Bone Flashcards

1
Q

What is the name of the cells that develop into osteocytes?

A

Osteoprogenitor cells –> Osteoblasts –> osteocytes

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2
Q

What is the difference between osteoblasts and osteoclasts?

A

Osteoblasts are the cells responsible for formation of bone, while osteoclasts are responsible for breaking down bone.

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3
Q

What is present in the extracellular substance of bone?

A

Present in the EC substance of bone is:¨

  1. Calcium phosphate (70%).
    - Appears as hydroxyapatite crystals (40x25x3 nm, between and within collagen fibrils and also in the ground substance)
  2. Collagen type 1
  3. Ground substance which is called osteoid in bone
    - Proteoglycan
    - Glycoproteins
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4
Q

What are some common glycoproteins present in bone?

A

Some common glycoproteins present in bone are:

  1. Osteonectin
  2. Osteocalcin
  3. Osteopontin
  4. Bone sialoprotein 2
  5. Proteases, alkaline phosphatase (enzymes)
  6. Bone morphogenetic proteins
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5
Q

What is the function of osteonectin?

A

Osteonectin binds crystals to collagen.

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6
Q

What is the function of osteocalcin?

A

Osteocalcin binds ca and participates in mineralization

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7
Q

What is the function of osteopontin?

A

Osteopontin binds cells with ground substance

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8
Q

What is the function of Bone sialoprotein 2?

A

Bone sialoprotein 2 strongly promotes mineralization.

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9
Q

What are the function of the enzymes proteases and alkaline phosphatase?

A

These enzymes participate in mineralization and bone modeling

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10
Q

What is the function of bone morphogenetic proteins?

A

Bone morphogenetic proteins promote differentiation of osteoblasts –> induce the formation of new bones

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11
Q

What is the form of osteoprogenitor cells?

A

Osteoprogenitor cells are spindle-shaped (like a spider)

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12
Q

What is the main function of osteoprogenitor cells?

A

Osteoprogenitor cells are active in fetal bone development. In mature bone, where there is no active new bone-development or remodeling, the osteoprogenitor cells become flattened and spindle-shaped cells closely applied to the bone surface (in the periosteum, vascular canals, and endosteum), where they are sometimes referred to as inactive osteoblasts.

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13
Q

What is the form of osteoblasts and is their cytoplasm basophilic or acidophilic?

A

Osteoblasts are cuboidal in shape and has a basophilic cytoplasm

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14
Q

What is the main role of the RER and Golgi in osteoblasts?

A

The RER and Golgi in osteoblasts are responsible for producing components of the extracellular substance and control its mineralization.

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15
Q

What is the main function of osteoblasts?

A

Osteoblasts are very active in fetal bone development and in mature bone repair and remodeling.

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16
Q

Where are the osteoblasts found in bone tissue?

A

Active osteoblasts are found in areas of remodeling and repair. Inactive osteoblasts are found in the endosteum and vascular channels.

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17
Q

What happens to the osteoblasts as the bone formation and remodeling processes come to an end?

A

The osteoblasts are then transformed into osteocytes

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18
Q

What form do osteocytes have?

A

Osteocytes are flattened and have a large nucleus.

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19
Q

How are the osteocytes interconnected to each other?

A

The osteocytes have long processes with gap junctions that interconnects the osteocytes to each other.

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20
Q

Which spaces do the osteocytes and their processes occupy in the extracellular substance of bone?

A

The non-mineralized spaces in EC substance. The osteocytes occupy lacunae and their processes occupy bone canaliculi.

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21
Q

Why is the diffusion of substances possible in osteocytes despite the fact that it is surrounded by the mineralized walls of lacunae and canaliculi?

A

Between the osteocytes and the mineralized walls of lacunae and canaliculi, there is a thin layer of fluid that is highly hydrated and non-mineralized.

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22
Q

What are the main functions of osteocytes?

A

Osteocytes participate in bone remodeling and in keeping the calcium balance in body fluids.

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23
Q

What are the three main types of osteocytes?

A

There are three types of osteocytes:

  1. Quiescent (resting) osteocytes.
  2. Formative osteocytes
  3. Resorptive osteocytes
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24
Q

What are the characteristics of quiescent osteocytes?

A

Quiescent osteocytes are the most numerous but has poorly developed organelles.

25
Q

What are the characteristics of formative osteocytes?

A

Formative osteocytes have more RER and Golgo and produce small amounts of extracellular substance.

26
Q

What are the characteristics of resorptive osteocytes?

A

Resorptive osteocytes have some RER, Golgi and lysosomes. They break down the surrounding EC substance by releasing proteinases (MMPs) that sets free Ca ions.

27
Q

What makes an osteocyte change its functional state and send signals to other osteocytes, osteoblasts, and osteoclasts?

A

Osteocytes react to changes in mechanical loads.

  1. They react to pulling forces acting on the cell membrane integrins.
  2. By the use of cilium, they react to movement and pressure of fluids in the periosteocytic space.
  3. They coordinate their activity by exchanging chemical signals (Ca, cAMP) via gap junctions.
28
Q

Where are osteoclasts produced?

A

Osteoclasts are produced in the bone marrow (macrophage-related).

29
Q

What is the main function of osteoclasts?

A

Osteoclasts are able to destroy both extracellular and intracellular bone tissue - crucial for bone formation, repair and remodeling.

30
Q

Are osteoclasts small or large, and do they have a nucleus?

A

Osteoclasts are large multinucleated cells.

  • They have multiple deep invaginations of the cell membrane.
  • They do also have numerous endocytotic vesicles - hydrolase vesicles and lysosomes.
31
Q

How (what is the steps) do osteoclasts digest bone?

A
  1. Seals of the space beneath the ruffled border by integrin ring.
  2. Release of H+ ions –> acidification and dissolution of hydroxyapatites
  3. Release of lysosomal enzymes (exocytosis of hydrolase vesicles) –> extracellular digestion.
  4. Endocytosis of predigested bone fragments and further intracellular digestion.
32
Q

What does bone marrow stromal cells secrete?

A

Bone marrow stromal cells secrete M-CSF which induces expression of RANK receptor in mononuclear osteoclast precursors.

33
Q

What special ligand do osteoblasts express?

A

Osteoblasts express a ligand for the receptor (RANKL). Binding of that ligand to the receptor induces differentiation and fusion of precursors into multinucleated osteoclasts.

34
Q

What substance do osteoblasts produce that blocks RANK - inhibits osteoclast formation?

A

Osteoprotegerin (OPG) blocks RANK.

35
Q

What is osteoporosis?

A

Osteoporosis is an diseased caused by excessive activity of osteoclasts resulting in a reduction in the amount of bone tissue components.

36
Q

What is bone lamella?

A

Bone lamella is the structural unit of mature bone and is about 3-5 micrometers thick.

37
Q

What are the components of lamella?

A

Lamella has mineralized substance with parallelly oriented collagen fibers. In the lacunae and the canaliculi, it is present osteocytes and their processes.

38
Q

What two types of mature bone do we have?

A
  1. Spongy bone (cancellous)

2. Compact bone.

39
Q

What is bone trabeculae?

A

Trabeculae are the thin columns and plates of bone that create a spongy structure in a cancellous bone, which is located at the ends of long bones and in the pelvis, ribs, skull, and vertebrae. This is built by parallel lamellae.

40
Q

Where do you find spongy bone?

A

You find spongy bone in flat and irregular bones, epiphyses of long bones.

41
Q

What do the concentric lamellae form in compact bone?

A

In compact bone (Haversian bone), concentric lamellae form osteon around blood vessels located in the central (Haversian) canals. Parallel osteons form the bone.

42
Q

Where do you find compact bone?

A
  1. In the shafts of long bones

2. The superficial (cortical) layer of other bones.

43
Q

What is the size of an osteon?

A

An osteon can vary from a few millimeters to 2 cm long. I can be up to 300 micrometers in diameter.

44
Q

What does an osteon contain?

A

An osteon contains 5-15 concentric bone lamellae with a vascular canal in the center containing a capillary, sometimes a nerve fiber, osteogenic cells, inactive osteoblasts, and osteoclasts.

  • The oxygen and nutrients do only come from the capillary in the Haversian canal. (No communication between osteons.
45
Q

What types of lamellae do you find in long bone shafts and where do you find it?

A
  1. Systemic lamellae (in osteons)
  2. Intersystemic lamellae (between osteons)
  3. Circumferential (near the inner and outer surface of the compact bone)
46
Q

What is Volkmann’s canal?

A

Volkmann’s canals are any of the small channels in the bone that transmit blood vessels from the periosteum into the bone and that communicate with the Haversian canals.

47
Q

What is periosteum?

A

The periosteum is a layer of dense connective tissue that contains blood vessels, osteoprogenitor cells, and inactive osteoclasts.

48
Q

What is endosteum?

A

Endosteum is a single layer of flat cells (inactive osteoblasts) lining the inner surfaces of the bone.

49
Q

Which two types of ossification do we have? (bone formation)

A
  1. Intramembraneous (flat bones)

2. Endochondral (long bones, skull base, vertebrae, pelvis)

50
Q

What are the steps of intramembranous ossification?

A
  1. Mesenchymal cells produce a small area of mineralized bone matrix (osteoid).
  2. Then mesenchymal cells differentiate into osteoprogenitor cells and osteoblasts which produce and mineralize the EC substance.
  3. The osteocytes becomes interconnected by cytoplasmic processes, surround themselves by mineralized EC substance and transform into osteocytes.
  4. Primary bone trabeculae are formed and undergo further remodeling. Spongy bone is formed this way.
51
Q

What are the steps of endochondral ossification?

A

Endochondral ossification leads to the transformation of fetal long bone built of hyaline cartilage into long-bone with bone marrow cavity and epiphyseal plates.

  1. Degeneration and mineralization of cartilage inside the shaft and formation of bone collar around the shaft.
  2. Invasion of periosteal bud with blood vessels and osteoprogenitor cells.
  3. Destruction of cartilage, the formation of bone marrow cavity and new bone.
  4. Formation of growth plates in the cartilage between shaft and epiphyses.
  5. After birth: Formation of secondary ossification centers in the epiphyses, ossification of the epiphysis.
  6. Ossification of growth plates, termination into bone growth.
52
Q

How are the extracellular substance mineralized?

A
  1. It begins with the formation of matrix vesicles released by degenerating chondrocytes and osteoblasts. These vesicles contain a high concentration of phosphate and calcium ions.
  2. Hydroxyapatite crystals grow inside these vesicles. These crystals pierce the vesicle membrane and become the centers (nidi) of crystallization.
  3. The crystals then grow and fuse invading the extracellular substance.
53
Q

What is intersystemic lamellae?

A

Intersystemic lamellae are remnants of ostens which were partially destroyed during remodeling.

54
Q

Does the articular cartilage (hyaline) contain perichondrium?

A

No

55
Q

What is the joint capsule made of?

A

The joint capsule is made of a fibrous layer (dense connective tissue)

56
Q

What is the synovial layer (membrane) made of?

A

The synovial layer is made of loose connective tissue.

  • Contains macrophages (A synoviocytes)
  • Fibroblasts (B synoviocytes) - secrete synovial fluid.
57
Q

Does the joint contain blood vessels?

A

Yes

58
Q

What is arthritis?

A

Arthritis is a mobility limiting condition caused by the degeneration of articular cartilage. Causes can be long-lasting micro-injuries and overloading.

59
Q

What is the cause of rheumatoid arthritis?

A

The cause of rheumatoid arthritis can be attack of the immune system against the connective tissue and cartilage of the joints. Often seen in younger patients.