Msk Week 2 Objective 2 (A,b,c)

Front 1

Ossification has started in most bones by which week of development?

Back 1

12th Week

Front 2

The first bone to ossify in the fetus by the 7th week is the?

Back 2

Clavicle

Front 3

In one sentence define 'endochondral bone formation.'

Back 3

Endochondral ossification describes the process whereby production of a hylaine cartilage model precedes bone formation.

Front 4

Give some examples of bones in the adult human body derived from endochondral ossification.

Back 4

Long bones, ribs, pelvis.
(anything below the skull except for the clavicle)

Front 5

In one sentence define 'intramembranous bone formation.'

Back 5

Intramembranous ossification occurs by direct differentiation of mesenchymal cells into osteoblasts in primitive loose CT.

Front 6

Give some examples of bones in the adult human body derived from intramembranous ossification.

Back 6

Flat bones of cranium, parts of the mandible, clavicles.

Front 7

When does endochondral ossification begin?

Back 7

In the second month of development

Front 8

As outlined in the Histology lab manual what are the 5 stages of endochondral ossification?

Back 8

1. Formation of bone collar around cartilage model
2. Cavitation of cartilage within the model
3. Invasion of internal cavities by the periosteal bud and spongy bone formation
4.Formation of medullary cavity, appearance of secondary centres in the epiphyses
5. Ossification of the epiphyses

Front 9

When does the perichondrium covering the hyaline cartilage become the periosteum?

Back 9

When the perichondrium is invaded by blood vessels. This changes the nutrition which induces mesenchyme differentiation into osteoblasts.

Front 10

How does the bone collar form?

Back 10

After invasion of blood vessels into the perichondrium, mesenchyme cells differentiate into osteoblasts which secrete osteoid and lay down the bony collar (woven bone which later remodels to lamellar/cortical bone)

Front 11

What happens in the primary ossification centre?

Back 11

Within the cartilage model, chondrocytes hypertrophy, there is a change in pH and the cartilage matrix starts to die, leaving a scaffolding.

Front 12

What function does the peritoneal bud provide?

Back 12

It brings into the bone:
- nutrient artery and vein
- nerve fibres
- lymphatics
- red marrow elements
- osteoblasts
- osteoclasts

Front 13

What is the function of an osteoclast?

Back 13

To erode dying/dead cartilage matrix

Front 14

What is the function of an osteoblast?

Back 14

To secrete osteoid, form trabeculae of spongy bone on top of the 'scaffolding' left by the dead/dying cartilage matrix.

Front 15

How do secondary ossifcation centres differ from primary?

Back 15

Secondary ossification centres do not form orderly cell columns and the spongy bone is retained as there is no medullary cavitation.

Front 16

As described in the Histology manual what are the 4 stages of intramembranous ossification?

Back 16

1. An ossification centre appears in the fibrous CT membrane.
2. Bone matrix (osteoid) is secreted within the fibrous membrane
3. Woven bone and periosteum form
4. Bone collar of compact bone forms and red marrow appears.

Front 17

How does the ossification centre form in intramembranous ossification?

Back 17

Selected centrally located mesenchymal cells cluster and differentiate into osteoblasts.

Front 18

How do osteocytes form?

Back 18

Osteoblasts trapped within the bone matrix become osteocytes.

Front 19

In contrast to endochondral periosteum formation (from perichondrium) how does the periosteum form in intramembranous ossification?

Back 19

Vascularized mesenchyme condenses on the external face of the woven bone and becomes the periosteum.

Front 20

Is existing adult bone intramembranous or endochondral bone?

Back 20

NEITHER! these names only refer to the initial bone formation.

Front 21

What is the function of a normal growth plate?

Back 21

Function: growth in length of long bones, accommodates functional stress

Front 22

The cartilage that remains in long bones between the __________ and the __________ is known as the growth plate.

Back 22

- epiphysis
- diaphysis

Front 23

In most humans when does the cartilagenous growth plate ossify?

Back 23

In most adults it ossifies in the mid 20's and growth arrests.

Front 24

What are the 5 zones of the growth plate?

Back 24

1) Reserve Zone
2) Proliferation Zone
3) Zone of hypertrophy
4) Zone of calcified matrix
5) Zone of resorption/osteogenic zone.

Front 25

In one sentence describe what the growth plate does?

Back 25

Bone growth in length by chondrocyte proliferation in region of growth plate adjacent to epiphysis.

Front 26

If chondrocytes are proliferating adjacent to the epiphysis, why doesn't the plate change in thickness?

Back 26

Because chondrocytes at the diaphyseal side of the growth plate hypertrophy, the matrix becomes calcified and chondrocytes die. Therefore, proliferation and destruction cancel each other out.

Front 27

What is happening at the reserve zone of the plate?

Back 27

Chondrocytes are flattened, and are resting in hyaline cartilage arranged in small clusters. These cells orient growth plate orienting factor.

Front 28

What is happening at the proliferation zone?

Back 28

Chondrocytes proliferate and lie in regular organized vertical columns, and produce large amounts of ECM proteins.

Front 29

What is happening in the zone of hypertrophy?

Back 29

Cell division ceases. Chondrocytes increase in size and arrange in clear columns.

Front 30

What is happening in the zone of calcified matrix?

Back 30

Here the matrix undergoes mineralization. Chondrocytes degenerate and die here. Blood vessels invade the area and pave the way for bone cell precursors.

Front 31

What happens in the zone or resorption (or osteogenic zone)?

Back 31

Osteoblasts begin to build bone on calcified matrix model. Degenerated chondrocytes are resorbed by chondroclasts or osteoclasts.