1. Bone Cartilage & Growth

Question 1

What are the 4 functions of bone?

Answer 1

Structural support
Protection
Leverage
Storage (mineral reservoir)

Question 2

What are the three cells found in bone?

Answer 2

Osteoblasts, Osteocytes, Osteoclasts

Question 3

What are osteoblasts? Describe their function

Answer 3

Derived from mesenchymal stem cells and are the primary cell in bone formation

Synthesise & secrete osteoid

Active in the mineralisation process

Question 4

What are osteocytes? Describe their function

Answer 4

Differentiated osteoblasts that are housed in lacunae & are arranged in concentric rings of bone called lamellae. They have interconnecting canaliculi which allow for contact between cell processes.

They balance the strength of the matrix by sensing the microcurrents created by bending on the bones and then either add or remove calcium

Question 5

What are osteoclasts?
Describe their function

Answer 5

Multinucleated cells derived from bone marrow that secrete protons creating an acidic environment causing demineralisation.

The side of the cell closest to the bone contains microvilli that extend into the bone’s surface, forming brush, border that is the cell’s active region

Question 6

What is the osteoid?

Answer 6

An organic ground substance secreted by osteoblasts.

It consists of numerous collagen fibres among other minerals

Question 7

What is the inorganic component of bone?

Answer 7

Composed of large crystals such as calcium and phosphate, which mineralise the osteoid, forming ossein

-Makes up 60-70% of dry weight
-Make bones radiopaque

Question 8

Describe mineralisation of bone

Answer 8

Inorganic components are transported & deposited into the osteoid from blood the vessels, using the collagen fibres as ‘scaffolding’. Transforming the uncalcified osteoid, to calcified Ossein

70-80% calcifies just before birth so its more malleable when moving through the birth canal

Question 9

What are the two bone tissue types called?

Answer 9

Woven & Lamellar

Question 10

What is woven bone?

Answer 10

The first type of bone laid down within the foetus.

It consists of ‘woven’ collagen fibres which calcify quickly.

-It is only after birth that this bone is then remodelled

-During fracture repair this bone is also laid down first

Question 11

What is lamellar bone?

Answer 11

Thin layers of osteoid secreted by osteoblasts in concentric ring (lamellae) within which collagen fibres are arranged in parallel.

The structural units are osteons (Haversian system).

Two types of bone are formed from this bone tissue:
-Cortical
-Trabecular

Question 12

What is fibrolamellar bone?

Answer 12

Arrangement of fibres to dissipate forces on the bone.

They are located on the periosteal surface

Question 13

What is osteonal bone?

Answer 13

Series of concentric rings made up of layers of bone matrix around a haversian canal

Primary Osteons
-Formed during appositional bone growth

Secondary Osteons
-Formed during bone remodelling

Question 14

What is a haversian canal?

Answer 14

A tube containing a blood vessel, lymphatic vessel and nerves through the bone

Question 15

What is a volkmanns canal?

Answer 15

Transverse vessels through bone and allow for communication between the haversian canals to the periosteum, endosteum & medullary cavity

Question 16

Outline Perichondral Ossification

Answer 16

Hyaline cartilage forms as a precursor to bone, it is surrounded by a membranous layer known as the perichondrium

The perichondrium delivers osteoblasts to the edge of the structure, ossifying itself forming the periosteal bone collar around the diaphysis. This ossification forms to each epiphyses forming the perichondrium

This bony structure prevents nutrients form diffusing into the cartilage precursor resulting in calcification of the cartilage matrix

Question 17

Outline Endochondral Ossification

Answer 17

Primary Ossification Centre:
Blood vessels penetrate the periosteal collar and chondroclasts remove the calcified cartilage creating empty spaces (medullary cavity) that become filled with connective tissue and blood vessels which deliver bone building materials.
Primary spongiosum is replaced by woven bone and then secondary spongiosum is replaced by lamellar bone

The cartilage matrix at the epiphyseal end continually expands until the perichondrium grows over the metaphyseal area of bone inhibiting its radial growth of the AECC. The epiphyseal growth plate is also formed

Secondary Ossification Centres
Occurs after the medullary cavity has been established.
Blood vessels proliferate into the epiphyseal areas delivering osteoblasts to build new bony tissue (Primary spongiosum is replaced by woven bone)

Question 18

Describe how longitudinal bone growth occurs

Answer 18

Interstitial Growth
-On the epiphyseal side of the growth plate chondrocytes actively proliferate stimulated by growth hormone IGF-1
-These then mature and hypertrophy becoming organised in their columns

Most of the chondrocytes in the calcified matrix die due to restricted nutrition diffusion

Endochondral ossification then occurs replacing the calcified matrix with bone

Question 19

Hoe does longitudinal growth stop?

Answer 19

At puberty, sex hormones speed up bone growth and mineralisation
-After this period, the physis becomes completely ossified and the bones have achieved their final length

Question 20

Explain the process of Intramembranous Ossification

Answer 20

Mesenchymal cells differentiate into osteoblast precursor cells which develop into osteoblasts.

These secrete an organic matrix known as osteoid which completely encloses the cells

During mineralisation the inorganic components are delivered by blood vessels and are laid down using the collagen fibres as scaffolding forming the bony matrix ossein

This conversion is controlled by growth hormones and vitamin D metabolite

As different functional forces begin to affect bone, it is remodelled as mineralisation continues