Histology

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