bone formation growth and remodoling Flashcards
(5 cards)
cartilage and bones
The skeleton is formed from two of the strongest and most supportive tissues in the body—cartilage and bone. In embryos, the skeleton is primarily made of hyaline cartilage, but in young children, most of the cartilage has been replaced by bone. Cartilage remains only in isolated areas such as the bridge of the nose, parts of the ribs, and the joints.
the replacement of cartilage
So basically, most bones—except for flat bones—develop using hyaline cartilage as a template. First, the hyaline cartilage gets covered in bone matrix, forming a hard outer layer called the bone collar, and this is done by osteoblasts (bone-forming cells).
2. As the embryo develops into a fetus, the area inside the bone collar is gradually replaced by bone tissue, while the inner cartilage begins to break down. This breakdown creates a hollow space called the medullary cavity, which later becomes filled with yellow bone marrow that stores fat.
appositional growth
How Bones Widen (Appositional Growth):
Osteoblasts in the Periosteum:
Osteoblasts are bone-forming cells found in the periosteum, the membrane surrounding the bone.
These cells add new bone matrix to the outer surface of the diaphysis (shaft of the bone), making the bone thicker and wider.
Osteoclasts in the Endosteum:
On the inner surface of the bone, osteoclasts (bone-breaking cells) in the endosteum remove bone from the inner face of the diaphysis wall.
This breaks down bone to enlarge the medullary cavity (the hollow inner space), keeping the bone light and functional.
Simultaneous Processes:
These two processes occur at about the same rate: osteoblasts add bone on the outside, while osteoclasts remove bone on the inside.
As a result, the bone widens and the medullary cavity enlarges, keeping the proportions of the bone balanced while it grows longer.
bone remodling after puberty
So basically, bones are not something that stay the same after puberty. Even after bones stop growing in length, they continue to remodel throughout life. This remodeling happens for two main reasons:
To control calcium levels in the blood
To respond to physical stress (like movement or muscle pull)
When blood calcium levels are low, the parathyroid hormone (PTH) is released. PTH sends signals to osteoclasts, which are bone-destroying cells. These cells break down bone tissue, releasing calcium into the blood.
When calcium levels in the blood are too high, osteoblasts (bone-building cells) take calcium from the blood and deposit it into the bone as hard calcium salts, which strengthens and hardens the bone.
The body also strengthens bones that are under a lot of physical stress—such as where large muscles are attached—by having osteoblasts build more bone matrix there.
If a person is not active (like someone who is bedridden), their bones can lose mass and weaken because there is no stress on them to keep them strong.
Eventually, osteoblasts that get trapped inside the bone matrix become osteocytes, which are mature bone cells that help maintain bone health over time.
rickets
Rickets is a disease of children in which the bones fail to calcify. As a result, the bones soften, and the weight-bearing bones of the legs become bowed. Rickets is usually due to a lack of calcium in the diet or lack of vitamin D, which is needed to absorb calcium into the bloodstream. Rickets is not seen very often in the United States. Milk, bread, and other foods are fortified with vitamin D, and most children drink enough calcium-rich milk. However, it can happen in infants nursed by mothers who become vitamin D deficient, and it remains a problem in some other parts of the world.
