Bones in Human – Structure, Bone Marrow, Bone Cells & Functions with MCQs

Structure of Bone

Bones are made up of two kinds of tissue:

1. Compact (cortical) bone: A hard outer layer that is dense, strong, and resilient. It makes up around 80 percent of adult bone mass.
2. Cancellous (trabecular or spongy) bone: This includes a network of trabeculae or rod-like structures. It is lighter, less dense, and more flexible than compact bone.
3. Periosteum: the dense, hard external shell that contains blood vessels and nerves.
4. Bone marrow: the jelly-like compound found inside the cavities of some bones (including the pelvis) that produces blood cells.

Bone marrow

Bone marrow is where blood cells are made. The 3 various types of blood cell made by bone marrow consist of:

• Red cell– carry oxygen around the body
• Leukocyte– make up the body’s body immune system
• Platelets– are used for clotting

Bone cells

Bones are not a fixed tissue however need to be continuously maintained and remodeled. There are 3 primary cell types involved in this process.

Osteoblasts: These are responsible for making new bone and repairing older bone. Osteoblasts produce a protein mixture called osteoid, which is mineralized and becomes bone. They also make hormones, consisting of prostaglandins.

Osteocytes: These are inactive osteoblasts that have actually become trapped in the bone that they have produced. They maintain connections to other osteocytes and osteoblasts. They are necessary for communication within bone tissue.

Osteoclasts: These are big cells with more than one nucleus. Their job is to break down bone. They release enzymes and acids to dissolve minerals in bone and digest them. This procedure is called resorption. Osteoclasts help remodel injured bones and develop pathways for nerves and blood vessels to travel through.

Types of Bones

There are four different kinds of bone in the body:

• Long bone— has a long, thin shape. Examples consist of the bones of the limbs (leaving out the wrists, ankles, and kneecaps). With the help of muscles, long bones work as levers to allow movement.
• Short bone— has a squat, cubed shape. Examples include the bones that make up the wrists and the ankles.
• Flat bone— has actually a flattened, broad surface. Examples include ribs, shoulder blades, breast bone, and skull bones.
• Irregular bone— has a shape that does not conform to the above 3 types. Examples include the bones of the spinal column (vertebrae).

Functions of Bones

Bones have many functions, consisting of the following:

Support: Bones offer a structure for the attachment of muscles and other tissues.

Defense: Bones such as the skull and rib cage protect internal organs from injury.

Movement: Bones make it possible for body movements by serving as levers and points of accessory for muscles.

Mineral storage: Bones serve as storage for calcium and phosphorus, essential minerals for various cellular activities throughout the body.

Blood cell production: The production of blood cells, or hematopoiesis, occurs at a red marrow found within the cavities of particular bones.

Energy storage: Lipids, such as fats, stored in adipose cells of the yellow marrow work as energy storage.

Repair of Broken Bones

In spite of remarkable strength, the bones might break. Throughout youth, the majority of fractures arise from the trauma that might twist or break the bones such as sports injuries, automobile accidents, falls, etc. In aging, bones become thin and weak and thus fractures take place more frequently.

A fracture is dealt with by a reduction which follows adjustment of the broken bone ends. There are two types of reduction: closed and open reduction. In closed reduction, the bone ends are coaxed back to their typical position by the doctor’s hand. In open reduction surgery is carried out and the bone ends are secured together with pins or wires.

After the damaged bone is reduced, it is incapacitated by a cast (or by traction) to permit the healing process to start. Recovery time is 8-12 weeks, but it is much longer for large weight-bearing bones and for bones of elderly individuals (because of their poorer blood circulation).

The repair process of a simple fracture takes place in four phases:

1. Hematoma Formation: When a bone breaks, the blood vessels in the bone itself, and possibly in the surrounding are torn leading to hemorrhage. As a result, a hematoma, a mass of clotted blood, forms at the fracture site. Soon after, bone cells deprived of food start to pass away, and the tissue at the fracture site becomes swollen and for this reason agonizing.
2. Soft Callus Formation: Next “soft callus” begins to form in 3-4 weeks. Blood vessels grow into the hematoma and clear up the particles. Fibroblasts and osteoblasts move into the fracture site and start to construct bone.
3. Bony Callus Formation: Osteoblasts and osteoclasts continue to migrate inward, increase quickly, and slowly convert the soft callus into a bony callus. Bone development begins 3-4 weeks after injury and continues up until a firm bony union is formed within 2-3 months later.
4. Remodeling: After several months bony callus is remodeled by getting rid of the excess material on the outside of the bone. The last structure of the remodeled area resembles that of the original unbroken bone since it responds to the very same set of mechanical stimuli.

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