TISSUES
STRUCTURAL ORGANIZATION
 Life is characterized by hierarchical orders
of organization
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Atoms
Molecules
Organelles
Cells
Tissues
Organs
Organ systems
Organism
(Population)
(Community)
(Ecosystem)
STRUCTURAL ORGANIZATION
 The cell is the lowest level of organization that can live
independently as an organism
STRUCTURAL ORGANIZATION
 In multicellular organisms, specialized cells are
grouped into tissues
 A tissue is a group of cells similar in structure and
performing a common function
 Organs are comprised of
combinations of various
tissues
 Organ systems include
multiple organs working
together
INTERCELLULAR JUNCTIONS
Neighboring cells within a multicellular
organism often adhere, interact, and
communicate through intercellular junctions
 Tight junctions
 Desmosomes
 Gap junctions
INTERCELLULAR JUNCTIONS
TISSUE TYPES
Four major tissue types
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
EPITHELIAL TISSUE
Sheets of cells covering body surfaces or lining
body cavities
Form boundaries between different
environments
 e.g., Epidermis of skin separates inside and outside
of body
 e.g., Epithelium lining urinary bladder separates
underlying cells from urine
EPITHELIAL TISSUE
Many diverse functions
 Protection
 Absorption
 Filtration
 Excretion
 Secretion
 Sensory reception
CLASSIFICATION OF EPITHELIA
Cell layers
Simple epithelia
 Single cell layer
 Facilitates absorption
and filtration
Stratified epithelia
 Two or more cell layers
 Common in highabrasion areas
 e.g., Skin surface, mouth
GLANDULAR EPITHELIA
A gland consists of one or more cells that
produce and secrete a product (secretion)
 Secretion: verb and noun
Endocrine vs. exocrine
Unicellular vs. multicellular
ENDOCRINE GLANDS
“Ductless glands”
 (Ducts are eventually lost)
Produce hormones
 Secreted directly into extracellular space via
exocytosis
Many (but not all) are epithelial derivatives
More information in their own chapter
EXOCRINE GLANDS
More numerous than endocrine glands
Secrete into body cavities or onto body surfaces
 (i.e., Not into extracellular space)
 Unicellular glands via exocytosis
 Multicellular glands via ducts
Diverse
 e.g., Mucous, sweat, oil, and salivary glands, etc.
EXOCRINE GLANDS
Multicellular Glands: Structural Classification
Simple
Compound
Tubular
Alveolar (acinar)
Tubuloalveolar
CONNECTIVE TISSUE
Found everywhere in the body
 Most widely distributed primary tissue
Four main classes
 Connective tissue proper
 Cartilage
 Bone tissue
 Blood
CONNECTIVE TISSUE
Major functions
 Binding and support
 Protection
 Insulation
 Transportation
Which of these functions are accomplished by
bone and cartilage? Fat? Blood?
CONNECTIVE TISSUE
Common Characteristics
 Common origin
 All connective tissues
arise from mesenchyme
(an embryonic tissue)
 Degrees of vascularity
 Avascular
 poorly vascular
 highly vascular
 Extracellular matrix
 Largely composed of non-living extracellular
matrix
CONNECTIVE TISSUE
Three main structural elements
 Ground substance
 Fibers
 Cells
 Ground substance + fibers = matrix
TYPES OF CONNECTIVE TISSUE
Connective Tissue Proper
Two subclasses
 Loose connective tissue
 Areolar
 Adipose
 Reticular
 Dense connective tissue
 Dense regular
 Dense irregular
 Elastic
TYPES OF CONNECTIVE TISSUE
Cartilage
Three varieties
 Hyaline cartilage
 Elastic cartilage
 Fibrocartilage
TYPES OF CONNECTIVE TISSUE
Bone (Osseous Tissue)
 Matrix similar to cartilage
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More abundant collagen fibers
Inorganic calcium and phosphate salts (hydroxyapatite)
Rocklike hardness
Ability to support
& protect
TYPES OF CONNECTIVE TISSUE
Bone (Osseous Tissue)
 Osteoblasts produce organic portion of matrix
 Bone salts then deposited on & between fibers
 Osteoblasts  osteocytes
 Osteocytes reside in
lacunae within the
matrix
 Vascular
TYPES OF CONNECTIVE TISSUE
Blood
 Very atypical connective tissue
 Does NOT connect things
 Provides NO mechanical support
 Why is it considered
connective tissue?
 Derived from
mesenchyme
TYPES OF CONNECTIVE TISSUE
Blood
 Various types of cells
 Blood plasma is fluid matrix
 Plasma proteins are “fibers”
 Various functions
 Transportation
 Protection
MEMBRANES
Continuous multiple sheets comprised of
 Epithelium
 Underlying layer of connective tissue
Three types of covering and lining membranes
 Cutaneous
 Mucous
 Serous
These membranes are multicellular structures,
and are quite different from the plasma
membrane of a cell
CUTANEOUS MEMBRANES
a.k.a., “Skin”
Organ system
Consists of
 Keratinized stratified squamous
epithelium
 “Epidermis”
 Thick layer of dense irregular
connective tissue
 “Dermis”
Dry membrane
MUCOUS MEMBRANES
a.k.a., “Mucosae”
Line body cavities open to exterior
 e.g., digestive, respiratory, & urogenital tracts
“Wet” membranes
 Bathed in secretions or
urine
 Often adapted for
absorption and secretion
 Many secrete mucus
 Not all (urinary)
SEROUS MEMBRANES
 a.k.a., “Serosae”
 Moist membranes found in closed ventral body cavities
 Consist of
 Simple squamous epithelium (mesothelium)
 Thin layer of loose connective (areolar) tissue
 Name based on location
 Pleura of lungs
 Pericardium of heart
 Peritoneum of
abdominopelvic cavity
SEROUS MEMBRANES
 Produce serous fluid
 Blood filtrate + hyaluronic acid secreted by mesothelium
 Lubricates facing surfaces of parietal and visceral layers
NERVOUS TISSUE
 Main component of the nervous system
 Brain, spinal cord, and nerves
 Regulates and controls body functions
 Two main cell types
 Neurons
 Generate and conduct
nerve impulses
 Supporting cells
 Non-conducting cells
that support, insulate,
and protect neurons
MUSCLE TISSUE
Highly cellular
Well vascularized
Responsible for most types of body movement
Possess myofilaments
 Actin and myosin
Three types
 Skeletal muscle
 Cardiac muscle
 Smooth muscle
SKELETAL MUSCLE
Skeletal muscle cells
 a.k.a., “Muscle
fibers”
 Long, cylindrical
cells
 Multinucleate
 Striated
 Voluntary
SKELETAL MUSCLE
 Forms organs called skeletal muscles
 Packaged by sheets of connective tissue
 Attached to bones of skeleton
 Contract to pull on bones or skin
 Movement results
CARDIAC MUSCLE
 Found only in the wall of the heart
 Contractions propel blood through blood vessels
 Cardiac muscle cells
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“Myocytes”
Striated
Uninucleate
Branching
Involuntary
SMOOTH MUSCLE
 Found mainly in walls of hollow organs
 e.g., Intestines, esophagus, blood vessels, etc.
 Contractions squeeze substances through these organs
 No visible striations
 Smooth muscle cells
 Spindle shaped
 Uninucleate
 Involuntary
BODY DEFENSES
Mechanical barriers are the body’s first line of
defense against injury and infection
 Skin and mucous membranes
 Respiratory cilia
 Acids secreted into stomach and from skin
Tissue injury breaches this first line of defense
 Stimulates inflammatory and immune responses
 Second and third lines of defense, respectively
 Tissue is ultimately repaired
TISSUE REPAIR
Injured cells release growth factors
 Stimulate cells to divide and migrate
Two major tissue repair means:
 Regeneration
 Replacement of destroyed tissue with same type of tissue
 Fibrosis
 Replacement with fibrous connective tissue (scar tissue)
Type of repair dependent upon
 Type of tissue damaged
 Severity of injury
TISSUE REPAIR
The regenerative capacity of different tissues
varies widely
 Some tissues regenerate extremely well
 e.g., Epithelial, bone, areolar connective tissue, bloodforming tissue
 Some tissues have a moderate regenerative capacity
 e.g., Smooth muscle, dense regular connective tissue
 Some tissues have a weak regenerative capacity
 e.g., Skeletal muscle, cartilage
 Some tissues have a virtually no functional
regenerative capacity
 e.g., Cardiac muscle, nervous tissue
TISSUE REPAIR
In non-regenerative tissue and severe wounds,
damaged tissue is replaced by fibrosis
Resulting scar tissue is strong, but lacks
flexibility, elasticity, and function of normal
tissue