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// ============================================================
// CONTENT
// ============================================================
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  // =============================================
  // SECTION 1: EPITHELIAL TISSUE
  // =============================================
  heading1("SECTION 1: EPITHELIAL TISSUE"),
  para("Lecture 5 - Epithelial Tissue 2024"),

  heading2("1.1 Overview of Body Tissues"),
  para("The human body is composed of four basic tissue types:"),
  bullet("Epithelial tissue"),
  bullet("Connective tissue"),
  bullet("Muscular tissue"),
  bullet("Nervous tissue"),
  para("Organs have two compartments:"),
  bullet("Parenchyma - cells responsible for the organ's specialized functions"),
  bullet("Stroma - supporting cells"),

  heading2("1.2 Definition & Functions of Epithelial Tissue"),
  para("Epithelial tissues are composed of polyhedral cells that line cavities of organs and cover the body surface."),
  para("Principal functions:"),
  bullet("Covering, lining, and protecting surfaces (e.g., epidermis)"),
  bullet("Absorption (e.g., intestinal lining)"),
  bullet("Secretion (e.g., parenchymal cells of glands)"),

  heading2("1.3 Cell Shape & Polarity"),
  para("Epithelial cells are classified by shape:"),
  bullet("Columnar - tall, column-shaped"),
  bullet("Cuboidal - equal width and height"),
  bullet("Squamous - flat, scale-like"),
  para("Cell nuclei match cell shape: elliptic, spherical, or flattened."),
  para("Epithelial cells show polarity:"),
  bullet("Basal pole - contacts connective tissue below"),
  bullet("Apical pole - faces a lumen or free surface"),
  bullet("Lateral surfaces - adjoin neighboring cells"),
  keyPoint("Papillae", "Small evaginations at the epithelium-connective tissue interface that increase contact area; common in areas subject to friction (skin, tongue)."),

  heading2("1.4 Basement Membrane"),
  para("A specialized extracellular sheet at the base of all epithelia. Visible with light microscope using glycoprotein stains."),
  para("Two layers seen by TEM:"),
  bullet("Basal lamina (20-100 nm thick) - closest to epithelial cells; electron-dense network of fine fibrils"),
  bullet("Reticular lamina - more diffuse and fibrous; contains type III collagen"),
  para("Basal lamina macromolecules:"),
  bullet("Laminin - large glycoproteins anchored by transmembrane integrins"),
  bullet("Type IV collagen - triple polypeptide chain monomers forming a network"),
  bullet("Entactin/Nidogen - adhesive glycoprotein holding laminin and type IV collagen together"),
  bullet("Perlecan - a proteoglycan bridging components"),
  bullet("Type VII collagen (anchoring fibrils) - binds reticular lamina to basal lamina"),

  heading2("1.5 Types of Epithelia"),
  para("Two main groups:"),
  bullet("Covering/lining epithelia"),
  bullet("Secretory (glandular) epithelia"),
  para("Classification is based on cell layers and cell shape:"),
  bullet("Simple - single layer of cells (all cells touch basement membrane)"),
  bullet("Stratified - multiple layers"),
  bullet("Pseudostratified - appears multilayered but all cells touch basement membrane"),
  bullet("Transitional (urothelium) - specialized stratified epithelium that can stretch"),

  heading2("1.6 Simple Epithelia"),
  bullet("Simple squamous - flat single layer; e.g., mesothelium (lining body cavities), endothelium (blood vessels)"),
  bullet("Simple cuboidal - cube-shaped cells; secretion and absorption; e.g., kidney tubules, thyroid follicles"),
  bullet("Simple columnar - tall cells; absorption and secretion; e.g., intestinal lining, stomach; may have microvilli (striated border)"),
  bullet("Pseudostratified columnar - common in respiratory tract; all cells touch basement membrane; nuclei at different levels"),

  heading2("1.7 Stratified Epithelia"),
  bullet("Stratified squamous (keratinized) - skin epidermis; dead surface cells filled with keratin"),
  bullet("Stratified squamous (non-keratinized) - wet surfaces like oral cavity, esophagus, vagina"),
  bullet("Stratified cuboidal - rare; found in some ducts"),
  bullet("Stratified columnar - rare; conjunctiva, part of male urethra"),
  bullet("Transitional epithelium - urinary bladder, ureter; cells change shape with distension"),

  heading2("1.8 Cell Junctions"),
  para("Lateral surfaces of adjacent epithelial cells are connected by:"),
  bullet("Tight junctions (zonula occludens) - seal the intercellular space; prevent paracellular transport"),
  bullet("Adherens junctions (zonula adherens) - belt of actin filaments connecting adjacent cells"),
  bullet("Desmosomes (macula adherens) - strong spot-like attachments; linked to intermediate filaments (cytokeratins)"),
  bullet("Gap junctions - allow direct communication between cells via connexins"),
  bullet("Hemidesmosomes - attach basal surface to basement membrane"),
  para("These junctions collectively form the junctional complex."),

  heading2("1.9 Specializations of Apical Surface"),
  bullet("Microvilli - finger-like projections increasing surface area; core of actin filaments; form 'brush border' or 'striated border'"),
  bullet("Stereocilia - long, non-motile microvilli; found in epididymis"),
  bullet("Cilia - motile projections (9+2 axoneme structure); move mucus/particles; e.g., respiratory epithelium, oviduct"),

  heading2("1.10 Glandular Epithelium"),
  para("Glands develop by proliferation of surface epithelium into underlying connective tissue."),
  bullet("Exocrine glands - retain connection with surface epithelium via ducts (e.g., sweat glands, salivary glands, pancreatic exocrine)"),
  bullet("Endocrine glands - lose ductal connection; secrete hormones directly into blood (e.g., thyroid, adrenals)"),
  para("Gland structure:"),
  bullet("Simple glands - ducts not branched"),
  bullet("Compound glands - ducts with 2 or more branches"),
  para("Secretory unit shapes:"),
  bullet("Tubular - short or long and coiled"),
  bullet("Acinar (alveolar) - rounded, sac-like"),
  bullet("Tubuloacinar - combination"),

  heading2("1.11 Types of Secretion"),
  keyPoint("Merocrine secretion", "Products released by exocytosis at apical surface. Most common. E.g., salivary glands, pancreas."),
  keyPoint("Holocrine secretion", "Entire cell disintegrates, becoming the secretion. E.g., sebaceous glands of hair follicles."),
  keyPoint("Apocrine secretion", "Loss of membrane-enclosed apical cytoplasm containing lipid droplets. E.g., mammary glands (combined with merocrine)."),

  sectionBreak(),

  // =============================================
  // SECTION 2: CONNECTIVE TISSUE - CELLS & ECM
  // =============================================
  heading1("SECTION 2: CONNECTIVE TISSUE - CELLS & ECM"),
  para("Lecture 8 Part I - 2021"),

  heading2("2.1 Introduction"),
  para("Connective tissues provide a matrix that supports and physically connects other tissues and cells in organs. The major constituent is the extracellular matrix (ECM)."),
  para("ECM consists of:"),
  bullet("Protein fibers (collagens, elastic fibers)"),
  bullet("Ground substance (anionic, hydrophilic proteoglycans, GAGs, multiadhesive glycoproteins)"),
  keyPoint("Origin", "Connective tissues originate from embryonic mesenchyme, derived mainly from the middle embryonic layer, the mesoderm."),
  keyPoint("Mesenchyme", "Viscous ground substance with few collagen fibers; mesenchymal cells are undifferentiated, spindle-shaped, with large nuclei and prominent nucleoli."),

  heading2("2.2 Cells of Connective Tissue"),
  para("Two categories of cells:"),
  bullet("Fixed/permanent residents - fibroblasts (originate locally from mesenchymal cells)"),
  bullet("Transient cells - macrophages, plasma cells, mast cells, leukocytes (originate from bone marrow hematopoietic stem cells)"),

  heading3("Fibroblasts"),
  para("The most common cells in connective tissue."),
  bullet("Synthesize and secrete collagen (most abundant protein in the body), elastin"),
  bullet("Produce GAGs, proteoglycans, and multiadhesive glycoproteins for ground substance"),
  bullet("Targeted by growth factors that influence cell growth and differentiation"),
  keyPoint("Myofibroblasts", "Fibroblasts involved in wound healing; have well-developed contractile function; enriched with actin (also found in smooth muscle cells)."),

  heading3("Adipocytes (Fat Cells)"),
  bullet("Found in connective tissue of many organs"),
  bullet("Large, mesenchymally derived cells"),
  bullet("Specialized for cytoplasmic storage of lipid as neutral fats"),
  bullet("Some produce heat (brown adipose tissue)"),
  bullet("Have major metabolic significance and medical importance"),

  heading3("Macrophages"),
  bullet("Characterized by well-developed phagocytic ability"),
  bullet("10-30 μm in diameter"),
  bullet("Eccentrically located, oval or kidney-shaped nucleus"),
  bullet("Present in connective tissue of most organs; also called 'histiocytes' by pathologists"),
  bullet("Secretory cells: produce enzymes for ECM breakdown, growth factors, cytokines for immune regulation"),
  bullet("When stimulated, can fuse to form multinuclear giant cells (only in pathologic conditions)"),
  keyPoint("Origin", "From bone marrow precursors → monocytes circulate in blood → cross into connective tissue → become macrophages. System called the Mononuclear Phagocyte System (MPS)."),

  heading3("Mast Cells"),
  bullet("Large, oval cells packed with prominent basophilic secretory granules"),
  bullet("Abundant near blood vessels"),
  bullet("Granules contain heparin, histamine, serotonin, proteases"),
  bullet("Release mediators by IgE-triggered degranulation - central to hypersensitivity/allergic reactions"),
  bullet("Key cell in inflammation"),

  heading3("Plasma Cells"),
  bullet("Derived from B lymphocytes"),
  bullet("Specialized for antibody (immunoglobulin) production"),
  bullet("Abundant rough ER gives 'clock-face' nucleus appearance (heterochromatin at periphery)"),
  bullet("Found in connective tissue of mucous membranes and lymphoid organs"),

  heading3("Leukocytes (White Blood Cells)"),
  bullet("Transient cells - migrate from blood into connective tissue"),
  bullet("Function for a few days then die by apoptosis"),
  bullet("Include neutrophils (most common), lymphocytes, eosinophils, basophils"),

  heading2("2.3 Collagen Fibers"),
  para("The most abundant fibers in connective tissue. Provide tensile strength."),
  bullet("Composed of collagen protein - the most abundant protein in the body"),
  bullet("Assembled from triple-helix procollagen molecules (secreted by fibroblasts)"),
  bullet("Cleaved extracellularly into tropocollagen → pack into collagen fibrils → fibers"),
  para("Key collagen types:"),
  bullet("Type I - most abundant; found in skin, tendon, ligament, bone; large fibers"),
  bullet("Type II - cartilage; thin fibrils; provides compressive strength"),
  bullet("Type III (reticular) - delicate scaffolding in hematopoietic tissues, liver, spleen"),
  bullet("Type IV - basement membrane; non-fibrillar; forms networks"),
  bullet("Type VII - anchoring fibrils connecting basement membrane to reticular lamina"),

  heading2("2.4 Elastic Fibers"),
  bullet("Less abundant than collagen; provide resilience (ability to stretch and recoil)"),
  bullet("Composed of elastin protein and fibrillin microfibrils"),
  bullet("Found in skin, lungs, arteries, ligaments (ligamenta flava of vertebral column)"),
  bullet("Stain poorly with H&E; visible with special stains (orcein, Weigert's)"),

  heading2("2.5 Reticular Fibers"),
  bullet("Type III collagen; very thin, delicate fibers forming 3D networks"),
  bullet("Argyrophilic - visible with silver stains (silver impregnation)"),
  bullet("Produced by reticular cells (modified fibroblasts)"),
  bullet("Framework for lymphoid organs, liver, bone marrow"),

  heading2("2.6 Ground Substance"),
  para("Watery, largely unstained extracellular material surrounding fibers and cells."),
  para("Components:"),
  bullet("Glycosaminoglycans (GAGs) - long, unbranched polysaccharide chains of repeating disaccharides; highly hydrophilic due to anionic sulfate/carboxylate groups"),
  bullet("Hyaluronic acid (HA/hyaluronan) - very long polymer of glucosamine-glucuronate; not sulfated; not bound to core protein"),
  bullet("Sulfated GAGs - chondroitin sulfate, keratan sulfate, heparan sulfate, dermatan sulfate; bound to proteoglycan core proteins"),
  bullet("Proteoglycans - core protein + GAG side chains; huge aggregates bound to HA via linker proteins; bind water, growth factors"),
  bullet("Multiadhesive glycoproteins - fibronectin, laminin; have binding sites for collagens and integrins; mediate cell-ECM adhesion and cell migration"),

  sectionBreak(),

  // =============================================
  // SECTION 3: CONNECTIVE TISSUE PROPER
  // =============================================
  heading1("SECTION 3: CONNECTIVE TISSUE PROPER"),
  para("Lecture 8 Part II - 2020"),

  heading2("3.1 Classification"),
  para("Two general classes, based on amount of collagen:"),
  bullet("Loose connective tissue (areolar tissue) - cells, fibers, and ground substance in roughly equal parts"),
  bullet("Dense connective tissue - fewer cells, collagen fibers predominate over ground substance"),

  heading2("3.2 Loose Connective Tissue (Areolar Tissue)"),
  bullet("Very common; supports epithelial tissue everywhere"),
  bullet("Forms the lamina propria beneath digestive, respiratory, and urinary epithelium"),
  bullet("Fills spaces between muscle and nerve fibers"),
  bullet("Surrounds most small blood vessels"),
  bullet("Composition: fibroblasts (most numerous), macrophages, mast cells, plasma cells + collagen, elastic, reticular fibers + ground substance"),
  bullet("Delicate consistency - flexible but not very resistant to stress"),
  bullet("Well-vascularized"),

  heading2("3.3 Dense Connective Tissue"),
  para("Adapted to offer stress resistance and protection."),
  bullet("Same components as loose CT but fewer cells; collagen predominates"),
  bullet("Less flexible; far more resistant to stress"),
  para("Two sub-types:"),
  keyPoint("Dense Irregular CT", "Collagen bundles randomly interwoven; no definite orientation. Resists stress from multiple directions. Found in dermis of skin, organ capsules."),
  keyPoint("Dense Regular CT", "Type I collagen bundles arranged in parallel; fibroblasts aligned along fibers. Resists prolonged/repeated stress in one direction. White in fresh state; almost inextensible."),
  para("Examples: tendons (muscle to bone) and ligaments (bone to bone)."),

  heading2("3.4 Tendons"),
  bullet("Tough band of fibrous CT connecting muscle to bone"),
  bullet("Dense regular CT fascicles encased in dense irregular CT sheaths"),
  bullet("Dry mass composition: ~86% collagen, 2% elastin, 1-5% proteoglycans, 0.2% inorganic components"),
  bullet("Tenocytes produce collagen molecules → collagen fibrils; communicate via gap junctions"),
  bullet("Mechanical properties depend on collagen fiber diameter and orientation"),
  keyPoint("Tendinopathy", "Various forms of tendon injury resulting in inflammation and degeneration of tendons, possibly leading to tendon rupture. Classification is difficult due to overlapping symptoms and histopathology."),

  heading2("3.5 Reticular Tissue"),
  bullet("Type III collagen fibers form a delicate 3D network"),
  bullet("Produced by reticular cells (modified fibroblasts that stay associated with fibers)"),
  bullet("Provides specialized microenvironments for cells in hematopoietic tissue and lymphoid organs"),
  bullet("Found in bone marrow, lymph nodes, and spleen"),

  heading2("3.6 Mucoid (Mucous) Connective Tissue"),
  bullet("Embryonic type of connective tissue"),
  bullet("Found mainly in umbilical cord and fetal organs"),
  bullet("Abundant ground substance composed chiefly of hyaluronic acid"),
  bullet("Jellylike consistency; sparse collagen fibers; scattered fibroblasts"),
  bullet("Also found in pulp cavities of young teeth - postnatal source of mesenchymal stem cells"),

  heading2("3.7 Adipose Tissue"),
  bullet("Connective tissue in which adipocytes predominate"),
  para("Two types:"),
  keyPoint("White adipose tissue (WAT)", "Single large lipid droplet per cell ('signet ring' appearance on H&E as fat is dissolved). Functions: energy storage, thermal insulation, mechanical cushioning, hormone production (leptin, adiponectin)."),
  keyPoint("Brown adipose tissue (BAT)", "Multiple small lipid droplets; abundant mitochondria with uncoupling protein 1 (UCP1/thermogenin). Functions: non-shivering thermogenesis (heat production). Abundant in newborns; important in hibernating animals."),

  sectionBreak(),

  // =============================================
  // SECTION 4: CARTILAGE
  // =============================================
  heading1("SECTION 4: CARTILAGE"),
  para("Week 12 - Cartilage 2025"),

  heading2("4.1 Overview"),
  para("Cartilage is a tough, flexible form of connective tissue, characterized by an ECM with high concentrations of GAGs and proteoglycans, which interact with collagen and elastic fibers."),
  para("Key properties:"),
  bullet("Avascular - receives nutrients by diffusion from perichondrium capillaries"),
  bullet("Alymphatic - lacks lymphatic vessels"),
  bullet("Aneural - lacks nerves"),
  bullet("Low metabolic activity (consistent with avascular status)"),
  bullet("High water content allows it to function as shock absorber"),

  heading2("4.2 Chondrocytes"),
  bullet("Cells of cartilage (Gr. chondros = cartilage + kytos = cell)"),
  bullet("Embedded in matrix cavities called lacunae"),
  bullet("Synthesize and maintain ECM components (collagen, hyaluronic acid, proteoglycans, glycoproteins)"),
  bullet("In groups of 2-8 cells within a lacuna = isogenous groups (result of chondrocyte division)"),
  bullet("Surrounded by a condensed matrix = territorial matrix (pericellular matrix); more basophilic"),
  bullet("Matrix between groups = interterritorial matrix"),

  heading2("4.3 Perichondrium"),
  bullet("Sheath of dense connective tissue surrounding cartilage (except articular cartilage)"),
  bullet("Interface between cartilage and supported tissues"),
  bullet("Contains: vascular supply, nerves, lymphatic vessels"),
  bullet("Two layers:"),
  para("   1. Outer fibrous layer - dense collagen and fibroblasts"),
  para("   2. Inner chondrogenic layer - contains chondroprogenitor cells (chondroblasts) for appositional growth"),
  keyPoint("Articular cartilage", "Lacks perichondrium; sustained by diffusion of O2 and nutrients from synovial fluid."),

  heading2("4.4 Three Types of Cartilage"),

  heading3("Hyaline Cartilage"),
  para("Most common type. Named for glassy, homogeneous, semitransparent appearance in fresh state."),
  para("Locations:"),
  bullet("Articular surfaces of movable joints"),
  bullet("Walls of larger respiratory passages (nose, larynx, trachea, bronchi)"),
  bullet("Ventral ends of ribs (costal cartilage) - articulates with sternum"),
  bullet("Epiphyseal (growth) plates of long bones - enables longitudinal bone growth"),
  bullet("Entire temporary embryonic skeleton (replaced by bone during ossification)"),
  para("Matrix composition:"),
  bullet("Dry weight: 40% collagen embedded in firm hydrated proteoglycan gel"),
  bullet("Principal collagen: type II (thin fibrils, not visible in H&E)"),
  bullet("Matrix appears basophilic due to proteoglycans"),
  keyPoint("Aggrecan", "Most abundant proteoglycan (~250 kD); has ~150 GAG side chains of chondroitin sulfate and keratan sulfate; hundreds of aggrecan molecules bound noncovalently to hyaluronic acid via link proteins = huge aggregates that bind and retain water."),

  heading3("Elastic Cartilage"),
  para("More pliable and distensible than hyaline cartilage."),
  bullet("Contains abundant elastic fibers in addition to type II collagen"),
  bullet("Elastic fibers stain with orcein or resorcin-fuchsin"),
  para("Locations:"),
  bullet("Auricle (pinna) of external ear"),
  bullet("External auditory meatus"),
  bullet("Eustachian tube"),
  bullet("Epiglottis"),

  heading3("Fibrocartilage"),
  para("Present in regions subjected to pulling (tensile) forces."),
  bullet("Dense network of coarse type I collagen fibers in matrix"),
  bullet("NO perichondrium"),
  bullet("Chondrocytes arranged in rows between thick parallel collagen bundles"),
  bullet("Intermediate between hyaline cartilage and dense regular CT"),
  para("Locations:"),
  bullet("Intervertebral discs (anulus fibrosus)"),
  bullet("Symphysis pubis"),
  bullet("Articular discs of knee (menisci) and temporomandibular joint"),
  bullet("Insertions of some tendons and ligaments into bone"),

  heading2("4.5 Cartilage Growth"),
  keyPoint("Interstitial growth", "From within - chondrocytes divide inside lacunae, each daughter cell secretes new matrix around itself, expanding from within. Occurs mainly in young/growing cartilage."),
  keyPoint("Appositional growth", "From outside - chondroprogenitor cells in the inner perichondrium divide and differentiate into chondroblasts, then chondrocytes at the periphery. This adds new tissue to the surface."),

  heading2("4.6 Cartilage Repair"),
  bullet("Limited repair capacity due to avascular nature"),
  bullet("Chondrocytes in avascular tissue cannot migrate readily to injury site"),
  bullet("Injuries to cartilage (especially articular) heal poorly"),
  bullet("Perichondrium has some repair capacity via chondroprogenitor cells"),

  heading2("4.7 Tendons (Extended Notes from Cartilage Lecture)"),
  para("A tendon connects muscle to bone and withstands tension."),
  bullet("Similar to ligaments (bone-to-bone) and fasciae (muscle-to-muscle); all made of collagen"),
  bullet("Histology: dense regular CT fascicles in dense irregular CT sheaths"),
  bullet("~86% collagen, 2% elastin, 1-5% proteoglycans, 0.2% inorganic components"),
  bullet("Tenocytes produce collagen fibrils; communicate via gap junctions"),
  bullet("Tendon injuries can cause tendinopathies - inflammation, degeneration, risk of rupture"),

  sectionBreak(),

  // =============================================
  // SECTION 5: SUMMARY TABLE
  // =============================================
  heading1("SECTION 5: QUICK REFERENCE SUMMARY"),

  heading2("5.1 Three Types of Cartilage - Comparison"),
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