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Histology
Microscopic structure and composition of tissues
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Histopathology
Study of both healthy and diseased tissue
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Histopathologist
A person who specialized in the study of both healthy and diseased tissue
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Epithelial tissue
- sheets of cells that cover all of the internal and external surfaces of the body and line all of the bodys cavities
- *Digestive tract, urinary tract and blood vessels*
- protect underlying tissues and may act to filter biochemical substances
- may absorb, secrete or excrete biochemical substances
- may play a role in the reception of sensory input
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Characteristics of Epithelia
- Each epithelial cell has an apical surface and a basal surface *apical surface faces the lumen or outside of the organ, basal surface faces the basal lamina and blood vessels*
- Lateral surfaces are connected to neighboring cells by junctional complexes
- Epithelial cells are avascular
- Most epithelial cells are innervated
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Cellular attatchments
- Tight juntions
- Desmosomes
- Gap junctions
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Tight Junctions
- Formed by the fusion of the outermost layers of the plasma membranes of adjoining cells
- Found in tissues which there can be no leaks (urinary bladder, digestive tract)
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Gap Junctions
- Tubular channel proteins (connexons) that extend from the cytoplasm of one cell to the cytoplasm of another
- Allow the exchange and passage of ions and nutrients
- Found in intestinal epithelial cells, the heart and smooth muscle tissue
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Basement Membrane
- Meshwork of fibers that cements the epithelial cell to the underlying connective tissue
- Also called the basal lamina
- Varies in thickness
- Helps prevent the cell from being torn off by intraluminal pressures
- Acts as a partial barrier between the epithelial cell and the underlying connective tissue
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Surface Specialization
- Surfaces of epithelial cells vary depending on where they are located and what role they play in the function of the tissue
- Smooth
- microvilli (brush border)
- cillia
- keratin
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Classification of epithelial tissue
- number of layers of cells *simple or stratified*
- shape of the cells *squamous, cuboidal and columnar*
- presence of surface specializations*cillia, keratin, etc.*
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Simple Squamous Epithelium
- fragile and thin
- found in the lining surfaces involved in the passage of either gas or liquid *lung, kidney*
- flat and smooth
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Simple Cuboidal Epithelium
- single layer of cube-shaped cells
- round, dark-staining nuclei aligned in a single row
- occurs in areas of the body where secretion and absorption take place*ovaries, thyroid, lining of ducts of the liver, pancreas, kidney, and salivary glands*
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Simple Columnar Epithelium
- Elongated and closely packed together
- nuclei aligned in a row at the base of the cell near the basement membrane
- found in may excretory ducts as well as the digestive tract
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Stratified Squamous Epithelium
- Multilayered
- occurs in areas of the body subject to mechanical and chemical stresses *lining of the mouth, esophagus, vagina and rectum*
- protects the underlying tissues
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Stratified Cuboidal Epithelium
- usually two layers of cuboidal cells
- found primarily along large excretory ducts*sweat glands, mammary glands,salivary glands*
- protects underlying tissues
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Stratified Columnar Epitheium
- sound only in select parts of the respiratory, digestive, reproductive systems and along some excretory ducts
- functions in secretion and protection
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Pseudostratified Columnar Epithelium
- cell nuclei are found at different levels across the length of the tissue
- some cells do not reach the luminal surface
- found in respiratory tract and in protions of the male reproductive tract
- *look like multi layered, they are not, still one layer*
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Transitional Epithelium
- stratified epithelium with a basal layer of cuboidal or columnar cells and a superficial layer of cuboidal or squamous cells
- found in areas of the body required to expand and contract as part of their normal function*bladder, urethra,ureters, calyxes of the kidney*
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Glandular Epithelium
- groups of cells that manufacture and discharge a secretion
- classification of glands is by
- 1- presence or absence of ducts,
- 2- number of cells that compose them, 3-shape of the secreting ducts,
- 4-complexity of the glandular structure,
- 5-type of secretion they produce
- 6-manner in which the secretion is stored and discharged
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Endocrine Glands
- glands that do NOT have ducts or tubules and whose secretions are distributed throughout the body
- produce and secrete hormones into the bloodstream or lymphatic system
- part of a complex biochemical network know as the endocrine system
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Exocrine glands
- discharge secretions via ducts directly into local areas (except for the goblet cell)
- unicellular or multicellular
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Goblet Cell
- unicellular exocrine gland
- ductless and composed of modified columnar epithelial cell
- found among columnar cells of the respiratory and digestive tracts and the conjunctiva of the eye
- secretes mucin - thick, sticky mixture of glycoprotiens and proteoglycans = mucus
- mucus functions in 2 ways, protect the apical surface of the epithelial layer and entrapment of microorganisms and foreign body
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Multicellular Exocrine Glands
- composed of a secretory unit and a duct
- secretory unit is usually surrounded by connective tussue rich in blood vessels and nerve fibers
- may be surrounded by myoepithelial cells that assist with the discharge of secretions into the glandular duct
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Classification of Exocrine Glands
- ducts
- -simple:the main duct in unbranched
- -compound:the main duct is branched
- shape of secretory portions
- -tubular:secretory cells form a long channel of even width
- -alveolar or acinar:secretory init forms a rounded sac
- -Tubuloalveolar or tubuloacinar:secretory units posses both tubular and alveolar qualities
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Classifications of exocrine glands
- merocrine glands package their secretions and release them via exocytosis as they are manufactured (the cells remain intact, only secrete at the top) pancreas, sweat glands, and salivary glands
- Apocrine glands store their secretions and then release the top part of the cell into the duct system(mammary tissue)
- Holocrine glands store their secretions and then release the entire contents of the cell, the entire cell is destroyed -move from the basal layer up (sebaceous glands)
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Types of secretions produced
- serous secretions
- -watery
- -contain a high concentration on enzymes
- mucous secretions
- -thich, viscous
- -compound of glycoproteins
- mixed exocrine glands contain both mucous and serous components
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Connective tissue Functions
- forms metabolic and structural connections between other tissues
- forms a protective sheath around organs and helps insulate the body
- acts as a reserve for energy
- provides the frame that supports the body
- composes the medium that transports substances from one region of the body to another
- plays a role in the healing process and in the control of invading microorganisms
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Connective tissue components
- extracellular matrix = extracellular fibers and ground substance
- cells
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Connective tissue components = Ground substance
- medium through which cells exchange nutrients and wast with the bloodstream
- amorphous, homogenous material
- ranges in texture from a liquid or gel to a calcified solid
- acts to protect the more delicate cells in envelopes
- serves as an affective obstacle for invading microorganisms
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Serous Membranes
- they line the walls and cover the organs
- the portion that lines the cavity wall = parietal
- the portion that covers the outer surface of the organs = visceral
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Serosal Fluid
its a transudate = able to pass through into the narrow spaces between the serosal layers
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Transudate in the...
- thorax = pleural fluid
- abdomen = peritoneal fluid
- heart = pericardial fluid
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Exudate
when cells, protein and other solid material mix with serous fluid, it becomes denser than a transudate
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Effusion
large amount of fluid enters a body cavity
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Ascites
effusion in the peritoneal space in the abdomenopelvic cavity
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Extracellular fibers - collagenous fibers
- strong, thick strands of collagen
- organized into bundles of long, PARALLEL fibrils composed of bundled microfibrils
- variable density and arrangement of fibers
- found in tendons and ligaments
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Extracellular fibers- reticular fibers
- thin, delicate, branched network of collagen
- provide support for highly cellular organs(endocrine glands, lymph nodes, spleen, bone marrow and liver)
- also found around blood vessels, nerves, muscle fibers and capillaries
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Extracellular fibers - elastic
- branched networks composed primarily of the protein elastin
- composed of coiled bundles of microfibrils
- occur in tissue commonly subjected to stretching (vocal cords, lungs, skin, walls of blood vessels)
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Connective Tissue Cell types
- Fixed cells = involved in the production and maintenance of the matrix (fibroblasts, chondroblasts, osteoblasts,adipocytes and reticular cells)
- Transient cells = involved in the repair and protection of tissue (leukocytes, mast cells, macrophages)
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Wandering Cells - cells that move in and out of connective tissue as needed
- 3 common types are...
- leukocyes
- mast cells
- macrophages
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Wandering cells
- leukocytes: found in blood and move into connective tissue in large numbers
- although larger than RBC, they squeeze through the walls of tiny blood vessels to enter the tissue - diapediesis
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Wandering cells:
- Mast cells: oval cells that are easily identified by the large dark-staining granules stored in the cytoplasm
- these granules contain histamine and heparin
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Wandering Cells:
- Macrophages: massive, irregular shaped phagocytizing scavangers
- engulf microbes, dead cells and debris that are subsequently digested in the macrophages lysosomes
- drawn to sites of infection and inflammation
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Kupffer cells
liver macrophages
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Microglial cells
brain macrophages
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Histocytes
connective tissue macrophages
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Dense Connective Tissue
- Dense regular
- Dense irregular
- Elastic
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Areolar Connective Tissue
- loose connective tissue
- fibers and cells suspended in a thick, translucent ground substance
- predominent cells is the fibroblast
- fibroblast manufactures the elastic, reticular and collagenous fibers
- surrounds every organ; forms the SQ layer that connects skin to muscle; envelopes blood vessels, nerves and lymph nodes; present in all MM
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Adipose Tissue
- loose connective tissue
- areolar tissue in which adipocytes predominate
- highly vascular
- acts as an energy storehouse and a thermal insulator
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Reticular Connective Tissue
- loose connective tissue
- network of thin reticular fibers and mainly fibroblasts suspended in a supportive ground substance
- forms the stroma (framework of several organs)
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Dense Regular Connective Tissue
- composed of tightly packed, paralled collagen fibers
- relitively avascular
- makes up tendons and ligaments
- can be found in fascial sheets that cover muscle
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Dense Irregular Connective Tissue
- Composed primarily of collagen fibers arranged in thick bundles
- fibers are interwoven to form a single sheet
- found in the dermis of the skin and in the fibrous coverings of many organs
- forms the tough capsule of joints
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Elastic Connective Tissue
- primarily composed of elastic fibers
- fibers may be arranged paralled or in interwoven patterns with fibroblasts and collagenous fibers interspersed
- found in spaces between vertebrae and in areas of the body that require stretching (walls of arteries, stomach, bronchi and bladder)
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Specialized Connective Tissue
- Cartilage - hyaline, elastic, fibrocartilage
- Bone
- Blood
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Cartilage
- found in joints and in the ear, nose and vocal cords
- forms a framework on which bone is formed
- Cells: chondrocytes live in the hollowed out pockets in the matrix called lacunae
- Matrix: ground substance is a gel made up of chondoitin sulfate, hyaluronic acid and chondronectin
- collagen fibers are most commonly found in the matrix, but elastic fibers are also present in varying amounts
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Hyaline Cartilage
- most common type of cartilage found in the body
- compsed of closely packed collagen
- found in joints at the ends of long bones, growth plates of long bones, tracheal rings and connections of the ribs to the sternum
- composes most of the embryonic skeleton
- enclosed within a perichondriium
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Elastic Cartilage
- contains elastic fibers in dense branching bundles
- flexible and can withstand repeated bending
- found in the epiglottis of the larynx and in the pinnea of the ears in animals
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Fibrocartilage
- usually found merged with hyaline cartilage and dense connective tissue
- contains thick bundles of collagen fibers with fewer chondrocytes than hyaline cartilage
- lacks a perichondrium; found in spaces between vertebrae of the spine, between bones in the pelvic girdle and int he knee joint
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Bone
- matrix is a combination of organic collagen fibers and inorganic calcium salts
- well vascularized
- haversian canal contains both a vascular and a nerve supply
- canaliculi are channels within the matrix that supports passage of blood vessels into deeper portions of tissue
- osteoblasts manufacture the fibers that are part of the matirx
- Lacunae and canaliculi are created as the osteoblasts manufacture the bony matrix
- osteocytes reside in the lacunae
- cellular extensions pass through the cabaliculi
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Blood
- Matix = ground substance = plasma, fibrous component = protein
- Cells = erythrocytes, leukocytes, thrombocytes
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Mucous Membranes = Mucosae
- line organs with connections to the outside environment ( mouth, intestines, nasal passages)
- usually composed of either stratified squamous or simple columnar epithelium covering a layer of loose connective tissue
- submucosa is the connective tissue layer that connects the mucosa to underlying structures
- may contain goblet cells or multicellular glands; can produce large quantites of mucus
- some mucosae also can absorb (the epithelial layer in the intestines)
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Serous Membranes = Serosae
- line walls and cover organs of the body cavities (thorax and abdomen)
- consists of a continuous sheet doubled over on itself to form 2 layers)
- the portion of the membrane that lines the cavity wall is called the PARIETAL layer
- the portion of the membrane that covers the outer surface of organs is called the VISCERAL layer
- in abdominopelivic cavity, visceral layers of serosa merge to form mesenteries
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Cutanous Membrane
- also called integument (skin)
- composed of an outer keratinized stratified squamous epithelium or epidermis
- epidermis is attatched to an underlying layer of dense irregular connective tissue called the dermis
- dermis contains collagenous, reticular and elastic fibers which enable skin to be both strong and elastic
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Synovial Membranes
- line the cavities of joints
- composed of loose connective tissue and adipose tissue covered by a layer of collagen fibers and fibroblasts
- manufacture the synovial fluid that fills the joint spaces
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Muscle Tissue
- composed of actin and myosin fibers
- 3 types of muscle tissue; skeletal, smooth, cardiac
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Skeletal Muscle
- large cells that contain hundreds of nuclei and mitochondria
- usually controlled through conscious efforts (VOLUNTARY MUSCLE)
- skeletal muscle cells are striated
- skeletal muscle cells are bundles of fibers held together by loose connective tissue
- the collagen fibers that surround the cells merge with the collagen fibers in tendons
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Smooth Muscle
- composed of small, spindle - shaped cells that lack striations
- muscle contractions cannot be consciously controlled (NONSTRIATED, INVOLUNTARY MUSCLE)
- found in walls of hollow organs, in endocrine glands and alongh the respiratory tract
- responsible for peristalsis in the GI tract, constrictions of blood vessels and emptying the urinary bladder
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Cardiac Muscle
- found only in the heart
- contains specialized pacemaker cells that supply the signal for the heart to contract at regular intervals
- entirely INVOLUNTARY AND STRIATED
- cardiac muscle cells connected to one another by intercalated disks (intercellular junctions)
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Nervous Tissue
- found in the brain, spinal cord and peripheral nerves
- composed of 2 general cell types; neurons and supporting neuroglial cells
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Neurons
longest cell in the body with three primary parts, 1 perikaryon=cell body containing the nucleus, 2 dendrites=short cytoplasmic extensions that receive nerve impulses, 3 axon=long, single extensions that conducts impulses away from the cell body
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Neuroglial cells
support the neurons
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Epithelial Tissue
- simple squamous
- simple cuboidal
- simple columnar
- stratified squamous
- stratified cuboidal
- stratified columnar
- transitional
- pseudostratified
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Connective Tissue
- Connective Tissue Proper: loose connective tisse = areolar, adipose and reticular tissue
- Dense Connective tissue: Dense regular, dense irregular and elastic
- Specialized Connective Tissue: cartilage = hyaline, elastic and fibrocartilage
- Bone: compact and cancellous
- Blood:
- Muscle tissue: skeletal(striated voluntary), cardiac (striated, involuntary), smooth ( nonstriated, involuntary)
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Tissue Healing and Repair
- Inflammation - the initial response to injuries in which the goal is to limit further damage and eliminate any harmful agents
- Repair - involves organization of granulation tissue and regeneration of lost tissue or formation of scar tissue
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Inflammation
- nonspecific reaction to injurty or disease
- steps: 1 vasodilation, 2 swelling, 3 clot formation,4 phagocytosis, 5 capillaries return to normal size, blood flow and fluid leakage into the affected area abate
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Formation of Granulation Tissue and Epithelialization
- tissues that form beneath the overlying flood clot or scabs
- compsed of a layer of collagen fibers infiltrated with capillaries (that have branched off existing capillaries in deeper layers of damaged tissue)
- granulation tissue is slowly replaced by fibrous scar tissue
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Classifiction of wound healing
- First Intention: egdes of wound held in close apposition, skin forms a primary union without formation of granulation tissue or significant scarring
- Second Intention: edges of wound seperated from eachother, granulation tissue forms to close the gap; scarring results
- Third Intention: contaminated would left open until contamination is reduced and inflammation subsides; later closed by first intention; also called delayed primary closure
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