L15- Disorders of Skeletal Development (background)

Question 1

list the functions of the skeletal system

Answer 1

• essential for mechanical support + protection of internal organs
• determines body size, shape
• mineral homeostasis (Ca, PO4, Na, Mg)
• houses hemopoietic tissue

Question 2

list the clinical manifestations of bone disease

Answer 2

• disability and deformity
• pain
• pancytopenia
• neurological dysfunction

Question 3

The organic matrix of bone is made out of (1) and gives bones their (2) function.

Answer 3

1- type I collagen (mainly) + proteoglycans

2- flexibility, tensile strength

Question 4

______ makes up 60% of total bone mass

Answer 4

Calcium Hydroxyapatite, Ca(10) PO4-(6) OH(2)

-essential part of bone matrix –> more predominant than bone cells

Question 5

Inorganic matrix:

• (1) describe its composition
• (2) describe its functions

Answer 5

1:

• mainly calcium hydroxyapatite, Ca(10) PO4-(6) OH(2)
• 99% Ca stores, 85% phosphate stores
• 65% Na, Mg stores

2:

• mineral homeostasis (and storage)
• bone strength

Question 6

list cellular component of bone and where they come from

Answer 6

• osteoprogenitor cells (stem cells) –> osteoblasts
• osteoblasts –> (synthesizes matrix) –> osteocytes
• osteocytes (mature osteoblasts) –> mechanosensory

-(hematopoetic progenitor cells –> osteoclast precursors –>) osteoclasts –> resorbs matrix

Question 7

Osteoblasts:

• (1) is the main function
• it will bind (2) in order to initiate (3) and or regulate (4)

Answer 7

1- synthesis of matrix proteins –> type I collagen
2- hormones (estrogen, PTH, T3/T4, vitD, glucocorticoids)
3- mineralization
4- osteoclast activity

Question 8

Osteoclasts:

• derived from (1)
• found in (2) location in bone
• (3) is a key cellular feature
• osteoclasts will release (4) for (5) function, leading to appearance of (6) seen in histology

Answer 8

1- HSC (hematopoetic stem cells)
2- bone surface
3- multinucleated
4- proteolytic enzymes
5- bone resorption
6- Howship's lacunae

Question 9

______ is the space found surrounding active osteoclasts

Answer 9

Howship’s lacunae

Question 10

briefly describe the development of bony matrix

Answer 10

Osteoid = non-mineralized matrix
(12-15 days of mineralization)
Bone = mineralized matrix

Question 11

list the different categorizations of bone types

Answer 11

Mineralization: non-mineralized (osteoid), mineralized

Structure: cortical (compact surface form), cancellous (inner trabecular / spongy)

Matrix Fiber arrangement: Woven (immature), Lamellar (mature)

Question 12

Woven Bone:

• seen normally in (1) situations
• (2) collagen bundle arrangement
• resistance to force is (uni/multi)-directional
• its presence is pathological if seen in (4)

Answer 12

Immature Bone
1- first laid down in fetal skeleton (forms quickly)
2- random orientation
3- multi-directional
4- adults (fracture, tumor)

Question 13

Lamellar Bone:

• seen normally in (1) situations
• (2) collagen bundle arrangement
• resistance to force is (uni/multi)-directional

Answer 13

Mature Bone, cortical and cancellous (trabecular)
1- normal mature bone
2- regular parallel bands of collagen in sheets
3- uni-directional – facilitates weight bearing

Question 14

Most bones are formed through (1) process, where (2) is the main feature.

Other bones are formed through (3) process as seen in the development of (4) bones.

Answer 14

1- endochondral ossification (most bones in body, especially long bones)
2- bone replaces embryonic cartilaginous skeletal framework

3- intramembranous ossification - de novo bone synthesis (no frame work)
4- flat bones: skull, face, parts of clavicle and pelvis

Question 15

describe the process of endochondral ossification

Answer 15

1) chondrocytes secretion –> mesenchymal condensations –> hyaline cartilage –> calcification –> cartliage anlagen
2) chondrocytes in anlagen –> apoptosis
3) BV invasion of dead cartilage
4) bone formation on the surface of residual calcified matrix

Question 16

list the zones of the epidermal growth plate (for endochondral ossification)

Answer 16

1) reserve zone (of cartilage)
2) zone of proliferation
3) zone of hypertrophy
4) zone of mineralization / calcification (chondrocytes die)
5) ossification zone: primary spongiosa –> secondary spongiosa

Question 17

Bones during childhood / adolescence undergo (1) growth and then (2) growth in adulthood; osteoblasts and osteoclasts will work (together/separately) as opposed to bone remodeling where they work (together/separately).

Answer 17

1- longitudinal growth
2- appositional growth
3- separately
4- together (as one unit)