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Musculoskeleton > Histology Of The Skeletal System > Flashcards

Histology Of The Skeletal System Flashcards

1
Q

Cartilage

A

Tough durable form of CT.

Serves as the precursor to bone in long bones

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2
Q

Two components of cartilage

A

Perichondrium and cartilage tissue

*three types of cartilage tissues

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3
Q

Perichondrium

A

Outer most layer that surrounds elastic and hyaline cartilages.

Surrounds the diaphysis and metaphysis of bones (not the epiphyses though).

Contains high levels of fibroblasts and chondrogenic progenitor cells

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4
Q

Fibroblasts

A

Produce and maintain ECM and type 1 collagen fibers in devolving bone and cartilage.

  • found only in fibrocartilage
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5
Q

Chondroblasts

A

Naive chondrocytes found at the periphery of hyaline and elastic cartilage that are not surrounded by ECM.

Usually arrive from the progenitor cells located in the perichondrium.

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6
Q

Chondrocytes

A

Mature chondrocytes that undergo mitotic divisions and gives rise to isogenous groups of chondrocytes.

Always have lacunae surrounding them

Produce type 2 collagen fibers and elastic fibers in ECM

Found in all types of cartilage

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7
Q

Hyaline cartilage

A

Most common type of cartilage

Contains mostly type 2 collagen fibers and ground substance rich with aggrecan.

Stains basophilic (Purple with darkest near the lacunae)

Has perichondrium all around it except at epiphyses in long bones

  • function is to provide low friction surfaces in joints and structural support for respiratory tract.
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8
Q

Common sites of hyaline cartilage

A

Synovial joints, epiphyseal plates of all bones, coastal cartilages nasal cartilages and rings of cartilage found in trachea, bronchi and larynx

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9
Q

Elastic cartilage

A

Contain type 2 collagen fibers and elastic fibers throughout the ECM

Stains normal

  • only cartilage with elastic fibers
  • possess perichondrium
  • function is to provide flexible shape and support of soft tissues
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10
Q

Common Locations for elastic cartilage

A

External ear, auditory tube, epiglottis and larynx

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11
Q

Fibrocartilage

A

A mix of hyaline cartilage and dense CT. Has type 2 and type 1 collagen fibers

Stains partially basophillic and
Acidophilic

  • only cartilage with type 1 collagen
  • no perichondrium
  • function is to provide cushioning and resistance to tearing and compression

Has cartilaginous and fibrous areas
- cartilaginous contains lacunae and chondrocytes and type 2 collagen

-fibrous contains chondroblasts and type 1 collagen

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12
Q

General locations of fibrocartilage

A

IVDs, pubic symphysis, meniscus, tendon insertions and some joints.

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13
Q

What embryological derivative does cartilage come from?

A

Paraxial somatic and lateral Mesoderm or neural crest cells (pending on wear it goes)

  • head cartilage = neural crest
  • limb cartilage = lateral plate mesoderm
  • all other cartilage = paraxial somatic mesoderm
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14
Q

Functions of cartilage

A

Facilitate movement at joints

Provide flexible support and mechanical protection

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15
Q

General Characteristics of cartilage

A

Avascular and lacks innervation

Located within lacunae when in bone.

Solid w/ non-mineralized ground substance

Has varying protein fibers based on type of cartilage

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16
Q

Aggrecan complex

A

Multiple proteoglycans attached to hyaluronan molecules in the ground substance of hyaline cartilage

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17
Q

Interstitial growth (growth from inside)

A

Chondrocyte proliferation produces isogenous groups of chondrocytes

  • gradually secrete ECM and generate growth from the inside out
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18
Q

Appositional growth

A

Progenitor cells differentiate into chondroblasts in the perichondrium.

  • most common type of postnatal growth of cartilage

growth from the outside out.

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19
Q

Repair of cartilage

A

Slow process as age increases due to avascular and low metabolic nature of cartilage, immobility of chondrocytes and limited proliferation of mature chondrocytes.

Dependent upon cells of perichondrium invading damaged area and producing new cartilage

Usually forms scars or bone when repaired.

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20
Q

Calcification of hyaline cartilage

A

Occurs via CaPO4 crystals accumulating in ECM

  • occurs naturally while aging and especially in areas of contact with bone tissue
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21
Q

Periosteum

A

Well-vascularized and innervated outer layer of bone

Has two specific layers
- Fibrous layer: outer layer of periosteum made up of dense irregular CT and fibroblasts

  • Cellular layer: deep layer containing osteoprogenitor cells.
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22
Q

Perforating (Sharpey) fibers

A

Collagen fibers Penetrate the periosteum into underlying bone tissue anchoring the periosteum, ligaments and tendons to the bone

23
Q

Endosteum

A

Single layer of CT lining the interior bone (medullary canal)

  • contains endosteal cells and osteoprogenitor cells
24
Q

Osteoblasts

A

Cells that secrete osteoid matrix which becomes ossified by calcium salt deposits.

Undergo apoptosis or differentiate into osteoclasts when done secretion of the ECM.

  • cuboidal shaped cells found only at the surfaces of bone matrix
25
Q

Osteoid matrix

A

Consists of Type 1 collagen, glycoproteins, proteoglycans and matrix vesicles

26
Q

Osteocytes

A

Monitor surrounding bone matrix and communicate with other osteocytes

  • primary job is modulating bone remodeling, possess mechanoreceptors and cell-to-cell communication
  • differentiate into osteoblasts when entrapped in bone matrix
27
Q

Osteoclasts

A

Large multinucleated cells that reabsorb old or damaged bone matrix

  • originate from monocytes
  • develops howships lacunae when reabsorbing bone.
28
Q

General characteristics of bone

A

Solid w/ mineralized ground substance

Protein fibers vary based on type of bone

Cells are located within lacunae

29
Q

Bone tissue types

A

Compact: dense outer layer of bone

Cancellous (spongy): soft hollow-like bone w/ interior spongy meshwork of bone trabeculae

All bone is well-vascularized and innervated

30
Q

Osteocalcin

A

Vitamin K-dependent poly peptide released by osteoblasts.

Bind Ca2 in blood and bring to matrix where matrix vesicles are increasing concentrations of PO4

PO4 + Ca2 = Hydroxyapatite crystals which aggregate together and form calcifications.

31
Q

Osteoclast breakdown of bone

A

Osteoclast ruffled border binds to bone

Vesicular zone of osteoclast releases vesicles with highly acidic protons in them

Protons release in bone matrix and break down hydroxyapatite molecules and collagen fibers

Ca2 molecules produced from break down are released into blood stream

Forms “HowShip Lacuna”

32
Q

Shapes of bones

A

Long

Short

Flat

Irregular

Seasmoid: form within tendons

33
Q

Parts of the bone

A

Diaphysis

Metaphyses

Epiphyseal line: reminant of growth plate

Epiphyses: covered by articular cartilage

34
Q

Intramembranous ossification vs Endochondral ossification

A

Intramembranous ossification:

  • Direct ossification. Is the least common form, bone the earliest form.
  • Primarily occurs in bones of skull and face, clavicle/sternum and scapula

Endochondral Ossification:

  • Indirect ossification. Most common and occurs second
  • primarily occurs in long, short and rib bones.
35
Q

Intramembranous osteogenesis steps

A
  • Ossification centers within mesenchyme give rise to osteoprogenitor cells and proliferate/differentiate into osteoblasts
  • Osteoblasts produce osteoid matrix which in turn forms woven bone and entrap osteoblasts within the lacunae of the woven bone.
  • step 2 continues enlarging the bone.
  • woven bone eventually remodels and is replaced with lamellar bone.
  • non-ossified mesenchyme develops into periosteum and endosteum.
36
Q

Endochondral ossification osteogenesis steps

A

Growth occurs at epiphyseal plates via interstitial growth.

  • hyaline cartilage, shaped similar to the bone to form, develops a “bone collar” of periosteum beneath perichondrium via.
  • chondrocyte hypertrophy occurs in underlying cartilage causing calcification around them and ultimately intimating apoptosis.
  • Perichondrium is invaded by osteoprogenitor cells and capillaries to form the Primary ossification center in the diaphysis.
  • osteoid is deposited in 1st ossification center and calcified into woven bone and compact bone.
  • at birth, secondary ossification centers develop in a similar fashion at the bone epiphyses.

Centers are divided by the epiphyseal line

37
Q

Zones of epiphyseal plate

A

1st- Zone of reserve cartilage: Primary zone that is made up of hyaline cartilage

2nd - Proliferative zone: below zone of reserve, contain rapidly dividing cartilage cells that secrete type 2 collagen and proteoglycans and become organized in columns parallel to long axis of bone

3rd-zone of hypertrophy: swollen terminally different chondrocytes which compress matrix and secrete type X collagen. Promotes vascularization in primary ossification center.

4th- zone of calcified cartilage: chondrocytes undergo apoptosis and release osteocalcin and matrix vesicles to form hydroxyapatite crystals.

5th- zone of ossification: bone tissue appears here (specifically woven bone).

38
Q

Why does the epiphyseal plate not change thickness?

A

Rates of chondrocyte proliferation and death are approximately equal.

39
Q

Zones of the epiphyseal plate that directly contribute to bone growth

A

Proliferative zone and hypertrophic zone.

Reserve zones job is to ensure the epiphyseal plate does not prematurely seal or move.

40
Q

Site of actual growth in longitudinal bone growth

A

Zone of calcified matrix

41
Q

Appositional Bone growth

A

Changes in Thickness of bones and/or the diameter of the marrow cavity.

Begins with formation of periosteum bone collar on the diaphysis.

Osteoblasts proliferate and produce osteoid matrix at the surface of the periosteum bone collar while osteoclasts remove bone in the endosteum.

-This usually occurs at an equal rate.

42
Q

When does the bone collar form on a child?

A

Late 1st trimester

43
Q

When does the primary and secondary ossification centers become produced?

A

At time of birth

44
Q

What causes the epiphyseal plate to fuse shut?

A

Primary and secondary ossification centers meet up and fuse together (usually late teens-20 years of age)

45
Q

Osteon formation steps

A

Cutting Cone: Osteoclasts form a “cutting cone” to tunnel through comapct bone and fill this cavity with mesenchyme and blood vessels

Reversal zone: Osteoblasts line the cavity wall and lay down osteoid matrix, generating the first and subsequent lamella. After which they apoptosis or differentiate into osteoclasts.

Closing cone: Continues in subsequent cycles forming rings of lamallae until only the central canal remains.

Central canal houses neuorvasculature.

46
Q

Lamellar bone is found in what types of bone?

A

Cancellous and compact bone

47
Q

Lamellar bone formation

A

After woven bone is initially laid down, it is removed by osteoclasts and new osteoid is produced by osteoblasts in an organized layering model.

Each layer traps osteoblasts within a lacunae (ring layer) that either undergo apoptosis or differentiate into osteoclasts.

External and internal lamellar layers in the marrow Canal and outer surface form compact bone

Inner layers form spongy bone from endosteum

48
Q

Haversian canals vs Volkman canals

A

Haversian canals are longitudinal through one osteon, whereas volkman canals are perpendicular and connect Haversian canals.

49
Q

Stages of fracture repair

A

Hematoma stage: torn blood vessels from fracture release blood around fracture that clots

Procallus stage: macrophages clean up hematoma tissue and dead cells. Ultimately replaced with soft fibrocartilage.

Bony callus stage: regenerating blood vessels invade procallus and proliferating osteoblasts and ultimately produces woven bone.

Remodeling stage: woven bone is remodeled via osteoclasts and osteoblasts into lamellar bones. Fully functional vasculature is reestablished.

50
Q

Metabolic role of bone

A

Serves as main reservoir for Ca2+

Done via exchange of hydroxyapatite -> interstitial fluid and vise verse.

51
Q

Two polypeptide hormones that regulate calcium homeostasis

A

-PTH: works by stimulating osteocyte differentiation (Directly) into osteoclasts (indirectly) and ultimately releases Ca2+ into the blood stream

PTH also causes osteoblasts to secrete RANKL in a paracrine fashion which further stimulates reabsorption.

  • Calcitonin: works by directly inhibiting osteoclast activity and opposing PTH levels. Ultimately lowers Ca2+ levels in blood stream.
52
Q

Synathoses

A

little to no movement.

Three subtypes:

  • synostoses: only a thin layer of dense CT. skull bones, interdigitating bones
  • syndesmoses: held together by only dense CT (ligaments). Tibiofibular and sacroilliac joints.
  • symphyses: contain a bad of fibrocartilage with articular surfaces of hyaline cartilage. pubic symphysis and Inter Vertebral Joints
53
Q

Diarthoses

A

Synovial joints that allow free joint movement

Contain hyaline cartilage that lines all articular surfaces.

Possess a joint capsule that encloses the joints w/ a fibrous outer layer and synovial fluid inner layer.

Ligaments cross these joints.

  • GH, limb Joints.
54
Q

How do osteoblasts generate bone?

A

Release osteocalcin matrix vesicles, collagen fibers and proteoglycans

Osteocalcin binds Ca with the PO in the matrix vesicles forming CAPO (hydroxyapatite)

Matrix vesicles serve as the site for hydroxyapatite formation.

Musculoskeleton (36 decks)

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