6-2. Ossification and Bone Growth Flashcards
Ossification
the process by which bone forms in the body
models
fibrous membranes and hyaline cartilege in the embryonic skeleton shaped like bones
Ossification begins around the __ week and __ eventually replaces most of the embryonic skeleton.
8; bone tissue
What are the two types of bone formation?
intramembranous ossification
endochondral ossification
Intramembranous ossification
when a bone develops from a fibrous membrane
What bones form from intramembranous ossification?
clavicles and cranial bones in skull
What bones form from endochondral ossification?
all bones except for the clavicles and cranial bones in the skull
Endochondral ossification
when a bone develops from hyaline cartilage models
Primary Ossification Center
blood vessels penetrate the perichondrium midway along shaft of cartilage model at this region
What are the steps of endochondral ossification, at the primary ossification center?
- Blood vessels penetrate the perichondrium midway along shaft of cartilage model at the primary ossification center. This stimulates the underlying cells to become osteoblasts and converts the perichondrium to periosteum.
- Osteoblasts secrete osteoid that encases the shaft of the model in a bone collar.
- Changes occur in the cartilage in the center of the shaft, resulting in calcification. The osteocytes die since nutrients can’t diffuse across the membrane, leaving cavities that merge to eventually form the medullary cavity.
- The periosteal collar thickens and lengthens in the shaft, but the cartilage model continues to grow rapidly at its epiphysis.
What are the steps of endochondral ossification, at the secondary ossification center?
shortly after birth, blood vessels enter the epiphyses, and osteoblasts begin to lay down bone there
The primary ossification center is located ___.
midway along the shaft of the cartilage model
The secondary ossification center is located ___.
the epiphyses
When secondary ossificaiton is complete, hyaline cartilage remains: ___.
at the tips of long bones as articular cartilage
at the junction of the diaphysis and epiphysis, forming the epiphysial plate
During infancy and youth, ___ bones grow in length, and ___ bones grow in thickness. Most bones stop growing during ___.
long; all; adolescence
What happens during appositional growth (growth in thickness)?
- osteoblasts beneath the periosteum add new bone tissue to the outer surface, producing a thicker and stronger bone
- at the same time, osteoblasts on the endosteal surface remove the bone lining the medullary cavity, to prevent it from becoming too heavy
What allows the diaphysis of long bones to continue growing in length?
the epiphysial plate
What happens during bone growth in length?
- cartilage cells on the epiphysial side of the plate divide quickly, increasing the thickenss fo thep late and pushing the epiphysius further from the diaphysis
- the older chondrocytes that have been pushed closer to the shaft enlarge, and the surrounding matrix calcifies, causing the cells to die and be replaced with spongy bone.
- the epiphyseal plate remains a constant thickness - the rate of cartilage growth is balanced by replacement with bony tissue
epiphyseal plate closure
cartilage cells in the plate are all replaced by bone and growth in length stops
Epiphyseal plate closure happens at __ yrs in females and __ in males.
18; 21
What are some factors affecting bone growth?
diet
hormones
exercise
aging
What diet is most conducive to bone growth?
rich in protein, calcium, phosphorus, Mg and Mn, plus vitamins A, C, and D
growth hormone
most important stimulus of bone growth during childhood released from pituitary gland.
Too little growth hormone results in ___; too much results in ____
pituitary dwarfism; gigantism
What are the roles of sex hormones in bone growth?
- promote the “growth spurt” seen in puberty
- masclinization/feminization of skeleton
- cause the epiphyseal plate to close
calcitonin
produced by the thyroid gland, accelerates calcium uptake by the bones - when levels are high, causes the excess to be deposited in bones
parathyroid hormone
released from the parathyroid glands when blodo calcium levels are low - stimulates osteoclasts to break down bone matrix, releasing calcuim from bones
When calcium levels are too high, ___ is produced.
calcitonin
When calcium levels are too low, ___ is produced
PTH (parathyroid hormone)
How does exercise help bone growth?
stimulates bone growth, causing mineral salts to be laid down making bones thicker and stronger. Bone grows in response to the demands made on it.
What happens to bones as we age?
calcium is lost from bones; there is also a decrease in protein production, leading to fewer collagen fibers and making bones brittle
Begins at age 30-40 in women and 60 in men
bone remodeling
in the adult skeleton, old bone is continually being removed (resorption) by the osteoclasts and replaced with new bone by the osteoblasts
Spongy bone on surface is remodeled into ___ early in life.
compact bone
Worn and injured bone is ____.
actively replaced
The distal end of the femur is remodeled every ___.
5-10 years
What is blood calcium essential for?
maintained in a narrow range of 9-11 mg/dl. Essential for muscle contraction, nerve impulse contraction, and blood clotting
