labs 6/7 – cartilage and bone cartilage and bone · cartilage and bone. 1. cartilage. is a...

Cartilage and BoneLabs 6/7 – Cartilage and Bone

IUSM – 2016

I. IntroductionII. Learning ObjectivesIII. KeywordsIV. Slides

A. Cartilage1. Hyaline2. Elastic3. Fibrocartilage

B. Bone1. General Overview2. Formation and Growth

a. Intramembranous formationb. Endochondral formationc. Appositional growthd. Internal remodeling

3. Typesa. Wovenb. Lamellar

i. Cancellous/Trabecularii. Cortical/Compact

C. Joints1. Synovial2. Intervertebral

V. SummarySEM of trabecular/cancellous bone. Inserm.

Cartilage and Bone

1. Cartilage is a specialized type of solid connective tissuewhich, along with bone, is distinguished by the relativerigidity of its extracellular matrix (ECM); it is easilydistinguishable from bone by its avascularity; it providesflexible support to tissues (e.g., ear, nose, larynx).

2. Types of cartilage (hyaline, elastic, and fibrocartilage) aredistinguished by the characteristics of their respectiveECM (e.g., the dominant type of fiber).

3. Bone is a specialized type of solid connective tissuecharacterized by a mineralized ECM that stores calciumand phosphate.

4. Woven bone (immature) differs from lamellar bone(mature) in its collagen fiber arrangement; all new boneis woven, but it becomes remodeled into lamellar bone,with few exceptions.

5. Lamellar bone has organized ECM sheets (lamellae); thedense bone that forms the outer cortex of most bones ofthe body is referred to as cortical bone; while the less-dense, inner bone which is not as compacted but insteadarranged in a lattice-like configuration is referred to ascancellous bone.

Labs 6/7 – Cartilage and BoneIUSM – 2016








V. Summary

Bone Formation and Joints

1. Bone formation occurs via two basic mechanisms:

a. Intramembranous ossification forms bonewithin mesenchyme (“membrane”).

b. Endochondral ossification forms bone byreplacing a cartilage model.

2. Regardless of the mechanism, all new bone is wovenbone which is remodeled into lamellar bone (eithercompact or trabecular), with organized sheets of bone(lamellae), by osteoclast and osteoblast activity.

3. Joints are places where bones meet (articulate),allowing at least the potential of bending or movement;examples include synovial joints (diarthrosis) andintervertebral joints.









V. Summary

Learning Objectives I – Cartilage and Bone

1. Understand the variations in structure and function of the three majortypes of cartilage, with regard to both the cellular and extracellularelements.

2. Understand the key ultrastructural features of the chondroblast and howthey relate to function.

3. Understand the structural features and functions of osteogenic cells:osteoblasts, osteocytes, and osteoclasts.

4. Know the major differences in structure and function between woven andlamellar bone, and between compact and cancellous bone.

5. Understand the structure and composition of an osteon and how it isformed.









V. Summary

Learning Objectives II – Bone Formation and Joints

1. Understand the differences and similarities between intramembranousand endochondral bone formation and the key function of the periosteumin bone growth.

2. Understand the organization of the epiphyseal growth plate and its role inendochondral bone formation and growth of long bones.

3. Understand the structure of a typical synovial joint, including the natureand functions of the synovium.









V. Summary

Keywords

Articular cartilageBoneCanaliculiCancellous boneCartilageCentral (Haversian) canalChondroblastsChondrocytesCompact boneElastic cartilageEndochondral ossificationEndosteumFibrocartilageGrowth plateHaversian systemHowship’s lacunaeHyaline cartilageIntervertebral jointInterstitial lamellaeIntramembranous ossificationJoint

LacunaeLamellaeLamellar boneMarrowOsteoblastOsteoclastsOsteocyteOsteoidOsteonPerforating (Volkmann’s) canalPerichondriumPeriosteumSynovial jointSynoviumTrabeculaeWoven boneZone of calcificationZone of hypertrophyZone of osteogenesisZone of proliferationZone of reserve cartilage









V. Summary

Trachea, Trichrome

look here forhyaline cartilage

what kind of epithelium lines the

lumen of the trachea?

thyroid gland

perichondrium

lumen









V. Summary

https://vmicro.iusm.iu.edu/virtual_h/002_bl_5.html

Trachea, Trichrome

hyalinecartilage

perichondriumperi = “around”chondrium = “cartilage”

hyaline (Gr. “glassy”) cartilage is the most common type of cartilage in the body; it contains the smallestproportion of fibers in the ECM (primarily type II collagen), giving it a fairly homogenous, glassy appearance









V. Summary


Trachea, Trichrome

perichondrium is dense regular CT essential for appositional growth and maintenance of cartilage; it consistslargely of type I collagen, fibroblasts, and progenitor cells for chondroblasts that divide and differentiate intochondrocytes; hyaline cartilage is three-dimensionally surrounded by perichondrium, expect as articularcartilage in joints; elastic cartilage also has perichondrium, but fibrocartilage does not

perichondrium

hyaline cartilagenotice the lack of vasculature within the cartilage; it relies

on diffusion from vessels in the perichondrium, limiting the maximal cartilage thickness

fibroblast

chondroblast

chondrocyte









V. Summary


Trachea, Trichrome

chondroblast

chondrocyte (cell) located in lacuna (space)

perichondriumhyaline cartilage

fibroblast

appositional growth occurs at the interface of the perichondrium and the cartilage as chondroblasts, fromperichondrial cells, actively synthesize new cartilage matrix; they secrete ECM components until they encasethemselves within the matrix – the small remaining, matrix-free space that the cell inhabits is called a lacuna(Lt. “little lake”); once encased, the cells are referred to as chondrocytes, which continue to synthesize andmaintain ECM components; both types of cells have basophilic cytoplasm rich in rER for collagen synthesisterminology note: the suffix –blast identifies immature, not fully-differentiated cell types; those cells differentiateinto mature, terminal cells identified by the suffix –cyte; fibroblasts are a slight exception to this rule, as the termfibrocyte is seldom used and has been newly applied to types of circulating mesenchymal progenitor cells









V. Summary


Trachea, H&E

perichondriumhyaline cartilage small clusters of

chondrocytes are referred to as isogenous groups and reflect interstitial growth

darker-staining territorial matrix surrounds isogenous groups

lighter-staining interterritorial matrix is located between groups of chondrocytes and reflects concentration differences in ECM components

the empty appearance of some lacunae is an artifact of slide preparation, as the cells either pull away from the matrix or are lost









V. Summary


Epiglottis, Masson AF

elastic cartilage

perichondrium

lamina propria(loose CT)

non-keratinzedstratified squamousepithelium

the epiglottis (protects entrance to larynx) consists of a core of elastic cartilage surrounded by loose CT and acovering of stratified squamous epithelium; elastic cartilage is similar to hyaline cartilage except that it containsan abundant network of elastic fibers in addition to type II collagen; visualization of the elastic fibers usuallyrequires special stains; it is found in the auricle of the ear, walls of the external auditory canals (auditorymeatus), auditory (Eustachian) tubes, epiglottis, and cartilages in the larynx









V. Summary


Elastic Cartilage, AFelastic cartilage

perichondrium

the separation of the tissue is an artifact of

slide preparation









V. Summary


Auditory Meatus, H&E

distinguishing elastic cartilage from hyaline cartilage can be tricky in H&E without specialized stains to showthe elastic fibers; however: the elastic fibers provide a more heterogeneous appearance to the cartilage vs. thesmooth, glassy appearance of hyaline; elastic cartilage has a greater density of chondrocytes with less ECMbetween them than in hyaline; and the chondrocytes in elastic cartilage tend to be larger than in hyaline

elastic cartilage

perichondrium

keratinized stratified squamous epithelium

hair follicle

sebaceous gland

ceruminous (earwax) gland

skin









V. Summary

Slide Overview

https://vmicro.iusm.iu.edu/virtual_h/msci_25_5.html

Fibrocartilage, H&ESlide Overview

the slide shows the pubic symphysis, which is the cartilaginous joint linking the pubic bones of the pelvic girdle;beyond the fibrocartilage, examples of many other tissue types and structures can be identified

tendon

periosteum

endochondral ossification

bone marrow within trabecular bone

adipocytes

skeletal muscle

adipocytes

attachment of muscle to the bone

skeletal muscle

cortical bone









V. Summary


Fibrocartilage, H&E

fibrocartilage is a combination of dense regular CT (type I collagen) and hyaline cartilage (type II collagen);the collagen bundles and chondrocytes are generally arranged in rows parallel to the direction of functionalstress; unlike hyaline and elastic cartilage, there is no distinct surrounding perichondrium in fibrocartilage; itis found in intervertebral discs, attachments of certain ligaments, and in the pubic symphysis

collagen bundle

chondrocyte in lacuna

fibroblast









V. Summary










V. Summary

Slide OverviewSlide 34: Bone, H&E

sections (1) and (2) are two rib segments from a fetal/newborn rabbit; (1) gives an example of a bone fractureand repair processes (the callus is a temporary formation of highly proliferative fibroblasts and chondroblastsextending from the periosteum down into the fracture to form new bone); (2) gives an example of endochondralossification (EC Oss) bone growth

1

2

fracture

callus

hyaline cartilage

EC Oss

corticalbone

trabecular bone










V. Summary


from the outside: (P) is periosteum, the dense connective tissue surrounding bone, with clearly visible collagenbundles; (Act P) is an area of more active periosteum with lots of cellular differentiation occurring; (Wb) iswoven or primary bone; (HC) are areas of hyaline cartilage; (M) is marrow with abundant blood cells; (Tb) ismature, lamellar trabecular bone; close examination shows endosteum on the edge of the bone bordering themarrow

Tb

Wb

M

Act P

P

HC

M










V. Summary


from the outside (top): (P) is periosteum with clearly visible collagen bundles; (Cb) is cortical bone with alamellar arrangement of bone matrix and osteons; (M) is marrow with abundant blood cells; (Tb) is trabecularbone with endosteum on the edge of the bone bordering the marrow; (Wb) is woven or primary bone which isnewly-formed bone with an irregular arrangement of collagen fibers (i.e., not lamellar)

PCb

M

Tb

PWb

Tb










V. Summary

Slide 34: Bone, H&E

periosteum is dense regular CT that surrounds the outer surfaces of bone (except at articulations) and attachesto the outer lamellae via collagenous Sharpey’s fibers (not always seen); it contains osteoprogenitor cells whichare capable of differentiating into osteoblasts and forming new bone (appositional growth); blood vessels passbetween the periosteum and bone through perforating (Volkmann’s) canals, with most blood directionallyflowing from the marrow cavities and draining out through periosteal veins

Slide Overview

periosteum(dense regular CT)peri = “around”osteum = “bone”

fibroblast

osteoprogenitor cells(osteoblasts)

osteocyte in lacuna










V. Summary


endosteum lines all the internal surfaces of bone (marrow cavities, osteons, and perforating canals); it isgenerally only a single cell-layer thick and consists of osteoblasts and bone-lining cells; inactive osteoblastsand bone-lining cells are generally flattened with only dark, elongated nuclei being visible; osteoblasts thatare actively secreting bone ECM components are much more round or cuboidal in appearance

endosteum

endosteum

osteocyte (cell) in lacuna (space)

hematopoietic cord where blood cell development occurs

red blood cells in vascular sinusoidhow new blood cells leave the marrow

stroma of bone marrow

trabecular bone

trabecular bone

marrow

-filled cavity










V. Summary


trabecular bone

marrow

osteoidlighter-stained area between endosteum and mature bone

endosteum with osteoblasts(round, plump cells)

osteocyte in lacuna

osteoid is the collagen-rich, non-mineralized precursor to true bone ECM; it is secreted by osteoblasts, such asthose of the endosteum, during bone growth, repair, and remodeling; the osteoblasts subsequently calcify theosteoid into hard bone matrix, and in the process, they become trapped in the matrix (in lacunae) and becomeosteocytes (similar to the process of chondroblasts becoming chondrocytes in cartilage)










V. Summary


osteoclasts (Gr. “bone breaking”) are large, acidophilic, multinucleated cells (generally 5-20 nuclei); they arecritical for bone remodeling and resorb bone by secreting organic acids which dissolve hydroxyapatite andlysosomal enzymes which break down the osteoid matrix; at the bone surface, osteoclasts are found withinsurface depressions caused by the resorption of bone called Howship's lacunae (or resorption bays)

osteoclast within Howship’s lacunaosteoclast within Howship’s lacuna






a. Intramembranous formation

b. Endochondral formationc. Appositional growthd. Internal remodeling




V. Summary

Intramembranous Ossification

1. Primary center of ossification: mesenchyme cells osteoblasts

2. Osteoblasts begin depositing bone matrix to form trabeculae or spiculesof woven bone (immature bone) extending radially from the ossificationcenter; osteoblasts become osteocytes

3. Marrow develops in spaces between trabeculae

4. Periosteum and endosteum develop from mesenchyme membrane onsurfaces of new bone

5. Woven bone is remodeled to form lamellar bone (compact and trabecular)

Fetal SkullLabs 6/7 – Cartilage and BoneIUSM – 2016









V. Summary

Side View Frontal Viewdeveloping tooth with surrounding intramembranous bone development of the jaw

tongue in the oral cavity

nasal cavity with cartilaginous nasal septum in the middle; surrounded by intramembranous bone development of the skull

Slide 130 – Fetal Skull

Slide Overview

see Slide 12a (464) and Slide 32 (NW) for

additional examples


http://medsci.indiana.edu/a464/virtual/464_12a_5.html

https://vmicro.iusm.iu.edu/virtual_h_nw/nw_hist_1_32.html

Fetal SkullLabs 6/7 – Cartilage and Bone

IUSM – 2016









V. Summary

trabeculae (or spiculae) of new woven bone are

dispersed within mesenchyme

look for osteoblasts on the surfaces of the bone, while osteocytes can be

seen contained within the lacunae of the bone

mesenchyme(primitive CT)


Fetal SkullLabs 6/7 – Cartilage and Bone

IUSM – 2016









V. Summaryeven though hyaline cartilage is present adjacent to the mesenchyme, it is not involved in the formation ofthe new bone seen occurring here via intramembranous ossification (not endochondral ossification)

hyalinecartilage

trabeculae ofwoven bone

(new bone)

periosteum(dense CT)

specialized olfactory epithelium

mesenchyme










V. Summary

Endochondral Ossification

Note: Because the rates of chondrocyte proliferation (in zone of proliferation) and destruction (in zone ofcalcification) are approximately equal, the epiphyseal plate does not change in thickness; instead, it is“displaced” away from the middle of the diaphysis, resulting in growth in length of the bone.

1. Zone of Reserve Cartilage: hyaline cartilage acts as source of cartilage to undergo ossification

2. Zone of Proliferation: normal chondrocytes multiply

3. Zone of Hypertrophy: chondrocytes enlarge and align

4. Zone of Calcification:* cartilage matrix calcifies providing scaffold for new bone; chondrocyte degenerate (apoptosis)

5. Zone of Ossification and Resorption:* osteoblasts invade and bone is deposited on the calcified matrix; osteoclasts begin the remodeling process

Unlike in intramembranous bone formation, endochondral ossification occurs when a hyaline cartilagemodel is replaced with bone; this more complex method of bone formation provides the benefit of having aload-bearing structure in place (cartilage) before the bone has formed; the bones of the extremities andload-bearing bones of the axial skeleton (e.g., vertebrae) are formed via this method, which can bespatiotemporally separated into the following zones:

Bone, H&ELabs 6/7 – Cartilage and Bone

IUSM – 2016








V. Summary

epiphyseal growth plateepiphysis(end of bone)

diaphysis(shaft of bone)

look here to see endochondral

ossificationhyaline

cartilagewoven bone

marrow



IUSM – 2016








V. Summary

zone ofreserve cartilage

zone of proliferation

zone of hypertrophy

zones of calcification & ossification

typical hyaline cartilage chondrocytes form rows or clusters of cells from successive mitotic divisions

chondrocytes greatly enlarge in size

matrix becomes calcified chondrocytes degenerate osteogenic cells and vessels

invade from the bone marrow osteoblasts form new bone








i. Cancellous/Trabecularii. Cortical/Compacti. Cortical/Compactii. Cancellous/Trabecular


V. Summary

Slide 13a (464): Bone, H&E

Slide 13 (464): Foot, H&E Slide 15a (464): Joint

Slide 42a (464): Fingertip

primary ossification

centers


http://medsci.indiana.edu/a464/virtual/464_13_5.html




IUSM – 2016








V. Summary

while endochondral ossification provides a means for bones to lengthen at the epiphyseal growth plate, bonesgrow wider (increase in diameter) via appositional growth at the interface between the bone and thesurrounding periosteum; osteoblasts differentiate from precursor cells and laydown new bone matrix (osteoid)onto the surface of the bone, increasing the overall width; the marrow cavity then also enlarges by resorptionof bone on the endosteal surface

periosteum(dense CT)

bone

osteoid (pale-staining)

osteoblasts

marrow

endosteum



IUSM – 2016








V. Summary

during internal remodeling of bone, osteoclasts invade a section of compact bone and resorb enough bone tocreate large resorption canals (often irregularly shaped borders with the dimensions of a new osteon); intothis newly created tunnel, blood vessels and osteoprogenitor cells enter; osteoblasts begin to deposit new bonealong the wall of the tunnel, forming lamellae (Lt. “thin plates”) of new bone; synthesis of new bone continuesfrom the periphery to the center of the canal, with concentric layers (rings) of new bone being deposited untilonly the small central canal of the osteon remains with the neurovascular bundle at the center

osteon

central canal

resorption canal

periosteum

cortical bone

marrow


a (464): Developing Bone, H&ELabs 6/7 – Cartilage and Bone

IUSM – 2016








V. Summary

woven bone

new bone, regardless of the process of its formation (e.g., intramembranous or endochondral formation) isconsidered immature due to its lack of organization of its bone matrix (it is non-lamellar bone); because of therandom arrangement of the osteocytes and the interspersed haphazard collagen fiber arrangement, new boneis referred to as woven bone; woven bone will be remodeled into cortical bone and trabecular bone


(464): Decalcified Bone, H&ELabs 6/7 – Cartilage and Bone

IUSM – 2016








V. Summary

resorption canal

endosteum

arrangement of parallel lamellae of bone matrix

osteocyte in lacuna

new woven bone is generally soon remodeled into lamellar bone which is named due to its distinctivelamellated architecture with parallel layers of sheets (lamellae) of bone matrix, as opposed to the haphazard,disorganized matrix arrangement of woven bone; both cancellous/trabecular/spongy and cortical/compactbone are types of lamellar bone










V. Summary

Slide 104: Bone, H&E

periosteum

cortical bone

a trabecula of cancellous bone(Lt. “lattice”)

marrow(with lots of adipocytes)

cancellous/trabecular/spongy bone is the “sponge-like” network of lamellar bone which extends from theperipheral cortical bone and fills the interior of bones; it consists of a series of interconnected trabeculae(Lt. “beam/timber”) composed of lamellae of bone matrix; the spaces between the trabeculae are continuousand filled with marrow; unlike the marrow shown above, most bones of the body are filled with yellowmarrow which is primarily adipose tissue


(464): Decalcified Bone, H&ELabs 6/7 – Cartilage and Bone

IUSM – 2016








V. Summary

marrowcortical bone

skeletal muscle periosteum resorption canalcentral canal of osteon osteocyte

cortical/compact bone is the compact, dense layer of bone tissue found at the periphery (cortex) of bones; it islargely composed of osteons (or Haversian systems) – functional units – which consist of concentric sheets(lamellae) of bone matrix surrounding a central canal (or osteonal/Haversian canal), which contains the bloodvessels and nerves that supply the osteon; osteon organization is generally only seen in cortical bone, but it maybe seen in large trabeculae of spongy bone; the overall architecture is best observed in ground bone


Ground Bone

look here to see osteons in cross-section(transverse)

look here to see osteons in longitudinal section









V. Summary

unlike the previous slides of bone which were chemically decalcified in order to permit them to be sectionednormally like other tissues, ground bone is not fixed but simply allowed to dry and then ground into thinsections; while most of the cells and tissue are lost, this method keeps the calcified bone matrix intact andpermits better appreciation of the bone architecture, especially of the osteons of compact bone


Ground BoneLabs 6/7 – Cartilage and Bone

IUSM – 2016








V. Summary

central canals

outline of2 osteons

Transverse Section



IUSM – 2016








V. Summary

lamella (sheet) of bone matrix

lacunae (spaces)

canaliculi(faint lines)

central canal

interstitial lamellae

Transverse Section

within each osteon, the concentric lamellae of bone matrix are clearly visible; lacunae, which in living bonecontain osteocytes, occur between the lamellae; from the lacunae, canaliculi (Lt. “small channels”) radiatethrough the lamellae connecting the osteocytes together and to the central canal (with neurovascular bundle);interstitial lamellae are remnants of osteons that have been partially resorbed during bone remodeling



IUSM – 2016








V. Summary

perforating (Volkmann’s) canals generally run perpendicular to osteons and provide links betweenindividual central (haversian) canals; they transmit neurovascular bundles between the periosteumand the bone

perforating(Volkmann’s)canals

Transverse Section










V. Summary

Slide 15a (464): Fetal Joint

look here to see Sharpey’s fibers and attachment of muscle to the bone(still cartilage this early in development)

synovium (synovial membrane) lines the interior of the joint capsule and secretes lubricating fluid into cavity

articular cartilage is similar to hyaline cartilage but lacks a perichondrium

joint cavity

skeletal muscle

periosteum










V. Summary

Slide 14a (464): Intervertebral Disc, H&E

vertebra(bone of vertebral column)

intervertebral discwith concentric rings of fibrocartilage

thin layer of hyaline cartilage

vertebra(bone of vertebral column)










V. Summary

Slide 23 (NW): Intervertebral Disc

annulus fibrosus(Lt. “fiber ring”)

concentric rings of fibrocartilage

nucleus pulposus(Lt. “fleshy core”)

gel-like, shock-absorbing tissue at center of disc

this large area of discoloration is an artifact of slide preparation

https://vmicro.iusm.iu.edu/virtual_h_nw/nw_hist_1_23.html









V. Summary

Common Confusion:Hyaline vs. Elastic Cartilage

Hyaline cartilage

Hyaline cartilage: most common form of cartilage; located inthe articular surfaces of movable joints, in the walls of largerrespiratory passages, in the ventral ends of ribs, and in theepiphyseal plates of long bones

Look for: (1) homogenous, slightly basophilic matrix; (2)chondrocytes arranged in small clusters of 2-4 cells

Elastic cartilage: similar to hyaline but with elastic fibers inECM providing elasticity to the tissue; found in canal of ear,Eustachian tube, epiglottis, and laryngeal cartilages

Look for: (1) presence of elastic fibers in ECM if specializedstains are used; (2) matrix is more heterogeneous and less“glassy” in appearance; (3) greater cell density, thus less ECMbetween cells; (4) larger chondrocytes than in hyaline

Elastic cartilage









V. Summary

Common Confusion:Hyaline vs. Fibrocartilage

Hyaline cartilage

Hyaline cartilage: most common form of cartilage; located inthe articular surfaces of movable joints, in the walls of largerrespiratory passages, in the ventral ends of ribs, and in theepiphyseal plates of long bones

Look for: (1) homogenous, slightly basophilic matrix; (2) lackof visible collagen fibers in matrix; (3) lacunae often containtwo or more chondrocytes (isogenous group); (4) lacunaeimmediately rimmed with basophilic matrix (less collagen,more GAGs); (5) generally surrounded by perichondrium(not seen here)

Fibrocartilage: found in intervertebral discs, in attachmentsof certain ligaments, and in the pubic symphysis; it isessentially a combination of hyaline cartilage and dense CT

Look for: (1) collagen fibers in eosinophilic matrix; (2)usually only individual chondrocytes in lacunae; (3) lacunaearranged in rows or clusters; (4) lack of perichondrium

Fibrocartilage









V. Summary

Common Confusion:Dense Regular CT vs. Fibrocartilage

Dense regular CT

Dense regular connective tissue: prominent in tendons,ligaments, and surrounding tissues and organs; collagenbundles and fibroblasts aligned in parallel to axis of functionalstress

Look for: (1) parallel, closely packed bundles of collagenseparated by very little ground substance; (2) fibroblasts arerelatively sparse and have elongated nuclei lying parallel to thefibers; (3) cytoplasm of fibroblasts is rarely revealed in H&Estains

Fibrocartilage: found in intervertebral discs, in attachments ofcertain ligaments, and in the pubic symphysis; essentially acombination of hyaline cartilage and dense connective tissue

Look for: (1) chondrocytes in lacunae; (2) collagen bundles arefewer, less densely-packed, and interspersed among cartilagematrix; (3) tissue generally lacks as uniformly parallel anorganization as seen in dense CT; (4) few fibroblasts are seen;(5) chondrocyte nuclei are more oval/round, with perinuclearcytoplasm generally evident, than fibroblast nuclei; (6)chondrocytes usually appear in linear clusters surrounded bycartilage matrix

Fibrocartilage









V. Summary

Common Confusion:Cartilage vs. Bone

Hyaline cartilage

Cartilage: a specialized type of solid connective tissue which,along with bone, is distinguished by its relative rigidity of theextracellular matrix (ECM); hyaline, the most common type, ispictured here

Look for: (1) lack of vasculature, lymphatics, and nerves; (2)large proportion of cells to ECM; (3) chondrocytes may occur aspairs within a lacuna and tend to be clustered together(isogenous groups) reflecting interstitial growth; (4)chondrocytes are usually larger and rounder than osteocytes;(5) matrix is often not uniform and tends to heterogeneouslystain; (6) lack of lamellar architecture

Bone: a specialized type of solid connective tissue which ischaracterized by a mineralized ECM that stores calcium andphosphate

Look for: (1) vasculature; note the central canal (osteon)containing visible erythrocytes; (2) more ECM and fewer cells;(3) osteocytes are singular and spaced apart; (4) osteocytesare smaller and more condensed than chondrocytes; (5) canalsand lamellar organization may be visible

Decalcified bone









V. Summary

Common Confusion:Woven vs. Lamellar Bone

Woven bone

Woven bone: immature, newly-synthesized bone; all new bone,regardless of process of formation, is woven bone; it lacks anorganized architecture for the fibers in the ECM

Look for: (1) lack of lamellar organization of ECM; (2) greatercell density than mature bone with seemingly randomarrangement of cells; (3) matrix contains more groundsubstance so more basophilic staining; (4) deposit of matrix andremodeling is not uniform giving overall mottled appearance

Lamellar bone: mature bone; remodeled from woven bone byosteoclasts and osteoblast activity; bone matrix is deposited andorganized in lamellae (sheets), either in long parallelarrangements on in concentric rings as in osteonal architecture;both cortical/compact bone and trabecular/spongy are lamellar

Look for: (1) less ground substance in matrix so moreeosinophilic staining; (2) lamellar (sheets) arrangement ofmatrix; (3) in cortical bone, osteons with evident central canals

Decalcified lamellar bone









V. Summary

Summary

1. Cartilage is a specialized type of solid connective tissue that, along with bone, is distinguishedfrom other CT by the relative rigidity of its extracellular matrix (ECM); it generally grows byeither appositional or interstitial growth; it consists of two major cell types:

a. Chondroblasts are generally located at the periphery of cartilage at the interface with thesurrounding dense CT (perichondrium); they secrete new cartilage matrix forappositional growth of cartilage, eventually becoming encased within the newly-synthesized matrix.

b. Chondrocytes are chondroblasts that have become encased in cartilage matrix; they arelocated in spaces in the matrix called lacunae and are responsible for ECM maintenanceand occasionally for interstitial growth of cartilage.

2. The three types of cartilage (hyaline, elastic, fibrocartilage) are distinguished by thecharacteristics of their matrix (e.g., the dominant type of protein fiber).

3. Bone, like cartilage, is a specialized type of solid connective tissue; however, it is characterizedby a mineralized ECM; newly-formed bone is referred to as woven bone due to its interlacedcollagen fibers; woven bone is replaced by lamellar bone (mature) with organized sheets ofbone matrix.

4. Lamellar bone is classified as either cortical/compact which is dense and located at the cortexof bones, or cancellous/trabecular which is has an intricate meshwork of bone that fills themedulla of bones, with the interconnected spaces within the meshwork are filled with marrow.

5. The functional unit of compact bone is the osteon, consisting of a central canal (containing aneurovascular bundle) and concentric rings of bone matrix called lamellae (osteocytes occupylacunae between adjacent lamellae).









V. Summary

Summary (cont.)

6. Bone formation occurs via one of two processes: in intramembranous ossification new boneforms directly from mesenchyme tissue, while in endochondral ossification bone tissuereplaces existing cartilage.

7. Bone tissue consists of three major cell types:

a. Osteoblasts derive from osteoprogenitor cells from mesenchyme stem cells; they secretetype I collagen and bone matrix proteins (osteoid) as well as calcify the matrix to formnew bone.

b. Osteocytes are mature osteoblasts which have become encased by osteoid; they are long-lived cells that maintain the bone matrix and are able to communicate via canaliculibetween lacunae with other osteoctes to respond to mechanical stressors on the bone.

c. Osteoclasts are multinucleated cells formed from the fusion of hematopoietic progenitorcells; they are responsible for bone resorption.









V. Summary

Cartilage and Bone Tissue Compare and Contrast

Terms Compare and Contrast (Similarities? Distinctive differences?)

Cartilage vs. Bone

Hyaline vs. Fibrocartilage

Chondroblast vs. Chondrocyte

Periosteum vs. Endosteum

Appositional vs. Interstitial growth

Cortical vs. Spongy bone

Woven vs. Lamellar bone

Intramembranous vs. Endochondral oss.

labs 6/7 – cartilage and bone cartilage and bone · cartilage and bone. 1. cartilage. is a...

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