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Histology > Exam 1: Bone > Flashcards

Exam 1: Bone Flashcards

1
Q

Definition of bone tissue

A

A dense, semi rigid, porous, calcified connective tissue

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2
Q

Bone is a composite tissue

A

Mineral - compressive strength

Collagen - tensile and bending strength

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3
Q

Minerals and collagen in bone

A

Minerals - mostly calcium and phosphate

Collagen - mostly type I

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4
Q

Bone hierarchical structure

A

Level 1 - Major components

Level 2 - Mineralized collagen fibril

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5
Q

Major components of bone

A

Organic - Collagen type I and non collagenous proteins

Mineral - hydroxyapatite
•Largest component of bone

Water
•Smallest component of bone

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6
Q

Mineralized collagen fibril

A

Bone basic building block

Collagen type I fibrils are arranged in a staggered way

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7
Q

Definition of bone organ

A

Rigid (but dynamic) organs that build endoskeleton of vertebrates

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8
Q

Functions of bone organ (5)

A

Mechanical support and weight bearing

Muscle attachment sites - movement

Protection of vital structures

Hemopoiesis - RBC and WBC production in red bone marrow

Mineral homeostasis (mostly calcium and phosphate)

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9
Q

Periosteum

A

External membrane, continues with tendons

Outer layer - connective tissue
•Protection

Inner layer - osteogenic layer
•Secretion of more bone

Sharpey’s fibers

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10
Q

Sharpey’s fibers

A

Bundles of Type I collagen fibers connecting periosteum to bone

Embedded directly into the bone

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11
Q

Bone cells stem cell lines

A
  1. Mesenchymal stem cell line

2. Hematopoietic stem cell line

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12
Q

Bone cells from mesenchymal line

A

Osteoblasts - active deposit

Bone lining cells - quiescence

Osteocytes - mature osteoblasts

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13
Q

Bone cells from hematopoietic line

A

Osteoclasts - active resorption

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14
Q

Osteoblasts

A

Line bone’s surfaces

Cytoplasmic processes to contact osteocytes

Secrete osteoid - un-mineralized organic bone material –> mostly collagen type I

Osteoid is typically deposited in layers called lamella

Later osteoblasts also take part in inducing mineralization

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15
Q

Osteoblast can follow 3 different courses

A
  1. Disappear from site of bone formation (apoptosis?)
  2. Become quiescence - bone lining cells
  3. Embedding themselves within osteoid and become osteocytes
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16
Q

Bone lining cells

A

“Resting” osteoblasts

Cytoplasmic processes to contact osteocytes

Remove osteoid - to enable osteoclast to resorb the mineralized matrix

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17
Q

Osteocytes

A

Mature osteoblasts imprisoned in the bone matrix in lacunae

Most of bone cells are osteocytes, last decades

Connected to other osteocytes and to osteoblasts/bone lining cells through cell processes running in canaliculi (lacunocanalicular system)

18
Q

Osteocytes and bone modeling and remodeling

A

osteocytes serve as bone “nervous system”

Bone modeling - osteocytes induce add/remove bone

Bone remodeling - osteocytes induce replacing “dead” bone

19
Q

Osteoclasts

A

Resorb mineralized bone from bone surface (Howship’s lacuna) or from within the bone tissue (Cutting cone)

Multinuclear

20
Q

Formation of bone called

A

Ossification

Osteogenesis

21
Q

Pathways of bone formation

A
  1. Intramembranous ossification: mesenchyme –> bone

2. Endochondral ossification: mesenchyme –> cartilage anlage –> bone

22
Q

Intramembranous ossification

A

Formation of flat bones

Also an essential process during the natural healing of bone fractures

23
Q

Steps in intramembranous ossification

A
  1. Embryonic mesenchyme condenses and angiogenesis starts
    Mesenchymal cells differentiate into osteogenic cells
  2. Osteogenic cell differentiate into osteoblasts, start to deposit osteoid and induce mineralization
    A “network” of trabecular-like structure starts to appear (bone spicules)
  3. More trabeculae form and mineralize
    Additional angiogenesis takes place
  4. Trabeculae at both “surfaces” fill gaps until the cortex is created (compact bone)
    They typical sandwich-like structure of flat bone is created
24
Q

Endochondral ossification

A

Bone develops from a pre-existing hyaline cartilage model

Most long, short, and irregular bones

Ends a puberty, when growth plates (physes) fuse, leaving an epiphysial line

25
Q

Steps in endochondral ossification

A
  1. Mesenchymal cell differentiate into chondroblasts
    •Chondroblasts deposit a hyaline cartilage model
    •Periosteum (osteoblasts) deposit a bone collar around the diaphysis (reinforcement)
    •Cartilage model elongates (interstitial growth) and thickens (appositional growth)
  2. Diaphysis starts to ossify
    •Primary ossification center is resorbed turning into marrow cavity
  3. Blood vessels invade marrow cavity
    •Trabeculae start to form
  4. Formation of secondary ossification centers at both epiphyses
    •The region of transition from cartilage to bone is formed (metaphysis)
  5. Trabecular bone forms at both epiphyses
    •Growth plate (hyaline cartilage) starts to function (interstitial growth)
26
Q

Bone modeling

A

Osteocytes recruit osteoblasts or osteoclasts to add to remove bone

Action of osteoblasts and osteoclasts not coupled

Can happen on any bone surface, but not within bone tissues
•Periosteum, endosteum, trabecular surface

27
Q

Bone remodeling

A

Osteocytes induce replacing “dead” bone or mineralized homeostasis (non targeted remodeling)

Osteoclasts remove bone tissue then osteoblasts deposit new bone to replace it

Action of osteoclasts and osteoblasts is coupled

28
Q

Outcome of bone remodeling from cutting cone

A

Cylindrical structure called secondary osteons or Haversian system

29
Q

Outcome of bone remodeling from Howship’s lacuna

A

Group of lamellae called a hemi osteon or trabecular packet (mostly in trabecular bone)

30
Q

What is a cement line

A

Surrounds secondary osteons and trabecular packets

Reversal line

31
Q

Cement line function

A

Stop progress of micro cracks

32
Q

Interstitial lamellae

A

Remnant of older osteons that were left behind after remodeling took place

33
Q

Cortical bone

A

Compact bone

Outer shell/surface - 5% porosity

34
Q

Trabecular bone

A

Cancellous bone, spongy bone

Lies within the cortical shell - 50-90% porosity

35
Q

Woven bone

A

Primary bone tissue

Loose packing and poor orientation of mineralized collagen fibrils

Laid down very rapidly and randomly - later replaced by lamellar bone (remodeling)

36
Q

Woven bone most common in

A

Young animals (mainly large mammals)

Fracture calluses

Some bone tumors (osteosarcoma)

37
Q

Fibrolamellar bone (plexiform bone)

A

Primary bone tissue

Mainly found in large and rapidly growing mammals

38
Q

Circumferential lamellar bone (CLB)

A

Primary bone tissue

Concentric lamellae under the periosteum or endosteum

Less vascularized

Remodels into secondary osteons

39
Q

CLB - lamellar zonal structure

A

A sequence of structures which repeat every year (like tree rings)

Most reptiles long bones

40
Q

Haversian bone

A

Secondary osteons

Secondary bone tissue

Concentric lamellae

Blood vessels in center (central canal)

Run parallel to the long axis of the bone

Cement line around osteon

41
Q

Haversian bone - Volkmann’s canals

A

Contain blood vessels that run between osteons and connect to the periosteum and endosteum

42
Q

Trabecular packets or hemi-osteons

A

Trabecular remodel almost exclusively on bone surface (Howship’s lacunae)
•Inner part constantly increases in mineral content

Crescent shaped , made of several lamellae

Separated from adjacent body by cement lines (similar to Haversian systems)

Histology (8 decks)

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