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Histology. Study of Tissues Epithelial Tissue Connective Tissue Nervous and Muscular Tissue Intercellular Junctions, Glands and Membranes Tissue Growth, Development, Death and Repair. The Study of Tissues. 200 Different cell types Four primary tissue classes epithelial tissue

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    1. Histology • Study of Tissues • Epithelial Tissue • Connective Tissue • Nervous and Muscular Tissue • Intercellular Junctions, Glands and Membranes • Tissue Growth, Development, Death and Repair

    2. The Study of Tissues • 200 Different cell types • Four primary tissue classes • epithelial tissue • connective tissue • muscular tissue • nervous tissue • Histology (microscopic anatomy) • study of tissues organ formation • Organ = structure with discrete boundaries • composed of 2 or more tissue types

    3. Features of Tissue Classes • Tissue = similar cells and cell products • arose from same region of embryo • Differences between tissue classes • types and functions of cells • characteristics of matrix (extracellular material) • fibrous proteins • ground substance • clear gels (ECF, tissue fluid, interstitial fluid, tissue gel) • rubbery or stony in cartilage or bone • space occupied by cells versus matrix • connective tissue cells are widely separated • little matrix between epithelial and muscle cells

    4. Tissue Techniques and Sectioning • Preparation of histological specimens • fixative prevents decay (formalin) • sliced into thin sections 1 or 2 cells thick • mounted on slides and colored with histological stain • stains bind to different cellular components • Sectioning reduces 3-dimensional structure to 2-dimensional slice

    5. Sectioning Solid Objects • Sectioning a cell with a centrally located nucleus • Some slices miss the cell nucleus • In some the nucleus is smaller

    6. Sectioning Hollow Structures • Cross section of blood vessel, gut, or other tubular organ. • Longitudinal section of a sweat gland. Notice what a single slice could look like.

    7. Types of Tissue Sections • Longitudinal section • tissue cut along longest direction of organ • Cross section • tissue cut perpendicular to length of organ • Oblique section • tissue cut at angle between cross and longitudinal section

    8. Epithelial Tissue • Layers of closely adhering cells • Flat sheet with upper surface exposed to the environment or an internal body cavity • No blood vessels • underlying connective tissue supplies oxygen • Rests on basement membrane • thin layer of collagen and adhesive proteins • anchors epithelium to connective tissue

    9. Simple Versus Stratified Epithelia • Stratified epithelium • contains more than one layer • named by shape of apical cells • Simple epithelium • contains one layer of cells • named by shape of cells

    10. Simple Squamous Epithelium • Single row of flat cells • Permits diffusion of substances • Secretes serous fluid • Alveoli, glomeruli, endothelium, and serosa

    11. Simple Cuboidal Epithelium • Single row cube-shaped cells with microvilli • Absorption and secretion, mucus production • Liver, thyroid, mammary and salivary glands, bronchioles, and kidney tubules

    12. Simple Columnar Epithelium • Single row tall, narrow cells • oval nuclei in basal half of cell • Absorption and secretion; mucus secretion • Lining of GI tract, uterus, kidney and uterine tubes

    13. Pseudostratified Epithelium • Single row of cells some not reaching free surface • nuclei give layer stratified look • Secretes and propels respiratory mucus

    14. Stratified Epithelia • More than one layer of cells • Named for shape of surface cells • exception is transitional epithelium • Deepest cells on basement membrane • Variations • keratinized epithelium has surface layer of dead cells • nonkeratinized epithelium lacks the layer of dead cells

    15. Keratinized Stratified Squamous • Multilayered epithelium covered with dead squamous cells, packed with keratin • epidermal layer of skin • Retards water loss and barrier to organisms

    16. Nonkeratinized Stratified Squamous • Multilayered surface epithelium forming moist, slippery layer • Tongue, oral mucosa, esophagus and vagina

    17. Stratified Cuboidal Epithelium • Two or more cell layers; surface cells square • Secretes sweat; produces sperm and hormones • Sweat gland ducts; ovarian follicles and seminiferous tubules

    18. Transitional Epithelium • Multilayered epithelium surface cells that change from round to flat when stretched • allows for filling of urinary tract • ureter and bladder

    19. Connective Tissue • Widely spaced cells separated by fibers and ground substance • Most abundant and variable tissue type • Functions • connects organs • gives support and protection (physical and immune) • stores energy and produces heat • movement and transport of materials

    20. Cells of Connective Tissue • Fibroblasts produce fibers and ground substance • Macrophages phagocytize foreign material and activate immune system • arise from monocytes (WBCs) • Neutrophils wander in search of bacteria • Plasma cells synthesize antibodies • arise from WBCs • Mast cells secrete • heparin inhibits clotting • histamine that dilates blood vessels • Adipocytes store triglycerides

    21. Fibers of Connective Tissue • Collagen fibers (white fibers) • tough, stretch resistant, yet flexible • tendons, ligaments and deep layer of the skin • Reticular fibers • thin, collagen fibers coated with glycoprotein • framework in spleen, lymph nodes, marrow • Elastic fibers (yellow fibers) • thin branching fibers of elastin protein • stretch and recoil like rubberband (elasticity) • skin, lungs and arteries stretch and recoil

    22. Connective Tissue Ground Substance • Gelatinous material between cells • absorbs compressive forces • Consists of 3 classes of large molecules • glycosaminoglycans – chondroitin sulfate • disaccharides that attract sodium and hold water • role in regulating water and electrolyte balance • Proteoglycan (bottlebrush-shaped molecule) • create bonds with cells or extracellular macromolecules • adhesive glycoproteins • protein-carbohydrate complexes bind cell membrane to collagen outside the cells

    23. Fibrous Connective Tissue Types • Loose connective tissue • gel-like ground substance between cells • types • areolar • reticular • adipose • Dense connective tissue • fibers fill spaces between cells • types vary in fiber orientation • dense regular connective tissue • dense irregular connective tissue

    24. Areolar Tissue • Loose arrangement of fibers and cells in abundant ground substance • Underlies all epithelia, between muscles, passageways for nerves and blood vessels

    25. Reticular Tissue • Loose network of reticular fibers and cells • Forms supportive stroma (framework) for lymphatic organs • Found in lymph nodes, spleen, thymus and bone marrow

    26. Adipose Tissue • Empty-looking cells with thin margins; nucleus pressed against cell membrane • Energy storage, insulation, cushioning • subcutaneous fat and organ packing • brown fat (hibernating animals) produces heat

    27. Dense Regular Connective Tissue • Densely, packed, parallel collagen fibers • compressed fibroblast nuclei • Tendons and ligaments hold bones together and attach muscles to bones

    28. Dense Irregular Connective Tissue • Densely packed, randomly arranged, collagen fibers and few visible cells • withstands stresses applied in different directions • deeper layer of skin; capsules around organs

    29. Cartilage • Supportive connective tissue with rubbery matrix • Chondroblasts produce matrix • called chondrocytes once surrounded • No blood vessels • diffusion brings nutrients and removes wastes • heals slowly • Types of cartilage vary with fiber types • hyaline, fibrocartilage and elastic cartilage

    30. Hyaline Cartilage • Rubbery matrix; dispersed collagen fibers; clustered chondrocytes in lacunae • supports airway, eases joint movements • Ends of bones at movable joints; sternal ends of ribs; supportive material in larynx, trachea, bronchi and fetal skeleton

    31. Elastic Cartilage • Hyaline cartilage with elastic fibers • Provides flexible, elastic support • external ear and epiglottis

    32. Fibrocartilage • Hyaline cartilage with extensive collagen fibers (never has perichondrium) • Resists compression and absorbs shock • pubic symphysis, meniscus and intervertebral discs

    33. Bone • Spongy bone - spongy in appearance • delicate struts of bone • covered by compact bone • found in heads of long bones • Compact bone - solid in appearance • more complex arrangement • cells and matrix surround vertically oriented blood vessels in long bones

    34. Bone Tissue (compact bone) • Calcified matrix in lamellae around central canal • Osteocytes in lacunae between lamellae • Skeletal support; leverage for muscles; mineral storage

    35. Blood • Variety of cells and cell fragments; some with nuclei and some without • Nonnucleated pale pink cells or nucleated white blood cells • Found in heart and blood vessels

    36. Nerve Tissue • Large cells with long cell processes • surrounded by smaller glial cells lacking processes • Internal communication between cells • in brain, spinal cord, nerves and ganglia

    37. Muscle Tissue • Elongated cells stimulated to contract • Exert physical force on other tissues • move limbs • push blood through a vessel • expel urine • Source of body heat • 3 histological types of muscle • skeletal, cardiac and smooth

    38. Skeletal Muscle • Long, cylindrical, unbranched cells with striations and multiple peripheral nuclei • movement, facial expression, posture, breathing, speech, swallowing and excretion

    39. Cardiac Muscle • Short branched cells with striations and intercalated discs • one central nuclei per cell • Pumping of blood by cardiac (heart) muscle

    40. Smooth Muscle • Short fusiform cells; nonstriated with only one central nucleus • sheets of muscle in viscera; iris; hair follicles and sphincters • swallowing, GI tract functions, labor contractions, control of airflow, erection of hairs and control of pupil

    41. Intercellular Junctions • All cells (except blood) anchored to each other or their matrix by intercellular junctions

    42. Tight Junctions • Encircle the cell joining it to surrounding cells • zipperlike complementary grooves and ridges • Prevents passage between cells • GI and urinary tracts

    43. Desmosomes • Patch between cells holding them together • cells spanned by filaments terminating on protein plaque • cytoplasmic intermediate filaments also attach to plaque • Uterus, heart and epidermis

    44. Gap Junctions • Ring of transmembrane proteins form a water-filled channel • small solutes pass directly from cell to cell • in embryos, cardiac and smooth muscle

    45. Endocrine and Exocrine Glands • Secrete substances • composed of epithelial tissue • Exocrine glands connect to surface with a duct (epithelial tube) • Endocrine glands secrete (hormones) directly into bloodstream • Mixed organs do both • liver, gonads, pancreas • Unicellular glands – endo or exocrine • goblet or intrinsic cells of stomach wall

    46. Exocrine Gland Structure • Stroma = capsule and septa divide gland into lobes and lobules • Parenchyma = cells that secrete • Acinus = cluster of cells surrounding the duct draining those cells

    47. Types of Exocrine Glands • Simple glands - unbranched duct • Compound glands - branched duct • Shape of gland • acinar - secretory cells form dilated sac • tubuloacinar - both tube and sacs

    48. Types of Secretions • Serous glands • produce thin, watery secretions • sweat, milk, tears and digestive juices • Mucous glands • produce mucin that absorbs water to form a sticky secretion called mucus • Mixed glands contain both cell types • Cytogenic glands release whole cells • sperm and egg cells

    49. Holocrine Gland • Secretory cells disintegrate to deliver their accumulated product • oil-producing glands of the scalp

    50. Merocrine and Apocrine Secretion • Merocrine glands release their product by exocytosis • tears, gastric glands, pancreas, etc. • Apocrine glands are merocrine glands with confusing appearance (apical cytoplasm not lost) • mammary and armpit sweat glands