MSK 03 - Bone-II Flashcards
How does an osteon develop?
What are the two ways that bone develops?
List the steps to intramembranous bone formation.
- Mesenchymal cells condense to form a primary ossification center, from which osteoblasts differentiate and begin secreting osteoid
- Osteoblasts become trapped in their own matrix and become osteocytes
- Ossification centers expand into spicules as more osteoblasts aggregate.
- Neighboring spicules fuse into bone trabeculae
- As bone trabeculae join together, spongy bone develops
- Blood vessels invade the area at the same time that undifferentiated mesenchymal cells give rise to bone marrow cells
- Periosteum forms from surrounding mesenchymal cells
- Numerous ossification centers fuse together forming bone
What are the major examples of bone developed via intramembranous bone formation?
Most of the flat bones of the skull
List the steps to endochondral bone formation
- Outline of bone in hyaline cartilage
- Formation of periosteum and subperiosteal bone collar for support in diaphyseal region
- Cartilage matrix is calcified
- Blood vessels erode into calcified cartilage
- Formation of periosteal bud consisting of osteogenic cells and blood vessels (primary ossification center)
- The subperiosteal collar thickens and bone forms on the calcified cartilage complexes
- Secondary ossification centers (in a similar manner) form in the epiphyses.
- Epiphyseal cartilage (epiphyseal growth plate) is formed between the primary and secondary ossificatoin centers
- Epiphyseal plate disappearance occurs at different times
- Fusion of diaphyseal and epiphyseal marrow cavities
How does the epiphyseal plate grow and what age do they typically fuse?
The epiphyseal plate continues to grow by adding new cartilage at the epiphyseal end while it is being replaced by bone at the diaphyseal end.
~20 years of age
What are the five histologically distinctive zones of the epiphyseal plate?
- Zone of reserve cartilage
- Zone of proliferation
- Zone of hypertrophy
- Zone of calcified cartilage
- Zone of resorption
What is found within the zone of reserve cartilage?
Small randomly arranged inactive chondrocytes
What is found within the zone of proliferation?
Rows of cartilage cells resulting from rapid mitotic divisions
What is found within the zone of hypertrophy?
Greatly enlarged chondrocytes separated by a thin cartilage matrix
What is found within the zone of calcified cartilage?
Coalesced lacunae and calcified interlacunar matrices. This calcification causes the chondrocytes to enter apoptosis
What is found within the zone of resorption?
Bone is beginning to be elaborated upon the calcified cartilage, and osteolytic activity begins to resorb the calcified bone-cartilage complex
List the steps to bone repair
- Bone blood vessel hemorrhaging is followed by blood clotting, and macrophages remove much of the debris via phagocytosis
- Fibroblasts proliferate in the periosteum and endosteum and surround the area internally and externally to isolate it
- A fibrocartilaginous callus is formed both internally and externally
- Bone is deposited in the fracture zone by intramembranous bone formation by osteoblasts derived from the osteogenic layer of the periosteum and endosteum near the fracture
- Chondrocytes also differentiate from this connective tissue and deposit cartilage, which will be replaced by bone by endochondral bone formation, thus forming a bony callus composed of primary bone
- Bony callus is eventually resorbed and replaced with secondary bone
Bone contains about ____ of the body’s calcium?
99%
What causes bone decalcification?
A diet inadequate in clacium
During what normal step in the bone life cycle is calcium transferred from the bone into the blood stream?
The remodeling of spongy bone
What are the two major reasons the body could be lacking calcium? What disease can this lead to?
What are the three key vitamins for bone growth and what happens if too much is present?
What are the four major hormones that affect bone growth?
Parathyroid hormone (PTH)
Calcitonin
Sex Hormones
Pituitary growth hormone (GH)
How does PTH affect bone growth?
How does calcitonin affect bone growth?
It inhibits matrix resorption and thus prevents the release of calcium from bone
How do sex hormones affect bone growth?
How does GH affect bone growth?
What is osteoporosis and how many types of it are there?
Osteoporosis means “porous bone” and it results from the progressive loss of bone density leading to an increased risk of fracture.
There are three types: Primary Osteoporosis Type 1 & 2, and Secondary Osteoporosis
What is Primary Osteoporosis Type 1?
Primary Osteoporosis Type 2
Osteoporosis from advanced age (70-80’s)
What is secondary osteoporosis?
