Bone Tissue Flashcards
(42 cards)
What are the functions of the bone?
Support Provides insertion to muscles. Protection of organs. A storehouse for minerals. The container for hematopoietic bone marrow.
How many bones do human adults have in their body?
206
What are the different classifications for bones?
Long bones, short bones, flat bones.
Describe the general structue of bone.
Spongy bones in the middle surrounded by compact bone.
Describe the appearance of spongy and compact bone.
Spongy bone is characterised by a mainly trabecular presence.
The compact bone appears as a compact layer of tissue that mainly characterises the diaphysis.
Describe the bone marrow stored inside bone tissue.
Yellow bone marrow - mainly formed by adipocytes
Red bone marrow - hematopoietic bone marrow.
What is the composition of bone tissue?
The tissue is formed by an extracellular matrix and cells.
The matrix is divided into organic and inorganic, where the inorganic is mainly calcium and phosphorus. They get together to form the hydroxyapatite.
The organic part is composed of collagen, proteoglycans and other non-collagenous proteins.
The cells present are osteroprogenitor cells, osteocytes, osteoblasts and osteoclasts.
What are the functions of hydroxyapitite in the bone?
It’s the major component of the mineralized extracellular component of the bone.
The hydroxyapatite is responsible for the hardness of bone tissue.
What are the functions of collagen and other proteins in the bone?
Collagen type I is found in the extracellular matrix of the bone tissue, it’s organised in a particular way that gives the bone tissue its strength.
There are also proteins responsible for adhesion of bone cells and regulation of bone homeostasis.
What would happen to the bone if either the mineral or collagen part was removed?
Mineral - the bone becomes very flexible.
Collagen - the bone becomes very fragile.
How can the bone be studied from a histological point of view?
Demineralization in acid solution (EDTA).
Removal of organic components with heat.
Describe the method used to study the inorganic part of the bone.
This is obtained by leaving the tissue in water solution for several days, the organic component is degraded to leave the inorganic component.
A specific equipment that contains a ‘sandpaper’ reduces the piece of bone to a very thin size.
This section usually doesn’t need to be stained, we could use the light and air passing through the empty spaces of the cells that were degraded.
Describe the appearance of bone after the organic part has been removed.
The black spots are called lacunae, and is where the osteocytes reside before being degraded.
While the fine structures are called canaliculi, which are very tiny channels in which the protrusions of the osteocytes were located.
Therefore this is a very fine way of making contacts between the central canal and the osteocytes present in the osteon.
Describe the appearance of bone after the inorganic part has been removed.
The nuclei of the osteocytes can be seen. The presence of the canaliculi can’t be appreciated in this image.
Although the CT proper in which blood vessels and nerves are contained can be observed, as well as the edges of the osteocytes.
Describe the non-lamellar structure of bone.
Immature bone is non-lamellar and is formed by woven collagen fibers.
Describe the non-lamellar (bundle or woven) structure of bone.
Immature bone is non-lamellar and is formed by woven collagen fibers.
Describe the lamellar structure of bone.
Immature bone is replaced by lamellar bone, so the organization of a mature bone tissue is a lamellar organisation.
On the surface of each lamella, small cavities are carved out called lacunae, which contains osteocytes (surrounded by tissues). A non-calcified extracellular matrix surrounds the osteocytes.
Each osteocyte communicates with a nearby osteocytes through the net of canaliculi. They are very important as they interconnect all lacunae with blood vessels.
Why are the canals present in lamellar bone?
The extracellular matrix of the bone tissue is mineralized (non-hydrated), and can not have any diffusion process occuring in the extracellular matrix.
There needs to be an internal network of canals that allows the passage of nutrients from the blood vessels to each of the osteocytes in the lacuna.
Describe the haversian system in a compact lamellar bone.
Lamellae forms cyclinders that are arranges inside one another.
The cavity delimited by the innermost lamella is called Haversian canal and contains blood vessels and nerves.
The set of lamellae surrounding a canal is called Haversian system (osteon).
What structure do the collagen fibers form on each lamella?
The collagen fibers (type I) form the supporting scaffold for the mineralized matrix of the lamellae.
Arranged in parallel but their orientation is antiparallel.
Direction changes in adjacent lamellae with an inclination of 90o, this creates an alternating pattern.
This helps the bone withstand tortion stress.
How do osteocytes contact nearby osteocytes?
Osteocytes have tiny protrusions which enter inside the canaliculi and make contact with nearby osteocytes.
There are formations of gap junctions in between.
What are perforating channels (Volkmann’s canals)?
At haversian canals, there are blood vessels passing through.
Perforating canals (Volkmann’s canals) connect blood vessels contained at the peripheral of the bone tissue with ones inside the compact bone.
What are interstitial systems?
In between complete osteons, there is lamellar bone that doesn’t form a real osteon.
These are called interstitial systems, which is proof that the bone is not static and undergoes remodeling through our lives.
What are circumstantial lamellae?
Layers of lamellae which runs for the entire circumference of the bone tissue not forming true osteons - circumferential lamellae.