The long bones are those that are longer than they are wide. They are one of five types of
bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
s: long,
short,
flat,
irregular and
sesamoid. Long bones, especially the
femur
The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg.
The Femo ...
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
The epiphyseal plate, epiphysial plate, physis, or growth plate is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, with ma ...
. 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 bone category includes 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
The phalanges (: phalanx ) are digit (anatomy), digital bones in the hands and foot, feet of most vertebrates. In primates, the Thumb, thumbs and Hallux, big toes have two phalanges while the other Digit (anatomy), digits have three phalanges. ...
of the fingers and toes, and the
clavicles or collar bones. The long bones of the human leg make up nearly half of adult height. The other primary skeletal component of height are the
vertebrae
Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
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 in the
medullary cavity the
bone marrow.
Structure
The outer shell of the long bone is made of
cortical bone also known as compact bone.
This is covered by a membrane of
connective tissue called the
periosteum. Beneath the cortical bone layer is a layer of spongy
cancellous bone. Inside this is the
medullary cavity which has an inner core of bone marrow, it contains nutrients and help in formation of cells, made up of yellow marrow in the adult and red marrow in the child.
File:Long bones - animation.gif, Long bones in human skeleton (shown in red)
File:Structure of a Long Bone.png, Parts of a long bone (Femur)
File:Blausen 0229 ClassificationofBones.png, Classification of bones by shape
File:Blausen 0401 Femur DistributionofForces.png, Distribution of forces on a long bone (Femur)
File:Os longum 1.png, Part of a long bone of a large ungulate
Clinical significance
There are two
congenital disorders of the long bones. In a disorder known as ''rachitis fetalis anularis'' the ends of the long bones (epiphyses) are enlarged.
Another disorder, ''rachitis fetalis micromelica'', is a deficiency in the growth (as a shortness) of the bones.
There is a surgical procedure called
distraction osteogenesis which is used to lengthen long bones.
References
External links
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