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Histology: The Study of Tissues

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Tissues and Histology

• Tissue Level of Organization– Epithelial – Connective– Muscle– Nervous

• Histology: Microscopic Study of Tissues

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Embryonic Tissue• Germ layers

– Endoderm• Inner layer

• Forms lining of digestive tract and derivatives

– Mesoderm• Middle layer

• Forms tissues as muscle, bone, blood vessels

– Ectoderm• Outer layer

• Forms skin and neuroectoderm

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Epithelium Characteristics

• Consists almost entirely of cells

• Covers body surfaces and forms glands

• Has free and basal surface

• Specialized cell contacts• Avascular• Undergoes mitosis

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Functions of Epithelia

• Protecting underlying structures

• Acting as barriers

• Permitting the passage of substances

• Secreting substances

• Absorbing substances

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Classification of Epithelium

• Simple– Squamous, cuboidal, columnar

• Stratified– Squamous, cuboidal, columnar

• Pseudostratified – columnar

• Transitional– Cuboidal to columnar when not stretched and

squamouslike when stretched

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Types of Epithelium

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Types of Epithelium

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Types of Epithelium

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Types of Epithelium

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Types of Epithelium

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Types of Epithelium

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Types of Epithelium

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Types of Epithelium

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Functional Characteristics• Cell layers and shapes

– Diffusion, Filtration, Secretion, Absorption, Protection

• Cell surfaces– Microvilli: Increase surface area absorption or

secretion

– Cilia: Move materials across cell surface

• Cell connections– Desmosomes, tight, gap

• Glands– Exocrine: Have ducts

– Endocrine: Have no ducts

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Cell Connections

• Functions– Bind cells together

– Form permeability layer

– Intercellular communication

• Types– Desmosomes

– Tight

– Gap

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Exocrine Glands

• Unicellular– Goblet cells

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Multicellular Exocrine Glands

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Exocrine Glands and Secretion Types

• Merocrine– Sweat glands

• Apocrine– Mammary

glands

• Holocrine– Sebaceous

glands

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Connective Tissue

• Abundant

• Consists of cell separated by extracellular matrix

• Diverse

• Performs variety of important functions

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Functions of Connective Tissue

• Enclosing and separating as capsules around organs

• Connecting tissues to one another as tendons and ligaments

• Supporting and moving as bones• Storing as fat• Cushioning and insulating as fat• Transporting as blood• Protecting as cells of the immune system

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Connective Tissue Cells• Specialized cells produce the extracellular matrix

– Suffixes• -blasts: create the matrix• -cytes: maintain the matrix• -clasts: break the matrix down for remodeling

• Adipose or fat cells• Mast cells that contain heparin and histamine• White blood cells that respond to injury or

infection• Macrophages that phagocytize or provide

protection• Stem cells

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Extracellular Matrix

• Components– Protein fibers

• Collagen which is most common protein in body

• Reticular fill spaces between tissues and organs

• Elastic returns to its original shape after distension or compression

– Ground substance• Shapeless background

– Fluid

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Connective Tissue Categories

• Embryonic or mesenchyme

• Adult– Loose– Dense– Connective tissue with special properties– Cartilage– Bone– Blood

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Loose Connective Tissue

• Also known as areolar tissue• Loose packing material of most organs and tissues• Attaches skin to underlying tissues• Contains collagen, reticular, elastic fibers and variety of cells

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Dense Connective Tissue• Dense regular

– Has abundant collagen fibers• Tendons: Connect muscles to bones

• Ligaments: Connect bones to bones

• Dense regular elastic• Ligaments in vocal folds

• Dense irregular• Scars

• Dense irregular collagenous• Forms most of skin dermis

• Dense irregular elastic• In walls of elastic arteries

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Dense Regular Connective Tissue

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Dense Irregular Connective Tissue

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Connective Tissue with Special Properties

• Adipose tissue– Consists of adipocytes

– Types• Yellow (white)

– most abundant, white at birth and yellows with age

• Brown– found only in specific areas of body as axillae, neck and near

kidneys

• Reticular tissue– Forms framework of lymphatic tissue

– Characterized by network of fibers and cells

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Adipose Tissue

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Reticular Tissue

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Cartilage

• Composed of chondrocytes located in spaces called lacunae

• Next to bone firmest structure in body

• Types of cartilage– Hyaline– Fibrocartilage– Elastic

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Hyaline Cartilage

• Found in areas for strong support and some flexibility– Rib cage and cartilage in trachea and bronchi

• Forms most of skeleton before replaced by bone in embryo

• Involved in growth that increases bone length

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Fibrocartilage

• Slightly compressible and very tough• Found in areas of body where a great deal of pressure

is applied to joints– Knee, jaw, between vertebrae

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Elastic Cartilage

• Rigid but elastic properties– External ears, epiglottis

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Bone

• Hard connective tissue that consists of living cells and mineralized matrix

• Organic and inorganic

• Types– Cancellous or spongy bone– Compact bone

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Bone

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Blood

• Matrix between the cells is liquid

• Hemopoietic tissue– Forms blood cells

– Found in bone marrow

• Yellow

• Red

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Bone Marrow

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Muscle Tissue

• Characteristics– Contracts or shortens with force– Moves entire body and pumps blood

• Types– Skeletal

• Striated and voluntary

– Cardiac• Striated and involuntary

– Smooth• Nonstriated and involuntary

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Skeletal Muscle

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Cardiac Muscle

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Smooth Muscle

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Nervous Tissue

• Found in brain, spinal cord and nerves

• Ability to produce action potentials

• Cells– Nerve cells or neurons

• Consist of dendrites, cell body, axons

• Consist of multipolar, bipolar, unipolar

– Neuroglia or support cells

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Neurons

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Neuroglia