Bone Structure, Growth and Repair

Question 1

Structure of long bones (adult)

Answer 1

Lecture slide

Question 2

Microanatomy of bone: cells of bone and their role and lineage and where they are found

Answer 2

1. Osteoprogenitor cell (develops into osteoblast)
   - found in periostenum and endostenum
2. Osteoblast (forms bone extracellular matrix)
   - in endostenum and on surfaces of bone
   -secrete osteoid (unminerlaised bone) which causes the start of depositing of minerals to form bone
3. Osteocyte (maintain bone tissue
   - extend cell processes out to communucate to the other cells listed here and therefore is the master of bone metabolism by sending signals to other cells.

(all bone cell lineage)

4. Osteoclast (bone resorption, the breakdown of boen extracelluar matrxi)
   (WBC lineage)

Question 3

Composition of extracellular matrix

Answer 3

This comprises water, collagen fibres that provides tensile strength (30%), and crystallised mineral salts (55%) such as calcium phosphate and calcium hydroxide that form hydroxyapatite.

The minerals crystalise within the collagen fibres which results in calcification of the bone, which makes the bone hard and strong to withstand the stresses produced by weight and movement

Question 4

Organisation of bone:
Compact bone
- why is it so strong/compact

Answer 4

arrangement of osteons and the collagen layer (or lamellae) within them make it resistant to stresses such as compression, tensile and torsion

Question 5

How do cells communicate with eachother if compact bone is so dense?

Answer 5

Due to the dense arrangement of osteons, osteocytes sent out long cell processes into a series of small channels in the bone matrix called canaliculi. This allow cell-cell communication and passage of nutrients and waste products.

Question 6

Spongy bone:
organisation

Answer 6

Has trabeculae arranged in a crosslink network of bony struts, making there lots of empty space (not dense like compact bone). The bone within them will contain irregular arrangement of lamellae. They contain osteocytes encased within the bone matrix and osteoclasts and osteoblasts are found on the bone surface within the endosteum

Question 7

when does Bone formation (ossificaiton) occur

Answer 7

1. development of embryo and foetus;
2. Growth in childhood through up to age 25
3. Remodelling: removal and replacement of new bone, adaptating to stresses, hormones and age throughout our lives
4. Fracture healing.

Question 8

two types of bone formation in normal developemtn and growth

Answer 8

Intramembraneous ossification and Endochondral ossification

Question 9

Intramembraneous ossification
-Forms what type of bones
- 4 step process with drawings

Answer 9

Bone forms directly from a fibrous membrane.
It is involved in the formation of the clavicles, mandible and flat bones of the skull.

1. Development of ossificaiton centre: Osteoblasts secrete organic extracellular matrix

2.Calification: Ca and other mineral salts are depoisited and extracellular matrix calclifes (hardens)

3. Formation of trabeculae: extracellular matrix develops into trabeculae that fuse to form spongy bone
4. Development of periostenum: mesenchyme at the periphery of the bone develops into periosteum

Question 10

Endochondral ossification
- what bones they form
- process

Answer 10

Begins in the fetus.
All other bones than clavicle, mandible and flat bones of the skull

1. Development of cartilage model: mesenchymal cells develop into chondroblasts which form the cartilage model
2. Growth of the cartilage model: Growth occurs by cell division of chondroblasts
3. development of primary ossification centre: In this region of the diaphysis bone tissue has replaved most of the cartiliage
4. Development of the medullary (marrow) cavity: Bone breakdown of osteoclasts forms the marrow cavity.
5. development of secondary ossification centre: in epiphysis of bone

6.Formation of articualr cartiliage and epiphyseal plate (both have hyaline cartiliage)

Question 11

How bones grow:
endochondral vs appositional

Answer 11

Bones grow longer by the process of endochondral ossification at the growth plates (during childhood and adolescence) , whereas bones grow wider (or outwards) by appositional growth on the outer layer

Question 12

Epiphyseal growth plate:
Draw the layers

Answer 12

Top:
Articular cartilaige
epiphysis
Zone of resting cartiliage
Zone of proliferating cartiliage (forms new chondrocytes)
Zone of hypertrophic cartilaige
Zone of calcified cartiliage (old chondrocytes are replcaed by bone)
Diaphysis

Question 13

Appositional growth steps

Answer 13

1. Ridges in peristeum create groove for periosteal blood vessel
2. Periosteal ridges fuse forming an endostenum lined tunnel
3. Osteoblasts in ensotenum build new concentric lamellae inward toward the centre of tunnel, forming new osteon
4. bone grows outward as osteoblasts in periostenum build new circumerferentail lamaellae. Osteon formation repeats as new periosteal ridges fold over blood vessels.

Question 14

regulators of bone remodelling

Answer 14

controlled by vitamins D, C and C,; hormones such as calcitonin, parathyroid hormone and growth hormone, as well as physical loading bearing exercise and the availability of minerals such as calcium, phosphorous and magnesium

Question 15

Fracture healing steps

Answer 15

Reactive phase: Formation of fracture hematoma

Repartivie phase:
Fibrocartiliaginous callus formation

Reparative phase:
Bony callus formation

Bone remodelling phase