Bone Development Histology Flashcards
Bones can be formed through what two mechanisms?
Intramembranous ossification and endochondral ossification
What are mesenchymal cells roles in intramembranous ossification?
Bone cells are differentiated directly from the mesenchymal cells to produce the osteoid
Intramembranous ossification leads to the production of what bones?
Leads to the production of flat bones of the skull and bones of the face
In what week of gestation does intramembranous ossification start?
Around week 8
What happens to the mesenchymal cells in endochondral ossification?
Mesenchymal cells are replaced by a hyaline cartilage model
What does the hyaline cartilage model do during endochondral ossification?
It initially takes the shape of the bone as well as the bones position, then the hyaline cartilage model is eroded and replaced by bone
Endochondral ossification leads to the production of what bones?
Most short and long bones of the body
During embryonic development when can one first see hyaline cartilage models?
6th week
Hyaline cartilage models are present in all long bones of the limbs by what week of gestation?
12th
What are the 4 steps of intramembranous ossification?
- development of the ossification center
- calcification
- woven bone and periosteum development
- replacement of woven bone
During intramembranous ossification what happens during the development of the ossification center part?
Some of the elongated, pale-staining, mesenchymal cells cluster, differentiate into osteoprogenitor cells, and then become more rounded, while their cytoplasm changes from eosinophilic to basophilic. This basophilic change is due to changes in the cytoplasm including the addition of more rough endoplasmic reticulum. These cells have now differentiation into osteoblasts. This cluster of osteoblasts creates the ossification center as the osteoblasts secrete organic extracellular matrix known as osteoid.
During intramembranous ossification what happens during the calcification part?
Calcium and other mineral salts are deposited around the framework of collagen fibers. Cells that are trapped in the calcifying osteoid are now called osteocytes and sit in lacunae.
During intramembranous ossification what happens during the woven bone and periosteum part?
What is being made here is primary bone (also known as woven bone or immature bone). Additionally, the mesenchyme at the periphery of the bone condenses and forms the periosteum
During intramembranous ossification what happens during the replacement of woven bone part?
The woven bone is then replaced by lamellar bone, forming compact and spongy bone. Specifically, with flat bones, spongy bone will be formed between two layers of compact bone.
What are the six steps of endochondral ossification?
- development of the fetal cartilage model
- a bone collar forms around the diaphysis and cartilage of shaft begins to calcify
- development of a primary ossification center in the diaphysis
- development of secondary ossification centers
- retention of hyaline cartilage as the articular cartilage and the epiphyseal plate
- epiphyseal plates ossify and form epiphyseal lines
With a H&E stain, calcified hyaline cartilage stains (a)_______, while newly formed bone stains (b)________.
(a) blue purple
(b) pink/red
Hyaline cartilage is composed primarily of type (a)__ collagen, while bone is composed of primarily type (b)__collagen.
(a) II
(b) I
The primary bone is (a)(eosinophilic or basophilic) and calcified cartilage is (b)(eosinophilic or basophilic)
(a) eosinophilic
(b) basophilic
Does the development of secondary birth centers happen before or after birth?
After birth
Secondary ossification centers are located where?
The epiphyses
What does puberty signal in terms of bone development?
Ossification of the epiphyseal plates
What are the five zones of the epiphyseal plate?
Zone 1: zone of resting/reserve cartilage Zone 2: zone of proliferating cartilage Zone 3: zone of hypertrophic cartilage Zone 4: zone of calcified cartilage Zone 5: zone of ossification
Where is the epiphyseal plate found in a long bone?
Found between the epiphysis and the flared portion of the diaphysis, known as the metaphysis
The zone of resting cartilage is closest to what part of the bone?
Epiphysis
The zone of ossification is closest to what part of the bone?
Metaphysis
Bones increase in width and diameter with what kind of growth?
Apositional
What happens at the endosteal and periosteal surfaces during apositional growth?
Endosteal: osteoclasts break down bone matrix
Periosteal: osteoblasts secrete bone matrix
What are the two controls involving bone remodeling?
Negative feedback loop for maintenance of calcium homeostasis and bone’s response to mechanical stress and gravity
What percent of your bone is remodeled each year?
5-10%
What two hormones are involved in bone homeostasis?
Calcitonin and parathyroid hormone
What does calcitonin do?
Stimulates calcium salt deposits in the bone, therefore decreases blood calcium levels
What does parathyroid hormone do?
Stimulates osteoclasts to degrade bone matrix and release calcium ions into the blood
