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Musculoskeletal > Bone Handout > Flashcards

Bone Handout Flashcards

1
Q

What is aggrecan?

A
  • Negatively charged proteoglycan monomer which attracts water molecules
  • This allows for the resilience of cartilage.
  • Multiple aggrecan molecules attach to Hyaluronic acid molecule to form an aggregate.
  • Charged aggregates attach to collagen via electrostatics.
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2
Q

Glycosaminoglycans + a core protein = ?

A

Proteoglycan monomer (aggrecan)

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3
Q

Perichondrium

A
  • Surrounds Hyaline and Elastic cartilage (except at articular surfaces).
  • Provides blood supply to chondrocytes and therefore is responsible for maintenance and growth of cartilage. Nutrient exchange via compression and diffusion.
  • Contains reserve cells
  • Outer layer is fibrous with type I collagen and fibroblasts
  • Inner layer contains chondroblasts

Note1: Fibrocartilage lacks Perichondrium.

Note2: Articular surfaces rely on synovium to provide nutrients since they lack perichondrium.

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4
Q

Cartilage Growth

A
  • Interstitial
  • Appositional
  • Interstitial growth occurs through mitosis of chondrocytes
  • Appositional growth occurs through maturation of chondroblasts in inner perichondrium.
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5
Q

Cartilage Repair

A
  • Limited capacity due to avascular nature
  • Scars if severely damaged

Clinical:

  • Severe damage can result in Osteoarthritis
  • Chondrocytes proliferate and release degrading enzymes and cytokines that destroy matrix.
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6
Q

Vertical Bone Architecture (Top to bottom)

A
  • Epiphysis
  • Epiphyseal plate (Growth plate)*
  • Metaphysis
  • Diaphysis

Note: In adults the epiphyseal plate is identified as epiphyseal line.

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7
Q

Histological Long Bone types

A

Woven = Immature bone
Compact= Outer portion of Mature bone
Spongy (aka Trabecular or Cancellous) = Inner portion of bone

-Woven bone has disorganized matrix.

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8
Q

Periosteum

A
  • Covers the outer surface of bones (except articular surfaces, and tendon/ligament insertions).
  • Vascularized
  • Contain osteoprogenitor cells.
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9
Q

Endosteum

A
  • Contain cells belonging to marrow stroma

- Source of cells that line Haversian canals.

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10
Q

1) Name all the Bone Cells

2) All except one is derived from Undifferentiated Mesenchymal cells. Which one?

A
  • Osteoprogenitor cells
  • Osteocytes
  • Osteoblasts
  • Osteoclasts
  • Lining cells

-Osteoclasts are of Hematopoetic lineage

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11
Q

What are Osteoprogenitor Cells?

A

-Differentiate into Osteoblasts when stimulated by transcription factor.

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12
Q

What are Osteoblasts?

A
  • Responsible for laying down bone.
  • Secrete type I collagen and Osteoid.

-Osteoid becomes calcified with Hydroxyapetite (source of calcium and phosphate).

Note: Contain receptors for Parathyroid Hormone.

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13
Q

What are Lining cells?

A

Lining cells are Osteoblasts that have finished laying down Osteoid.

  • Found in endosteum
  • Found lining the Haversian (central) canals in compact bone and the spicules of spongy (or Trabecular/cancellous) bone.
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14
Q

What are Osteocytes?

A

Osteocytes are Osteoblasts that have been completely surrounded by calcified matrix.

  • Maintain the Matrix.
  • Involved with Calcium Homeostasis.
  • Found in Lacunae.
  • Contain long cellular processes that extend into cannaliculi and allow them to communicate via Gap Junctions.
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15
Q

Name the Different States of Osteocytes

A
  • Quiescent
  • Formative
  • Resorptive

Note: Based on environmental conditions, osteocyte can synthesize and degrade.

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16
Q

What are Osteons?

A

Highly organized structures that form Functional unit of bone.

  • Long structures that run parallel to diaphysis of bone.
  • Consists of a Central canal with blood vessels, nerve, and lining cells within it.
  • Perforating vessel connects to Central Canal.
  • Lacunae with Osteoblasts
  • Resorptive channels with Osteoclasts
17
Q

Cancellous Bone

A
  • Lack a central canal
  • Blood supply from highly vascular marrow cavity.

-Osteoclasts are present on the outer surface of Trabeculae in Cancellous (aka Spongy or Trabecular bone).

18
Q

What are Osteoclasts and where do they come from?

A
  • Multinucleated large cells of Hematopoetic lineage.
  • Develop from a stem cell and the fusing of many monocytes.
  • Contain RANK on their surface.
  • Contain receptors for Calcitonin (but not for PTH).

-Involved with the breakdown, remodeling, and resorption of bone.

19
Q

Describe the Ruffled border of Osteoclasts

A
  • Infoldings on the surface of Osteoclasts which create a microenvironment.
  • Microenvironment is Acidic
  • Site of Hydrolytic enzyme release
  • Site of ATP-dependent Proton pump for H+ release.
  • Site of endocytosis of debris from breakdown process

Clinical: Bisphosphonates induce Apoptosis in Osteoclasts and are used as Osteoporosis Rx.

20
Q

Type I Collagen

A
  • Comprises 90% of bone matrix.

- Ground Substance makes up the other 10%

21
Q

What is BMP?

A
  • Bone Morphogenic Protein
  • Can induce differentiation of Osteoblasts.

Clinical: Can be given after Orthopedic Surgery to stimulate Bone Growth.

22
Q

What is a Proteoglycan?

A

Glycosaminoglycans attached to a Protein core.

23
Q

What is Ground Substance made up of?

A
  • Proteoglycans
  • Multiadhesive Proteins
  • BMP
  • Cytokines
24
Q

What are Multiadhesive Proteins?

A

-Attach cells to mineralized matrix.

2 types:

  • Osteonectin: Attaches Collagen to Hydroxyappetite
  • Osteopontin: Attaches Cells to Matrix.
25
Q

What is Periosteum?

A
  • Richly vascular layer that surrounds bone.
  • Contain quiescent cells that still have Osteogenic potential when bone repair is needed.

-Periosteum connects to bone via Collagen fibers.

26
Q

What are the 2 different processes of Bone Formation?

A

-Termed Osteogenesis.

2 Processes:

  • Intermembranous
  • Enchondral

Intermembranous Formation:

  • Bone formed directly from Mesenchymal cells with no Cartilage intermediate.
  • Occurs in Flat bone and during Development of Compact bone.

Enchondral Formation:

  • Hyaline Cartilage is formed from Mesenchymal cells which then gets Calcified.
  • Occurs at Growth plate during development AND during Fracture healing.
  • Occurs in Short and Long bones.
27
Q

Describe Fetal Bone Development

A
  • Fetus starts off with Hyaline Cartilage Template (skeleton)
  • Template covered with Perichondrium.
  • Blood Vessels invade and a Periosteal collar forms around diaphysis.
  • This provides stability for the bone.
  • Calcification of Cartilage begins in the center Diaphysis. This becomes the Primary Ossification center.
  • Compact bone begins to develop along Diaphysis.
  • Bone lengthening begins at Epiphyseal growth plate. This is the Secondary Ossification center (The Epiphysis).
  • Bone replaces cartilage, except at the Articular surface of bone to leave behind Articular Cartilage.
28
Q

Describe the Functional arrangement of Chondrocytes at the Growth Plate.

A

Resting zone:
-Resembles normal Cartilage.

Proliferating zone:
-Chondrocytes are divided and form linear columns.

Hypertrophic zone:
-Glycogen rich Chondrocytes

Calcified zone:
-Chondrocytes that have underwent Apoptosis

Ossification zone:

  • Site where early bone is formed.
  • Recall Woven (immature) bone is formed first and then remodeled into mature bone.
29
Q

Describe Fracture Healing

A
  • Involves Enchondral Bone formation.
  • Several stages.

Inflammation Stage:

  • Hematoma (Clot) forms and recruits inflammatory infiltrate.
  • Growth factors stimulate bone regrowth.

Repair Stage:

  • Fibrocartilaginous (soft) callus forms.
  • Gets calcified and becomes a hard callus.
  • Enchondral bone formation makes trabecular bone
  • Intermembranous bone formation makes compact bone

-Woven bone appears first.

Remodeling stage:
-Woven bone becomes Lamellar bone.

Musculoskeletal (9 decks)

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