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- 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)
What is the main source of the physical properties of bone and cartilage?
the extracellular matrix, specifically it's composition/arrangement
Why are bones organs?
because they are made up of multiple types of tissues and have a blood supply
What does bone have that adult cartilage doesn't?
bone has blood vessels, but adult cartilage is avascular
What's the dark area?
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
What are the two main components of hyaline cartilage?
- Collagen Type II fibrils (car-TWO-ladge)
- cartilage proteoglycan
- 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
territorial & interterritorial matrices
- territorial matrix: proteoglycan-rich region outside the chondrocytes
- interterritorial matrix: area between the territorial matrices
fluid synthesized by synovium, the fibrous connective tissue surrounding a joint, that lubricates two articular surfaces that touch one another
molecules that consist of a protein core with glycosaminoglycan (GAG) side chains (usually chondroitin sulfate)
relationship between proteoglycans and collagen
- 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
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
- hybrid of hyaline + dense CT
- no perichondrium
- collagen I + collagen II
- chondrocytes + fibroblasts
- Interstitial growth
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
Mature hyaline cartilage is mostly:
- MATRIX; chondrocytes are usually there as individuals
- mature hyaline cartilage picture
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
- 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
Why don't articular cartilages have a perichondrium?
because they need a smooth surface for frictionless contact
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
- an irreversible destruction of cartilage matrix (and sometimes adjacent bone)
- matrix metalloproteinases (MMPs) & enzymes stimulated by inflammatory cytokines degrade cartilage proteoglycans
What are the two general forms of arthiritis?
- osteoarthritis (OA): comes from general wear & tear
- rheumatoid arthritis (RA): is an autoimmune disorder
Matrix Metalloproteinases (MMPs)
proteins that have a metal component and break down matrixes
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
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
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
- 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
Where is fibrocartilage found?
intervertebral discs & certain ligament attachments
- 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
- 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
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
Where is elastic cartilage found?
in the outer ear, epiglottis, larynx
- 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
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
- newly synthesized, unmineralized, uncalcified bone matrix that is first to be laid down
- subsequently undergoes mineralization
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)
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
- 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
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
What are the arrows pointing to?
- 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
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
- 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
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
What are the different regions of long bones?
- External surfaces
the end of the bone that has the articular cartilage, the 2o center of ossification, & the epiphysial disc
the funnel-shaped region starting with the spicules at the "bottom" of the epiphysial disc, and extending to the shaft (diaphysis) of the bone
- 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
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)
extremely dense and found in the areas that require maximum support (eg. the wall of the shaft of a long bone)
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
- 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
highly organized w/ collagen fibers in parallel sheets (lamellae)sheet fibers differ in orientation which imparts strength
- 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)
- 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
Volkmann (transverse) canals
- transverse or oblique vascular channels that connect adjacent Haversian canals & communicating with the periosteum + marrow cavity
- only present in compact bone
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
- 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
- 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
a layer of connective tissue that lines the bone surface facing the marrow (medullary) cavity; also contains cells that have osteogenic capability
stem cells are available on:
ALL surfaces of bone tissue
Where are the only places blood vessels are found in bone?
the Haversian, Volkmann canals, or bone marrow
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
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
- 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
- GENETIC disorder that results from defective osteoclasts (bone resorption) characteized by dense, heavy bones
- overgrowth, thickening, & hardening of bones
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
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
Elastic cartilage: looks very similar to hyaline but here there's branching which is NOT seen in hyaline)
fibrocartilage: is striated, has a territorial matrix, and is basophilic, meaning it's making a lot of proteins (proteoglycans to be specific)
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?
All of the following are characteristics of each type of cartilage EXCEPT:
Extensive blood supply: cartilage is avascular