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Chapter 5

Lecture Outline

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Histology

• Study of Tissues

• Epithelial Tissue

• Connective Tissue

• Nervous and Muscular Tissue

• Intercellular Junctions, Glands and Membranes

• Tissue Growth, Development, Death and Repair

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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

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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

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Embryonic Tissues

• Embryo begins as single cell– divides into many cells and layers (strata)

• 3 Primary germ layers– ectoderm (outer)

• forms epidermis and nervous system

– endoderm (inner) • forms mucous membrane lining GI tract and respiratory

system and digestive glands

– mesoderm (middle) becomes mesenchyme• wispy collagen fibers and fibroblasts in gel matrix• gives rise to muscle, bone, blood

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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

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Sectioning Solid Objects

• Sectioning a cell with a centrally located nucleus

• Some slices miss the cell nucleus

• In some the nucleus is smaller

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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.

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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

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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

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Simple Versus Stratified Epithelia

• Simple epithelium– contains one layer of cells– named by shape of cells

• Stratified epithelium– contains more than one layer– named by shape of apical cells

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Simple Squamous Epithelium

• Single row of flat cells• Permits diffusion of substances• Secretes serous fluid• Alveoli, glomeruli, endothelium, and serosa

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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

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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

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Pseudostratified Epithelium

• Single row of cells some not reaching free surface

– nuclei give layer stratified look

• Secretes and propels respiratory mucus

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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

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Keratinized Stratified Squamous

• Multilayered epithelium covered with dead squamous cells, packed with keratin– epidermal layer of skin

• Retards water loss and barrier to organisms

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Nonkeratinized Stratified Squamous

• Multilayered surface epithelium forming moist, slippery layer

• Tongue, oral mucosa, esophagus and vagina

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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

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Transitional Epithelium

• Multilayered epithelium surface cells that change from round to flat when stretched– allows for filling of urinary tract– ureter and bladder

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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

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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

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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 and lymph nodes

• Elastic fibers (yellow fibers)– thin branching fibers of elastin protein– stretch and recoil like rubberband (elasticity)– skin, lungs and arteries stretch and recoil

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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

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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

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Areolar Tissue

• Loose arrangement of fibers and cells in abundant ground substance

• Underlies all epithelia, between muscles, passageways for nerves and blood vessels

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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

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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

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Dense Regular Connective Tissue

• Densely, packed, parallel collagen fibers

– compressed fibroblast nuclei

• Tendons and ligaments hold bones together and attach muscles to bones

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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

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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

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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

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Elastic Cartilage

• Hyaline cartilage with elastic fibers • Provides flexible, elastic support

– external ear and epiglottis

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Fibrocartilage

• Hyaline cartilage with extensive collagen fibers (never has perichondrium)

• Resists compression and absorbs shock– pubic symphysis, meniscus and intervertebral discs

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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

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Bone Tissue (compact bone)

• Calcified matrix in lamellae around central canal• Osteocytes in lacunae between lamellae • Skeletal support; leverage for muscles; mineral

storage

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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

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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

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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

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Skeletal Muscle• Long, cylindrical, unbranched cells with

striations and multiple peripheral nuclei– movement, facial expression, posture, breathing,

speech, swallowing and excretion

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Cardiac Muscle• Short branched cells with striations and

intercalated discs– one central nuclei per cell

• Pumping of blood by cardiac (heart) muscle

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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

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Intercellular Junctions

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

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Tight Junctions• Encircle the cell joining it to surrounding cells

– zipperlike complementary grooves and ridges• Prevents passage between cells

– GI and urinary tracts

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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

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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

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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

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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

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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

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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

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Holocrine Gland

• Secretory cells disintegrate to deliver their accumulated product– oil-producing glands of the scalp

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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

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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

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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

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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

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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

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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)

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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)

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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)

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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

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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

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Wound Healing of a Laceration

• Clot forms• Scab forms on

surface• Macrophages

start to clean up debris

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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

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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