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tissues
Collections of specialized cells that perform limited, yet specific functions
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histology
study of tissues
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List 4 Tissue types
- 1) Neural (2%)
- 2) Epithelial (3%)
- 3) Connective (45%)
- 4) muscle (50%)
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context: 4 tissue types
neural
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context: 4 tissue types
epithelial
- 3%
- covers inside & outside & forms glands
- epithelial =
- epithelia (cells covering external and internal surfaces): external (Body surface and lining of involutions; communicates with outside world) - skin, GI tract, respiratory tracts, urogenital tracts; internal (Lining of cavities and blood vessels & exocrine glands; does NOT communicate with outside world) - endothelium, mesothelium
- + glands (structures made of cells that produce secretions)
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4 functions of epithelial tissue
- 1. protection - Abrasion, dehydration, chemicals, biologicals
- 2. transport - Absorption or Excretion, Variable Permeability; tissue specific, Barrier influenced by
- hormones, mechanical stress
- 3. secretion - glands
- 4. provide sensation -large sensory nerve supply
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4 characteristics of epithelia
- 1. polarity- extracellular: apical (smooth or not) side has cilia to sweep debris in respiratory tract and microvilli is to increase surface area 20X in the digestive tract; lateral side contacts neighboring cells; basal side contacts 'underlying stuff'; basolateral side is the lower sides and bottom
- + Intracellular: organelles
- 2. avascular - lack blood vessels so get nutrients via diffusion or absorption from apical or basal
- 3. regenerative - replace lost or damaged (being scraped constantly) and continual division of stem cells
- 4. cell attachment: to attach to neighboring cells and to underlying 'stuff' via:
- a) intercellular cement: hyaluronic acid
- b) cell adhesion molecules - transmembrane proteins that tie the cytoskeleton (actin, microtubules) to the cytoskeleton of neighboring cells, proteins in the underlying extracellular matrix; can serve as receptors; contribute to cell junctions
- c) cell junctions - 4 types: tight, adherens, gap, desmosomes (button and hemi)
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context: 4 tissue types
connective
- 45%
- provides support for other tissues, transports material, energy storage
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2 categories of connective tissue
- 1. classic/proper: connects epithelium to the rest of the body
- 2. non-classic (fluid and supporting) : bone, blood, fat, lymph, cartilage
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context: 2 categories of connective tissue
classic/proper 3 components
- 1. cells - permanent resident: fibroblasts (MOST abundant and main source of ground substance and fibers), mesenchymal cells (C.T. stem cells and in epithelium and allows for regeneration), adipocytes (for energy storage, insulations, and shock absorbers); not permanent residents/varies: melanocytes (make and store pigments called melanin), immune cells (lymphocytes and macrophages)
- 2. ground substance - it is viscous (impedes movement), water soluble (diffusion of O2), and fill spaces between cells or cells and fibers
- 3. fibers - 3 types: collagen, elastic, reticular
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context: classic/proper 3 components
ground substance
- composed of proteoglycans (proteins + glycosaminoglycans)
- composition of the proteoglycans is varied in each CT type
- with 4 types of glycosaminoglycans:
- 1. hyaluronic acid - intracellular cement. Aggregates proteins (la brea tar pits for microbes), glue to hold cell together and impede bacteria
- 2. chondroitin sulfate - found in cartilage
- 3. dermatan sulfate - found in dermis
- 4. keratan sulfate - found in cornea
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context: classic/proper 3 components
fibers (3)
- 1. collagen
- 2. elastic
- 3. reticular
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context: classic/proper 3 components: 3 types of fibers
collagen
- MOST abundant protein in body (35%)
- with 40 different types of collagen molecules
- MOST abundant fiber: it is long, straight, unbranched, resistant to unidirectional stress, braided like rope making it stronger than steel, it will be the strength of ligaments and tendons.
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context: classic/proper 3 components: 3 types of fibers
elastic
- contain protein elastin
- it is branched and wavy fibers
- allowing for stretching and returning to original shape
- found in: vessels, alveoli, tendon, ligaments
- doesn't dominate in any one structure
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context: classic/proper 3 components: 3 types of fibers
reticular
- aka fibroblasts
- contain some protein subunits as collagen, but different arrangement
- synthesized by these reticular/fibroblasts cells
- function to resist forces applied from many directions
- forms an interwoven network called stroma
- common location/function: stabilize the functional cells (parenchyma) of organs, the position of b.v. & nerves within organs. Component of reticular tissue
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context: 2 categories of connective tissue of the nonclassic component
2 systems
- 1. blood in the circulatory system - matrix (connective tissue not bone): plasma + soluble fibers; cells: red blood cells to transport oxygen, platelets for clotting, white blood cells for immunity
- 2. lymph in the lymphatic system - matrix: lymph + soluble fibers; cells: white blood cells (lymphocytes) hang out in lymph nodes and monitor the body for infection
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6 functions of connective tissue (no exposure to outside environment)
vascular compared to epithelial
- 1. structural framework
- 2. connects different types of tissues
- 3. transports fluids/dissolved material
- 4. protection
- 5. storing energy
- 6. defense
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context: 4 tissue types
muscle
- 50%
- movement (active & passive)
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underlying stuff
- basal lamina (lamina lucida, lamina densa) of the basement membrane (basal lamina + reticular lamina connective tissue)
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3 classifications of CAMS (cell adhesion molecules)
- 1. cadherins - link cytoskeletons of neighboring cells
- 2. integrins - link the cytoskeleton to proteins in matrix
- 3. selectins -transient cell-cell binding in bloodstream
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4 types of cell junctions
- 1. tight junctions
- 2. adherens junctions
- 3. gap junctions
- 4. desmosomes
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context: 4 types of cell junctions
tight junctions
- -cell membranes of adjacent cells are tightly stitched together via interlocking proteins
- - no passage of water or solutes between cells: depends on the junctional proteins
- -limits movement of integral proteins
- Location: lateral surfaces
- ex: digestive tract, blood brain barrier
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context: 4 types of cell junctions
adherens junction
- -usually found in epithelial tissue, below a tight junction
- - an adhesion belt (Cadherins of CAM connect a web of cytoplasmic actin in cell #1 to a web of cytoplasmic actin in cell #2; actin of adjacent cells and cells can work together) encircles neighboring cells together
- Location: lateral surfaces
- ex: cardiac muscle, digestive tract
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context: 4 types of cell junctions
gap junctions
- allow for movement of small molecules and ions into adjacent cells and between cell membranes (via the gap)
- connexons: interlocking channel proteins that hold adjacent cells together at gap jxns; open to form a hydrophilic pore and allow passage of ions and small molecules
- Location: lateral surfaces of cells that require rapid intercellular communication
- ex: cardiac and smooth muscle, synapses
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context: 4 types of cell junctions
desmosomes
- cell subject to high mechanical stress (skin) that can stretch, bend, twist, compress
- Dense areas: concentration of CAM + intermediate filaments of cytoskeleton
- two types:
- 1. button: located on lateral surface; attaches adjacent cells via cadherins
- 2. hemi: "half desmosomes" located on basolateral surface; attaches cell to basal lamina via integrin
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2 types of classification of epithelia
- 1. shapes - flat vs cube vs column
- 2. # of layers - one (simple: located inside body so not for protection but for diffusion of "vitals"; location: lungs and blood vessels) vs many (stratified: protection is priority; location: body surface)
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4 types of epithelia cells
- 1. squamous - simple: most delicate, for absorption or excretion; located in line blood vessel (endothelium) and body cavity (mesothelium) - that doesn't communicate with the outside
- -stratified: increase mechanical stress, tough but need mechanical stress, tough but need to be kept moist; located in esophagus, anus, vagina + keratin = water resistance in skin.
- 2. cuboidal - simple: limited protection due to being only one layer, absorption, secretion; located in glands and ducts
- -stratified: RARE. more protective (where secretions can be more rough) because of more layers, absorption and secretion; located in ducts (sweat glands)
- 3. columnar - simple: protection from chemical insult, absorption and secretion, apical side typically have microvilli; located in intestines
- -pseudostratified: protection, absorption and secretion, apical side typically ciliated; located in bronchi
- -stratified: RARE. protection from low pH; located in urethra (due to urine)
- 4. transitional - tolerates repeated cycles of stretching/recoil; located in bladder (empty looks stratified, full looks simple)
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2 types of Glandular epithelia (yay finally!)
- 1. endocrine glands
- 2. exocrine glands
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context: 2 types of Glandular epithelia
endocrine glands
- aka "ductless glands"
- release secretions into interstitial fluid (surround fluid) --> bloodstream
- secretions: hormones into bloodstream
- location: thyroid, pituitary
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context: 2 types of Glandular epithelia
exocrine glands
- release secretions into ducts that open onto epithelial surface (NOT into the bloodstream)
- enzymes enter digestive tracts, sweat, tears, milk
- 3 classifications based on types of secretion
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context: exocrine glands
3 classifications of types of secretion
- 1. serous glands
- 2. mucous glands
- 3. mixed exocrine glands
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context: 3 classifications of exocrine glands
serous glands
- watery solution containing enzymes
- ex: parotid salivary glands
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context: 3 classifications of exocrine glands
mucous glands
- secrete mucins
- ex: submucosal gland of small intestine
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context: 3 classifications of exocrine glands
mixed exocrine glands
- contain >1 type of gland cell therefore produces 2 different secretions
- ex: serous and mucus, submandibular salivary glands
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goblet cells
- the ONLY unicellular gland with each cell producing secretions
- located: scattered in both simple and pseudostratified columnar epithelium
- function: secrete mucin glycoproteins for protection and lubrication
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4 types of Membranes
- membranes = epithelium + connective tissue
- 1. mucous
- 2. synovial
- 3. cutaneous
- 4. serous
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context: 4 types of Membranes
mucous membranes
- line passageways that communicate with outside digestive, respiratory, urogenital
- protected and moisturized via mucous (thicker secretion from glands)
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context: 4 types of Membranes
synovial membranes
- decrease friction between articulating bones (joints)
- it is lubricated by synovial fluid (ground substance)
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context: 4 types of Membranes
cutaneous membranes
- covers exterior of body surface
- thick, dry, and water resistant
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context: 4 types of Membranes
serous membranes
- line "sealed" body cavities and covers organs to minimize friction
- it is lubricated by transudate (thin blood)
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