TISSUES

STRUCTURAL ORGANIZATION Life is characterized by hierarchical orders

of organization 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 JUNCTIONSNeighboring cells within a multicellular

organism often adhere, interact, and communicate through intracellular junctions Tight junctions Desmosomes Gap junctions

INTERCELLULAR JUNCTIONS

TISSUE TYPESFour major tissue typesEpithelial tissueConnective tissueMuscle tissueNervous tissue

EPITHELIAL TISSUESheets of cells covering body surfaces or lining

body cavitiesForm 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 TISSUEMany diverse functions

Protection Absorption Filtration Excretion Secretion Sensory reception

CLASSIFICATION OF EPITHELIACell layersSimple epithelia

Single cell layer Facilitates absorption

and filtration

Stratified epithelia Two or more cell layers

Common in high-abrasion areas e.g., Skin surface, mouth

GLANDULAR EPITHELIAA gland consists of one or more cells that

produce and secrete a product (secretion) Secretion: verb and noun

Endocrine vs. exocrineUnicellular 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 derivativesMore information in their own chapter

EXOCRINE GLANDSMore numerous than endocrine glandsSecrete 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 GLANDSMulticellular Glands: Structural ClassificationSimpleCompound

TubularAlveolar (acinar)Tubuloalveolar

CONNECTIVE TISSUEFound everywhere in the body

Most widely distributed primary tissueFour main classes

Connective tissue proper Cartilage Bone tissue Blood

CONNECTIVE TISSUEMajor functions

Binding and support Protection Insulation Transportation

Which of these functions are accomplished by bone and cartilage? Fat? Blood?

CONNECTIVE TISSUECommon 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 TISSUEThree main structural elements

Ground substance Fibers Cells

Ground substance + fibers = matrix

TYPES OF CONNECTIVE TISSUEConnective Tissue ProperTwo subclasses

Loose connective tissue Areolar Adipose Reticular

Dense connective tissue Dense regular Dense irregular Elastic

TYPES OF CONNECTIVE TISSUECartilageThree varieties

Hyaline cartilage Elastic cartilage Fibrocartilage

TYPES OF CONNECTIVE TISSUEBone (Osseous Tissue) Matrix similar to cartilage

More abundant collagen fibers Inorganic calcium salts Rocklike hardness Ability to support

& protect

TYPES OF CONNECTIVE TISSUEBone (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 TISSUEBlood Very atypical connective tissue

Does NOT connect things Provides NO mechanical support

Why is it considered connective tissue? Derived from

mesenchyme

TYPES OF CONNECTIVE TISSUEBlood Various types of cells Blood plasma is fluid matrix Plasma proteins are “fibers” Various functions

Transportation Protection

MEMBRANESContinuous 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 MEMBRANESa.k.a., “Skin”Organ system Consists of

Keratinized stratified squamous epithelium “Epidermis”

Thick layer of dense irregular connective tissue “Dermis”

Dry membrane

MUCOUS MEMBRANESa.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 TISSUEHighly cellularWell vascularizedResponsible for most types of body movementPossess myofilaments

Actin and myosinThree types

Skeletal muscle Cardiac muscle Smooth muscle

SKELETAL MUSCLESkeletal 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

“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 DEFENSESMechanical 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 REPAIRInjured cells release growth factors

Stimulate cells to divide and migrateTwo 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 REPAIRInflammation Injured cells, macrophages, and mast cells release

inflammatory chemicals Dilation and increased permeability of capillaries Plasma and leukocytes enter

injured area Plasma proteins form clot

Halts blood loss Isolates injured area Prevents spread of microbes Forms scab

TISSUE REPAIROrganization Blood clot replaced by granulation tissue

Capillaries Proliferating fibroblasts

Produce growth factors, collagen fibers

Pull margins of wound together

Macrophages Digest clot

Granulation tissue ultimately becomes scar tissue

TISSUE REPAIRPermanent Repair Surface epithelium begins to regenerate

Grows under scab Scab ultimately detaches Epithelium fully regenerated

Fibrous material beneath epithelium matures and contracts Scar tissue beneath

epithelium Scar may be visible or not

TISSUE REPAIRThe regenerative capacity of different tissues

varies widely Some tissues regenerate extremely well

e.g., Epithelial, bone, areolar connective tissue, blood-forming 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 REPAIRIn non-regenerative tissue and severe wounds,

damaged tissue is replaced by fibrosisResulting scar tissue is strong, but lacks

flexibility, elasticity, and function of normal tissue