Wk 2: Basic Tissue Properties and Processes; Oral Mucosa

What is the smallest living unit of organization in the body?

cell

What is a tissue?

Group of cells with similar characteristics of form and function together: tissue

What forms an organ?

Collection of similarly specialized cells and tissues form: organ

What are the 4 basic histologic tissue types?

epithelial, connective, muscle, nerve

What is regeneration?

individual cells die and removed from tissue and new ones take their place for most tissue in the body - Natural renewal of tissue and organs

How does regeneration occur?

Occurs through growth and differentiation of new cells and intercellular substances

What oral tissue type does not undergo regeneration?

tooth enamel

What is injury?

alteration in environment that causes tissue changes

What may severe injury result in?

necrosis with its cell death

What atypical responses may result from less severe injury instead of healing?

hyperplasia, hypertrophy, atrophy

What etiologies may cause injury to orofacial tissue?

physical injury, chemical injury, infection, nutritional deficiency, toxicity

What is necrosis?

Irreversible cell injury and eventual cell death due to pathologic processes

What occurs during necrosis?

Uncontrolled cell death resulting in swelling of its organelles, plasma membrane rupture; eventual cell lysis with spillage of intracellular contents into surrounding tissue can lead to further tissue damage

How does necrosis differ from apoptosis?

Unlike programmed cell death that occurs with apoptosis from signals inside the cell, necrosis occurs due to overwhelming injury from outside the cell and is almost always associated with inflammation.

What innate or natural defenses protect against injury?

intact skin or oral mucosa that acts as physical barrier to injury; flushing action of tears and saliva removes foreign substances; components of both fluids also have antimicrobial activity; resident microbiota on the skin and within oral mucosa prevents pathogenic colonization; inflammation process and its white blood cells (WBCs); immune response activation

What is epithelium?

tissue type that covers and lines both external and internal body surfaces including vessels and small cavities

What functions can epithelium perform besides serving as a protective covering or lining?

tissue absorption, secretion, sensory and other specialized functions

What are the embryonic origins of epithelium of the skin and oral mucosa, respiratory and digestive tract, and urinary tract?

Both epithelium of the skin and oral mucosa: similar ectodermal origin; Those lining respiratory and digestive tract: endodermal origin; Those lining urinary tract: derived from mesoderm

What are the basic histologic properties of epithelium?

closely grouped polyhedral or multifaceted epithelial cells surrounded by very little or no intercellular substance or extracellular fluid; avascular having no blood supply of its own; cellular nutrition consisting of oxygen and metabolites diffuses from the underlying connective tissue

Why is epithelium highly regenerative?

its deeper germinal cells capable of reproduction by mitosis

What occurs to epithelial cells as they move from deeper germinal layers to the surface?

Usually also undergo cellular differentiation: as they move from deeper germinal layers to surface of the tissue to be shed or lost

What is an exception to the process of epithelial cellular maturation?

the junctional epithelium of the gingival sulcular region that is attached to the tooth surface

What structures join epithelial cells to each other and to nearby noncellular surfaces?

intercellular junctions: provided for by desmosomes except in more superficial layers; hemidesmosomes tightly join epithelial cells in some cases to nearby noncellular surfaces

Where is the basement membrane located?

between most epithelium and deeper connective tissue such as with both skin and oral mucosa

What are the 2 main categories of epithelium based on arrangement into layers of cells?

simple and stratified

What is simple epithelium and what are its types?

single layer of epithelial cells; simple squamous, simple cuboidal, simple columnar

What is simple squamous epithelium and where is it found?

flattened platelike epithelial cells - Lining blood and lymphatic vessels, heart, serous cavities as well as interfaces in lungs and kidneys

What is endothelium?

simple squamous epithelium lining of these vessels and serous cavities

What are important properties of endothelium?

Strong lining creates barrier between blood or lymph and surrounding tissue; spaces within connected endothelial cells where blood cells can move in and out of blood vessels as well as other substances

What is simple cuboidal epithelium and where is it found?

cube-shaped cells that line ducts of various exocrine glands such as those of salivary glands, also kidneys

What is simple columnar epithelium and where is it found?

rectangular cells such as in lining of other types of salivary gland ducts and gastrointestinal tract; as well as inner enamel epithelium of maturing tooth germ: whose cells become enamel-producing ameloblasts

Why is pseudostratified columnar epithelium considered a type of simple epithelium?

all cells line up to contact inner surface of basement membrane even if not all cells reach outer surface of the tissue

What type of epithelium is found in the respiratory mucosa of the nasal cavity?

ciliated pseudostratified columnar epithelium

What type of epithelium makes up most epithelium in the body and includes the superficial layer of both skin and oral mucosa?

stratified squamous epithelium

What are rete ridges or rete pegs?

extensions formed by epithelial tissue during interdigitation of outer epithelium with deeper connective tissue

What are the 2 forms of stratified squamous epithelium?

nonkeratinized or keratinized

What is keratin?

Tough fibrous as well as opaque and waterproof protein impervious to pathogenic invasion and resistant to friction

How is keratin produced?

Produced during maturation of keratinocytes as they migrate from near basement membrane to surface of keratinized tissue

What is turnover time?

time taken for cell to divide during mitosis and pass through entire width of tissue

How does cellular turnover of epithelium occur?

as newly formed deepest cells migrate superficially from formation near basement membrane

What are the turnover times of buccal mucosa and skin epithelium?

buccal mucosa has turnover time of 14 days; skin epithelium at 20-30 days

What causes a faster epithelial turnover time?

higher level of mitosis in deepest dividing cells near basement membrane

What is the basement membrane?

thin acellular structure always located between any type of epithelium and underlying connective tissue

What are the 2 layers of the basement membrane?

basal lamina and reticular lamina

What is the superficial layer of the basement membrane and what forms it?

basal lamina; Formed by epithelium

What attachment mechanisms are part of the basement membrane?

hemidesmosomes with attachment plaque as well as tonofilaments from epithelium and anchoring collagen fibers from connective tissue

What are the functions of connective tissue?

support, attachment, packing, insulation, storage, transport, repair, defense

How does connective tissue histology compare with epithelium?

connective tissue usually composed of fewer cells spaced farther apart and containing larger amounts of extracellular matrix between cells: except for adipose tissue

What are fibroblasts?

Most common cell - flat and elongated spindle-shaped cell with cytoplasmic processes at each end extending from surface of the cell

What do fibroblasts synthesize?

certain types of protein fibers and intercellular substance needed to sustain connective tissue

What changes can fibroblasts show due to aging and inactivity?

reduction in: intracellular fluid, mitochondria, rough endoplasmic reticulum

What is the most common type of collagen protein and where is it found?

type I collagen; Found in: teeth, lamina propria of oral mucosa, dermis of skin, skeletal bone, tendons, virtually all other types of connective tissue

Which cells are responsible for synthesis of type I collagen?

fibroblasts and osteoblasts which produce fibers and intercellular substance as well as bone such as the jaws respectively; And odontoblasts which produce dentin

What are elastic fibers and what ability do they give tissue?

composed of microfilaments embedded in protein elastin; Has ability to stretch and then to return to its original shape after contraction or extension

How is connective tissue classified according to consistency?

Soft: loose, dense, specialized; Firm: different types of cartilage; Rigid hard: bone; Fluid: blood with all its components as well as lymph

What are the dermis and hypodermis?

Dermis: connective tissue proper in skin found deep to epidermis; Hypodermis: subcutaneous tissue composed of loose connective tissue and adipose tissue even deeper to dermis

What is the periodontal ligament (PDL)?

dense connective tissue between alveolar bone proper of alveolar process (ABP) and tooth with its cementum (C)

What is adipose tissue?

specialized connective tissue as well as glandular tissue since regulates the body’s energy storage of lipids

What composes adipose tissue?

lipid-containing adipocytes or fat cells along with large blood vessels and nerves

What is cartilage?

Firm but flexible nonmineralized type of connective tissue in the body

What composes cartilage?

cells and matrix; surrounding medium: mostly collagen fibers and intercellular substance

What is the perichondrium?

fibrous connective tissue sheath containing blood vessels

How does avascular cartilage receive its nutrition?

from this associated surrounding tissue

What are the 2 types of cells found in cartilage and their functions?

immature chondroblasts: produce cartilage matrix internal to perichondrium and mature chondrocytes: maintain cartilage matrix

What are the 3 types of cartilage?

hyaline, elastic, fibrocartilage

How do hyaline, elastic, and fibrocartilage differ?

Hyaline cartilage: most common type found in the body and contains only collagen fibers as part of its matrix; Elastic cartilage: similar to hyaline: except has numerous elastic fibers in its matrix in addition to its numerous collagen fibers; Fibrocartilage: never found alone and merges gradually with its adjacent hyaline cartilage: such as in outer part of bones of TMJ

What are the 2 ways cartilage can develop or grow in size?

interstitial growth and appositional growth

What is interstitial growth?

growth from deep within the tissue by mitosis of each chondrocyte; Producing larger numbers of daughter cells within single lacuna (each of which secretes more matrix) and expanding the tissue

What properties of cartilage affect its response to trauma or surgery?

cartilage has some flexibility resulting from its fibers in matrix; has no inorganic or mineralized materials; avascular; depends on its surrounding connective tissue for its cellular nutrition; has no nerve supply within its tissue

What are the functions of bone?

protective and structural support for soft tissue and as attachment mechanism; aids in movement; manufactures blood cells through its red bone marrow; energy bank through its yellow marrow; storehouse for calcium and other minerals

Why does bone repair quickly compared with cartilage?

Because bone vascularized with its own blood supply: repairs quickly compared with avascular cartilage

What is the periosteum and what are its layers?

double-layered dense connective tissue sheath; Outer layer: contains blood vessels and nerves; Inner layer: contains single layer of bone-forming cells osteoblasts

What structures are found deep to the periosteum?

Deep to periosteum dense layer: compact bone; Deep to compact bone: spongy bone or cancellous bone

What is the endosteum?

Lining medullary cavity of bone on inside of layers of both compact bone and cancellous bone; Has same composition as periosteum: but thinner layer

What is bone marrow according to the source?

Gelatinous substance where: stem cells of the blood located, lymphocytes created, B cells mature

What is the composition of mature bone matrix?

cells and partially mineralized matrix 60% inorganic mostly calcium hydroxyapatite (Hap) that gives bone its hardness; collagen fibers and intercellular substance packed between bone cells and bone matrix

What is osteoid?

Bone matrix initially produced: later undergoes mineralization

What produces osteoid and assists in its mineralization?

Osteoid produced by osteoblasts: cuboidal cells that come from fibroblasts; Osteoblasts also involved in later mineralization of osteoid to produce bone

What are osteocytes and lacunae?

Osteocytes: present within fully mineralized bone: which later will form mature entrapped osteoblasts by surrounding bone; Cell body of osteocyte surrounded its product bone except for space immediately around it: lacuna

What are canaliculi?

tubular canals of bone matrix containing cytoplasmic processes of osteocyte; Canals provide for interaction between osteocytes

What are lamellae, the Haversian system, and Haversian canal?

Bone matrix in compact bone formed into closely apposed sheets: lamellae; Highly organized arrangement of concentric lamellae in compact bone: Haversian system; Haversian canal: central canal within each osteon surrounded by lamellae

What does the Haversian canal contain?

longitudinally running blood vessels, nerves with small amount of connective tissue lined by endosteum

What are the 2 methods of bone development?

intramembranous and endochondral ossification

What is intramembranous ossification and what bones are formed by it?

production of osteoid between 2 dense connective tissue sheets eventually replaces outer connective tissue; Maxilla and most of mandible formed by intramembranous ossification

What is endochondral ossification and what part of the jaw is formed by it?

production of osteoid within hyaline cartilage model that subsequently becomes mineralized and cells undergo death; Head of mandibular condyle of lower jaw formed by endochondral ossification with its multidirectional growth capacity

What occurs during bone remodeling throughout life?

bone in the body: constantly being remodeled or regenerated; Bone undergoes removal in certain areas and new bone production occurs in other areas; With 2 processes balancing each other within healthy body

How does orthodontic therapy move teeth through bone remodeling?

Appliances during bioefficient orthodontic therapy put pressure on one side creating zone of compression in periodontal ligament on opposite side, which leads to bone resorption. On same side, zone of tension develops causing deposition of new bone.

What is blood?

fluid type of connective tissue that serves as transport medium for cellular nutrients

What does plasma carry?

plasma proteins, blood cells, metabolites; water, salts, and enzymes; nutrients, hormones, and proteins

What is serum?

fluid product distinguished from plasma from which it is derived due to removal of clotting proteins

What is the most common cell in the blood and what are its characteristics?

red blood cell (RBC) or erythrocyte; Biconcave disc that contains hemoglobin which binds then transports oxygen and carbon dioxide; Has no nucleus; Does not undergo mitosis

What are platelets or thrombocytes?

smaller than RBCs and disc-shaped; Have no nucleus; Function in clotting mechanism; not considered true blood cells but instead fragments of bone marrow cells (or megakaryocytes)

What are WBCs and what are the 5 types?

white blood cell (WBC) or leukocyte; involved in defense mechanisms of the body including inflammation and immune response; neutrophils, lymphocytes, monocytes, eosinophils, basophils

What are the hematocrit and buffy coat in centrifuged blood?

RBCs settle to bottom: because also denser than rest as fraction: hematocrit; WBCs along with platelets form intermediately-placed buffy coat with plasma fraction superior

What is the most common WBC in the blood?

neutrophil or polymorphonuclear (PMN) leukocyte

What percentage of the total blood WBC count is made up of PMNs and what is their main function?

54-62%; Main function phagocytosis: including pathogenic microorganisms and tissue debris

Which blood cells are the first to appear at an injury site when the inflammatory response is triggered?

PMNs

What happens to PMNs after phagocytosis?

Individually undergo apoptosis shortly after phagocytosis

What is the 2nd most common WBC in blood and what percentage of WBC count does it make up?

lymphocyte; 25-33% of WBC count

What are the 3 types of lymphocytes?

B cell, T cell, natural killer cell