Skeletal tissue

Question 1

Two way of bone formation

Answer 1

Intramembranous ossification - from mesenchyme cells
Endochondral ossification - from cartilage

Question 2

Name the initial trabecular network that laid down in process of bone formations

Answer 2

Primary spongiosa which then transformed into a mature bone

Question 3

Steps involved in intramembranous ossification

Answer 3

1. Vascularisation of mesenchyme, leads mesenchymal stem cells aggregation while in ECM of cellulose and proteoglycan
2. Mesencymal stem cells differentiate into osteoblasts which then converts into osteoid which are unmineralized.
3. Numerous osteogenesis centers develop and fuses eventually - the formed trabeacula gives a spongy appearance known as primary spongiosa
4. Cellulose fibre arranged randomly in this newly created bone matrix - called woven bone
5. Calcium phosphate deposition occurs into bone matrix or osteoid leads to mineralization of the bone
6. This process further leads to osteoblast deposition as osteocyte and remodeling by osteoclast and closure of perivascular channel.

Question 4

Formation of lamellar bone from woven bone

Answer 4

1. Cellulose fibers organized into a bundle with regular orientation
2. Lamella starts organizing into concentric arrangement around central Haversian canal consisting of a blood vessel forms osteons or Haversian system. Membranous bone remains spongy - covered by lamellar internal and external compact bone
3. Periosteum and endosteum are formed from external and internal connective tissue.

Question 5

Bones produced by intramembranous ossification

Answer 5

Clavicle
Cranial bones
Flat bones Skull

Question 6

Steps involved in endochodral ossification

Answer 6

1. Starts when proliferated chondrocytes deposits ECM containing type II collagen
2. Hypertrophy of chondrocytes - release collagen type X specific for hypertrophic chondrocytes
3. Leads to release of VEGF from chondrocytes for angiogenesis - mark as the primary bone development centre
4. Apoptosis of chondrocytes leads to calcification of the matrix
5. Perichondrial cells forms periosteal collar around mid-point of the shaft - diaphysis
6. blood vessels starts invading spaces occupied by chondrocytes on either ends of the shaft - secondary centre of ossification
7. Preosteoblast and blood stem cells deposits from perivascular connective tissue
8. preosteoblast converts to osteoblast then deposit to produce osteoid
9. secondary centre forms into epiphyses.

Question 7

Bones produced by endochondral ossification

Answer 7

Bones of extremities, vertebral column and pelvic bones

Question 8

Different types of bone cells

Answer 8

Osteoprogenitor cells - derived from mesenchymal cells produces osteoblasts
Osteoblast: forms osteoid and facilitate mineralisation, Osteoblast trapped in mineralised bone matrix referred to as osteocytes
Osteoclast: derived from monocytes, phagocytes in skeletal tissue
causes bone resorption

Question 9

Bone remodelling and regulation

Answer 9

1. Remodelling depends on balancing act of osteoblast and osteoclast activity (deposition vs resorption)
2. Osteoclast contains RANK receptor and Osteoblast contains RANKL. interaction between RANK and RANKL increases osteoclasts differentiation and bone resorption
3. Osteoblast produces osteoprotegerin that blocks RANK-RANKL activity and reduces bone resorption
4. PTH increases osteoclast activity and bone resorption
5. Estrogen increases osteoprotegerin activity and reduces osteoclast activity

Question 10

Osteon

Answer 10

produced by concentric arrangement of lamellar bone around central haversian canal consisting of bone vessel

Question 11

Canaliculi

Answer 11

Cytoplasmic process of osteocyte communication and transfer of nutrients from haversian canal to osteocytes further away in concentric ring.