TOB L8

Question 1

Describe the composition of bone

Answer 1

Specialised connective tissue
Comprised of calcified ECM

Contains 3 principal cells:

1. Osteoblasts
   synthesise organic components of bone
   Increase conc of Ca2+. Once encased in bone, become osteocytes
2. Osteocytes - found in cavities between bone layers. Bone maintenance.
3. Osteoclasts - multinucleated macrophage-related cells - involved in bone resorption

Question 2

Stages of osteogenesis

Answer 2

Osteogenesis = bone formation

1. Endochondral ossification
2. Intramembranous ossification

Question 3

Describe endochondral ossification

Answer 3

• Method of bone formation
  -One of two main processes in which bones are formed during foetal development + growth of long bones
• MODEL OR TEMPLATE OF FUTURE BONE FORMED FROM HYALINE CARTILAGE (Pre-existing hyaline cartilage template replaced by bone)
• Osteoblasts invade cartilage template
• These osteoblasts originate from circulating osteoprogenitor cells (have potential to differentiate into osteoblasts)
• Osteoblasts deposit osteoid (protein matrix)
• Osteoid acts as substrate for calcification

Question 4

What is osteoid mostly made of?

Answer 4

Osteoid comprised of Type I collagen
Secreted by osteoblasts
Osteoid undergoes calcification as hydroxyapatite crystals become embedded between collagen fibres

Question 5

Describe intramembranous ossification

Answer 5

Second stage of osteogenesis

Bone formation takes place within “membranes” or “condensations” of mesenchymal tissue
Osteoblasts differentiate from local mesenchymal cells + deposit osteoid

Question 6

State an example of a bone that develops by intramembranous ossification

Answer 6

Parietal bone

Question 7

State an example of a bone that develops by endochondral ossification

Answer 7

Developing long bones
Metacarpals of foetal hand

Question 8

Diagram showing hyaline cartilage in pre-pubertal femur

Answer 8

Growth plates, (epiphyseal plates) = areas of hyaline cartilage located at the ends of long bones, including femur. 6 Plates are responsible for longitudinal bone growth (contributes to increase in length) during the growing years of an individual.

Question 9

Diagram showing coronal section of pre-pubertal femur

Answer 9

Coronal = cross sectional

Question 10

Diagram showing epiphysis of an adult long bone

Answer 10

Question 11

Detailed process of endochondral ossification

Answer 11

1. Early stage of foetal development (utero). skeletal elements incl long bones start as hyaline cartilage models (templates)
2. End of 1st trimester, bone collar forms around middle of long bone. Due to deposition of bone tissue (OSTEOID) on surface of cartilage template. Causes underlying hyaline cartilage to degenerate

3.Capillaries + osteoprogenitor cells invade bone collar. Invasion creates PRIMARY OSSIFICATION CENTER - region where first bone tissue formed. Osteoprogenitor cells differentiate into osteoblasts. Osteoblasts secrete osteoid
Osteoid is calcified (process where minerals are deposited, calcium + phosphorus)
Woven bone formed.

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