bone formation and development

Question 1

in early stages of embryonic development, embryos skeleton consists of:

Answer 1

• fibrous membrane
• hyaline cartilage

Question 2

bone development is called

Answer 2

ossification (osteogenesis)

Question 3

two osteogenic pathways

Answer 3

• intramembranous ossification
• endochondral ossification

Question 4

chondroblasts

Answer 4

• cell responsible for forming new cartilage
• as matrix surrounds chondroblasts, they become chondrocytes

Question 5

intramembranous ossification

Answer 5

• compact and spongy bones develop directly from sheets of mesenchymal (undifferentiated) connective tissue

Question 6

what bones are formed via intramembranous ossification

Answer 6

-flat bones of the face
- most cranial bones
- clavicles (collarbones)

Question 7

1st step in intramembranous ossification

Answer 7

begins when mesenchymal cells in embryonic skeleton gather and differentiate into specialized cells, such as osteogenic cells and capillaries

Question 8

first cells to form in intramembranous ossification?

Answer 8

• some mesenchymal cells become osteogenic cells > osteoblasts
• early osteoblasts appear in a cluster called an ossification centre

Question 9

what do osteoblasts secrete during intramembranous ossification

Answer 9

osteoblasts secrete osteoid- an uncalcified bone matrix which hardens as mineral salts are deposited leading to the entrapment of osteoblasts.
- once trapped> osteocytes

Question 10

how do new osteoblasts form during ossification

Answer 10

as osteoblasts transform into osteocytes, osteogenic cells in the surrounding connective tissue differentiate into new osteoblasts

Question 11

what is formed around capillaries during intramembranous ossification

Answer 11

• osteoid secreted around capp. results in trabecular matrix, while osteoblasts on the surface of the spongy bone become the periosteum

Question 12

what does periosteum create during intramembranous ossification

Answer 12

creates a protective later of compact bone on top of the trabecular bone

Question 13

how does red bone marrow form during intramembranous ossification

Answer 13

trabecular bone crowds nearby blood vessels, which eventually condense into red marrow

Question 14

when does intramembranous ossification begin and end

Answer 14

beings in utero during fetal development and continues into adolescence

Question 15

how do flat bones of cranium grow

Answer 15

continue to grow through childhood separated b immobile joints called sutures

Question 16

how is the clavicle formed during ossification

Answer 16

forms by intramembranous ossification from two primary ossification centres that fuse together in utero and later ossify to form the mature clavicle with articular cartilage

Question 17

endochondral ossification

Answer 17

• bones develop by replacing hyaline cartilage
• template that is completely replaced by new bone

Question 18

how does endochondral ossification compare to intramembranous ossification in terms of time

Answer 18

endo. takes much longer

Question 19

which bones form through endochondral ossification

Answer 19

bones at the base of the skull and long bones form

Question 20

what happens at 6-8 weeks of conception in a long bone

Answer 20

• mesenchymal cells differentiate into chondroblasts which form the cartilaginous skeletal precursor of the bone

Question 21

what is the perichondrium?

Answer 21

is a membrane that covers the cartilage during the early stages of endochondral ossification
- dense, irregular connective tissue surrounding cartilage

Question 22

how do chondrocytes change as more matrix is produced in endochondral ossification

Answer 22

• as more matrix produced, chondrocytes in the centre of the cartilaginous model grow in size
• surrounding matrix calcifies

Question 23

what happens when the matrix calcifies

Answer 23

• nutrients can no longer reach the chondrocytes, leading to their death and the disintegration of the surrounding cartilage

Question 24

what happens after the chondrocytes die in endochondral ossification?

Answer 24

after chondrocytes die, blood vessels invade resulting spaces enlarging the cavities and carrying osteogenic cells- which become osteoblasts

Question 25

invasion of blood vessels in endochondral ossification lead to...

Answer 25

blood vessels enlarge the spaces, and these spaces eventually combine to form the medullary cavity

Question 26

what happens when cap. penetrate the cartilage

Answer 26

cap penetrating the cartilage transform the perichondrium into the bone-producing periosteum

Question 27

what do osteoblasts form around the cartilage of the diaphysis

Answer 27

osteoblasts form a periostea collar of compact bone around the cartilage of the diaphysis

Question 28

what happens at the end of the bone (epiphyses) during ossification

Answer 28

chondrocytes and cartilage continue to grow at the epiphyses, increasing the bones length as bone replaces cartilage in the diaphysis

Question 29

what remains as cartilage after the fetal skeleton is fully formed

Answer 29

articular cartilage remains at the joint surfaces and the epiphyseal plate remains between diaphysis and epiphysis for longitudinal growth

Question 30

what is the epiphyseal plate and where is it located

Answer 30

the epiphyseal plate is the area of growth in a long bone made of hyaline cartilage, where ossification occurs in immature bones

Question 31

what happens on the epiphyseal side and diaphysial side of the epiphyseal plate?

Answer 31

- on epiphyseal side, cartilage is formed - on disaphyseal side , cartilage is ossified, causing the diaphysis to grow in length

Question 32

epiphyseal plate has four zones of cells

Answer 32

- reserve volume - proliferative zone - zone of maturation and hypertrophy - zone of calcified matrix

Question 33

reserve zone

Answer 33

small chondrocytes that secure the plate to the epiphysis

Question 34

proliferative zone

Answer 34

chondrocytes that undergo mitosis to replace those lost at the diaphysial end

Question 35

zone of maturation and hypertrophy

Answer 35

older and larger chondrocytes that mature closer to the diaphysis

Question 36

zone of calcified matrix

Answer 36

chondrocytes that are dead due to calcification and where osteoblasts deposit bone tissue

Question 37

what happens in the reserve zone of the epiphyseal plate

Answer 37

the reserve zone contains small chondrocytes that don't participate in growth but secure the epiphyseal plate to the epiphysis

Question 38

what happens in the proliferative zone

Answer 38

the proliferative zone has slightly larger chondrocytes that divide by mitosis to replace dead chondrocytes at the diaphysial end

Question 39

zone of maturation and hypertrophy

Answer 39

contains older, larger chondrocytes closer to the diaphysis, contributing to longitudinal bone growth

Question 40

zone of calcified matrix

Answer 40

most chondrocytes are dead, osteoblasts from the diaphysis invade the area to deposit bone tissue

Question 41

how does epiphyseal plate contribute to bone growth

Answer 41

allows for longitudinal bone growth through cell division and maturation of chondrocytes, followed by ossification

Question 42

what happens when the chondrocytes in the epiphyseal plate stop proliferating

Answer 42

when chondrocytes stop proliferating and cartilage is replaced by bone, longitudinal growth stops, and epiphyseal plate becomes an epiphyseal line

Question 43

what is the appositional growth in bones?

Answer 43

the process where bones increase in diameter, and it can continue even after longitudinal growth stops

Question 44

how do osteoclasts and osteoblasts contribute to bone growth in diameter?

Answer 44

- osteoclasts resorb old bone lining in the medullary cavity, while osteoblasts produce new bone tissue beneath the periosteum, increasing the bones diameter

Question 45

what is modelling in bone growth?

Answer 45

- process where bone is resorbed along the medullary cavity and new bone is deposited beneath the periosteum - increases both the bones diameter and the diameter of the medullary cavity