HUBS lecture 4- Bone tissue and its microscopic structure Flashcards
• Describe the microscopic structure of bones • Describe how bone maintains homeostasis • Describe a bone pathology relating to lack of homeostasis (osteoporosis)
what are the 2 components of bone
Bone is made up of connective tissue cells and ECM
ECM has 2 components
oragnic-33% of bone
inorganic-67%
Describe the organic and inorganic bits
ORGANIC:
-makes one-third of bone matrix
-formed of collagen(protein)- if this is removed the bone becomes brittle and breaks easily.
- Ground substance( proteoglycans)
- Function= resists tension( pulling things away)
INORGANIC
- 67% of bone matrix
formed of mineral salts–> provides hardness, bones will become bendy when removed.
Function= resists compression( putting things together)
Describe the cellular comp of bone
Makes up only 2 %
- Four types of cells
Osteogenic cells
Osteoblasts
Osteocytes
(Mature bone cells )
Osteoclasts
Together these cells maintain bone homeostasis
–>Balance of bone destruction and formation that means the amount of bone stays the same
Describe each of the bone cells, including function and location
Osteoblasts- makers:
osteogenic cells produce them
Function- to build bones, they synthesise, deposit, and mineralise osteoid, then they differentiate into OSTEOCYTES
Location- wherever new bone is forming under the endosteum or periosteum.
OSTEOCYTES-maintainers (maintain bone tissue), recycle protein and minerals from matrix. come from osteoblasts.
Location-trapped within the calcified bone in lacunae.
Osteoclasts- Destroyers
secrets enzymes and acids to dissolve the bone matrix- causing bone remodelling
Compact bone structure
compact bone had the osteon structure. It’s made up of circumferential lamellae and osteons.
- Osteon: longitudinal (lengthwise) a unit within the compact bone.
—>Provide a pathway for nutrients to get to cells in the ECM - Central canal - contains blood
vessel and nerves - Lamellae - a series of cylinders
formed of ECM around the central canal.
—->Form the shape of the osteon
—–>Collagen fibres within lamellae
resist forces - Lacunae= ‘lakes’ for osteocytes
Osteon - Canaliculi = channels for nutrients to travel to osteocytes through the ECM
Cancellous bone structure
Made up of struts of Trabeculae(lamella bone). Osteocytes are located within lucane but on the surfaces of the trabeculae.
- is synthesised outwards
-no blood vessels
- functions as a shock absorber, bone is strong yet flexible.
- Trabeculae form along the lines of stress to provide strength.
where there is crossing over of lines of stress there will be a point of weakness in the bone, likely place for deuteriation of the trabeculae.
- the cavities also function to lighten the bones, so that muscles are able to move them more easily. marrow fills the cavities between trabeculae.
Why trabecular bone ( cancellous)
organisation of trabeculae resist force from multiple directions.
- directs force from body weight in single direction down shaft.
- spreads force distally
trabeculae channel weight around the ilia into femora.
Bone remodelling
allows bone to grow, appositional growth( width)
osteoblasts add bone matrix in lamellae to bone surface
osteoclasts remove bone from the medullary cavity.
Bone homeostasis
Balance of osteoblasts( makers) and osteoclasts( destroyers)
bone is constantly being made/destroyed.
- allows body to mobilise calcium and other minerals from bone matrix.
PROCESS called Remodelling
-allows bone to respond plastically
- shape change possible through life to resist strain.
AMOUNT OF BONE STAYS THE SAME.
What happens if bone homeostasis isn’t maintained.
body has requirements to maintain homeostasis. without these there is an imbalance in osteoblastic/osteoclastic activity.
Imbalance–> osteoporosis
- loss of cortical bone, in cancellous bone trabeculae become thinner.
