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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
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