mucus • Protects and lubricates

30. EXOCRINE GLANDS Multicellular Glands • Structurally more complex • Two parts • Epithelium-derived duct • Secretory unit • Surrounded by connective tissue • Supplies blood vessels and nerves • Capsule divides gland into lobes

31. Multicellular Glands: Structural Classification Simple Compound Tubular Alveolar (acinar) Tubuloalveolar EXOCRINE GLANDS

32. EXOCRINE GLANDS Multicellular Glands: Mode of Secretion • Merocrine glands • Most common • Secrete products by exocytosis • e.g., Pancreas, sweat & salivary glands • Holocrine glands • Accumulate products within, then rupture • Replaced by division of underlying cells • e.g., Sebaceous (oil) glands • Apocrine glands • Present in other animals, maybe in humans • Accumulate beneath surface, pinch off • e.g., Lipid droplets from mammary glands

33. CONNECTIVE TISSUE • Found everywhere in the body • Most widely distributed primary tissue • Four main classes • Connective tissue proper • Cartilage • Bone tissue • Blood

34. CONNECTIVE TISSUE • Major functions • Binding and support • Protection • Insulation • Transportation • Which of these functions are accomplished by bone and cartilage? Fat? Blood?

35. CONNECTIVE TISSUE Common Characteristics • Common origin • All connective tissues arise from mesenchyme (an embryonic tissue) • Degrees of vascularity • Avascular • poorly vascular • highly vascular • Extracellular matrix • Largely composed of non-living extracellular matrix

36. CONNECTIVE TISSUE • Three main structural elements • Ground substance • Fibers • Cells • Ground substance + fibers = matrix

37. GROUND SUBSTANCE • Unstructured material filling space between cells • Contains fibers • Composed of • Interstitial (tissue) fluid • Cell adhesion proteins • “Glue” attaching cells to matrix elements • Proteoglycans • Glycosaminoglycans (GAGs) attached to a protein core • Large, negatively charged polysaccharides • e.g., Hyaluronic acid, etc. • Traps H2O • Holds fluid  facilitates diffusion of dissolved substances between blood capillaries and cells

38. FIBERS • Three types of fibers provide support • Collagen fibers • “White” fibers • Strongest and most abundant • Tensile strength > steel • Elastic fibers • “Yellow fibers” • Long, thin, branching fibers • Contain the protein elastin • Can stretch and recoil • Reticular fibers • Fine collagenous fibers • Networks surround and support soft tissue of organs

39. CELLS • Each major class of connective tissue is derived from a fundamental cell type (_____-blast) • Fibroblast  connective tissue proper • Hematopoietic stem cell  blood • Chondroblast  cartilage • Osteoblast  bone • ___-blasts ultimately derived from mesenchyme

40. CELLS • Each major class of connective tissue is derived from a fundamental cell type (_____-blast) • Fibroblast  connective tissue proper • Hematopoietic stem cell  blood • Chondroblast  cartilage • Osteoblast  bone • Assume mature form (___-cyte) after matrix is made • Less active • Maintain health of matrix • Revert to –blast form to repair and regenerate matrix

41. CELLS • Connective tissue is a home for many other cell types • Fat cells • Leukocytes • Macrophages • Mast cells • These last three types of cells will be dealt with in great detail in the blood chapter • Macrophages and mast cells will be dealt with in some detail now

42. CELLS • Mast cells • Cluster along blood vessels • Detect foreign substances • e.g., microorganisms • Release secretory granules to initiate local inflammatory response • Macrophages • Descended from monocytes • Relatively large phagocytic cells • “Eat” foreign material • Mobile or fixed

43. TYPES OF CONNECTIVE TISSUE Embryonic Connective Tissue: Mesenchyme • Star-shaped mesenchymal cells • Fluid ground substance • Arises early in embryonic development • Differentiates into all other connective tissues

44. TYPES OF CONNECTIVE TISSUE Connective Tissue Proper • Two subclasses • Loose connective tissue • Areolar • Adipose • Reticular • Dense connective tissue • Dense regular • Dense irregular • Elastic

45. TYPES OF CONNECTIVE TISSUE Loose Connective Tissue: Areolar • Functions • Supporting and binding other tissues • Fibers • Holding body fluids • Ground substance • Defending against infection • Leukocytes • Macrophages • Storing nutrients • Fat cells

46. TYPES OF CONNECTIVE TISSUE Loose Connective Tissue: Areolar • Most widely distributed connective tissue • Functions • Supporting and binding other tissues • Fibers • Holding body fluids • Ground substance • Defending against infection • Leukocytes • Macrophages • Storing nutrients • Fat cells

47. TYPES OF CONNECTIVE TISSUE Loose Connective Tissue: Areolar • Loose arrangement of fibers • Remainder of matrix appears to be empty space • Occupied by ground substance • Provides reservoir of salts and water for surrounding body tissues • Holds amount of fluid equivalent to blood volume • Most body cells obtain nutrients and release wastes into this tissue fluid • Inflammation  edema

48. TYPES OF CONNECTIVE TISSUE Loose Connective Tissue: Areolar • Ground substance rich in hyaluronic acid • Makes ground substance viscous • Can impede microbes • Can also impede movement of cells • Some leukocytes secrete hyaluronidase • Enzyme liquefying hyaluronic acid • Some bacteria also produce this enzyme

49. TYPES OF CONNECTIVE TISSUE Loose Connective Tissue: Areolar • Fibroblasts predominate • Numerous macrophages • Fat cells singly or in small clusters • Occasional mast cells • Other cell types also sparsely present

50. TYPES OF CONNECTIVE TISSUE Loose Connective Tissue: Adipose (Fat) Tissue • Similar to areolar tissue in structure and function • Greater nutrient-storing ability • Adipocytes predominate • Adipose cells / fat cells • 90% of tissue’s mass • Among body’s largest cells • Cells packed tight • Scanty matrix • Oil droplet occupies most of cell volume • Nucleus and thin crescent of cytoplasm visible on periphery