Bone tissue

• The bone is a living tissue. It is able to react to what the body is going through because it has cells as well as calcified extracellular matrix. the cells can communicate and change what the body is doing.
• Bone can become more robust and respond through the forces.
• They can respond to trauma and if bones break, the bone tissues will reform to recreate it.
• The bones are a connective tissue that help support other tissues and organs and helps maintain their structure and shape.
• The connective tissues are:

  • interphalangal joints
  • ligaments to hold the bone together
  • cartilage on top of the bones
• The bones have 2 extracellular components:

  1. inorganic portion - made of minerals to make the bone hard
  2. organic portion - organic molecules
• The inorganic portion makes up 67% of the bone. the mineral is called hydroxiyapitite and other calcium minerals, making the bone hard and resistant to compression. When pushed, it does not bend,.
• The organic portion makes up 33% of the bone. It contains collagen fibers which give the bone flexibility when pulled or stretched. The collagen fibres also act as scaffolding for osteoblasts to build new bone matrix around them.
• The cellular component of the bone makes up 2% by its weight, there are 4 different types.

  1. Osteogenic cells
  2. Osteoblasts
  3. Osteocytes
  4. Osteoclasts

  All maintaining homeostasis.
• Osteogenic cells are stem cells that produce osteoblasts.
• Osteoblasts create new bones (matrix) responsible for bone growth.
• Osteocytes is what osteoblasts convert to making them mature cells.

  • They stop making bone and stay in the matrix.
  • Maintain the bone
  • Recycle protein and minerals
  • Communicates with other cells
• Osteoclasts removes bone from the matrix.
• Gross Structure of bones:

  • compact bones
  • cancellous

  they both are made from the same matrix but structured different.
• The trabaculae goes off in different directions is cancellous.
• The osteon has lacunae and a mineralised matrix. It is cylinders packed together.
• Compact bones shen looked at macroscopically, they are dense, impenetrable and on the inside, there are holes from outside to inside for blood supply.
• Compact bones if looked microscopically, they have the osteon structure.
• Osteons are a longitudunal unit within the compact bone to provide a pathway for nutrients to get to the cells containing:

  • Central canal
  • Lamallae
  • Lacunae
  • Caniculi
• The central canal contains blood vessels and nerves
• The lamallae is made of inorganic portion, formed from the ECM around the central canal.

  • forms shape of osteon
  • contains collagen fibres
• The lacunae live between the lamallae, they are dark circles that maintain osteo cells
• The canalculi get the blood supply to the osteo cells by channeling through the ECM.
• The cancellous bone is made up of a branching structure going in different directions. There is no central canal because the bone is directly in contact with the bloody supply
• The trabaculae is surrounded by bits of red marrow and struts of lamallae
• Red marrow fills the cavities between trabaculae
• Osteocytes housed between lacuna in between lamallae
• Trabaculae is able to resist force that comes from different directions. It is shock absorbing and it directs force from the body weight in a single direction down he shaft.
• in the pelvis bone, the trabaculae enables to take all the weight in and take it out into one direction and into the legs.
• When forming bone on the outside, we also take away from the inside. When we grow, we get longer and wider = appositional growth
• Osteoblasts add bone matrix in the lamallae to the bone surface
• Osteoclasts remove bone from the medullary cavity
• To get homeostasis, we balance osteoblasts and osteoclasts
• Bone remodelling is when our body always forms and destroys because our body is storing irons and calcium, so we need to mobilise them in order to use them.
• To maintain balance, we need enough calcium for osteoblasts to make bones. Without this, it can cause an imbalance called osteopenia.
• When cancellous bones squish, they cause compression fractures by the weight coming down.