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IMS: Microanatomy > Cartilage and Bone > Flashcards

Cartilage and Bone Flashcards

1
Q

Cartilage

A
  • Specialized connective tissue
  • Has a semi-rigid extracellular matrix that is highly hydrated and has viscoelastic properties
  • Predominantly avascular
  • Has a capacity for continued interstitial and appositional growth
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2
Q

Functions of Cartilage

A
  • Found in areas that require soft tissue support along with flexibility
    • Trachea
    • Larynx
    • Eustachian tube
    • External ear
    • Nose
  • Found in areas where needed as a developmental precursor for much of the skeleton
    • Bones that undergo endochondrial ossification
  • Found on joint surfaces, particularly in synovial joints ⇒ articular cartilage
    • Enhances movement
    • Cushions surfaces transmitting mechanical stress
    • Acts as a shock absorber
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3
Q

Types of Cartilage

A
  1. Hyaline Cartilage
    • Most common
    • Type II collagen
  2. Elastic Cartilage
    • Type II collagen and elastic fibers
  3. Fibrocartilage
    • Type I collagen
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4
Q

Perichondrium

A
  • Dense fibrous CT that surrounds hyaline and elastic cartilage structures except within joint capsules
    • Fibrocartilage has no perichondrium
  • Functions in the growth and maintenance of cartilage
  • Rich in Type I collagen fibers
  • Houses the vascular supply to cartilage tissue
  • In actively growing cartilage the perichondrium appears as a two layered structure
    • Outer layer
      • Fibrous
      • Poor in cells
      • Comprised primarily of fibroblasts and Type I collagen
    • Inner layer
      • Cellular
      • Composed of chondroblasts and chondrogenic cells
  • Chondroblasts associated with the perichondrium capable of producing new cartilage matrix through appositional growth
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5
Q

Chondrogenic Cells

A
  • Derived from mesenchymal cells
  • Can differentiate into chondroblasts
  • Found within the inner cellular layer of the perichondrium
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6
Q

Chondroblasts

A
  • Found within the inner layer of perichondrium
  • Responsible for secreting cartilage matrix at the surface of the cartilage
  • When they become completely surrounded by matrix they are known as chondrocytes
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7
Q

Chondrocytes

A
  • Cells occupy spaces called lacunae
  • With mitotic division tend to occur in groups of up to 8 cells called isogenous groups
  • Active chondrocytes by LM basophillic with perinuclear clear staining area representing the golgi zone
  • Mature active chondrocytes have the typical characteristics of a secretory cell
  • As cell ages become heterochromatic, lipid vacuoles accumulate, increased glycogen stores.
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8
Q

Cartilage Extracellular Matrix

A
  • Includes fibers, proteoglycans with sulfated GAGs, and adhesive glycoproteins
  • Forms a semi-firm gel
    • Basophillic and PAS + due to sulfated GAGs
    • Territorial marix
      • Directly surrounds chondrocytes
      • Higher concentration of sulfated GAGs and less water
      • More basophillic
    • Interterritorial matrix
      • Lighter staining
      • GAGs more dispersed
  • Fibers
    • Varys depending on cartilage type
    • Collagen forms ~ 50% dry weight of cartilage
  • Ground substance
    • Consists of sulfated GAGs for proteoglycans
    • Proteoglycans bound to hyaluronan core via link proteins to form aggrecan aggregates
  • Matrix is 60-80% water by weight because negatively charged GAGs attract water
    • Gives cartilage its resilience and compressive resistance
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9
Q

Cartilage Histogenesis

A
  • Most cartilage derived from the mesoderm
    • Except cartilage of the branchial arches which is dervied from neural crest ectoderm
  • Cartilage cells differentiate from mesenchyme into chondroblasts
  • Mesenchyme surround the developing cartilage becomes the perichondrium
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10
Q

Cartilage Nutrition

A
  • Most cartilage is avascular
    • Except very rapidly growing cartilage which may contain cartilage canals
      • House branches of the perichondrial vessels
  • Nutrients diffuse through intervening matrix
    • Limits the thickness of cartilage to a few mm
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11
Q

Cartilage Growth

A
  1. Appositional growth
    • Growth that takes place on inner surface of perichondrium along a free surface
    • Produces increase in size by adding material to the periphery
    • Mesenchymal cells → chondrogenic cells → chondroblasts → chondrocytes once enclosed by matrix
  2. Interstitial growth
    • Growth due to mitosis of chondrocytes within the matrix
      • Forms isogenous groups
    • Chondrocytes within an isogenous group grow and secrete matrix thus moving apart from one another
    • Results from expansion from within
    • Great advantage for growth
    • Adaptive reason for the retention of cartilage by the growing skeleton
    • Important during periods of rapid growth as part of endochondrial ossification or at articular surfaces where perichondrium absent
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12
Q

Cartilage Degeneration

A
  • Occurs in deep areas of thick cartilage because cells cannot get nutrients from diffusion
  • Chondrocytes begin to atrophy and shrink
  • Cartilage may calcify
  • Process important as part of normal process of endochondrial bone formation
  • Also occurs as cartilage ages ⇒ osteoarthritis
    • Articular surfaces can become undulated
    • Loss of protective articular cartilage will affect underlying bone causing chronic inflammation
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13
Q

Cartilage Regeneration

A
  • Very limited ability to regenerate
  • Chondrogenic ability of perichondrium limited to active growth periods before adulthood
  • Intra-cartilage division of chondrocytes too slow to repair damage
  • Acute injuries during adulthood results in deposition of vascularized CT which eventually loses vascularity and persist as fibrous tissue
  • Cartilage suited for transplantation without marked immune response
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14
Q

Hyaline Cartilage

A
  • Most common type
  • Glassy non-fibrous matrix composed primarily of Type II Collagen
  • Found in fetal and growing skeletons prior to ossification
    • Persists at growth plates of immature long bones until skeletal maturity
  • Remains cartilaginous in adults in:
    • Articular surfaces of bones
    • Reinforces/supports areas of respiratory tract
    • Forms costal-sternal border
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15
Q

Articular Cartilage

A
  • Found on the articular surface of bones especially in synovial joints
  • Specialized form of hyaline cartilage
  • Has no perichondrium
  • Cells and fibers are more regularly arranged
    • Vertical rows deep
    • Horizontal rows near surface
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16
Q

Elastic Cartilage

A
  • Most cellular type of cartilage with larger cells
  • Matrix more opaque than hyaline
  • Contains elastic fibers and Type II Collagen
  • Has perichondrium
  • Less susceptible to degeneration than hyaline
  • Not susceptible to calcification as with hyaline
  • Found:
    • Eustachian tube
    • External auditory canals
    • Ear
    • Epiglottis
    • Cuneiform cartilages of larynx
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17
Q

Fibrocartilage

A
  • Matrix with numerous bundles of thick collagen fibers
    • Mainly Type I collagen
  • More fibrous and less cellular than other cartilage
  • Always associated with and grading into dense CT
  • No perichondrium
  • Chondrocytes may be in isogenous clusters or single file in isogenous columns between fiber bundles
  • More acidophillic d/t Type I fibers
  • Greater tensile strength than hyaline
    • Able to withstand repeated tension and friction
  • Found in areas where tissue experiences compressive stresses in one direction and tensile stresses in another direction
    • Annulus fibrosus of intervertebral discs
    • Pubic symphysis
    • Regions where tendons or ligaments attach to bone
    • Joint menisci
18
Q

Bone

A
  • Specialized connective tissue
  • Extracellular matrix is mineralized
    • Provides strength to resist tension and compression
    • Serves as a store for calcium
19
Q

Bone

The Organ

A
  • Consists of bone tissue and other associated tissues:
    • Hemopoietic marrow
    • Fat
    • Blood vessels
    • Nerves
    • Cartilage
    • CT of periosteum
    • Etc
20
Q

Bone

The Tissue

A
  • Specialized CT with mineralized matrix
  • Organic components:
    • Cells
    • Collagen
      • provides flexibility and tensile strength
  • Inorganic components (mineralized):
    • Provides rigidity and compressive strength
  • Together makes the bone strong yet resilient
  • Dynamic structure which responds via remodeling
  • Can only grow appositionally
21
Q

Methods of

Bone Preperation

A
  1. Ground sections
    • Preserve the inorganic (mineral) components
  2. Decalcified sections
    • Preserve the organic components such as cells and collagen
22
Q

Functions of bone

A
  1. Structural functions
    • Lever system to which muscles attach allowing for posture and movement
    • Framework of support of soft tissues
    • Protection of internal organs
  2. Metabolic functions
    • Provides a location for marrow for hematopoiesis
    • Storage/metabolism of minerals
      • Calcium
      • Phosphorus
23
Q

Classification of bones by shape

A
  • Classified by bone shape
    • Long bones
    • Short bones
    • Flat bones
    • Irregular bones
    • Sesamoid bones
24
Q

Parts of long bone

A
  1. Diaphysis
    • The shaft
    • Contains the marrow cavity
  2. Metaphysis
    • Flared region between diaphysis and epiphysis
  3. Epiphysis
    • Ends of the long bone
25
Q

Tissue Distribution

in

Bone

A
  1. Cancellous bone (aka spongy bone, trabecular bone)
    • Plates of bone organized into interconnected vertical and horizontal struts
    • Marrow occupies the spaces in spongy bone
    • Found primarily in:
      • Flat bones of the skull
      • Ends of long bones
      • Inside other “spongy” bones such as vertebrae
  2. Compact bone (aka cortical bone)
    • Densely packed bone matrix
    • Forms the outer cortex of all bones
    • Found in abundance along the shafts of long bones
26
Q

Periosteum

A
  • Covers the exterior of a bone except at articular surfaces
  • Continuous with CT of tendons and skeletal muscles
  • Two layers
    • Outer fibrous
    • Inner cellular
  • Sharpey’s fibers insert into the bone surface and connect the periosteum to the bone tissue
  • Provides the vascular supply to the bone
  • Serves as a source of osteoprogenitor cells
27
Q

Endosteum

A
  • Thin single cell layer of CT which covers the interior surfaces of bone
  • Covers most internal surfaces of bone including Haversian canals, Volkmann’s canals, and marrow cavity
  • Contains osteoprogenitor cells
28
Q

Sharpey’s Fibers

A
  • Bundles of collagen fibers that insert into bone tissue
  • Prominent where tendons and ligaments insert on bone
  • Also connect the periosteum to the bone tissue
29
Q

Medullary Cavity

A
  • Spaces of spongy bone filled with bone marrow
  • Forms the inner portion of the bone
  • Contains hemopoietic cells
  • Bone marrow sinusoids provide a barrier between the hemopoietic compartment and the peripheral circulation
30
Q

Bone

Vascular Supply

A
  • Fairly extensive blood supply
  • Nutrient arteries
    • Long bones usually have a nutrient artery that penetrates the bony collar of the diaphysis and divides in the marrow cavity
    • Branches then enter the Haversian canals
  • Periosteal arteries enter the Haverisan canals from the outer surface of the bone
  • Metaphyseal and epiphyseal arteries
31
Q

Bone

Organic Matrix

A
  • Collagen
    • Major organic constituent of bone - about 90% of the organic matrix
    • Type I collagen
  • Ground substance
    • About 10% of the organic matrix
    • Proteoglycans
      • GAG’s
        • Chondroitin sulfate
        • Keratin sulfate
    • Glycoproteins
      • Osteocalcin
        • binds to hydroxyapatite crystals
      • Osteonectin
        • binds calcium
        • important in regulating mineralization
      • Osteopontin
        • binds to hydroxyapatite and other components for adhesion of cells to matrix
      • Sailoproteins
        • For cell adhesion to the matrix
32
Q

Bone

Inorganic Matrix

A
  • About 65% dry weight of bone
  • Ca10(PO4)6(OH)2 crystals similar to hydroxyapatite
    • Crystals deposited in the gaps between collagen fibers
    • Calcification lags behind fiber formation
    • New unmineralized bone called osteoid
33
Q

Osteoprogenitor Cells

A
  • Determined but not differentiated mesenchymal cells
  • Derived from pluripotent stromal cells in bone marrow and other CT
  • When activated, divide and produce osteoblasts
  • Characteristics:
    • Flattened cells
    • Found in inner layer of periosteum or endosteal lining of bone
    • Resembles young fibroblasts
34
Q

Osteoblasts

A
  • Cells that synthesize bone
    • Secretes collagen and ground substance as unmineralized osteoid
    • Secrete matrix vesicles that contribute to the mineralization process
      • Vesicles slowly accumulate mineral over time
  • Forms a single layer of cells on surfaces of developing or remodeling bone
  • Characteristics:
    • Cuboidal
    • Typical characteristics of protein-secreting cells
  • Connected to each other by processes that end in gap junctions
  • Once they become surrounded in matrix that they produce cells are considered osteocytes
  • Quiescent osteoblasts that line the surfaces of a bone formation region after osteoid production is complete are called bone lining cells
  • Has receptors for parathyroid hormone (PTH), Vit D3
    • ​Important in regulation of osteoclast activity and calcium levels
  • Has estrogen receptors
  • Cell membranes rich in alkaline phosphatase ⇒ used as a marker enzyme
35
Q

Osteocytes

A
  • Mature, differentiated cells, derived from osteoblasts that have become buried in mineralized bone matrix
  • Reside in lacunae
  • Communicate with one another through cell processes joined by gap junctions
    • Processes run through small fluid filled canals called canaliculi
  • Functions:
    • Involved in mineral homeostasis
    • Can likely remove mineral from a limited region surrounding the lacuna via osteogenic osteolysis
    • Have mechano-sensory role in the stimulation of remodeling
36
Q

Osteoclasts

A
  • Cells responsible for the resorption of bone
  • Large, multinucleated cells
  • Structural syncitium
  • Derived from a common bone marrow precursor as monocytes
    • Differentiate first into uninucleate osteoclast precursors
    • Activated precursors fuse to produce mature multinucleated osteoclasts
  • Create resorption bays called Howship’s Lacunae along the surface of bone being removed
    • Ruffled border formed by folds of the plasma membrane that increase cell surface area and represents the zone of contact with bone
    • Actin microfilaments in the clear zone surrounding the ruffled border healp seal the cell to the bone surface
  • Release of acid (H+) by the osteoclasts into the Howship’s lacunae to dissolve the mineral crystals
  • Organic matrix degraded by lysosomal enzymes ⇒ collagenases
  • Activity indirectly stimulated by PTH through osteoblasts
  • Activity directly inhibited by calcitonin
37
Q

Hormonal Control of Bone

A
  • Role of Parathyroid Hormone
    • When [PTH] high, osteoblasts stimulate maturation of osteoclasts through release of macrophage colony stimulating factor and expression of RANKL molecules on their own membrane
    • Osteoclast precursors have RANK receptors which bind the RANKL stimulating them to differentiate and fuse with one another
    • When [PTH] low, osteoblasts release osteoprotegerin
      • This can bind RANKL to prevent it from stimulating differentiation of osteoclasts
  • Role of Estrogen
    • High [estrogen]:
      • increases osteoblast production of osteoprotegerin.
        • Binds more RANKL, decreasing production of osteoclasts
      • Suppresses RANKL production
      • Prolongs life of osteoblasts
    • Post-menopausal women have decreased estrogen levels thus favoring bone loss leading to osteoporosis
38
Q

Macroscopic Divisions of

Bone: The tissue

A

Cancellous vs compact bone

Differentiated based on the amount of space (porosity) of the bone.

39
Q

Woven Bone

A

Applies to both cancellous and compact bone.

AKA immature bone

  • A form of immature non-lamellar bone tissue
  • First bone to appear during bone formation
    • Eventually replaced by lamellar bone during the growth and remodeling process
  • Found in areas of injury repair
  • Characteristics:
    • Deposited quickly during growth and fracture repair
    • Randomly oriented collagen fibers and cells
    • Highly cellular
    • More porous & less dense than lamellar bone
    • Not as strong as lamellar bone
40
Q

Lamellar Bone

A
  • Bone organized into layers of aligned collagen called lamellae
  • Layers usually seperated from one another by a single layer of osteocytes
  • Slow deposition due to highly organized structure
  • Stronger material better able to resist biomechanical loads than woven bone
  • Found in both cancellous and compact bone tissue types
    • In cancellous bone
      • lamellae will not form Haversian systems
      • Instead form layers on the surface of the trabeculae that make up cancellous bone
    • In compact bone
      • Lamellae will either be circumferential or in Haverisan systems

Circumferential Lamellar Bone

  • Organized into linear sheets that encircle the bone
  • In adults primarily found as the outer circumferential lamellae and inner circumferential lamellae
    • Encircles the bone just deep to the periosteum and just superficial to the endosteum respectively

Haversian System

(Secondary Osteons)

  • Represents bone that has formed by the secondary remodeling process
  • Forms much of the bone matrix in adult human compact bone
  • As we age, more lamellar bone will remodel to form Haversian systems
41
Q

Haversian System Structure

A
  • Layers of lamellae arranged concentrically around a central Haversian canal
  • Haversian canal
    • Long tubular branching structures that run predominantly longitudinally through the bone
    • Act as vascular channels which run longitudinally through the center of the osteon
    • Contains blood vessels and nerves which supply the bone tissue
  • Volkmann’s Canals
    • Obliquely oriented vascular canals linking the Haversian canals of neighboring osteons
    • Allows blood to pass through a large network throughout the bone
    • Some also connect with vessels in the marrow cavity or periosteum
  • Cells within an osteon communicate with one another via cellular processes/gap juctions that run along the canaliculi
    • Communication between osteons limited due to cement lines
  • Cement lines
    • Marks the outer edge of each Haversian system
    • Represent reveral lines where osteoclasts stopped resorbing bone and osteoblasts started refilling the space
    • Functionally seperates neighboring osteons since canaliculi generally do not cross cement lines
  • Interstitial lamellae
    • Remnants of old Haversian systems or circumferential lamellae
    • Found between exsiting HAversian systems
    • Formed as a result of the remodeling process

IMS: Microanatomy (16 decks)

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