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