Histology

1. Histology • Study of Tissues • Epithelial Tissue • Intercellular Junctions and Glands • Connective Tissue • Membranes • Muscular Tissue • Nervous Tissue

2. The Study of Tissues • Histology (microscopic anatomy) • study of tissues and how they form organs • Tissue • group of similar cells and cell products (i.e., ECM) • Organ • composed of 2 or more tissue types (almost always connective and epithelial; usually includes muscle and nervous) • Four primary tissue classes • epithelial tissue • connective tissue • muscular tissue • nervous tissue

3. Features of Tissues • Differences between tissues • type and function of cells • characteristics of the surrounding matrix (extracellular matrix; ECM) • ground substance made from proteins, sugars, and sometimes minerals • called many different names (ECF, ECM, tissue fluid, interstitial fluid, basement membrane) • amount of space occupied by cells versus matrix • very little ECM exists between epithelial and muscle cells • connective tissue cells are widely separated by ECM

4. Epithelial Tissue • One or more layers of closely adhering cells • Forms a flat sheet with the upper surface exposed to the environment or an internal body cavity • one side of tissue exposed to “outside” • Sits on basement membrane (at the basal surface of cells) • thin layer of collagen and adhesive proteins • anchors epithelium to underlying connective tissue; provides support

5. Layers • Simple epithelium • contains one layer of cells • named by shape of cells • Stratified epithelium • contains more than one layer • named by shape of apical (surface) cells • deepest cells (basal cells) sit on basement membrane

6. Shape • Squamous (squashed) • Allows rapid diffusion of substances; secretes serous fluid • Cuboidal (square) • Absorption & secretion; produces mucus • Columnar (rectangular) • Absorption & secretion; produces mucus • Often ciliated

7. Epithelial Functions

8. Intercellular Junctions • All cells except blood cells are anchored to each other (or to the matrix surrounding them) by intercellular junctions formed by adhesion proteins

9. Desmosomes • Patch between 2 cells holding them together against mechanical stress • CONNECTING • gap between cells is spanned by mesh of filaments • often called adhesion junction

10. Tight Junctions • Encircle the cell, joining it to surrounding cells • BARRIER • prevents substances and bacteria from passing between cells

11. Gap Junctions • Transmembrane proteins form a water-filled channel • Small solutes (metabolites and ions) pass directly from cell to cell • COMMUNICATING • aka electrical synapse

12. Cell to Cell Junctions

13. Endocrine and Exocrine Glands • Glands secrete substances • Exocrine glands connect to surface with a duct (tube) • Endocrine glands secrete their products (hormones) directly into bloodstream • Some glands are mixed • gonads release gametes and secrete hormones into blood • pancreas secretes digestive enzymes and hormones

14. Types of Exocrine Secretions • Serous glands • produce thin, watery secretions • sweat, milk, tears and digestive juices • Mucous glands • produce a glycoprotein, mucin, that helps form a sticky secretion called mucus • nasal, reproductive, respiratory secretions • Cytogenic glands release whole cells • produce gametes

15. Endocrine Glands • Produce chemical signals that cause a response • hormone • Released into blood!!

16. Connective Tissue • Consists of widely spaced cells separated by fibers and ground substance • Most abundant and variable tissue type • Functions • connects structures to each other • gives support and protection (physical & immune) • stores energy • movement and transport of materials

17. Ground Substance of Connective Tissue • Gelatinous or rubbery material found in between cells • Consists of large molecules • proteoglycans • embedded in plasma membranes • create a strong bond to other cells or extracellular matrix • glycoproteins • protein-carbohydrate complexes that bind plasma membrane to collagen or proteoglycans outside the cells

18. Cells of Connective Tissue • Fibroblasts produce protein fibers and ground substance • Osteocytes (bone) and chondrocytes (cartilage) • Blood cells • Erythrocytes • Leukocytes • Macrophages phagocytose foreign material • Neutrophils phagocytose bacteria • Plasma cells synthesize antibodies • Mast cells in skin secrete heparin that inhibits clotting and histamine that dilates blood vessels • Adipocytes or fat cells store triglycerides

19. Fibers of Connective Tissue • Collagen fibers • tough • resistant to stretch, yet flexible • tendons, ligaments and deep layer of the skin (dermis) • Elastic fibers • thin branching fibers made of elastin • stretch & recoil like rubberband (elasticity) • give skin, lungs and arteries ability to stretch and recoil • Reticular fibers • thin collagen fibers coated with glycoprotein • form framework for spleen and lymph nodes

20. Types of Fibrous Connective Tissue • Loose connective tissue • contains gel-like ground substance between cells • Dense connective tissue • fibers fill the spaces between cells • 2 types varying in fiber orientation • dense regular connective tissue • dense irregular connective tissue

21. Adipose Tissue • Large, empty-looking cells with thin margins • Nucleus pressed against cell membrane • Energy storage, insulation, cushioning • Subcutaneous fat beneath skin and surrounding organs

22. Cartilage • Supportive connective tissue with rubbery matrix • Chondroblasts produce cartilage matrix, once surrounded by cartilage  chondrocytes • No blood vessels so diffusion must bring in nutrients and remove wastes • injured cartilage heals slowly • Major types of cartilage depend upon fiber types • hyaline, fibrocartilage and elastic cartilage

23. Fibrocartilage Cartilage containing extensive parallel collagen fibers Resists compression and absorbs shock in some joints Pubic symphysis and intervertebral discs Hyaline Clear, glassy matrix; fine dispersed collagen fibers; chondrocytes in small clusters enclosed in lacunae Joints; supportive material in larynx, trachea, bronchi Cartilage

24. Bone • Spongy bone looks spongy in appearance • delicate struts of bone • always covered by compact bone • Compact bone looks solid in appearance • more complex arrangement • cells and matrix vertically oriented

25. Blood • Variety of cells and cell fragments • white blood cells, red blood cells, and platelets • Found in heart and blood vessels

26. Mucous Membranes • Consists of epithelium, connective (basal lamina or lamina propria) and underlying muscular tissues • Lines passageways that open to the exterior: digestive, respiratory, urinary and reproductive • Mucous coating and movement of cilia trap and remove foreign particles and bacteria from internal surfaces of body

27. Cutaneous, Synovial and Serous Membranes • Cutaneous membrane (skin) • stratified squamous epithelium resting on layer of connective tissue • relatively dry layer serves protective function • Synovial membrane lines joints • secretes synovial fluid rich in hyaluronic acid into the joint • Serous membrane (serosa) – internal membrane • covers organs and walls of body cavities, produces serous fluid

28. Muscular Tissue • Elongated cells that respond to stimuli by contracting • Function is to exert physical force on other tissues • move hand • push blood through a vessel • expel urine • Important source of body heat • Three types of muscle • skeletal, cardiac and smooth

29. Skeletal Muscle • Long, cylindrical, unbranched cells with striations • Movement, facial expression, posture, breathing, speech, swallowing and excretion

30. Cardiac Muscle • Short branched cells with striations and intercalated discs • Pumps blood

31. Smooth Muscle • Short cells; nonstriated • 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

32. Nervous Tissue • Large neurons with long cell processes surrounded by much smaller glial cells lacking dendrites and axons • Found in brain, spinal cord, nerves & ganglia • Communication and control of bodily functions