Bones are such structures, which serve in maintaining the structural framework of a human body. Additionally, they provide protection to internal organs from any injury, assist in movement of muscles, store and release several minerals, and produce blood cells.
The matrix of bones comprises of 25% water, 25% fibres, and 50% crystallised mineral salts. Calcium phosphate is the most commonly found salt. Crystallization and hardening of such salts are initiated by bone-building cells, and this process is known as CALCIFICATION.
Bone tissue comprises of four types of cells, namely:
- Osteogenic cells – stem cells, which tend to divide, producing osteoblasts.
- Osteoblasts – bone-building cells.
- Osteocytes – mature, trapped bone cells.
- Osteoclasts – bring out resorption (or, breakdown) of bones.
In the human body, there exist mainly two types of bones:
- Compact bone – cortical bone; comprise 80% of the total skeletal system; stronger; composed of concentric units called osteon.
- Spongy bone – trabecular bone; includes rest 20% of the skeletal system; lighter; produces red blood cells.
OSTEOGENESIS / OSSIFICATION
Ossification is the process of bone formation. Initial bone formation takes place while we are still in embryo or fetal stage. Bones form from the pre-existing connective tissue. Later, during infancy, childhood, and adolescence, the bones only grow in length and thickness. Now, at certain places, cartilage also loads the pre-existing bones. At about 18 years of age in females and 21 in males, the bones cease to grow. The process is assisted by assimilation of several minerals which aid the bone formation.
REPAIR AND RESORPTION
Formation of bones is completed before birth. However, these bones need to renew themselves continually. Bone remodelling is the process of ongoing replacement of old tissue by the new one. Firstly, the bones get reabsorbed. This is aided by osteoclast cells. During resorption, minerals and fibres from the bones are removed. Next, new substances are added to the bone, and this phenomenon is termed as bone deposition. Replacement is useful in eliminating injured bones. Moreover, new bone is usually less prone to any injury or fracture.
- While a common fracture might be easy to detect through an x-ray, but the stress fracture isn’t. This type of fracture causes a series of microscopic fractures inside the bones. It can result from repeated, strenuous activities such as running, jumping, and aerobics. It is accompanied with long-term soft tissue inflammation as well.
- Osteoporosis is a condition of porous bones. Calcium rather being absorbed by bones, is lost in urine, faeces, and sweat. Fractures are prevalent in this condition. It is usually age-related in women but may occur due to other conditions. People with family history of the disease, small body build, inactive lifestyle, smoking habits, and a diet low in calcium and vitamin D are more prone to the condition.
- Rickets is a disease in which bones become soft and rubbery due to vitamin D deficiency. Hence, bones deform easily. It is common in children.
- Osteomalacia is similar to rickets, except that it occurs in adults.
- Osteogenic sarcoma is the cancer of bones. It most commonly occurs in teenagers, in the sites such as femur, tibia, and humerus.
- Soaking a bone in an acidic medium causes the bone to become rubbery and flexible.
- The clavicle that is the collarbone is the last to stop its growth.
- While you’re reading this sentence, remodelling of about 5% of the total bone is taking place in your body.
- In one’s lifetime, new bones never replace few parts of the thigh bone.
- Out of all suffering from osteoporosis, around 80% of them are women. This is because of reduced bone mass in women after menopause.