The long bones are those that are longer than they are wide. They are one of five types of bones: long, short, flat, irregular and sesamoid. Long bones, especially the femur and tibia, are subjected to most of the load during daily activities and they are crucial for skeletal mobility. They grow primarily by elongation of the diaphysis, with an epiphysis at each end of the growing bone. The ends of epiphyses are covered with hyaline cartilage ("articular cartilage"). The longitudinal growth of long bones is a result of endochondral ossification at the epiphyseal plate. Bone growth in length is stimulated by the production of growth hormone (GH), a secretion of the anterior lobe of the pituitary gland.
The long bones include the femora, tibiae, and fibulae of the legs; the humeri, radii, and ulnae of the arms; metacarpals and metatarsals of the hands and feet, the phalanges of the fingers and toes, and the clavicles or collar bones. The long bones of the human leg comprise nearly half of adult height. The other primary skeletal component of height are the vertebrae and skull.
The outside of the bone consists of a layer of connective tissue called the periosteum. Additionally, the outer shell of the long bone is compact bone, then a deeper layer of cancellous bone (spongy bone) which contains red bone marrow. The interior part of the long bone is the medullary cavity with the inner core of the bone cavity being composed of yellow marrow in adults, and red marrow in young children.
Famous quotes containing the words long and/or bone:
“It is marvelous indeed to watch on television the rings of Saturn close; and to speculate on what we may yet find at galaxy’s edge. But in the process, we have lost the human element; not to mention the high hope of those quaint days when flight would create “one world.” Instead of one world, we have “star wars,” and a future in which dumb dented human toys will drift mindlessly about the cosmos long after our small planet’s dead.”
—Gore Vidal (b. 1925)
“Fowls in the frith,
Fishes in the flood,
And I must wax wod:
Much sorrow I walk with
For best of bone and blood.”
—Unknown. Fowls in the Frith. . .
Oxford Book of Short Poems, The. P. J. Kavanagh and James Michie, eds. Oxford University Press.