Skeletal System: Formation

Question 1

What is CALCIFICATION?

Answer 1

Deposition of Ca (hardens tissues, but no OSTEOCYTES)

Question 2

What is OSSIFICATION?

Answer 2

BONE formation (with OSTEOCYTES), occurs during fetal development

Question 3

What are the 2 methods of OSSIFICATION?

Answer 3

1) INTRAMEMBRANOUS

2) ENDOCHONDRAL

Question 4

Quick vague overview of INTRAMEMBRANOUS OSSIFICATION (IO)

Answer 4

It begins in fetus, forms FLAT BONES of skull, mandible, and part of the clavical, starts w/in CT membrane

Question 5

1st step of IO

Answer 5

Nutrient artery brings MESENCHYMAL CELLS

Question 6

2nd step of IO

Answer 6

MESENCHYMAL CELLS divide and become OSTEOGENIC CELLS, which divide and become OSTEOBLASTS

Question 7

3rd step of IO

Answer 7

OSTEOBLASTS produce BONE MATRIX around COLLAGEN FIBERS, form thin struts of BONE = OSSIFICATION center

Question 8

4th step of IO

Answer 8

OSTEOBLASTS on surface of struts produce more BONE, struts thicken, connect to form TRABECULAE

Question 9

5th step of IO

Answer 9

CELLS specialize, take on new functions

• Trapped bv (blood vessels?), CELLS between TRABECULAE form RED BONE MARROW
• CELLS surrounding BONE form PERIOSTEUM
• OSTEOBLASTS in PERIOSTEUM form outer COMPACT BONE
• OSTEOBLASTS trapped in BONE become OSTEOCYTES

Question 10

Quick vague overview of ENDOCHONDRAL OSSIFICATION (EO)

Answer 10

Begins in fetus, forms all bone except parts of skull, mandible, and clavicle, starts w/ HYALINE cartilage model

Question 11

1st step of EO

Answer 11

Primary ossification center forms in mid-region (use notes to see the process, it’s too much to type and I’m lazy)

Question 12

2nd step of EO

Answer 12

MEDULLARY CAVITY forms

• OSTEOCLASTS remove SPONGY BONE in mid region to form MEDULLARY CAVITY
• OSTEOBLASTS remodel SPONGY BONE into OSTEONS = forms thick layer of COMPACT BONE
• OSTEOBLASTS and OSTEOCLASTS form endosteum which lines MEDULLARY CAVITY
• Blood vessels in MEDULLARY CAVITY form RED BONE MARROW = blood formation

Question 13

3rd step of EO

Answer 13

Secondary ossification center forms in ends (around time of birth)
- repeat steps a - h in EPIPHYSIS

Question 14

4th step of EO

Answer 14

Cartilage remaining at BONE ends become ARTICULAR CARTILAGE to reduce friction and rubbing between bones

Question 15

5th step of EO (part a)

Answer 15

Cartilage remaining at EPIPHYSEAL GROWTH PLATE allows bone lengthening

• EPIPHYSEAL PLATE has zones of resting, dividing, hypertrophying, and calcifying cartilage
• At puberty, hormones stimulate BONE to grow faster than cartilage
• in adult, all EPIPHYSEAL CARTILAGE has been replaced by bone so no further lengthening can occur (see chart in notes)

Question 16

5th step of EO (part b)

Answer 16

BONES thicken by appositional growth

• OSTEOCLASTS in ENDOSTEUM remove MATRIX enlarging MEDULLARY CAVITY
• OSTEOBLASTS in PERIOSTEUM add BONE in circumferencial lamellae
• Circumferencial lamellae remodeled into OSTEONS (see notes for pictures)