Limbs 1: Development & Growth of Bone

Question 1

Function of bone

Answer 1

Support of the body shape
System of levers for muscle action
Protection of internal organs
Site of blood cell formation
Mineral storage pool

Question 2

What are the 2 mechanical properties of bone

Answer 2

Cable-like flexibility/resistance to TENSION

Pillar-like stiffness/resistance to COMPRESSION

Question 3

What allows for cable-like flexibility in bone

Answer 3

collagen + other bone proteins (= osteoid)…. resistant to tension

Question 4

What allows for pillar like stiffness in bone

Answer 4

by impregnation of collagen with crystalline mineral… allowing resistance to COMPRESSION

Question 5

Which mineral is collage impregnated with in bone

Answer 5

(hydroxyapatite – a complex calcium hydroxyphosphate)… it’s crystalline

Question 6

Types of bone tissue

Answer 6

Lamellar (=mature bone)

Woven (=immature bone)

Question 7

T/f woven bone is commonly found in adult bone

Answer 7

F In adults woven bone is only found in repairing fractures… and pagets

Question 8

What are the ends of bone called, and what is between this and the shaft

Answer 8

Ephiphysis (PROXIMAL= nearer to trunk, DISTAL=further)

metaphysis separates epiphysis from the shaft (diaphysis)

Question 9

What is the name of the shaft

Answer 9

Diaphysis

Question 10

What is the name of the hollow part inside bone

Answer 10

Medullary cavity

Question 11

What is the name of the arteries that enter the epiphysis, metaphysis and diaphysis

Answer 11

Epi- eiphysial artery
Meta- metapyseal artery
Diaphysis - nutrient arteries which go through a nutrient foramen into the medullary cavity, then branch to supply the bone, and even back out to the periosteum

Question 12

T/f periosteum is purely fibrous

Answer 12

F. it also is cellular

Question 13

Role of periosteum

Answer 13

Key roles in bone growth and repair

Vascular

Sensory nerve supply is good

Question 14

T/f periosteum is vascularised, but with poor sensory nerve supply

Answer 14

F… both vasuclarised and good sensory supply

Question 15

What is an osteogenic cell

Answer 15

A cell which develops into an osteoblast (precurosr)

Question 16

What is osteoblast a precursor to

Answer 16

osteocyte

Question 17

What is the function of an osteoblast

Answer 17

forms bone marrix (i.e. secretes the collagen fibrils)

Question 18

What is the function of osteocyte

Answer 18

Maintains bone tissue

Question 19

T/F an osteocyte differentiates into an osteoclast

Answer 19

F, osteoblast forms osteocyte, but osteoclast separate

Question 20

Function of osteoclast

Answer 20

Resoprtion (breakdown of bone matrix using lysosomal enzymes)… they have ruffled border

Question 21

When does skeleton begin to form, when does growth stop

Answer 21

The skeleton starts to form at 6 weeks of fetal life and growth continues in some bones until 25 years of age.

Question 22

How is lamellar bone arranged

Answer 22

CORTICAL (Outer hard layer of compact lamellar bone)

TRABECULAR/CANCELLOUS/SPONGY (Inner layer of interlacing struts of lamellar bone)

Question 23

T/f spongy bone is woven as it is immature

Answer 23

FALSE!!! the spongy bone is lamellar…. woven is immature bone, which spongy bone is not

Question 24

Structure of cortical bone

Answer 24

Osteon, the chief structural unit of compact (cortical) bone, consisting of concentric bone layers called lamellae, which surround a long hollow passageway, the Haversian canal. Made up of osteocytes with lots of processes

As well as instersitital lamellae

Question 25

What is contained within the harvesian canal

Answer 25

neurovascular bundle

Question 26

Structure of trabecular bone

Answer 26

Trabeculae are the spikes, and there are spaces between them which bone marrow fits into Also in concentric circles but not called osteons.... it's all interstital lameallae. No harvesian canals running inside. Osteoblasts are aligned along trabeulae of new bone (underneath is the osteocyte network)

Question 27

State the 2 tpes of ossification and when each happens.. both in developng foetus

Answer 27

Intramembranous (in existing vascular connective tissue) --> FLAT BONES endochondral (within existing foeatal cartilage models) --> OTHER BONES

Question 28

In which type of ossification is ostein deposited around collagen

Answer 28

Intramembranous

Question 29

What happens in intramembronous ossification

Answer 29

Mesenchymal stem cells within fibrous connective tissue (vascular connective tissue) differentiate into osteoblasts. These form ossification centres Osteoid laid down (collagen). Osteoblasts which get trapped in the bone matrix called osteocytes Mineralises to form spicules then trabeculae. This is woven bone It then remodels further to form lamellar bone. (note, there is still trabcular and cortical within this) https://www.youtube.com/watch?v=xXgZap0AvL0

Question 30

What happens in endochondral ossification

Answer 30

Within existing cartilage There are chondrocytes which are secreting a matrix. Enclosed in a perichondrium. Then hypertrophy of chondrocytes in the centre of the cartilage model. They resorb the surrounding matrix. The remaining cartilage matrix is calficied and the condrocytes die Stem cells in the perichondrium divide to form osteoblasts. Periosteal bud with capillaries and osteoblasts invade the calcified cartilage reason--> Primary ossification centre. PERIPHERAL OSTEOCLASTS CUT CHANNELS FOR SPROUTING VESSELS Bone is built on the calficied cartilagte Then later on, a secondary ossification centre forms in the epiphysis. This replaces calcified cartilage with mostly spongy bone. Osteoclasts resorb bone in the diaphysis creating medullar cavity. The gap between the primary and secondary ossification centres is the epiphyseal growth plate.... all future growth oiccutrs here An area of cartilage remains over the epiphysis *=articular cartilage)

Question 31

How does osteoblast get into foetal calcified cartilage

Answer 31

Periosteal osteoclasts cut channels for sprouting vessels Osteoblasts enter with vessels to build bone round them

Question 32

Stages of intramembranous ossification

Answer 32

osteoblasts secrete osteoid, which they becomeme trapped in forming ossification centre Osteoblasts become osteocytes... as they do this, they cause osteogenic cells to convert into osteoblasts... so you get osteocytes in the cnetre and a ring of osteoblasts around outside. Calficiation occurs Osteocytes in the centre become trabecular bone and cortical bone The new osteoblasts on the outside become periosteum

Question 33

Why is endochondral ossficiation needed

Answer 33

in children, there are large forces on the long bones, so you can't really get frowth from the end of the bone (as it's being compressed by force)....

Question 34

What is the solution fo disruption of terminal appositional growth due to large forces on bone

Answer 34

1. Shaft ossified 2. Epiphysis ossifies 3. The region in between the ossified shaft and epiphysis conitnues growing (growing cartilage plate).... the bit in between ossified epiphysis and diaphysis is called epiphyseal plate... it keeps growing, and then then becomes calcified, grows some more, that bit gets calfified etc.

Question 35

When will growth cessation occur

Answer 35

Growth cessation when cartilage growth ceases and plate is over-run by ossification

Question 36

State stages of endochondral ossification

Answer 36

1. Primary ossification centre forms in the shaft. Shaft becomes calcified. At this stage the eiphysis is still cartlage 2. Secondary ossification centre forms in epiphysis, and ossification ocrrus here.. epiphyseal plate left in between

Question 37

When does the child's writst ossify

Answer 37

In child’s wrist (lower) epiphyses ossify in 2nd year

Question 38

When do eiphyseal paltes remain until

Answer 38

Epiphyseal plates (dark) remain cartilaginous until growth ceases after puberty

Question 39

What is the key to growth and remodelling in bones

Answer 39

large blood supply – cells are never far from nutrients and O2 Osteocytes maintain matrix but can activate osteoblasts for new bone building Osteoclasts are giant cells specialised for destruction of bone matrix

Question 40

What is apposition

Answer 40

Apposition – addition to exterior at periosteum

Question 41

How does apposition occur

Answer 41

Osteoblasts and osteoclasts create ridges and grooves on bone surface Blood vessels align in grooves Osteoblasts build new osteons round vessels Osteoclasts remove bone from endosteal surface

Question 42

Identify different fracture types

Answer 42

...

Question 43

How do fractures heal

Answer 43

1. Bleeding- haematoma is infiltrated with fibrous matrix and invaded by cartilage/bone progenitors The haematoma is contained within the periosteum

Question 44

What type of bone occurs in fracture repair

Answer 44

woven

Question 45

What if high blood Ca2+ level (hypercalcaemia)

Answer 45

Calcitonin released by parafollicular thyroid cells; breakdown of bone matrix by osteoclasts inhibited; uptake of Ca2+ into bone matrix is promoted.

Question 46

What if blood Ca2+ low

Answer 46

Parathyroid Hormone (PTH) released by chief cells of parathyroid gland; osteoclast bone resorption activity promoted; increases Ca2+ re-absorption by the kidneys.

Question 47

Outline he adaptable features of bone

Answer 47

Can grow without compromising its support functions Increases or decreases bulk and density in response to pattern of use Can alter its external and internal shape in response to pattern of use – remodelling Can repair when fractured