Histology - Lectures 9/10 Bones

Front 1

Osteogenic Cells

Back 1

Are spindle shaped connective tissue cells - derived from mesenchyme located in periosteium and endosteym.
Differentiate into osteoblasts which secrete the organic matrix that entraps these cells

Front 2

Affect of low O2 on osteogenic cells?

Back 2

May cause them to change into chondriogenic cells.

Front 3

Osteocytes

Back 3

Are entrapped (live in cavities) called lacunae. Derive from osteoblasts which become trapped in the matrix that they secrete.
Are mature bone cells housed in lacunae and maintain communication through gap junction extending through canaliculi

Front 4

Osteoclasts

Back 4

Osteolyis by creating acid environment that decalcifies bone. Acid hydrolases, collgenous and enzymes degrade decalcified material and cell reabsorbs it. They are derived from monoblasts and are giant multinucleated cells. Are located in depression called Howship's lucanae.

Front 5

Periosteum and Endosteum

Back 5

Periosteum is dense irregular connective tissue that is a membrane that lines the outside of bones. Contains inner layer of osteogenic cells and osteoblasts.
Functions to supply blood to bone.
Appositional growth occurs from osteoblasts from periostium.

Front 6

Bone Matrix composition

Back 6

Organic portion is made of 95% type 1 collagen and ground substance. Contains chondroitin 4 sulfate, chondroitin 6 sulfate and osteomucoid. Has abundance of tyrosine and leucine.
Inorganic portion - 50% dry weight of calcium

Front 7

Sharpey's Fibers

Back 7

Are collagen fibers of the periostium that penetrate the bone matrix, function to attach periosteum to bone.

Front 8

Osteoblasts

Back 8

Derived from osteogenic cells, basophilic. Resemble cuboidal layer as the secrete matrix. As synthesis declines, they become flat. Have cytoplasmic processes that bring them into close contact with other osteoblasts
PAS positive granules - prescursors of GAGS
-becomes entrapped in ow matrix and ceases function to become osteocyte

Front 9

4 Regions of Osteoclasts:

Back 9

1) Ruffed Border - finger live evaginations where active absorption occurs
2) Vesicular region - composed of vesicle-like structures
3) Clear Zone - region of cytoplasm around ruffed border containg microfilaments, which assist osteoclast in keeping contact with bony surface
4) Basal Region - houses the organelles and nuclei

Front 10

Bone Reabsorption

Back 10

Lysozmal enzymes packed in golgi and H+ produced are released into attached bone matrix. acidification of this space facilitates calcium phosphate breakdown from bone. Bone matrix is removed and resorption takes place into cytoplasm of osteoclasts. Digested further and transferred to blood.

Front 11

Compact Bone and Spongy bone

Back 11

1) Adult bone where matrix is laminated. Is very dense.
2_ Filled with spaces, contain bone marrow in long bone - either red hemopoietic cells or yellow fat.

Front 12

Primary Bone

Back 12

Is immature bone (IB) or woven bone. Contains high osteocytes and irregular collagen.
Is remodeled and replaced by secondary or mature bone, except in places like tooth or tendon insertion sites.

Front 13

Secondary Bone

Back 13

Is mature or lamellar bone
Contains haversion system or osteons. Has calicifed matrix arranged in layers of lamellae surround H-cannel.

Front 14

Lamellae

Back 14

Have special arrangement in diaphysis, there is outer and inner circumferential as well as the Haversion systems.

Front 15

Volkmann's Canal

Back 15

Connects haversion canals to the marrow cavity

Front 16

Endosteum

Back 16

Consists of osteogenic cells which line the marrow cavity, volkmann's canal and the Haversion canal.

Front 17

Development of Haversion System - 1

Back 17

1) New Haversion forms under periosteium, longitudinal ridges form and periosteal cell differentiate into osteoblast
2) ridges fuse and groove becomes a bony tunnel enclosing BV

Front 18

Development of Haversion System -2

Back 18

3) Additional bone lamellae are deposited around the tunnel and converted into haversion canal
4) Volkmann canal extending across diaphysis, appositional growth widens the shaft of the bone

Front 19

Intramembranous Bone formation

Back 19

Involves bone formation development within layer of condesned mesenchyme.
- beings with mesenchymal cells condensing to form primary ossification center, give rise to osteoblasts which secrete osteoid.
-spongy bone first developed then BV invade and ossification centers fuse
-flat bones of skull are formed this way

Front 20

Bone Trabeculae

Back 20

Fused spicules - name given to bone developing at these sites.

Front 21

Know these slides

Back 21

Front 22

Endochondral Bone Formation

Back 22

Occurs via a hyaline cartilage template that is laid down and then replaced with bone
1) outline of bone in cartilage
2) formation of periosteum
3) cartilage is calcified
4) Formation of periosteal bud, which have osteogenic cells and BV (primary ossification)

Front 23

Back 23

6) Secondary ossification centers form in epiphyses. Epiphyseal plate (cartialge) forms between primary and secondary ossifcationc enters
3) epiphyseal plate eventuallly disappears
2) Diaphysis and epiphysis marrow cavities fuse

Front 24

How is the secondary ossification center involved growth?

Back 24

Epiphyseal plate adds new cartilage at one end while being replaced at other end. Diapyseal bone and epiphyseal bone eventually become continuos at 20 years.

Front 25

What are the 5 distinctive zones at the epiphyseal plate?

Back 25

Zone of Reserve Cartilage - contains cartilage with small inactive chondrocytes
Zone of cell proliferation: - rapid mitotic divisions five rise to row of cartilage cells
Zone of Cell maturation and hypertrophy: chondrocytes become enlarged and contain glycogen
Zone of Calcifying cartilage: cartilage becomes calcified
Zone of provisional ossification - osteoclasts and osteoblasts break down calcified cartilage and replace with bone

Front 26

Process of Bone Repair

Back 26

1) Hemorrhaging is followed by blood blotting and macrophages remove much of debris
2) Fibroblasts proliferate in periosteium and endosteum to form callus
3) Chondrocytes also differentiate from connective tissue to form cartilage that is replaced by bone via endocondral bone formation - forming bony callus
4) Bony callus is reabsorbed and replaced with secondary bone

Front 27

Functions of bone

Back 27

-support for body and attachment of muscles
-dynamic tissue, undergoes changes in shape
-growth is directed toward applied stress and resorption where pressure is applied
-99% calcium reserve

Front 28

Importance of Vitamin D

Back 28

Can results from low instake calcium which results in inadequate absorption of vitamin D in intestine. Results in poorly calcified bone. Leads to rickets in children and osteomalacia in adults.
- Needed for ossification, too much causes resorption

Front 29

Importance of Vitamin A

Back 29

Deficiency inhibits proper bone formation and growth, while excess accelerate ossification of epiphyseal plates. Results in small stature

Front 30

Importance of Vitamin C

Back 30

Needed for collage formation, its deficiency results in scurvy, characterized by poor bone growth

Front 31

Parathyroid Hormone influence on bone

Back 31

Stimulates osteoclasts to resorb and release calcium, elevation blood calcium. May active osteocytes to initiate osteolysis from their lacunae, elevate blood calcium
-Excess renders bone more susceptible to fracture and calcium deposition in arterial walls and kdiney

Front 32

Calcitonin influence on bone

Back 32

Hormone inhibits matrix resorption, preventing release of calcium

Front 33

Pituitary Growth Hormone

Back 33

Stimulates epiphyseal cartilage growth. Excess produces giant and lack produces dwarf.

Front 34

Sex Hormone influence

Back 34

Influences epiphyseal ossification. Excess results in small stature, lack results in tall stature.