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Histology > Bone Tissue > Flashcards

Bone Tissue Flashcards

1
Q

in the structure of bone, describe the bone matrix…

- two portions of bone matrix

A
  1. inorganic portion of bone matrix is composed of calcium, phosphate, micarbonate, citrate, magnesium, potassium and sodium - also hydroxyapatite crystals
  2. organic portion of bone matrix is consists of typle I collagen. with a ground substance that contains chondroitin sulphate and keratin sulphate.
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2
Q

in the structure of bone, waht is bone sialoprotein?

A

bone sialoprotein is a matrix protein that binds to integrins of the osteoblasts and osteocytes and is thus related to the adherence of bone cells to bone matrix

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3
Q

in the structure of bone, what are osteocalcin and osteopontin?

A

osteocalcin and osteopontin are glycoproteins that bind to hydroxyapatite asa well as integrins on osteoblasts and osteocytes

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4
Q

in the structure of bone, what is the periosteum?

  1. describe its structure…
  2. how is the periosteum connected to the bone surface?
A

the periosteum is a non-calcified connective tissue covering bone on its external surfaces, except at synovial articulations and muscle attachments.
1. periosteum is composed of an outer dense fibrous connective tissue (collegenous layer) and an inner cellular osteoprogenitor layer

 2. sharpey fibres (type I collagen) attach the periosteum to the bone surface
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5
Q

what is the function of the periosteum of bone?

A

the periosteum functions to distribute blood vessels to bone

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6
Q

in the structure of bone, what is the endosteum?

A

the endosteum is a thin specialised connective tissue that lines the marrow cavitives and supplies osteoprogenitor cells and osteoblasts for bone growth and repair

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7
Q

bone cells: what are osteoprogenitor cells?

  1. derived from…
  2. location…
  3. what can they differentiate to?
A

osteoprogenitor cells are spindle-shaped cells

  1. derived from the embryonic mesenchyme
  2. they are located in the periosteum and the endosteum
  3. osteoprogenitor cells are capable of differentiating into osteoblasts.
    - however, at low oxygen tensions they may change into chondrogenic cells
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8
Q

bone cells: what are osteoblasts cells?

  1. what do they secrete/produce?
  2. derived from…
  3. what do they mature to?
A

osteoblsats are the cells responsible for the production of the organic portion of the bone matrix - including type I collagen, proteoglycans and glycoproteins - secreted as osteoid (uncalcified bone matrix)
osteoblasts possess cytoplasmic processes with which they contact other osteoblasts and osteocytes - communicating via gap junctions.
an actively secereting osteoblasts has a well developed golgi complex and abundant RER.

  1. osteoblasts secrete organic portion of the bone matrix as well as producing:
    • macrophage colony stimulating factor
    • RANKL
    • osteocalcin (bone mineralisation)
    • osteopontin (zone sealing formation)
    • osteonectin
    • bone sialoprotein
  2. osteoblasts are derived from osteoprogenitor cells under the influence of bone morphogenic protein (BMP) family and transforming factor-B
  3. a fully embedded osteoblast within a lacunae and surrounded by the bone matrix it has secreted is called an osteocyte.
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9
Q

bone cells: what are osteocytes?

1. what do osteocytes contain?

A

osteocytes are mature bone cells housed in their own lacunae.
osteocytes have narrow cytoplasmic processes that extend throughout canaliculi in the calcifies matrix - which maintain communication with other osteocytes via gap junctions between their processes

  1. osteocytes contain abundant heterochromatin, little RER and small golgi complex
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10
Q

bone cells: what are osteoclasts?

  1. derived from…
  2. stimulation of osteoblasts that involve osteoclasts
A

osteoclasts are large, motile, multinucleated (<50) cells that resorb bone

  1. osteoclasts are derived from the mononuclear-phagocyte system.
    - they possess surface cell receptors
  2. osteoblasts stimulated by PTH promote osteoclast formation.
    osteoblasts stimulated by calcitonin inhibit osteoblast formation by stimulating osteoid production and deposition of calcium
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11
Q

where are osteoclasts found?

A

osteoclasts form and reside in depressions called Howship’s lacunae - areas of bone resorption

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12
Q

what are Howship’s Lacunae?

A

Howship’s lacunae are formed by the resorption of bone by osteoclasts. they house osteoclasts.

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13
Q

what are the 4 regions of an osteoclast?

A
  1. Basal zone
  2. ruffled border
  3. clear zone
  4. vesicular zone
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14
Q

what is the basal zone of an osteoclast?

A

the basal zone of an osteoclast houses most organelles and is the furthest region from the subosteoclastic compartment

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15
Q

what is the ruffled border of an osteoclast?

A

the ruffled border is the site of bone resorption.
the ruffled border is composed of irregular fingerlike cytoplasmic projections extending into the subclastic compartment - becomes Howship’s lacunae through further bone resorption

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16
Q

what is the clear zone of an osteoclast?

A

the clear zone surrounds the ruffled border of an osteoclast.
the clear zone contains actin filaments at the periphery that helps osteoclasts maintain contact with the bony surface and isolates the region of osteolytic activity

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17
Q

what is the vesicular zone of an osteoclast?

A

the vesicular zone contains exocytotic and endocytotic vesicles travelling between the howship’s lacunae and the inferior of the cell.

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18
Q

what does osteopontin do?

what cell secretes osteopontin?

A

osteopontin is secreted by osteoblasts and is used to seal the zone between the osteoclasts and the subosteoclastic compartment

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19
Q

how is bone resorbed by osteoclasts? (3 steps)

A
  1. osteoclasts secrete acid, which decalcifies the surface layer of bone
  2. proteolytic enzymes are secreted by osteoclasts to degrade the organic protion of the bone matrix
  3. osteoclasts resorb the organic and inorganic portions of the bone matrix and release them into connective tissue capillaries.
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20
Q

classification of bone: what are the two types of bone under gross observation?

A
  1. spongy/cancellous bone

2. compact/dense bone

21
Q

classification of bone: what is spongy bone?

A

spongy or cancellous bone is composed of interconnected trabecullae. bony trabecullae surround cavities filled with bone marrow.
the trabecullae are lined on both surfaces by a single layer of osteoblasts.

SPONGY bone is always surrounded by COMPACT bone

22
Q

classification of bone: what is compact bone?

A

compact bone has no trabecullae or bone marrow cavities

23
Q

classification of bone: what are the two types of bone under microscopic observation?

A
  1. primary/woven/immature bone

2. secondary/lamellar/mature

24
Q

classification of bone: what is primary bone?

A

primary bone is the first compact bone produced during feotal development or bone repair

primary bone conatins many osteocytes and large, irregulary arranged type I collagen bundles

primary bone has a low mineral content

primary boneis remodelled and replaced by secondary bone

25
Q

classification of bone: what is secondary bone?

A

secondary bone is the compact bone found in adults

secondary bone has a calcified matrix arranged in layers called lamellae. each lamella being 3-7um thick

secondary bone contains osteocytes in lacunae between lamellae.

26
Q

In compact bone, what are the 3 element that characterise lamellae organisation?

A
  1. Haversian systems (osteons)
  2. interstitial lamellae
  3. outer and inner circumferential lamellae
27
Q

describe haversian systems of lamellae in compact bone…

A

Haversian systems are long cylindrical structures that run parallel to the long axis of the diaphysis

  - Haversian systems are composed of 4-20 lamellae surrounding a central haversian canal, which contains blood vessels, nerves and loose connective tissue.
  - lined by osteoprogenitor cells and osteoblasts
  - often surrounded by an amorphous cementing substance
  - interconnected by Volkmann canals, which connect to the periosteum and endosteum and carry the neurovascular system.
28
Q

what are Volksmann canals?

A

Volksmann canals interconnect Haversian systems and connect to the periosteum and endosteum carrying the neurovascular supply.

29
Q

in the organisation of lamellae, what are interstitial lamellae?

A

interstitial lamellae are irregullary shaped lamellae between Haversian systems. they are remnants of remodeled Haversian systems.

30
Q

in the organisation of lamellae, describe the outer and inner circumferential lamellae…

A

the outer and inner circumferential lamellae are located at the external and internal surfaces of the diaphysis.

31
Q

what two processes do histogenesis of bone occur?

A
  1. intramembranous bone formation
  2. endochondral bone formation

both produce histologically identical bone. bone formation and resorption of bone occurs throughout life

32
Q

what is the process of intramembranous bone formation?

what type of bone is it involved in forming?

A

process of intramembranous bone formation:
1. mesenchymal cells in the vasuclar zone condense into primary ossification centres, differentiate into osteoblasts and begin secreting osteoid

  1. as calcification occurs, osteoblasts become trapped in their own matrix and becomes osteocytes. centres of developing bone are called trabeculae (fused spicules)
  2. fusion of bony trabecullae produces spongy boe as blood vessels invade the area - other undifferentiated mesenchymal cells gives rise to the bone marrow
  3. the periosteum and endosteum develop from portions of the mesenchymal layer that do not undergo ossification
  4. mitotic activity of the mesenchymal cells gives rise to osteoprogenitor cells within the inner layer of the developing periosteum

intramembranous bone formation is the process by which most flat bones are formed.

33
Q

what are the two stages of endochondral bone formation?

what type of bone is it involved in forming?

A

process of endochondral bone formation…
endochondral bone formation begins with a hyaline cartilage template for the bone. process occurs in the formation of long bone

two stages of endochondral bone formation involves the development of two ossification centres:

  1. primary centre of ossification develops at the midriff of the diaphysis of the hyaline cartilage model:
  2. secondary centre of ossification deveops at the epiphysis
34
Q

what are the events that occur in the primary ossification centre?

A
  1. vascularisation of the perichondrium - transformation of chondrogenic cells to osteoprogenitor cells - forming the periosteum
    2. osteoblasts elaborate matrix deep to periosteum forming a subperiosteal bone collar
    3. chondrocytes at cartilagenous core undergo hypotrophy and degenerate - marrow spaces
    4. osteoclasts create perforations in bone collar that permit the periosteal bud to enter the newly formed spaces in the artilagenous model. cartilage becomes calcified
    5. newly developed osteoblasts elaborate bone matrix that becomes calcified on the surface of calcified cartilage
    - calcified cartilage-calcified bone complex
    - calcified cartilages stain basophilic
    - calcified bone stains acidophilic
    6. subperiosteal bone collar becomes thicker and elongates towards the epiphysis
    7. osteoclasts begon to resorb the CC-CB complex thus enlarging the primitive marrow cavity
    8. repetition of this sequence results in bone formation spreading towards the epiphysis
35
Q

what are the events that occur in the secondary ossification centre?

A

the events are similar to those that occur in the primary ossification centre with the exception of a bone collar formation.

 - when epiphysis are filled with bone matrix produced by osteoblasts differentiated by invaded osteoprogenitor cells, cartilage remains in two areas
        1. articular surfaces
        2. epiphyseal plates
 - epiphyseal plates continue to grow by adding new cartilage at the epiphyseal end while it is being replaced by bone at the diaphyseal end (bone lengthening)
 - ossification and growth ceases at around 20 years old
36
Q

describe the process of bone lengthening

at what age does bone lengthening stop?

A

in the secondary ossification centre:
- epiphyseal plates continue to grow by adding new cartilage at the epiphyseal end while it is being replaced by bone at the diaphyseal end (bone lengthening)

 - ossification and growth ceases at around 20 years of age
37
Q

what are the 5 distinct zones of the epiphyseal plates?

A
  1. zone of reserve
    - cartilage on the epiphyseal side of the plate. pocess small, randomly arranged, inactive chondrocytes
  2. zone of proliferation (of chondrocytes)
    - region of rapid mitiotic division
  3. zone of cell hypertrphy and maturation
    - chondrocytes are enlarged
  4. zone of calcification
    - chondrocytes die and cartilage is calcified
  5. zone of ossification
    - osteoblasts eaborte bone matrix
    - forming CC-CB complex
    - then resorbed and replaced by bone
38
Q

what are osteonectin, proteoglycans and sialoprotein know to stimulate?

A

calcification

39
Q

how is bone calcified?

A
  1. matrix vesicles released by osteoblasts cntain high concentrations of Ca2+ and PO43- ions along with organic compounds and enzymes
  2. calcium pumps in matrix membrane bring in calcium, forming calcium hydroxyapatite crystals - puncturing vesicles
  3. now free calcium hydroxyapatite crystals in the matrix becomes NIDI of crystalisation
  4. enzymes free phosphate and react with calcium forming calcium phosphate
  5. calcium phosphate begins to calcify the matrix around the NIDI of cystalisation
  6. water removed
  7. NIDI of mineralisation enlarge and fuse eventually calcifying the entire matrix
40
Q

how is a bone fracture repaired?

A

a bone fracture damages bone matrix, cells and blood vessels in the region accompanied by localised haemorraging and blood clot formation.

1. proliferation of osteoprogenitor cells - in periosteum and endosteum of the fracture. cellular tissue surrounds the fracture and between damaged bone
2. formation of a bony callus
        - fibrous connective tissue and hyaline cartilage formed
        - endochondrial bone formation of primary bone
        - also intramembranous bone formation or primary bone
        - trabeculae of primary bone join ends forming a bony callus
        - primary bone resorbed and replaced by mature bone
41
Q

how is vitamin D involved in bone formation?

what is the result of an excess or deficiency of vitD?

A

vitamin D is involved in the absorption of calcium from small intestine and in bone formation

excess = bone absorption

deficiency = rickets in children (poorly calcified, soft bone) and osteomalacia in adults (calcium deficiency)

42
Q

what are 3 hormones involved in bone formation?

A
  1. parathyroid hormone (PTH)
  2. calcitonin
    3 pituitary growth hormone
43
Q

how is PTH involved in bone formation?

A

Parathyroid hormone activates osteoblasts to secrete osteoclast-stimulating factor which activates osteoclasts to resorb bone, thus elevating blood calcium levels

44
Q

how is calcitonin involved in bone formation?

A

calcitonin is produced by parafollicular cells (C cells) of thyroid
calcitonin eliminates the ruffled border of osteoclasts and inhibits bone matrix resorption, thus preventing the reserve of calcium

45
Q

how is pituitary growth hormone (somatotropin) involved in bone formation?
what does a deficiency in children cause?
what does an excess in adults cause?

A

somatotropin is produced by the pars distalis of the pituitary gland and is involved in overall growth stimulation

deficit in children = dwarfism
excess in adult (growing years) = pituitary gigantism and acromegaly

46
Q

what bone cells occupy Howship’s lacunae?

A

Osteoclasts occupy Howship’s lacunae.

osteoclasts are multinucleated that produce proteolytic enzymes. osteoclasts are derived from the monocyte precursors.

47
Q

the inner layer of the periosteum is lined with…?

A

osteoprogenitor cells.

the outer layer is fibrous. the periosteum functions to distribute blood vessels to the bone; appositional bone growth takes place her

48
Q

where can hyaline cartilage be found?

A

articulating ends of long bones

hyaline cartilage grows both interstitially and appositionally. it is avascular and contains type II collagen

Histology (16 decks)

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