Bone Growth Flashcards
what are the two types of bone in the mature skeleton? [2]
how can these be subdivided? ^
what are the two types of bone in the mature skeleton? [2]
- *- lamellar bone
- woven bone**
how can these be subdivided?
- *lamellar bone:**
i) cortical
ii) cancellous / trabecuar bone
characteristic features AND locations of:
a) Cancellous / trabecular bone (lamellar bone)
b) cortical bone (lamellar bone)
lamellar = in layers
cortical bone (lamellar bone)
- a concentric circle structure called an osteon formed from layers of bones
- Every single bone has an outer section of bone that is very dense and full of osteons, running in columns on the outside of the bone.
Cancellous / trabecular bone (lamellar bone)
- spongy
- inside of bone
- trabecular bone gives more flexibility/tensile strength compared to the compressibility of the cortical bone.
where do you find woven bone? [1]
what is overall structure like?
where do you find woven bone? [1]
Immature bone, found in fracture healing bone, and in some pathological conditions
what is overall structure like?
The laying down of the extracellular matrix is hap-hazard and quick to provide quick attachment between the two sides of the fracture to reconnect the broken down bone back together again when you don’t have time, and when there is more time it will be replaced with lamellar bone.
Composition of bone:
- what is bone matrix composed of? (organis and inorganic)
Composition of bone:
what is bone matrix composed of?
35-40% organic:
- 28% collagen (mainly Type 1 for tensile strength), Packaged and sent out by osteoblasts
- 5% Proteoglycans/ glycoproteins (compressive strength and calcium binding)
- Bone promoting growth factors
60% inorganic
- *- 95% Calcium hydroxyapatite (Ca10(PO4)6(OH)2).** This precipitates onto the collagen fibre, however it doesn’t coat it completely. It coats the collagen fibre in blocks, so still gives the collagen fibres flexibility.
- Approximately 5% water due to small proportion of water held by proteoglycans
all bone cells come from the same WHAT cell? [1]
describe development pathway of bone cells? [3]
all bone cells come from the same osteoprogenitor cell? [1]
osteoprogenitor cell -> osteoblast -> osteocyte
at what point do osteoblasts become osteoytes? [1]
what is role of osteclasts? how do u recognise?
osteoblasts become osteocytes when they’re encased in collagen matrix
osteoclast:
- large, multi-nucleated cells which are macrophage derived.
- they are produced from haemopoietic stem cells derived in adult bone, and they patrol the bone to monitor its status and whether it needs to be removed.
what are the two mechanisms of bone ossification [2]
where do each mainly occur?
Intramembranous
- Mainly the skull bones and skull vault
- Bone forms directly from osteoblasts
Endochondral
- Mainly everywhere else
- Chondroblast creates cartilage precursor that converts to bone
Both form bone that looks the same histologically when formed
where do u find the epiphysis and diaphysis of bone?
name two places that undergo intramembranous ossification? [2]
name two places that undergo intramembranous ossification? [2]
- flat bones of skull (frontal, nasal, parietal, vomer, mandible)
explain how intramembranous ossificatin occurs xo
- ossification centre appears in fibrous connective tissue membrane: here mesenchymal cells condense and differentiate as osteogenic cells: osteoblasts
- Osteoblasts secrete bone matrix (osteoid) & matrix becomes calcified with calcium hydroxyapatite
- trapped osteoblasts become osteocytes
- Mesenchyme on outside condenses: **periosteum
-**
blood vessels growing to supply the bone with nutrients will bring in osteoclasts, which can then remodel the bone into compact/cortical bone on the outside and trabecular bone on the inside.
Explain how primary endochondral ossification occurs xo
_Endochondral ossification: t_wo step process: produces cartilage and then changes this cartilage to bone
- Mesenchymal cells condense and differentiates into chondroblasts to produce hyaline cartilage model extracellular matrix (so they use collagen type 2 rather than collagen type 1).
- the perichondrium forms around cartilage model and holds all the mesenchymal cells next to the condensing bone
- To begin with, ECM make more collagen type 2, more proteoglycans: causes cartilage to grow in legnth and width (into the shape of the bone): causes to be further away from nutrient source
- chondrocytes now in the middle will begin to deteriorate as there is no blood supply into this cartilage
- this creates cavities, right in the centre, where the cartilage used to be. When they die, this triggers calcification as it triggers a Ph change: It releases vesicles in the chondrocytes with enzyme like alkaline phosphatase which changes the ph and encourages calcification of the matrix.
At this time, a blood vessel known as the nutrient artery can penetrate the perichondrium and begin to bring in osteoclasts from the haemopoietic cells to start remodelling: break down some of the spongy bone to create a marrow, or medullary, cavity in the centre.
Bone on the inside and bone on the outside grow towards each other to completely replace the cartilage.
explain how secondary endochondral ossification occurs xo
secondary ossifcation:
- In the last stage of prenatal bone development (8-9 months): the centres of the epiphyses begin to calcify.
- Secondary ossification centres form in the epiphyses as blood vessels and osteoblasts, osteocytes and osyteoclasts enter these areas and convert hyaline cartilage into spongy bone.
at what stage does hyaline cartilage persist at the epiphyseal plate? why?
Until adolescence, hyaline cartilage persists at the epiphyseal plate (growth plate), which is the region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones
Epiphyseal growth plate active/open until 18-25 years then closes
During this process, cartilage cells stop dividing and all of the cartilage is replaced by bone. The epiphyseal plate fades, leaving a structure called the epiphyseal line or epiphyseal remnant, and the epiphysis and diaphysis fuse.
what are 5 stages of epiphyseal growth plate?
- Zone of resting cartilage
- Zone of proliferating cartilage
- Zone of hypertrophic cartilage
- Zone of provisional calcifcation
- zone of ossification
how does appositional growth of bone occur? (to the side)
- osteoprogenitors in periosteum differentiate as osteoblasts – secrete new bone matrix to form compact, cortical bone (osteons) and grow on either side of a blood vessel.
- these ridges get bigger and eventually form a tunnel with a blood vessel right in the centre.
- Inside tunnel: Former periosteum becomes endosteum due to being enclosed inside the bone due to bone growth. It still has progenitor cells
- Osteoblasts make new bone lamellae filling tunnel
