Bone Histology and Function - Lectures 3 Flashcards
What is Bone Histology looking at?
The microarchitecture of bone and bone cells and their makeup
On average, how many bones are there in the adult skeleton?
206
How many adult teeth do you have?
32
How many bone elements do you have as a baby?
over 300
What is supernumerary?
more of something
Why is 206 an average of bones in the body?
because you can have more or less due to congenial absences, amputation, or developmental issues
What do bones do?
- protect organs
- provide structure for the body (ie. muscle attachments)
- give us the ability to move
- mineral storage (ie calcium)
- produce blood cells (in the red bone marrow in the epiphyses of the bone)
- form the skeleton (anchors for muscles so we can move)
- bone marrow
Bone is a ______ of two different elements.
Matrix
What are the two components that bone is made up of? How much do each of the components make up of the bone
- an organic and inorganic component
- collagen (organic) 90%
- hydroxyapatite (inorganic) 10%
What does collagen do for the bones?
- provides flexibility to them
- helps resist compressive forces (ie when you walk you have a compressive force from above and below the bone)
- allows the bones to flex slightly to resist the compressive forces
What does hydroxyapatite do for the bones?
provides rigidity to the bones so they are able to hold our weight
What is hydroxyapatite composed of?
calcium phosphate
What other parts of the bone helps it resist compressive forces?
it’s structure
What is the Periosteum?
the tough vascular membrane covering the outside of living bone
What goes between the bone and the periosteum?
blood vessels
How is a bone bruised?
when it is hit hard enough (but doesn’t break) and the blood vessels between the periosteum and the bone body break
What is the Endosteum?
the cellular membrane that lines the inside of the living bone and it medullary cavities
How many areas can a long bone be separated into? What are they?
- 3
1. proximal epiphysis (top)
2. diaphysis (middle)
3. distal epiphysis (bottom)
When you are developing and growing, are the epiphyses fused to the diaphysis of a long bone?
no
Why aren’t the epiphyses fused to the diaphysis in development?
because it allows the diaphysis to grow longitudinally and a bit transversely
What is another word for diaphysis?
shaft
What does the fusing of the epiphyses to the diaphysis signal?
that growth has stopped
What is the epiphyseal line? What is another name for it? What is it’s consistency?
- the epiphyseal line is the line that forms when the epiphysis has fully fused to the diaphysis
- it is the union between the epiphysis and the diaphysis
- it is also known as the “growth plate”
- dense
Where is the yellow marrow housed?
In the medullary cavity in the diaphysis
What is the metaphysis? When is it easier to distinguish?
- the ends of the diaphysis before the epiphyses have fused to it
- easier to distinguish in younger bones when the epiphyses are detached
What is an epiphysis?
The end of a bone
What is the diaphysis?
the middle part or shaft of the bone
Is the epiphyseal line made up of trabecular bone?
no
What kind of bone are the epiphyses and the metaphyses made out of?
- trabecular bone (spongy bone)
What shape is the trabecular bone? What does it help with?
- honeycomb shape
- its shape helps to resist those compressive forces at the ends of the bone
What type of bone is subchondral bone? What specific type of bone does it refer to?
- subchondral bone is cortical bone
- it is a specific type of bone that is under cartilage
Where is a common place to find subchondral bone?
at joints since they are covered in cartilage
what is the epiphyseal line made out of?
compact/cortical bone
what type of bone covers the entire outline of the bone and is directly underneath the periosteum?
cortical bone
what type of bone is the diaphysis and medullary cavity made out of?
cortical bone
what type of bone are the epiphyses and metaphases made out of?
trabecular bone
what is the Haversian System referring to?
- a cellular structure that makes up the cortical bone and gives it its density
- it strictly refers to the structure of cortical/compact bone
what is the Haversian system characterized by?
primary and secondary osteons
what is an osteon?
a complete circular unit with a central blood vessel that is surrounded by rings of bone with other structures in them
Is the complete circular osteon structure a primary or a secondary osteon?
a secondary osteon
what type of bone is the osteon structure made of?
Lamellar bone
What is Lamellar bone? What type of bone does it form?
- strong and well organized bone
- forms compact/cortical bone and trabecular bone
what bone is trabecular and cortical bone made out of?
well organized Lamellar bone
what creates the “high-rises” for the secondary osteons the in Haversian system?
Lamellar bone
What connects the secondary osteons in the Haversian system?
by a transverse canal called the Volkmann’s canal
What is the canal for the blood vessel that runs vertically in each secondary osteon?
the Haversian canal
What do the Volkmann’s canals house?
blood vessels that run transversely which allows them to connect with other blood vessels in the Haversian and other Volkmann’s canals
What is a Lacunae?
a little space within the secondary osteons of the Haversian system that house bone cells
What are Canaliculi?
tiny little canals that connect each Lacunae and provide the bone cells within then the nourishment they need to stay alive
What do the terms primary and secondary refer to when discussing osteons in the Haversian System?
they refer to time,
the primary osteon is one that is preexisting and to the secondary osteon,
the primary (older) osteon is what gets absorbed into the secondary (newer) osteon
what is a secondary osteon?
a complete “tower”
what happens to a secondary osteon once it is complete and begins to age?
a new osteon will grow beside it and begin to take some of its bone material and take from the surrounding secondary osteons. this process of the new osteon taking material away from the secondary osteons shift the secondary osteons into primary osteons since they are now primary and preexisting to the new osteons forming beside them
define what a primary osteon is
- an osteon that has been “remodelled” and had its material taken from the new secondary osteon that has formed around it
- it is preexisting and therefore primary to the secondary osteon that has formed completely beside it
What does a secondary osteon do when it is forming?
it takes material from the primary osteons around it to completely form
which is older a primary or secondary osteon
a primary osteon is older
eventually, will a primary osteon completely disappear?
yes because its material will eventually become reabsorbed into the newer secondary osteons forming around it
what is the importance with distinguishing primary versus secondary osteons?
it tells you how often that bone is turning over and tells you how active the bone is
if there are a lot of secondary osteons within the cortical bone’s Haversian system, what does that tell you about the bone? what if there are less secondary osteons?
- many secondary osteons mean the bone is very active in remodelling and active in its growth
- less secondary osteons mean that the bone is slowing down in its growth
Define an Osteoblast?
a bone cell that builds two types of bone, immature/woven bone and mature bone
In what way does an Osteoblast build bone? What is the outcome of this?
- an osteoblast will build bone around itself
- sometimes it will become trapped in the bone its built around itself and becomes an osteocyte
What is an Osteocyte? What is it nourished by?
- a bone cell that lives in the Lacunae (a stationary osteoblast that built bone around itself and is now stuck)
- it is nourished by the canaliculi
Can an Osteocyte still build bone?
no
What is an Osteoclast?
a bone cell that cleans the bone (dissolves bone)
How does an Osteoclast clean/dissolve bone?
it used ruffled membrane to dissolve and move along the bone
What is woven/immature bone?
- the first type of bone material that an osteoblast lays down
- it is deposited really quickly and disorganized
- it is coarse, fibrous, and weak
- it is the initial fetal bone, used to repair injured bones, or in bone tumours
What is mature bone?
- the reworked immature/woven bone that is stronger bone made by osteoblasts
- it is lamellar bone
- well organized
What are the different conditions that a bone will form under?
- Endochondral Ossification
- Intramembranous Ossification
Explain Endochondral Ossification.
- begins for a cartilaginous precursor (since in utero before bone is formed it is essentially cartilage)
- overtime the bone that will eventually become the medullary cavity and the diaphysis will start to from in the primary ossification centre
- a bone collar will begin to form around the outside of this cartilage to let the bone in the primary ossification centre know its parameters of growth
- then the periosteum forms
- the epiphyses will form later in secondary ossification centres
- eventually the medullary cavity forms
- eventually after the bone has grown more the epiphyses will then fuse to the diaphysis
How can epiphyseal growth help with juvenile age estimation
looking at how far along the epiphyses have grown and at what stage of epiphyseal fusion the bone is at can help with juvenile age estimation
What bones will grow from Endochondral Ossification?
long bones and some irregular bones
Explain Intramembranous Ossification.
- begins within membranes (the bone growth need the fibrous tissue)
- within a membrane the osteoblasts begin to lay down irregular bone and begin trapping themselves within bone and become osteocytes
- the osteoblasts then form trabecular bone
- then the cortical bone will form around it
What is the structure called that is trabecular bone sandwiched between compact/cortical bone called? What kind of bones have this?
- this structure is called Diploë
- this structure forms the bones of the skull
What bones are formed from Intramembranous Ossification?
- Cranial bones
- sesmoid bones that can form in ligaments
Can bones other than the cranial bones have the Diploë structure?
no
What is the largest sesmoid bone?
the kneecap
What is bone Modelling?
- bone forming and developing to its adult form starting in utero
- can also refer to when fractures are being repaired (woven bone laid down that is then replaced by lamellar bone)
What type of bone replaces immature/woven bone?
mature/Lamellar bone
What is bone Remodelling?
- the process of the bone fixing minor fractures or stress related issues
- its a continued removal and replacement of mature bone
- still happens when you’re not growing
- can lead to issues like osteoporosis which is a defect of bone remodelling
What is Osteoporosis and what is it a result of?
- it is when the bone gets weakened by bone remodelling
- a loss in bone density where the holes within the trabecular bone are getting larger
What is bone Remodelling responsive to?
muscle growth since muscle growth stimulates bone growth
Do the Osteoblasts and Osteoclasts stop working after a bone has finished growing?
no they just slow down and work on minor repairs and upkeep
When the bone is in the process of Modelling and Remodelling, how the bone is shaped and what state the bone will be in is a product of what law?
Wolff’s Law?
Explain Wolff’s Law.
- “The law of bone transformation”
- It explains that the shape of the bone and how strong or weak it is is a consequence of the mechanical forces that are acting on that bone
- bones are shaped the way they are due to the forces that they are resisting
