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Chapter 4
Histology: The Study of
Tissues
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Tissues and Histology
• Tissues are collections of similar cells and
the substances that surround them.
• Tissue Level of Organization
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Epithelial
Connective
Muscle
Nervous
• Histology: Microscopic Study of Tissues
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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
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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
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Loose
Dense
Connective tissue with special properties
Cartilage
Bone
Blood
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Loose Connective Tissue
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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
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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
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