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long bones
- form of bone in most adult tissue
- has a long shaft made up of bone tissue whose ECM has both organic & mineral components
- has cartilage covering both ends (articular surfaces)
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What is the main source of the physical properties of bone and cartilage?
the extracellular matrix, specifically it's composition/arrangement
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Why are bones organs?
because they are made up of multiple types of tissues and have a blood supply
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What does bone have that adult cartilage doesn't?
bone has blood vessels, but adult cartilage is avascular
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hyaline (clear) cartilage
- covers the articular surfaces and is as a smooth (slippery) surface that's resilient in order to function as a shock absorber
- the surface articulates with the articular cartilage of an adjacent bone to form a joint
- in the presence of lubricating, synovial fluid, there's almost no friction between the two surfaces
- lots of embryonic cartilage starts out hyaline
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What are the two main components of hyaline cartilage?
- Collagen Type II fibrils (car-TWO-ladge)
- cartilage proteoglycan
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- hyaline cartilage
- amorphous matrix that consists of thin, unbanded collagen fibrils and proteoglycans (which look granules)
- has cells (chondrocytes) enclosed within lacunae, regions of the matrix
- chondrocytes are surrounded by avascular ECM w/ collagen II & aggrecan
- has territorial & interterritorial matrices & exhibits appositional & interstitial growth
- basophilic b/c chondroitin sulfates are present
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territorial & interterritorial matrices
- territorial matrix: proteoglycan-rich region outside the chondrocytes
- interterritorial matrix: area between the territorial matrices
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synovial fluid
fluid synthesized by synovium, the fibrous connective tissue surrounding a joint, that lubricates two articular surfaces that touch one another
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proteoglycan
molecules that consist of a protein core with glycosaminoglycan (GAG) side chains (usually chondroitin sulfate)
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relationship between proteoglycans and collagen
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aggrecan
- numerous proteoglycans bound to a long linear glycosaminoglycan (GAG) eg. hyaluronic acid
- proteoglycans = of core protein + GAG side chains (eg. chondroiten sulfate)
- other GAG = hyaluronic acid, what the individual proteoglycans are attached to
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fibril associated collagen
- Type IX (9) acts to stabilize collagen
- coats the surface of fibrillar collagen (type II) and cross-links with adjacent fibrils
- hypothesized that the degradation of these cross-links could contribute to degradation of the cartilage matrix as a whole and therefore cause conditions like arthritis
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fibrocartilage
- hybrid of hyaline + dense CT
- no perichondrium
- collagen I + collagen II
- chondrocytes + fibroblasts
- Interstitial growth
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What is this a picture of and what are the two arrows pointing toward?
- this is an electron micrograph of hyaline cartilage
- the leftmost arrow it pointing to a chondrocyte
- the arrow on the right is pointing toward the matrix
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Mature hyaline cartilage is mostly:
- MATRIX; chondrocytes are usually there as individuals
- mature hyaline cartilage picture
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What are the two types of hyaline cartilage growth?
- 1) interstitial growth: chondrocytes WITHIN the matrix divide, deposit more matrix between themselves, & gradually move apart
- 2) appositional growth: perichondrial cells transform into chondrocytes and synthesize cartilage matrix at the SURFACE of the cartilage
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perichondrium
- fibrous (DENSE) connective tissue over the surface of most cartilages (EXCEPT articular cartilages) that attaches the cartilage to adjacent tissue
- perichondrial cells are fibroblastic-like
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Why don't articular cartilages have a perichondrium?
because they need a smooth surface for frictionless contact
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What is the process shown in this picture and where is it occurring?
- this picture depicts clusters of 2 - 4 chondrocytes (called isogenic clusters) that form during interstitial growth
- cartilage in this stage is probably embryonic and rapidly growing
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Arthritis
- an irreversible destruction of cartilage matrix (and sometimes adjacent bone)
- matrix metalloproteinases (MMPs) & enzymes stimulated by inflammatory cytokines degrade cartilage proteoglycans
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What are the two general forms of arthiritis?
- osteoarthritis (OA): comes from general wear & tear
- rheumatoid arthritis (RA): is an autoimmune disorder
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Matrix Metalloproteinases (MMPs)
proteins that have a metal component and break down matrixes
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What disease state is this picture depicting?
- the large pink blobs are the only cartilage that remains
- can also see some multinucleated cells that will eventually break down the cartilage
- symptoms = joint pain, stiffness, swelling --> muscle weakness
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rheumatoid arthritis (RA)
- systemic autoimmune, inflammatory disease characterized by chronic joint inflammation and destruction of bone/articular cartilage.
- synovium is thought to play a major role in the destructive processes (only a minor role in OA); it becomes enlarged and thickened due to the influx of monocytes/lymphocytes from circulation
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What is the majority of cartilage in adults? What are two other forms of cartilage?
- adults have mostly hyaline cartilage
- 1) elastic cartilage
- 2) fibrocartilage
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- arrows are pointing to Fibrocartilage
- has features of both dense connective tissue and cartilage matrix
- dense CT features: thick type I collagen fibers --> toughness
- cartilage matrix features: thin type II collagen fibrils + cartilage proteoglycan --> resiliency & flexibility
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Where is fibrocartilage found?
intervertebral discs & certain ligament attachments
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intervertebral discs
- consist of an outer ring of fibrocartilage (annulus fibrosis) & an inner gelatinous component (nucleus pulposus)
- structures that separate & cushion vertebrae in the spinal column from each other, and permit passage of nerves from the spinal cord to tissues the nerves innervate
- medical correlate: herniated or natural compression of a disc disrupts nerves
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- elastic cartilage
- connective tissue that has cartilage matrix components and a network of elastic fibers
- elastin makes the cartilage flexible and able to withstand repeated bleeding
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elastic cartilage has:
- a perichondrium w/ chrondrogenic cells
- is hyaline cartilage-like w/ branching elastic fibers (special stains)
- an avascular ECM
- territorial & interterritorial matrices; basophilia mainly due to chondroitin sulfates
- & appositional and interstitial growth
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Where is elastic cartilage found?
in the outer ear, epiglottis, larynx
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bone
- 1) term for a tissue consisting of specific cells (osteoblasts and osteocytes) & mineralized matrix arranged in ordered patterns
- 2) organ that has bone tissue as a major component as well as blood vessels and other tissue types (eg. hematopoietic and adipogenetic tissues
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What are the 3 principal functions of bones?
- 1) to provide a protective covering for the brain, spinal cord, & thoracic viscera
- 2) to provide rigid internal support for extremities
- 3) to store calcium that can be drawn on to meet metabolic needs
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osteoid
- newly synthesized, unmineralized, uncalcified bone matrix that is first to be laid down
- subsequently undergoes mineralization
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the extracellular matrix of bone has both:
- organic and inorganic components
- organic matrix is 95% type I collagen
- inorganic matrix is mostly hydroxyapatite (calcium-phosphate in a crystalline form)
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How can the restoration/reconstruction of bone be achieved?
- by implanting decalcified bone matrix (or certain components of bone matrix) into non-bone tissues
- matrix "induces" cells within responding tissue to undergo a complete sequence of endochondral bone formation
- BMPs (bone morphogenic proteins) are a class of molecule responsible for this induction
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osteoblasts (OB)
- synthesize and secrete unmineralized bone matrix (osteoid) [lays down/makes new bone]
- derived from mesenchyme
- they adopt a cuboidal shape and have an epithelial-like arrangement
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How do osteoblasts typically stain?
- basophilically b/c their cytoplasm contains an abundant amount of RER
- their nuclei are at one end & a large Golgi complex is sits between it and the cell's secretory surface
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What are the arrows pointing to?
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- osteocytes
- mature cells of bone tissue derived from osteoblasts buried within the bone matrix
- live in the lacunae of the bone matrix
- b/c they make fewer proteins than osteoblases they stain WEAKLY basophilic, w/ a small Golgi and sparse RER
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How do osteocytes communicate with osteocytes in adjacent lacunae?
- by extending cell processes through canaliculi, slender radiating channels
- in these channels cell processes make gap junctions with processes from the neighboring cells
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- osteoclast
- large, multinucleated giant cells derived from MONOCYTES that are responsible for bone removal & resorption
- they release acid (to remove mineral) and proteolytic enzymes (eg. MMPs to degrade collagen/other organic components)
- a region of tight adhesion keeps degradation localized
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Where are osteoclasts found during bone development?
- along the surface of spicules (pieces) of bone at sites where bone resorption is occurring
- oftentimes this is on the side of the spicule opposite the side where osteoblasts are depositing new bone
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What are the different regions of long bones?
- Epiphysis
- Metaphysis
- Diaphysis
- External surfaces
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Epiphysis
the end of the bone that has the articular cartilage, the 2o center of ossification, & the epiphysial disc
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Metaphysis
the funnel-shaped region starting with the spicules at the "bottom" of the epiphysial disc, and extending to the shaft (diaphysis) of the bone
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Diaphysis
- the walls of the central portion of a tubular bone
- the shaft (tubular portion) of the bone; metaphysis of one end to the metaphysis of the opposite end
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What can be found at the external surfaces of bone?
- either covered (over most of their surface) by a periosteum (dense connective tissue) or by cartilage (over their articular surfaces)
- they can also be bare (at the sites of attachments of ligaments and tendons)
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compact bone
extremely dense and found in the areas that require maximum support (eg. the wall of the shaft of a long bone)
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Spongy (cancellous) bone
- forms a porous meshwork consisting of branching and anastomosing delicate pieces of bone tissue called spicules or trabeculae
- it is generally located within their interior of a bone organ (eg. the medullary/marrow cavity)
- it doesn't have transverse canals b/c blood vessels can just move through open matrix
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Woven bone
- produced early in development & the early stage in fractures healing
- characterized by coarse interlaced collagen fiber bundles
- has more osteocytes than matrix (compared to lamellar bone)
- nourished by blood vessels in the adjacent connective tissue
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Lamellar bone
highly organized w/ collagen fibers in parallel sheets (lamellae)sheet fibers differ in orientation which imparts strength
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Haversian Bone
- highest order of bone – the most organized and biomechanically the strongest
- it consists of lamellar bone that is organized around blood vessels forming cylindrical, structural units called Haversian systems (osteons)
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haversian systems/osteons
- lamellae arranged concentrically around longitudinal vascular channels called Haversian canals
- within lamella collagen fibers changes orientation which imparts structural strength to the osteon (and to the bone tissue overall)
- through the Haversian canal at the center of each osteon is part of the vascular plexus that nourishes the bone
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Volkmann (transverse) canals
- transverse or oblique vascular channels that connect adjacent Haversian canals & communicating with the periosteum + marrow cavity
- only present in compact bone
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circumferential (outer and inner) lamellae
- occur as two types based on their location:
- outer are found just beneath the periosteum and encircle the entire bone
- inner are found immediately beneath the endosteum and encircle the marrow cavity
- the osteons and interstitial lamellae are “banded” by these circumferential lamellae for added strength
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interstitial lamellae
- angular regions of parallel lamellae that lie among neighboring osteons
- they're fragments of previously generated osteons that were partially replaced during bone reorganization
- they have no associated blood vessel channel
- they contain osteocytes within lacunae and canaliculi, which connect to adjacent osteons
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Periosteum
- a tough layer of dense connective tissue called the periosteum that surrounds the outer surface of bone organs, EXCEPT at the articular surfaces
- it's firmly attached to bone tissue by Sharpey fibers, bundles of penetrating collagen fibers
- the innermost cells of the periosteum can become osteoblasts if activated during growth or injury repair
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Endosteum
a layer of connective tissue that lines the bone surface facing the marrow (medullary) cavity; also contains cells that have osteogenic capability
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stem cells are available on:
ALL surfaces of bone tissue
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Where are the only places blood vessels are found in bone?
the Haversian, Volkmann canals, or bone marrow
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Bone tissue contains ____major types of cells. _________, _________, and _________ all come from the same mesenchymal precursors and are called bone-makers. _______ are derived from monocytes and is called bone-breaker.
- Bone contains 4 major types of cells
- osteogenic (osteoprogenitor) cells, osteoblasts, and osteocytes are all derived from mesenchyme
- osteoclasts: bone-breaker, derived from monocytes
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osteogenic (osteoprogenitor) cells
- mesenchymal stem cells that make bone tissue-producing cells
- they're located in the inner periosteum, endosteum, and various blood vessel canals that radiate throughout mature bone tissue
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Osteoporosis
- the loss of calcium from bone
- can occur due to a number of factors (eg. too much parathyroid hormone --> hyperparathyroidism)
- increased osteoclastic activity causes an imbalance in skeletal turnover; bone resorption exceeds bone formation
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Osteopetrosis
- GENETIC disorder that results from defective osteoclasts (bone resorption) characteized by dense, heavy bones
- overgrowth, thickening, & hardening of bones
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Where are transverse canals found?
- transverse canals are only present in compact bone (B.) because in spongy bone (A & C) blood vessels can just move through the open meshwork
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What type of cartilage does the perichondrium, a CT capsule containing fibroblast-like chondrogenic cells and type I collagen fibers, surround?
- Elastic & Tracheal cartilage
- NOT hyaline or fibrocartilage
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Elastic cartilage: looks very similar to hyaline but here there's branching which is NOT seen in hyaline)
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fibrocartilage: is striated, has a territorial matrix, and is basophilic, meaning it's making a lot of proteins (proteoglycans to be specific)
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You are asked to analyze an unknown sample of firm CT ECM using antibodies for collagens I-VII, fibrillin & some proteoglycans & GAGs. You find aggrecan, collagen II, and hyaluronan. Which of the following is most likely the source of your sample matrix?
hyaline cartilage
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All of the following are characteristics of each type of cartilage EXCEPT:
Extensive blood supply: cartilage is avascular
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