Histology: The Study of Tissues

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Chapter 4

• 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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Membranes

• Mucous
• Line cavities that open to the outside of body
• Secrete mucus
• Serous
• Line cavities not open to exterior
• Pericardial, pleural, peritoneal
• Synovial
• Line freely movable joints
• Produce fluid rich in hyaluronic acid

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Inflammation

• Response when tissues damaged or with an immune
  response
• Manifestations
• Redness, heat, swelling, pain, disturbance of
  function
• Mediators
• Include histamine, kinins, prostaglandins,
  leukotrienes
• Stimulate pain receptor and increase blood vessel
  permeability

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Tissue Repair

• Substitution of viable cells for dead cells
• Skin repair
• Primary union Edges of wound close together
• Wound fills with blood
• Clot forms
• Scab
• Pus
• Granulation tissue
• Scar
• Secondary union Edges of wound not close
• Clot may not close gap
• Inflammatory response greater
• Wound contraction occurs leading to greater
  scarring

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Tissue Repair
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Tissues and Aging

• Cells divide more slowly in older than younger
  people
• Tendons and ligaments become less flexible and
  more fragile
• Arterial walls become less elastic
• Rate of blood cell synthesis declines in elderly
• Injuries are harder to heal in elderly