What is the characteristic feature of mammalian bone?
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Answer:
There are only three characteristics that are unique to mammals: the presence of hair in their bodies, three middle ear bones, and mammary glands...
Answer:
Bones are not dead, or finished structures. They are a living and growing part of any animal. All bones have blood vessels and nerves supplying them nutrients and information. Bone tissue contains three different types of specialised generative cells called 'Osteoblasts', 'Osteocytes' and 'Osteoclasts'. Osteoblasts are the most common, they form the bone matrix around themselves by laying down collagen fibres and depositing the crystals of mineral material. They are the real bone builders. Osteocytes are branched cells. They lie embedded in the bone matrix where they monitor and help control the mineral balance of the body. Osteoclasts break down the matrix during normal bone renewal and growth, they are also important in the healing of fractures.
Mammal bone material may appear spongy 'Cancellous bone' or hard and solid 'Compact Bone' depending on how much empty space there is within the matrix. Bone matrix consists of two parts, an inorganic portion (around 65% dry weight) and an organic portion (around 35% dry weight). The inorganic portion is a lattice of tiny (microscopic) crystals of hydroxy-apatite [Ca3(PO4)2]3.Ca(OH)2. As well as the main minerals of calcium and phosphorous, bones also contain sodium, magnesium, carbonate and citrate. Mammal compact bone has several layers to it. On the outside is the Periosteum, then a layer of lamellae called the 'outer circumferential lamellae'. The centre is made up of Haversian canals and their supporting lamellae. The inside is lined with another layer of lamellae called the 'inner circumferential lamellae' then outside of this is the Endosteum. Bone arises or is created within a matrix of connective tissue (cartilage) as a result of the action of specific bone cells called osteoblasts.
The long bones of mammals have three parts. The long central part of the bone which is called the diaphysis or shaft. The flared area just before the end of the bone which is called the metaphysis and the rounded ends called the epiphyses, singular epiphysis.
The centre part of the larger round bones is hollow. The hollow centre is called the medullary cavity, it is filled with bone marrow. bone marrow comes in two sorts, either red or yellow. Yellow bone marrow is mostly fat. Red bone marrow is a partly fat but it is interlaced with a network of blood vessels, connective tissue, and blood-forming cells. It is in the Red Bone Marrow that the formation of Blood Cells occurs.
Mammal bone is an incredibly strong substance, like fibreglass it is good at surviving a variety of stresses. However it does sometimes get damaged. When it does the body's automatic bone healing mechanisms swing into action. The broken ends/parts of the bone will first be held together by a special callus, a poorly differentiated mass of new cartilage and bone. This callus is like an internal bandage, it is gradually replaced by new structured bone material. This final process takes time, from a few weeks to a about a year, depending on the size of the bone, the degree of damage, the location of the fracture, how much stress the regenerating bone is under and the patient's age and health.