Chapter 4 Histology

1. Chapter 4 Histology Biol 2401

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

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

5. 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

7. 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

9. Glands • A gland is a cell or organ that secretes substances in the body or releases them for elimination. • 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

10. 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

11. 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

12. 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

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

14. 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

15. Mucous Membranes • Epithelium, lamina propria and muscularis mucosae • Lines passageways that open to the exterior: reproductive, respiratory, urinary and digestive • Mucous (movement of cilia) trap and remove foreign particles and bacteria from internal body surfaces

16. Membrane Types • Cutaneous membrane = skin • stratified squamous epithelium over connective tissue • relatively dry layer serves protective function • Synovial membrane lines joint cavities • connective tissue layer only, secretes synovial fluid • Serous membrane (serosa) –internal membrane • simple squamous epithelium over areolar tissue, produces serous fluid • covers organs and lines walls of body cavities

17. Membranes Cutaneous Membrane Serous Membrane Synovial Membrane

18. Tissue Growth • Hyperplasia = tissue growth through cell multiplication • Hypertrophy = enlargement of preexisting cells • muscle grow through exercise • Neoplasia = growth of a tumor (benign or malignant) through growth of abnormal tissue

19. Changes in Tissue Types • Tissues can change types • Differentiation • unspecialized tissues of embryo become specialized mature types • mesenchyme to muscle • Metaplasia • changing from one type of mature tissue to another • simple cuboidal tissue before puberty changes to stratified squamous after puberty

20. Stem Cells • Undifferentiated cells with developmental plasticity • Embryonic stem cells • totipotent (any cell type possible) • source = cells of very early embryo • Pluripotent (tissue types only possible) • source = cells of inner cell mass of embryo • Adult stem cells (undifferentiated cells in tissues of adults) • multipotent (bone marrow producing several blood cell types) • unipotent (only epidermal cells produced)

21. Tissue Shrinkage and Death • Atrophy = loss of cell size or number • disuse atrophy from lack of use (leg in a cast) • Necrosis = pathological death of tissue • gangrene - insufficient blood supply • gas gangrene - anaerobic bacterial infection • infarction - death of tissue from lack of blood • decubitus ulcer - bed sore or pressure sore • Apoptosis = programmed cell death • cells shrink and are phagocytized (no inflammation)

22. Tissue Repair • Regeneration • replacement of damaged cells with original cells • skin injuries and liver regenerate • Fibrosis • replacement of damaged cells with scar tissue • function is not restored • healing muscle injuries, scarring of lung tissue in TB or healing of severe cuts and burns of the skin • keloid is healing with excessive fibrosis (raised shiny scars)

23. Tissue Engineering • Production of tissues and organs in the lab • framework of collagen or biodegradable polyester fibers • seeded with human cells • grown in “bioreactor” (inside of mouse) • supplies nutrients and oxygen to growing tissue • Skin grafts already available • research in progress on heart valves, coronary arteries, bone, liver, tendons

24. Wound Healing of a Laceration • Damaged vessels leak blood • Damaged cells and mast cells leak histamine • dilates blood vessels • increases blood flow • increases capillary permeability • Plasma carries antibodies, clotting factors and WBCs into wound

25. Wound Healing of a Laceration • Clot forms • Scab forms on surface • Macrophages start to clean up debris

26. Wound Healing of a Laceration • New capillaries grow into wound • Fibroblasts deposit new collagen to replace old material • Fibroblastic phase begins in 3-4 days and lasts up to 2 weeks

27. Wound Healing of a Laceration • Epithelial cells multiply and spread beneath scab • Scab falls off • Epithelium thickens • Connective tissue forms only scar tissue (fibrosis) • Remodeling phase may last 2 years