04 cartilages and bone

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HISTOLOGY & EMBRYOLOGY Teaching PPT

Transcript of 04 cartilages and bone

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HISTOLOGY &EMBRYOLOGY

Teaching PPT

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CARTILAGE AND BONE

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CartilageI. CARTILAGEⅠ . Introduction

A. A rigid tissue, capable of providing support, connection and sliding surface for joints.

B. Composed of firm intercellular material (cartilage matrix) and cells (chondrocytes).

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Cartilage1. Structure & Features Cartilage: Cartilage tissue + perichondrium Cartilage tissue: Cells + matrix (fibers+ g.s.) The g.s. is semi-solid & semi-rigid. No B.V., lymphatics & nerves. (It nourished by diffusion)

I. CARTILAGE

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3 types of cartilage: (mainly based on the type of fibers)

hyaline cartilage elastic cartilage fibrocartilage

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Ⅱ . Hyaline Cartilage -- most common and best studiedA. Skeleton of early embryo; supporting structures of respiratory passages (nose through bronchi; larynx, trachea etc), ventral ends of ribs and articular ends of bones in a joint.

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2. Hyaline carti lage trachea

A. Ground substances( gives cartilage firm property)Toluidine blue: metachromasia Avascular, but hydrated, facilitating diffusion of nutrients.

Has small cavities called lacunae occupied by cells. Matrix close to the lacune is more intensely stained than the remaining and called cartilage capsule.

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Chemical composition is similar to that of L.C.T. ( more chondroitin so

basophilic in H & E sections. ) & chondronectin(ChN)

Cartilage lacunae: matrix cavity Cartilage capsule: on the surface of the lacunae; strong basophilic

cap

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B. Fibers Collagenous fibril (D=10-

20nm) made up of type II collagen,

invisible in LM (delicate & same refractive index as the g.s.)

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C. Chondrocytes1. Young chondrocytes are flat and singly fill lacunae at the periphery. 2.Toward the center, cells round up and mature, and may appear in groups designated isogenous groups, derived from a single cell.

Located in cartilage lacunae Basophilic

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LM: Peripheral chondrocytes: less mature; small & flat; single; Central chondrocytes: more mature; round; isogenous group.

EM: shows abundant RER and well-developed Golgi complex,responsible for synthesis and secretion of matrix.

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D. Perichondrium: Dense connective tissue sheath around the cartilage.

Outer layer: more collagenous fibers; is protective Inner layer: more b.v. & cells, containing osteoprogenitor cells (→ chondrocytes → new cartilage tissue)

Function: protection, nutrition, repairing

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E. Carti lage growth & regeneration

Appositional growth: Osteoprogenitor cells in perichodrium

produce new layer of cartilage tissue from outside

Interstitial growth: Chondrocytes: increase the number of

cells (mitosis) & the amount of matrix from within

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3. Elastic carti lageLocation: external ear; epiglottis

etc.Structure: elastic fiber (dense & closely packed) + chondrocytesFeature: more elasticity

& flexibility

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4. Fibrocarti lageLocation: intervertebral disk; symphysis pubis; end of tendons etc.Structure: collagenous fiber (A large number, in parallel bands), less g.s. (acidophilic) & chondrocytes

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BoneI I . BoneⅠ . Bone Tissue (Osseous Tissue) Specialized connective tissue with calcified matrix, thus firmer(hard & rigid ) than cartilage, and provides support, movement, protection and a storage site for calcium.

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Bone1. Characterist ics:• bone tissue + medullary

cavity & bone marrow + periosteum & endosteum

• bone tissue= cells + bone matrix (fibers + calcified g.s.)

I I . Bone

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Organic (35%); inorganic (65%)• Organic part: collagenous fibers (90%) amorphous g.s.: proteins & GAG ( chondroitin s., keratin s.) is

much less than in cartilage. to unit the fibers together. Glycoproteins: osteocalcin osteonectin osteopontin

2. Bone matrix

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Function: be responsible to toughness & resilience, Imparts resilience to bone.

• Inorganic part (bone mineral): Calcium phosphate in the form of

hydroxyapatite crystal be responsible to hardness & rigidityImparts hardness to bone.

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• bone lamella : the form that bone matrix arranged in

a. plywood-like layers (lamellae) with the fibers parallel in one layer and rectangular between adjacent layers. apatite lie alongside the collagen fibrils. The bone so called lamellar bone

b. * lacunae & canaliculi in the lamellae

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b. Basic structure form of bone matrix giving bone maximum strength.

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3. Cells

Osteoprogenitor cells

Osteoblasts Osteocytes Osteoclasts

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A. Osteoprogenitor cell

Location:located on surface of the osseous tissue, In periosteum &EndosteumLM: Small, spindle shape,weak basophilicFunction: Stem cell, differentiate into osteoblast

when active osteogenesis.

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B. Osteoblast (bone-forming cells)

Develop from osteoprogenitor cells.

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B. Osteoblast

Location: at surface of bone tissue in a layer;

LM: cuboidal cells, strong basophilic, large pale nuclear w/ obvious nucleolus

EM: short processes &gap junctions; rich in rER & Gl. indicate active protein synthesis.

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※Newly-formed, uncalcified organic matrix is called osteoid.

※Osteoid is soon calcified with calcium salt deposition initiated by matrix vesicles probably derived from osteoblasts.

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release matrix vesicle (Ca++)

osteoblast fibers g.s

osteoblasts

Function:

osteoid

embedded Osteoblasts osteocytesbone tissue

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C. Osteocyte mature bone cells

a. Osteoblasts become trapped inside the calcified matrix and become osteocytes.b. No longer produce osteoid and lose most of RER and basophilia, weak basophilic and flattened.

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c. Cell bodies: Flat & ovoid, in lacunae, and cytoplasmic processes,long fine, in canaliculi to form gap junctions with adjacent osteocytes, providing for intercellular communication.d. tissue fluid fills inlacunae & canaliculi,Osteocytes and their processes are bathed in tissue fluid, which are from blood vessels in Haversian canals.

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Function: Maintain & renew the bone matrix; Exchange the Ca2+ b/w tissue fluid and blood, stable of blood Ca2+

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D. Osteoclast

bone resorptive cells Location:a. Often found in depression on the bone surface involved in bone resorption.

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b. Giant multinucleate(2-

50), irregular in shape and acidophilic, formed by fusion of monocytes.c. Ruffled border (irregular microvilli) on the surface adjacent to bone and lysosomes in the cytoplasm are evidence of bone resorption.

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Lysosomal enzymes and organic acids are released into extracellular space and break down organic and mineral components of bone.

EM: Mv.(ruffled border); Lysosomes; Phagocytosis vacuolesOthers: Mit. rER.

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Function: Clear zone: attached the bone surface toform a closed microenvironment Osteoclasts release lysosomal enzymes (proteinases, carbonic anhydrase), & acids (citric acid, lactic acid) to dissolve the bone matrix Mv.: increase the absorptive area & absorbthe dissolved products * belong to mononuclear phagocyte system

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4. Bone architecture

long bone diaphyses ( ) (campact bone) epiphyses ( ) (sponge bone)

Bone tissue is covered by connective tissue sheaths and harbors bone marrow in the central cavity.

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A. Spongy bone

Spongy bone exists also as lamellar bone and in the form of interconnecting trabeculae

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A. Spongy boneLocation: at the end & inner surface of a long boneStructure: Parallel lamellae trabeculae osteocytes spongy-like network The canaliculi open to the marrow cavity

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B. Compact bone Circumferential lamellae Osteon (Haversian system) Interstitial lamellae

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Circumferential lamellae :follow the outer and inner circumferences of the diaphysis.

arranged in concentric circles. outer ~ : 10-40 layersinner ~ : fewer layers

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Osteons or Haversian systems the structural unit of compact bone. It contains several concentrically arranged lamellae and a central canal (Haversian canal) with CT, blood vessels, nerves, and cells.

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4. Volkmanns canals crossly perforate the circumferential lamellae and bring blood vessels into the compact bone.5. Between or within bone lamellae are living cells (osteocytes) in lacunae connected to one another by canaliculi, the innermost of which connected to the central canals.

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• Cylindrical units;• 8-20 layers of Osteon lamellae (Haversian~ ) Central canal (b.v. / n.f. / tissue fluid in it), the canaliculi open to the canals; • cement line wraps around the unit;• Volkmann’s canals (perforating canals) communicate w/ the central canals.

b.  Osteon (Haversian system)

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c. Interstit ial lamellae: Irregular lamellae

and fill spaces b/w the osteons;

It is the remanets of osteons during reconstruction.

I .L

os

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5. Periosteum a layer of dense connective tissue covering the external surface of bone

outer layer: dense c.t., thicker;

the perforating f. (Sharpey’s fibers) fix the periosteum to bone;

inner layer: containing osteoprogenitor cells , small b.v. & n.

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6. Endosteum a thin layer of bone lining cells on inner surface of bone.

thin c.t. & a layer of bone lining cells (special osteoprogenitor cells) w/ processes.

Differentiate into osteoblasts for ossificationAttract osteoclasts

Lining the surface ofthe marrow cavitiesto maintain the stability of Ca2+ in lacune

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5. Periosteum

Osteoprogenitor cells present in both throughout life -- can give rise to osteoblasts in case of fracture.

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Qestions What is the cartilage and the cartilage

tissue? How many cartilage types in the human

body? Describe the Hyaline cartilage. What is the bone and the bone tissue? Describe the structure and function of the

cells in bone tissue. Describe the architecture of the compact

bone.

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7. Osteogenesis

Intramembranous ossification Intracartilaginous ossificationA. Intramembranous ossification Mesenchyme → → → CT membrane Mesenchymal cells → → osteogenic cells → osteoblasts fibers & g.s. osteoid Osteoid Ca2+ bone matrix Osteoblasts osteocytes bone tissue

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B. Intracarti laginous ossif ication

i.  formation of the cartilage model ii. perichondrial ossification & formation of the bone collar

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iii. cartilage degeneration & formation of the primary ossification centeriv. formation of medullary cavity & bone

growth (long & thick)

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成骨区Zone of ossification

软骨储备区Zone of reserve

cartilage

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v.  occurrence of the secondary ossificationcenter & formation of the epiphysis

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Vi. Epiphyseal plate replaced by bone tissue

Vii. reconstruction of bone

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Regulation factors of bone development• Hormones: growth hormone, thyroid hormone,

parathyroid hormone, calcitonin• Vitamin: vitamin A, vitamin C, vitamin D• Other bioactive factors: TGF(transforming growth factor )β, prostatin,

EGF(epidermal growth factor)], interleukin 1 , 6

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Summary • Cartilage tissue and bone tissue belong to the c.t.

• Cartilage tissue consists of cells, fibers and g.s (cartilage lacuna / cartilage capsule)

• cartilage cells: chondrocyte (immature / mature / isogenous groups), osteoprogeniter cell

• bone tissue consists of organic & inorganic component

• bone cell: osteogeniter cell, osteoblast, osteocyte, osteoclast.

• ground substance: bone lamella, lacuna, canaliculi

• compact bone architecture: Circumferential lamellae / Osteon (Haversian system) / Interstitial lamellae

• ossification: Intramembranous & Intracartilaginous

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BYE BYE