Histology

1. Study of tissues -cells similar in structure and perform a common function • 4 types: • Epithelial • Connective • Muscle • Nervous Histology

2. What is necrosis? • Necrosis is tissue death. It occurs if the blood supply to an area is stopped for too long. When this happens the tissues die due to a lack of oxygen to the cells.

3. Preparing tissues for microscopy • Fixed – preserved • Artifacts – distortions not seen in living tissue • Sectioned – cut into slices thin enough light can pass through • Stained – organic dyes used to enhance contrast • Transmission electron microscopy (TEM) – uses electrons for detailed contrast • Scanning electron microscopy (SEM) – 3D pictures of tissue surface

4. Epithelial Tissue • Covers a surface or lines a cavity • Glandular epithelium – exocrine glands • Forms boundaries • Basement Membrane: Network of protein fibers that forms barrier between epithelium and connective tissue • Protection • Absorption – molecules pass into blood or lymph • Filtration – passage of solvent thru a membrane • Excretion – eliminate waste • Secretion – release aqueous solution • Sensory reception

5. Characteristics of Epithelium • Polarity • Apical surface – exposed • Microvilli • Increase surface area • Allow absorption and secretion • Cilia • Beat to move materials across surface • Basal Surface – attached • Basal lamina – adhesive glycoproteins • Specialized Contacts • Tight Junctions • Prevents passage of water and solutes • Interlocking membrane proteins • Basal adhesion belt binds cells together • Desmosomes • Durable interconnections • 2 types: • Button desmosomes- small disk • Hemidesmosomes – half button shape

6. More Characteristics of Epithelium • Supported by connective tissue • Reticular lamina – Extracellular collagen network • Avascular but innervated • No blood vessels, nutrients obtained from diffusion • Nerve supply • Regeneration • Cells are continually replaced • Epithelial cells only survive 1-2 days

7. Squamous Epithelium • Simple Squamous • Thin and flat cells, 1 Layer • Function: diffusion & filtration • Found: forms capillary walls (endothelium), lining air sacs of lungs, kidneys, lining body cavities (mesothelium) • Stratified Squamous • Thin and flat cells, More than 1 layer, most common epithelia • Function: protection • Found: in places of mechanical stress, skin surface, lining tongue, mouth, esophagus, and anus

8. Cuboidal Epithelium • Simple Cuboidal • Box shaped cells, 1 layer • Function: Secretion or absorption • Found: covering surface of ovaries, lining kidney tubules, salivary ducts, and pancreatic ducts • Stratified Cuboidal • Box shaped cells, 2 layers, rare • Function: strengthen lumen walls • Found: ducts of large sweat glands, salivary glands, mammary glands, and pancreas

9. Columnar Epithelial • Simple Columnar • Tall, rectangular cells, 1 layer • Function: absorption (microvilli) & secretion • Found: Lines stomach, intestinal tract, excretion ducts, gall bladder • Pseudostratified Columnar • Single layer irregularly shaped cells (looks like multiple layers) • Function: protection, secretion • Found: Lining respiratory passageways (ciliated), and auditory tubes

10. Transitional Epithelial Tissue • Transitional • 3-6 layers of rounded cells • Function: Withstands stretching • Found: Lines urinary bladder and portions of ureters and urethra

11. Exocrine Glandular Epithelia Exocrine glands: excrete secretions usually thru ducts onto surface • Unicellular • Goblet & mucous cells scattered among epithelial cells • Secrete mucin (glycoproteins & water) via exocytosis • Multicellular– Secretory sheet, classified by pattern of ducts • ex – mucin lining stomach Mode of Secretion: • Merocrine: via exocytosis • Ex. Skin Perspiration, Mucus Glands, Saliva, mammary glands (milk) • Apocrine: lose cytoplasm and secretory product • Ex. Mammary glands(lipids) • Holocrine – cell fills with secretion then bursts and dies • Ex. Sebaceous glands – oils from base of hair

13. Classification of Connective tissues: 3 Types • Connective Tissue Proper • Syrupy ground matrix • Ex. Loose (areolar, adipose) & Dense (tendons & ligaments) • Blood - Fluid Connective tissue • Cells suspended in watery ground substance w/dissolved proteins • CartilageSupporting Connective Tissue • Dense ground substance • (Hyaline, Elastic, Fibrocartilage) • Bone Supporting Connective Tissue

14. Connective Tissues • 3 Main Components • Specialized cells • Mostly nonliving extracellular matrix that surrounds cells • Protein Fibers – collagen, elastic, reticular • Ground Substance (fluid) – fills space between cells • Interstitial fluid, Cell Adhesion Proteins, Proteoglycans • Functions (vary widely) • Binding & Supporting - framework • Transport materials – fluid with dissolved material • Storing Energy– fat in adipose tissue • Insulating • Protect Organs

15. Connective Tissue Proper: Cell Types • Fibroblasts • Produce and maintain connective tissue fibers and ground substance • Local maintenance & repair • permanent • Macrophages • Defense: Engulf damaged cells and pathogens • Release chemicals to stimulate immune response • Fixed or migrating (reinforcement) • Adipocytes • Permanent fat cells store nutrients • Droplet of lipid pushes nucleus to side • Mast Cells • Mobile, found near blood vessels • Have vesicles filled with chemicals to be released after an injury or infection • Heparin -anticoagulant • Histamine – leaky capillaries • Proteases & other enzymes

16. Connective Tissue Fibers • Collagen • Long, straight, unbranched, flexible • Elastic • Protein – elastin • Wavy, branched, stretchy • Reticular Fibers • Thin, branching interwoven network

18. Ground Substance • Fills spaces between cells, surrounds fibers • Connective tissue proper – clear, colorless, syrupy to slow movement of pathogens

19. Loose Connective Tissue • Areolar Tissue • Contains all cells and fibers of connective tissue proper • Separates skin from muscles • Provides padding • Allows movement • Extensive blood supply • Adipose tissue-90% adipose cells • Behind eyes, kidneys, heart, abdomen, buttocks, and breasts • Reticular Tissue- dominated by reticular fibers • Lymph nodes, bone marrow, and spleen

20. What is the difference between white fat and brown fat? • White fat • Pale yellow in color • Found in adults • Used for insulation, long term energy storage, & cushion • Brown fat • Highly vascular, contains lots of mitochondria • Found in infants and young kids • Metabolically very active, breaks down lipids fast • Instead of absorbing energy, it releases heat to warm circulating blood to increase body temperature

21. Dense (Fibrous) Connective Tissue Consists of mostly collagen fibers • Dense Regular– collagen fibers are parallel to resist tension • Poorly vascularized • Tendons – connect skeletal muscle to bone • Aponeuroses – flat tendons (muscle to muscle or bone) • Ligaments – contain elastic fibers, connect bone to bone • Fascia – binds together muscles, bv, and nerves • Dense Irregular– meshwork of thick collagen fibers • Provides support in many directions (i.e. skin dermis) • Joint and organ capsules

22. Fluid Connective Tissues • Blood • Plasma- watery matrix w/dissolved proteins • Red blood cell (rbc) • White blood cells (wbc) • Platelets

23. Cartilage Supporting Connective Tissue: • Cartilage – gel w/embedded fibers • Chondrocytes – cells found in lacunae derived from chondroblasts • Avascular, therefore difficult to repair • Lacks nerves • Types: • Hyaline – tightly packed collagen fibers, tough but flexible • Connects ribs to sternum, supports passageways of respiratory tract, covers bone surfaces in joints, tip nose, embryonic skeleton • Elastic – elastic fibers, resilient and flexible • Flap of outer ear (pinna), epiglottis, auditory tube • Fibrocartilage – mostly collagen fibers, durable and tough • Between vertebrae, between pubic bones, around or within joints

24. Hyaline Cartilage Elastic Cartilage Fibrocartilage

25. Bone Supporting Connective Tissue: • Osseous tissue: Bone • Matrix – hard calcium and flexible collagen, very little ground substance • Osteocytes found w/in lacunae • Lacunae surround blood vessels • Canaliculi extend from central (Haversian) canal

26. Osseous Tissue

27. Muscle Tissue • Muscle tissue – interaction between the myofilaments myosin and actin create a contraction, highly vascular • Skeletal – striated voluntary muscle • Large, multinucleated cells (long and slender) • Incapable of dividing, but produced through stem cells • Striations (series of bands) • Only contract when stimulated by nerves • Cardiac – striated involuntary muscle • Smaller striated cells, single nucleus • Interconnected by intercalated discs • Limited ability to repair • Pacemaker cells establish a regular rate of contraction • Smooth – nonstriated involuntary muscle • Walls of blood vessels, hollow tube=like organs • Small, slender cells w/ one nucleus • Actin and myosin are scattered so no striations • Can be repaired • Can contract on own or by nervous system

28. Nervous Tissue • Specialized for conducting electrical impulses and responding to stimuli • 2 Types Cells: • Neurons – communicate thru electrical events • Neuralgia – physical support for neural tissue, supply nutrients to neurons • Long cells w/ 3main parts: • Cell body w/ nucleus • Dendrites – branching projections that receive info • Axon – long projection (w/synaptic terminals) relays info to other cells • Limited ability to repair

30. Membranes • Membranes - epithelia and connective tissues combine to form 4 types of membranes: • Mucous Membranes • Serous membranes • Cutaneous membranes • Synovial membranes

31. Cutaneous Membrane • Aka Skin – covers surface of body, thick, dry • Stratified squamous epithelium and underlying dense connective tissue

32. Mucous Membranes • Mucosae – line cavities with exterior contact • Digestive, respiratory, reproductive, and urogentitaltracts • Epithelial surfaces kept moist • Ex. • Simple columnar epithelia of dig. tract • Stratified squamous epithelia of mouth • Transitional epithelia of urinary tract

33. Serous Membranes • Minimizes friction when organ moves • Line internal subdivisions of ventral body cavity • Parietal – lines inner surface of cavity • Visceral – lines outer surface or organs • Simple epithelia supported by loose connective tissue • Pleura – covers pleural cavity and lungs • Peritoneum – lined abdominal cavity and associated organs • Pericardium – lines pericardial cavity and heart

34. Synovial Membranes • Lines articulation (joint) capsule • Loose connective tissue and incomplete layer of epithelial tissue • Produce synovial fluid for smooth movements

35. Mucous Membrane Serous Membrane Cutaneous Membrane Synovial Membrane

36. Tissue Injury and Repair • Inflammation • In response to pathogens, impact, abrasion, extreme temperatures, or chemical irritation • Mast cells release histamine and heparin that dilate blood vessels to induce swelling, warmth, redness and pain • Regeneration • Fibroblasts produce dense collagen fibers called fibrous tissue (scar tissue) • Fibrosis is the permanent replacement of normal tissues with fibrous tissue (i.e. heart and muscle tissues)

37. Tissues and Aging • Speed and effectiveness of tissue repair decreases with age (change of hormones and lifestyle) • Epithelia gets thinner, bones become brittle, cardiac muscle fibers and neurons cannot be replaced • Osteoporosis – inactivity, low calcium, and decrease in estrogen result in poor bone strength