Bone+Development

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(Courtesy of [|http://www.flickr.com/photos/urbanoutback/52719741/)] =The Human Skeleton= Say "skeleton" to children and you probably conjure up in their minds a structure of rigid sticks, or a clickety-clacking collection of rattling bones dangling under a halloween moon. A look at almost any drawing of the human skeleton system bears the image of dry sticks of bones, stripped of skin and flesh, and muscle and tendons: a gross carcaricature of a living human being. Our living bones are quit different. Yes, they are rigid, but not entirely. They have the capability of bending a little and growing and repairing themselves. They are shaped and fitted so that they permit the smooth grace and coordination power displayed and accomplished by an athlete or a ballerina, unlike a wooden puppet whose motions are jerky. Our bones do many things. Some, like the collarbone or clavicle, gives support to other body structures. The skull and ribs encase and protect vulnerable organs. Others, like the bones that makeup our hands and fingers, give us mechanical advantages, leverage and movement. Bones as tiny as the ossicle in the middle ear have fibrations, which enable us to hear. Ear Bones By: http://flickr.com/photos/guccibear2005/166906207/ To think of bones as a simple structural member like a solid steel girder in a skyscraper, ignores the fact that bone is living tissue. It is one of the busiest tissues in our bodies, a chemical factory that is continually receiving, processing and shipping a variety of mineral salts, blood components, and other vital materials throughout the body. Medical textbooks name a total of 206 bones making up the skeletal system of a normal adult human being. The word "normal" and "adult" are significant. A newborn baby normally has 33 vertebrae making up the backbone ( also called spinal column or spine), by the time a person reaches adulthood, the number of individual vertebrae will shrink to 26. The nine bottom vertebrae fuse naturally into just 2. We loose 60 bones as we grow up. Some perfectly normal adults have extra bones or missing bones. Example, although the normal number of ribs is 12 pairs, some adults may have 11, others may have 13. Rib Cage By: http://flickr.com/photos/19851490@N00/142278824/ A practicing Physician might be hard pressed to identify each of our 200 - plus bones and describe its function. To gain a general understanding of various functions, capabilities, and weaknesses of our bones is to visualize the skeleton system as standing coatrach about six feet high. Call the central pole the backbone ten inches down from the top (the top of the skull) is a horizontal crossbar (your shoulders - collar bones and shoulder blades) about a foot and a half across. Sixteen or so inches below the bottom of the top crossbar is another, shorter crossbar, broader and thicker (the pelvic gridle). The coatrack with its two crossbars is now a model of the bones of the head and trunk called the axial skeleton. Its basic unit is the backbone, which are attacked to the skull at the top, then the shoulder gridle, ribs, and at the bottom of the pelvic gridle. Hanging down from the two ends of the top crossbar and doing the same at the lower crossbar would simulate what is called the appendicular skeleton- arms and hands, legs and feet. Now lets make the coatrack stand on its new legs, cut off the central pole just below the lower bar and you have the two main components of the skeletal system. Within the axial skeleton framework lies the most vital organs of the body. People have gone on living with the loss of a hand or leg, but nobody can live without a brain, heart, liver, lung or kidney. Heart By: http://flickr.com/photos/patrlynch/450128330/ Brain By: http://flickr.com/photos/17657816@N05/1971828859/

The bones of the skull have, as their most important function the protection of the brain and sense organs. Within the skull are the jaw bones that support the teeth and enables us to bit and chew our food. The skull or cranium consists of eight individual plate like bones which have fused together in the process of growth. The teeth enamel is the hardest substance in the human body. It covers the exposed surface of the tooth. [|**View David J Colbran's map**] Taken in (See [|more photos here]) Skull By : http://flickr.com/photos/driki/5953928/ The [|backbone] begins at the base of the skull. It is supported by the topmost cervical (neck) vertebrae. When you think of the backbone, this word comes to suggest something solid, straight, and unbendable. However, the backbone isn't like that. It consist of 26 knobby, hollowed - out bones - vertebrae held together by muscles, lifaments, and tendons. Its not straight when you stand, but has definite backward and forward overtures. Some of its most important structures( the disk between the vertebrae) are not made of bone, but of cartilage. Backbone/spine By: http://flickr.com/photos/killbyte/55019897/ The appendicular skeleton consist of the arms, hands, and fingers. As well as the legs, feet and toes. These bones allow humans to perform complex movements, from physical rigors of the olympic decathalon to creating an elaborate piece of network. The key points in the appendicluar skeleton is the axial skeleton. Thsi is where the ends or edges of bones lie close together and must work or against one another in order to achieve coordinated movement. These key points are the joint - no the bones at all but non- bony space between the bones. Courtesy of gettyimages.com Our bones, like all our tissue, change as we frow up, mature, and finally grow old. There are changes in the chemical activity and composition of bone representative of each stage of life. Young childrens bones at the end of edges are mainly cartilage, forming a growing surface on the bone that gradually is replaced by hard bone as full size is attained. A childs bones are more pliable than those of a grown adult. As an adult ages, the bonesturn form resilient hardness to a more brittle hardness. This accounts for the greater danger of broken bones in older people. The changes with age are indications of the great amount of chemical acitivity going on within the bones. Our bones are amply supplied and penetrated by blood vessels. There is a constant building up and breaking down, and interchange of materials between blood and bone. A living bone is composed of several different kinds of tissue. There are two types of bone tissue in the same bone: compact and spongy. Also, the bone is sheathed in a tough mebraneous tissue called the periosteum, interlocked with blood vessels. Within most of the large and longer bones of the body, as well as in the interior of the skull bones and vertebrae, are two more kinds of tissue: [|red marrow and yellow marrow]. Courtesy of gettyimages.com Within the spongy bone areas, red marrow produces enormous numbers of red blood cells at rate of millions per minute. These are needed for growth as well for replacement of red cells, which also die in enormous numbers. Red marrow in children are in greater numbers than that of adults. With age, yellow marrow composed mainly of fat cells, begins to fill the interior bone cavities formerly occupied by red marrow. Spongy Bone By : http://flickr.com/photos/goosegrl172/586655848/ Bone serves as a storage and distribution center for one of the most important elements in the body. Calcium, in the form of Calcium Phosphate, is the basic chemical of bone tissue. Calcium must always be present in the bloodstream at a certain level to ensure normal heartbeat, blood clotting, and muscle contraction. When the calcium levels in the blood is deficient, the bones release some calcium into the bloodstream. When the blood has enough Calcium, the bone reabsorbs it. Like most tissues, broken bones can repair itself. However, it is a process that will proceed even if the ends are not aligned or set. A break in the bone causes a sticky material to be deposited by the blood around the broken ends. This material begins the formation of a protective lumpy sleeve, called a callus, around the broken ends. Mainly cartilage, the callus hardens into spongy bone, within a month or two. The spongy bone begins to be reduced in size by bone dissolving cells produced in the marrow, while at the same time the spongy bone in the area of the break is beginning to be replaced by hard bone. Depending on the particular bone involved and the severity of the fracture, the bone broken can be completely healed within four to ten months.

B [|**View MR38's map**] Taken in (See [|more photos here]) one Fracture By: http://flickr.com/photos/poligraf/213161824/

A healthy bodies bones main mechanical functions are : support, movement, and protection. These functions can become impaired by physical injuries resulting in a fracture or dislocation. The stack of vertebrae called the backbone is vulnerable to a number of painful conditions from top to bottom, especially in the lower region o fthe back. Back troubles become increasingly common with age. Areas where bones interact are also very susceptible to injury because of the stress and strains they undergo even in people who are not very active. Normal wear and tear also takes its toll on our bones and joints. The bone structure or their alignment at a joint may be altered slightly with age, making one bone or another prone to slipping out of the joint causing a disslocation. It is not advisable to make demands on our skeletal system at 40 years as we did at 20. Joints are also the site of arthritus.

The interior bone tissues can become infected and diseased. If gone untrated the infected bones can become very serious. A cacterial infection known as osteomyelitis attack the boney tissue, it can destroy large portions of bone unless antibodies are started at once. Disorders of the skeletal system generally reveals themselves early and clearly by pain. Any severe or lingering pain of the joints or bones should be looked at by ones Physician. The skeletal system is not meant to hurt. What may seem as unavoidable aches such as your foot could be a sign of something more serious. Consulting a physician could prevent much present and future misery.

=Intramembranous Ossification= [|Intramembronous Ossification] is the formation of bone, usually the flat bones found in the skull of clavicle. It develops from a [|fibrous membrane]. A main difference between Intramembranous Ossification and endochondral ossification, the other type of bone formation is the absence of cartilage in the process. The fibrous connective tissue membranes during intramembranous ossification are formed by [|mesenchymal cells]. There are certain stages in Intramembranous Ossification.

Stage 1
In the fibrous connective tissue membrane, an ossification center appears. This is located on a mesenchymal cell cluster and osteoids and osteoblasts form the ossification center.

Stage 2
Within the fibrous membrane, a bone matrix is secreted. This bone matrix is an osteoid. The osteoids that are secreted form the osteoblasts mineralize within a few days. Osteoblasts that become trapped form into osteocytes.

Stage 3
In Stage 3, the periosteum and woven bone form. The growing osteoid settles between the embryonic blood vessels. These form a messy, random netweork. It is a network of trabeculae. On the external surface of the forming bone, around the woven bone, vascularized mesenchyme condenses to form a periosteum

Stage 4
Red marrow appears and bone collar forms for the compact bone. In the compact bone, a woven bone collar is formed by thickening trabeculae. The trabeculae are later replaced by a mature lamellar bone. Songy bone, or diploe, which contains distinct trabeculae persists internally and the vascular tissue forms into red marrow.

=Endochondral Ossification= Endochondral ossification forms bone tissue and differs from intramembranous ossification in that it forms by replacing hyaline cartilage. Endochondral ossification normally begins in the second month of fetal development. Endochondral ossification uses hyaline cartilage as models for bone construction to form many vertebrae bones as well as long bones.

Stage 1
During the first stage, the collar bone forms around the hyaline cartilage. The collarbone provides support for new bones.

Stage 2
Second, cavitation of the hyaline cartilage model occurs.

Stage 3
Third, the periosteal and spongy bone form within the now hollow area.

Stage 4
Now the medullary cavity is able to form. Following the formation of the medullary cavity a secondary ossification center will form; the secondary ossification center will be required to complete stage 5. The secondary ossification centers are located in the epiphyseal plate. Secondary ossification centers follow the same growth steps as above. However, eventually with continued growth and replacement of cartilage by bone the epiphyseal plate will close. Then, only the articular cartilage will remain.

Stage 5
Finally, ossification of the epiphysis will occur. Now hyaline cartilage will only appear in two places: the epiphyseal plates and articular cartilages.

=Growth in Length of Long Bones= Long bones, longer in length compared to width, grow in length as a result of endochondral ossification. A growth hormone encourages the growth of long bones. Growths in length in long bones occur because cartilage continuously grows; cartilage is continuously replaced by new bone. Long bones consist of a long shaft, diaphysis, and epiphyses at each end covered by articular cartilage. The growth of long bones occurs when cartilage alongside the shaft arrange in a pattern. An organized pattern ensures fast and effective growth of bone tissue. Then, cells within the epiphyseal plate next to the resting cartilage form three zones. The three zones include a growth zone, a transformation zone, and an osteogenic zone. In the growth zone, cells obviously grow. Mitosis of the cells results in the new cells pushing the epiphysis out or away from the diaphysis (resulting in longitudinal growth). The transformation zone is where old cells expand. Three important things happen in the transformation zone. The matrix of the area becomes calcified and hard. The cartilage cells die and then the matrix deteriorates. The osteogenic zone includes new bone formation. All three-growth zones are important to endochondral ossification and the growth of long bones. Long bones include the femurs, tibias, fibulas, ulnas, humerii, radii, and phalanges. Remodeling is another process that occurs in long bones. Bone remodeling happens when bone is resorbed and added due to collaborating osteoblasts and osteoclasts.