Exam 1: Bone

Question 1

Definition of bone tissue

Answer 1

A dense, semi rigid, porous, calcified connective tissue

Question 2

Bone is a composite tissue

Answer 2

Mineral - compressive strength

Collagen - tensile and bending strength

Question 3

Minerals and collagen in bone

Answer 3

Minerals - mostly calcium and phosphate

Collagen - mostly type I

Question 4

Bone hierarchical structure

Answer 4

Level 1 - Major components

Level 2 - Mineralized collagen fibril

Question 5

Major components of bone

Answer 5

Organic - Collagen type I and non collagenous proteins

Mineral - hydroxyapatite
•Largest component of bone

Water
•Smallest component of bone

Question 6

Mineralized collagen fibril

Answer 6

Bone basic building block

Collagen type I fibrils are arranged in a staggered way

Question 7

Definition of bone organ

Answer 7

Rigid (but dynamic) organs that build endoskeleton of vertebrates

Question 8

Functions of bone organ (5)

Answer 8

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)

Question 9

Periosteum

Answer 9

External membrane, continues with tendons

Outer layer - connective tissue
•Protection

Inner layer - osteogenic layer
•Secretion of more bone

Sharpey’s fibers

Question 10

Sharpey’s fibers

Answer 10

Bundles of Type I collagen fibers connecting periosteum to bone

Embedded directly into the bone

Question 11

Bone cells stem cell lines

Answer 11

1. Mesenchymal stem cell line

2. Hematopoietic stem cell line

Question 12

Bone cells from mesenchymal line

Answer 12

Osteoblasts - active deposit

Bone lining cells - quiescence

Osteocytes - mature osteoblasts

Question 13

Bone cells from hematopoietic line

Answer 13

Osteoclasts - active resorption

Question 14

Osteoblasts

Answer 14

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

Question 15

Osteoblast can follow 3 different courses

Answer 15

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

Question 16

Bone lining cells

Answer 16

“Resting” osteoblasts

Cytoplasmic processes to contact osteocytes

Remove osteoid - to enable osteoclast to resorb the mineralized matrix

Question 17

Osteocytes

Answer 17

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)

Question 18

Osteocytes and bone modeling and remodeling

Answer 18

osteocytes serve as bone “nervous system”

Bone modeling - osteocytes induce add/remove bone

Bone remodeling - osteocytes induce replacing “dead” bone

Question 19

Osteoclasts

Answer 19

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

Multinuclear

Question 20

Formation of bone called

Answer 20

Ossification

Osteogenesis

Question 21

Pathways of bone formation

Answer 21

1. Intramembranous ossification: mesenchyme –> bone

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

Question 22

Intramembranous ossification

Answer 22

Formation of flat bones

Also an essential process during the natural healing of bone fractures

Question 23

Steps in intramembranous ossification

Answer 23

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

Question 24

Endochondral ossification

Answer 24

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

Question 25

Steps in endochondral ossification

Answer 25

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)

Question 26

Bone modeling

Answer 26

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

Question 27

Bone remodeling

Answer 27

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

Question 28

Outcome of bone remodeling from cutting cone

Answer 28

Cylindrical structure called secondary osteons or Haversian system

Question 29

Outcome of bone remodeling from Howship's lacuna

Answer 29

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

Question 30

What is a cement line

Answer 30

Surrounds secondary osteons and trabecular packets Reversal line

Question 31

Cement line function

Answer 31

Stop progress of micro cracks

Question 32

Interstitial lamellae

Answer 32

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

Question 33

Cortical bone

Answer 33

Compact bone Outer shell/surface - 5% porosity

Question 34

Trabecular bone

Answer 34

Cancellous bone, spongy bone | Lies within the cortical shell - 50-90% porosity

Question 35

Woven bone

Answer 35

Primary bone tissue Loose packing and poor orientation of mineralized collagen fibrils Laid down very rapidly and randomly - later replaced by lamellar bone (remodeling)

Question 36

Woven bone most common in

Answer 36

Young animals (mainly large mammals) Fracture calluses Some bone tumors (osteosarcoma)

Question 37

Fibrolamellar bone (plexiform bone)

Answer 37

Primary bone tissue Mainly found in large and rapidly growing mammals

Question 38

Circumferential lamellar bone (CLB)

Answer 38

Primary bone tissue Concentric lamellae under the periosteum or endosteum Less vascularized Remodels into secondary osteons

Question 39

CLB - lamellar zonal structure

Answer 39

A sequence of structures which repeat every year (like tree rings) Most reptiles long bones

Question 40

Haversian bone

Answer 40

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

Question 41

Haversian bone - Volkmann's canals

Answer 41

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

Question 42

Trabecular packets or hemi-osteons

Answer 42

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)