Flashcards in BL - Bone And Intermembranous Ossification Deck (30):
What is intramembranous ossification?
Development of bones from condensations of mesenchymal tissue (not involving cartilage). Most flat bones develop this way.
Give some examples of flat bones.
Skull, clavicle, scapula, pelvic bones.
What is a nidus?
A small cluster of mesenchymal stem cells formed during the first stage of intramembranous ossification.
Describe the stages of intramembranous ossification. (Hint - nidus -> osteoprogenitor -> osteoblasts -> spicules -> trabeculae -> lamellae)
Mesenchymal cells form a nidus, MSCs become osteoprogenitor cells (more Golgi and RER), these become osteoblasts which lay down extracellular matrix with type I collagen (osteoid), osteoid mineralises to bone spicules, these join to form trabeculae, these merge to form woven bone, finally replaced by lamellae.
What is an osteoblast called when it is surrounded by osteoid?
What makes osteoclasts easy to identify on images?
They have multiple nuclei.
What is cancellous/spongy bone?
A network of fine bony columns, with the spaces filled by bone marrow. It combines strength with lightness.
What is compact/cortical bone?
Dense bone that forms external surfaces and comprises most of the skeletal mass.
What is the difference between osteocyte arrangement in mature and immature bone?
Immature bone - osteocytes randomly arranged. Mature bone - osteocytes arranged in concentric lamellae of osteons.
What do the Haversian and Volkmann's canals carry?
Blood vessels, lymph vessels and nerves.
How can Haversian and Volkmann's canals be differentiated on images?
Volkmann's canals have no concentric lamellae surrounding them, while Haversian canals do.
How are nutrients passed between osteocytes?
They have very slender cytoplasmic processes which reach out to adjacent osteocytes via canaliculi.
What is the trabeculae of cancellous bone?
The network of spiny bone processes that make up the framework of spongy bone. No Haversian or Volkmann's canals here.
What do osteoclasts release when part of a cutting cone?
H+ ions and lysosomal enzymes, which bore through the bone.
What is the composition of bone?
65% mineral, 23% collagen, 10% water, 2% non-collagen proteins
What are the lamellae though to be able to do to help prevent fracture?
Slip over each other.
How does bone resist fracture?
It has great tensile and compressive strength and a degree of flexibility.
What are the four stages of fracture repair?
Haematoma formation, fibrocartilaginous callus formation, bony callus formation, bone remodelling.
What happens during haematoma formation?
A mass of clotted blood forms due to broken blood vessels, bone cells at fracture edge die. Swelling/inflammation, phagocytic cells and osteoclasts start to remove dead tissue. Macrophages remove blood clot.
Which stage of fracture repair is this? New blood vessels infiltrate haematoma, procallus forms, collagen fibres and hyaline cartilage splint the bone. Osteoblasts begin to form spongy bone at the fracture site.
Fibrocartilaginous callus formation.
Describe the stages of bony callus formation.
Trabeculae develop as fibrocartilaginous callus is converted to a bony callus of cancellous bone. Endochondral ossification replaces all cartilage with cancellous bone.
How long does bone remodelling (the final stage of fracture repair) take place for?
Why is the final, remodelled bone the same shape as the bone before the fracture?
It responds to the same set of mechanical stressors.
Tim breaks his leg (fool) and loses a chunk of bone, meaning bony union and callus formation is not possible. His brother donates a chunk of bone to replace it. What is this called?
What is osteoporosis?
A metabolic bone disease when mineralised bone is decreased in mass to the point that it no longer provides sufficient mechanical support.
Osteoporosis associated with aging results from incomplete filling of what?
Osteoclast resorption bays.
At what age does bone mass peak?
Describe some risk factors for osteoporosis.
Genetic factors, insufficient calcium intake, insufficient calcium and vitamin D absorption, less exercise, cigarette smoking.
Which type of osteoporosis is due to an increase in osteoclast number as a result of oestrogen withdrawal?