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 Paramecium Amoeba

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 intracellular 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 high-abrasion 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” Produce hormones (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 Four main classes 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 More abundant collagen fibers Inorganic calcium salts 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 “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 Inflammation 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 REPAIR Organization 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 REPAIR Permanent 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 REPAIR The 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 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