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The Tissue Level of Organization

 

 

Tissues and tissue types

      Tissues are:

    Collections of specialized cells and cell products organized to perform a limited number of functions

   Histology = study of tissues

      The four tissue types are:

    Epithelial

    Connective

    Muscular

    Nervous

 

Epithelial tissue

      Includes glands and epithelium

    Glands are secretory

      Is avascular

      Forms a protective barrier that regulates permeability

      Cells may show polarity

 

Functions of epithelium

      Physical protection

      Control permeability

      Provide sensation

      Produce specialized secretions

 

Specializations of epithelium

      Perform secretory functions

      Perform transport functions

      Maintain physical integrity

      Ciliated epithelia move materials across their surface

 

Maintaining the integrity of epithelium

      Cells attach via cell adhesion molecules (CAM)

      Cells attach at specialized cell junctions

    Tight junctions

    Desmosomes

    Gap junctions

 

Structure of typical epithelium

      Basal lamina attaches to underlying surface

    Lamina lucida

    Lamina densa

      Germinative cells replace short-lived epithelial cells

 

Classification of epithelia

      Number of cell layers

    Simple

    Stratified

      Shape of apical surface cells

    Squamous

    Cuboidal

    Columnar

 

Glandular epithelia

      Exocrine glands

    Secrete through ducts onto the surface of the gland

      Endocrine glands

    Release hormones into surrounding fluid

 

Glandular secretions can be:

      Merocrine (product released through exocytosis)

      Apocrine (involves the loss of both product and cytoplasm)

      Holocrine (destroys the cell)

 

Glands

      Unicellular

    Individual secretory cells

      Multicellular

    Organs containing glandular epithelium

    Classified according to structure

 


Connective Tissues

Connective tissue functions:

      Establishing a structural framework

      Transporting fluids and dissolved materials

      Protecting delicate organs

      Supporting, surrounding and interconnecting tissues

      Storing energy reserves

      Defending the body from microorganisms

 

Connective tissues contain

      Specialized cells

      Matrix

     Composed of extracellular protein fibers and a ground substance

 

Connective tissue proper

      Contains varied cell populations

      Contains various fiber types

      A syrupy ground substance

 

Fluid connective tissue

      Contains a distinctive cell population

      Watery ground substance with dissolved proteins

      Two types

    Blood

    Lymph

 

Supporting connective tissues

      Less diverse cell population

      Dense ground substance

      Closely packed fibers

      Two types

    Cartilage

    Bone

 

Connective tissue proper

      Contains fibers, a viscous ground substance, and a varied cell population

    Fibroblasts

    Macrophage

    Adipocytes

    Mesenchymal cells

    Melanocytes

    Mast cells

    Lymphocytes

    Microphages

 

Connective tissue proper

      Three types of fiber

     Collagen fibers

     Reticular fibers

     Elastic fibers

 

Connective tissue proper

      Classified as loose or dense

      Loose

    Embryonic mesenchyme, mucous connective tissues

    Areolar tissue

    Adipose tissue

    Reticular tissue

      Dense

    Dense regular CT

    Dense irregular CT

 

 

Fluid connective tissues

      Distinctive collections of cells in a fluid matrix

      Blood

    Formed elements and plasma

   Red blood cells, white blood cells and platelets

    Arteries carry blood away, veins carry to the heart

    Capillaries allow diffusion into the interstitial fluid

      Lymph

    Interstitial fluid entering the lymphatic vessels

 

Supporting connective tissues

      Cartilage and bone support the rest of the body

      Cartilage

    Grows via interstitial and appositional growth

    Matrix is a firm gel containing chondroitin sulfate

    Cells called chondrocytes

    Cells found in lacunae

    Perichondrium separates cartilage from surrounding tissues

    Three types: hyaline, elastic and fibrocartilage

      Has osteocytes

    Depend on diffusion through canaliculi for nutrients

      Little ground substance

      Dense mineralized matrix

      Surrounded by periosteum


Membranes

Membranes are simple organs

      Form a barrier

      Composed of epithelium and connective tissue

      Four types

    Cutaneous

    Synovial

    Serous

    Mucous

 

Mucous membranes

      Line cavities that communicate with the exterior

      Contain lamina propria

 

Serous membranes

      Line sealed internal cavities

      Form transudate

      Cutaneous membrane

     Covers the body surface

      Synovial membrane

     Incomplete lining within joint cavities


The Connective Tissue Framework of the Body

Organs and systems are interconnected

      Network of connective tissue proper consisting of

    Superficial fascia

    Deep fascia

    Subserous fascia

 


Muscle Tissue

Muscle tissue

      Specialized for contraction

      Three types

    Skeletal

    Cardiac

    Smooth

 

Skeletal muscle

      Cells are multinucleate

      Striated voluntary muscle

      Divides via satellite cells

 

Cardiac muscle

      Cardiocytes occur only in the heart

      Striated involuntary muscle

      Relies on pacemaker cells for regular contraction

 

Smooth muscle tissue

      Non-striated involuntary muscle

      Can divide and regenerate

 


Neural Tissue

Neural tissue

      Conducts electrical impulses

      Conveys information from one area to another

 

Neural tissue cells

      Neurons

    Transmit information

      Neuroglia

    Support neural tissue

    Help supply nutrients to neurons

 

 

Neural anatomy

      Cell body

      Dendrites

      Axon (nerve fiber)

    Carries information to other neurons

 


Tissue Injuries and Aging

Inflammation and regeneration

      Injured tissues respond in coordinated fashion

      Homeostasis restored by inflammation and regeneration

 

Inflammatory response

      Isolates injured area

      Damaged cells, tissue components and dangerous microorganisms removed

    Infection avoided

      Regeneration restores normal function

 

 

Aging and tissue repair

      Change with age

      Repair and maintenance less efficient

      Structure altered

      Chemical composition altered

 

Aging and cancer incidence

      Incidence of cancer increases with age

      70-80% of all cases due to exposure to chemicals or environmental factors