Download - Histology - The Study of Tissues
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Histology - The Study of Tissues• Whole body contains ~200 different cells types• Four primary tissue classes
– epithelial tissue– connective tissue– muscular tissue– nervous tissue
• Histology (microscopic anatomy)– study of tissues and how they form organs
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Epithelial Tissue• One or more layers of closely adhering cells• Forms a flat sheet with the upper surface exposed to the
environment or an internal body cavity• Blood supply• Nerve supply• Sits on ___________________________
– thin layer of collagen and adhesive proteins– anchors epithelium to underlying connective tissue
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Connective Tissue• Consists of widely spaced cells separated by
fibers and ground substance• Most abundant and variable tissue type• Functions
– connects organs to each other– gives support & protection (physical & immune)– storage of energy & heat production– movement & transport of materials
• Ground substance - gelatinous material – Absorbs compressive forces– Slows pathogen spread
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3 Fibers of Connective Tissue• _______________ fibers
– tough, resist stretch yet flexible– locations?
• _______________ fibers– thin collagen fibers coated with glycoprotein– locations?
• Elastic fibers– thin branching fibers; stretch/recoil like rubberband– locations?
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Cells of Connective Tissue• Fibroblasts produce fibers & ground substance• Macrophages wander through connective tissue
phagocytizing foreign material & activating immune system -- arise from ___________________________
• Neutrophils wander in search of bacteria• Plasma cells synthesize antibodies – arise from
______________________• Mast cells secrete _________________________ &
_____________________• Adipocytes or fat cells store
_______________________
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Adipose Tissue
• Large, empty-looking cells with thin margins; nucleus pressed against cell membrane
• Energy storage, insulation, space filled as cushioning• Subcutaneous fat beneath skin & surrounding organs
– brown fat found in ________________ animals produces heat only no ATP
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Types of Fibrous Connective Tissue• Embryonic - mesenchyme• Loose connective tissue
– contains gel-like ground substance between cells• areolar• reticular• adipose
• Dense connective tissue – fibers dense• dense regular connective tissue• dense irregular connective tissue• elastic
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Intercellular Junctions
• All cells except blood are anchored to each other or to the matrix surrounding them by intercellular junctions
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Tight Junctions• Tight junctions completely encircle the cell
– zipperlike pattern of grooves & ridges– Prevents ________________________________– common in GI and
urinary tracts
Tight Junction enlarged
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Desmosomes• Patch between 2 cells holding them together against
mechanical stress– adjacent thick protein plaques connected by protein filaments– cytoplasmic intermediate filaments also attach to plaque
• Does not __________ the cell• Common in uterus,
heart and epidermis
Desmosome enlarged
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Gap Junctions• Known as _________________________ junctions
• Ring of 6 transmembrane proteins form a channel
• Small solutes pass directly from cell to cell
• Found in embryos, cardiac &smooth muscle
Gap Junction
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Endocrine & Exocrine Glands• Glands secrete substances for elimination or for use
elsewhere in the body– composed predominantly of epithelial tissue
• Exocrine glands use ________________________• Endocrine glands have ___________________• Mixed organs
– liver secretes bile into ducts + albumin into blood– gonads release gametes + secrete hormones into blood– pancreas secretes digestive enzymes + hormones
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Exocrine Gland Structure
• __________ = capsule & CT extensions called septa divide gland into lobes & lobules
• ____________________ = cells that synthesize the secretions
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Types of Exocrine Glands
• Simple glands have a unbranched duct• Compound glands have a branched duct
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Types & Modes of Secretion
• Serous glands– produce __________________________ secretions
• sweat, milk, tears & digestive juices
• Mucous glands– produce a glycoprotein, mucin that absorbs water to
form a sticky secretion called mucus• Mixed glands contain both serous & mucous cells• Variations in modes secretion (next)
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Holocrine Gland
• Secretory cells disintegrate in order to deliver their accumulated product & some cell fragments
• Oil-producing glands of the scalp are an example
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Merocrine & Apocrine Secretion
• Merocrine glands release their product by exocytosis– tears, gastric glands, pancreas, etc.
• Apocrine glands – mammary glands?
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Mucous Membranes
• Consists of epithelium, lamina propria & muscularis mucosae
• Lines passageways that open to the exterior• Mucous coating & movement of cilia trap & remove
foreign particles & bacteria from internal surfaces of body
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Synovial & Serous Membranes
• Synovial membrane lines joints (only connective tissue comprises this layer)– secretes synovial fluid rich in hyaluronic acid into the
joint • Serous membrane (_________) –internal membrane
– simple squamous epithelium and areolar tissue covers organs and walls of body cavities, produces serous fluid
– ____________________lines blood vessels and heart– mesothelium lines pleural, pericardial and peritoneal
cavities
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Changes in Tissue Types• Tissues are capable of changing from one type
to another• Differentiation
– unspecialized tissues of embryo to specialized mature types (mesenchyme to muscle)
• Metaplasia– changing from one type of mature tissue to another– Example : smoking
• Stem cells
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Tissue Growth
• Hyperplasia – rapid tissue growth through cell multiplication
• Hypertrophy – enlargement of preexisting cells– muscle cells grow through exercise
• Neoplasia – growth of a tumor (benign or malignant) through
growth of abnormal tissue
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Tissue Shrinkage and Death
• Atrophy is shrinkage from loss of cell size/number– due to aging or lack of use (leg in a cast)
• Necrosis is pathological death of tissue– gangrene is due to insufficient blood supply– bacterial infections and lack of blood
• Apoptosis is programmed cell death– cells shrink & are phagocytized (no inflammation)
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Tissue Repair• Damaged tissues are repaired in 2 ways:• Regeneration
– replacement of dead or damaged cells with original cells– restores normal function– skin injuries & liver regenerate
• Fibrosis– replacement of damaged cells with scar tissue (collagen)– helps hold organ together -- function is not restored– healing muscle injuries, scarring of lung tissue in TB or
healing of severe cuts & burns of the skin– keloid - healing w/excessive fibrosis (raised shiny scars)