What Is Bone? - Types And Functions

What is Bone?

Bone is a rigid, calcified connective tissue forming the skeleton of vertebrates. Bone tissue is continuously growing, remodeling, and repairing itself. It contributes to homeostasis of the body by providing support and protection, producing blood cells, and storing minerals and.

Structure of Bone

Bone is a complicated tissue with various components to enable it to achieve substantial strength and other functionality. A general overview of the composition of bone:

Periosteum

• The periosteum is a tough connective tissue sheath that covers the bones except at the ends of the joints.

• It protects the bone, assists in fracture repair, helps nourish bone tissue, and serves as an attachment point for ligaments and tendons.

Compact Bone

• About 80% of the skeleton is compact bone and 20% is spongy bone. Compact bone tissue contains few spaces and is the strongest form of bone tissue.

• It is found beneath the periosteum and makes up the bulk of the diaphyses of long bones.

• It provides protection and support and resists the stresses produced by weight and movement.

Spongy Bone

• Spongy bone tissue, also referred to as trabecular or cancellous bone tissue.

• In contrast to compact bone tissue, spongy bone tissue does not contain osteons.

• It is always located in the interior of a bone, protected by a covering of compact bone.

• It makes up most of the interior bone tissue of short, flat, sesamoid, and irregularly shaped bones. In long bones, it forms the core of the epiphyses.

Bone Marrow

• Soft tissue within bones

• It is the site of blood cell production. Bone marrow may be red or yellow.

Blood Vessels and Nerves

• The blood vessels supply nutrients and remove waste from bone tissue.

• The nerves provide sensory input, and regulate bone metabolism.

Types of Bones

Bones, based on their shapes and structures, fall under many different categories, all of which perform various functions within the body.

Long Bones (Femur, Tibia, Humerus)

• The bones are generally longer than they are wide and are characterised as levers to provide mobility.

• Examples: Femur, tibia, humerus.

Short Bones (Skull, Ribs, Sternum)

• These bones are of approximately equal dimensions (length, width, and thickness), providing some support with minimal movement.

• Examples: Carpals (wrist bones), and tarsals (ankle bones).

Flat Bones

• They are thin and usually curved to offer extensive surfaces for muscle attachment. They also act to protect vital organs.

• Examples: Skull bones, ribs, sternum.

Irregular Bones (Vertebrae, Pelvis)

• Bones of complex shapes that do not fit into any of the above categories. They perform supportive and protective functions while allowing for many movements.

• Examples: Vertebrae, and pelvic bones.

Sesamoid Bones (Patella)

• Small oval-shaped bones that are embedded in tendons. They absorb friction while also protecting the tendons from stress themselves.

• Examples: Patella, sesamoid bones of hands and feet.

Bone Cells

The bone tissue is maintained and remodelled by specialised cells with quite distinct roles in its health and repair. Four types of cells are present in bone tissue:

Osteoprogenitor cells

• These are unspecialized bone stem cells derived from mesenchyme, the tissue from which almost all connective tissues are formed.

• They are the only bone cells to undergo cell division and the resulting cells develop into osteoblasts.

• They are found along the inner portion of the periosteum.

Osteoblasts

• Osteoblasts are bone-building cells.

• They synthesize and secrete collagen fibers and other organic components needed to build the bone tissue and initiate calcification.

Osteocytes

• Osteocytes are mature bone cells and the main cells in bone tissue

• They maintain metabolism, such as the exchange of nutrients and wastes with the blood.

• Like osteoblasts, osteocytes do not undergo cell division.

Osteoclasts

• Osteoclasts are huge cells derived from the fusion of monocytes (a type of white blood cell).

• In response to certain hormones, osteoclasts help regulate blood calcium level. They are also target cells for drug therapy used to treat osteoporosis.

Functions of Bone

Bones perform several crucial functions that are very vital to the general health and function of the body. These include:

Structural Support and Movement

The skeleton serves as the structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles. It acts as points of attachment for the muscles and serves as levers to facilitate movement at joints.

Protection of Organs

The skeleton protects the most important internal organs from injury. For example, cranial bones protect the brain, and the rib cage protects the heart and lungs

Mineral storage

Bone tissue stores several minerals, especially calcium and phosphorus, which contribute to the strength of bone. It stores about 99% of the body’s calcium. On demand, bone releases minerals into the blood to maintain mineral balances (homeostasis) and to distribute the minerals to other parts of the body.

Blood Cell Formation

Within certain bones, red bone marrow produces red blood cells, white blood cells, and platelets, a process called hemopoiesis. In a newborn, all bone marrow is red and is involved in hemopoiesis. With increasing age, much of the bone marrow changes from red to yellow.

Energy Storage

Yellow bone marrow consists mainly of adipose cells, which store triglycerides. The stored triglycerides are a potential chemical energy reserve

Bone Growth and Development

Bone growth and development are processes by which bone tissue is produced, ultimately forming the adult skeleton, from infancy through adolescence. These processes are complicated and involve many phases and steps, including ossification.

Ossification (Intramembranous & Endochondral)

The process by which bone forms is called ossification or osteogenesis. The two patterns of bone formation, which both involve the replacement of a preexisting connective tissue with bone.

In the first type of ossification, called intramembranous ossification, bone forms directly within mesenchyme. In the second type, endochondral ossification, bone forms within hyaline cartilage that develops from mesenchyme.

Growth Plates and Bone Growth in Children

Growth plates, or epiphyseal plates are areas of cartilage at the end of long bones that grow and slowly ossify as a child ages. Thereby, lengthening the bone until they eventually close post-puberty.

Bone Health and Diseases

Taking good care of your bones is important as some diseases will affect their strength and function. Adequate calcium intake, along with vitamin D and weight-bearing exercises, support bone density and strength.

The common diseases related to bone are:

Osteoporosis

Osteoporosis is a condition of porous bones. The bone resorption (breakdown) is more than bone deposition (formation). This is due to depletion of calcium from the body as calcium is lost in urine, feces, and sweat than is absorbed from the diet. Bone mass becomes so depleted that it becomes prone to fractures.

Osteoarthritis

Osteoarthritis is a degenerative disease of joints whereby the cartilage of joints wears out, causing pain and stiffness.

Rickets

A condition that results from the deficiency of vitamin D, which causes soft or weak bones in children.

Bone Fractures

A fracture or fissures is any break in a bone. Fractures in bone due to trauma, tension, or illness, that require a medical process to heal.

Bone NEET MCQs (With Answers & Explanations)

Important topics that are frequently asked in NEET exam are:

• Structure of Bone

• Types of Bones and its location

• Bone Cells

• Functions of Bone (Mineral storage, blood cell formation)

• Bone Disorders

Practice Questions for NEET

Q1. Bone eating cells are

1. Osteocytes

2. Osteoblasts

3. Osteoclasts

4. Fibroblasts

Correct answer: 3) Osteoclasts

Explanation:

Osteoclasts are multinucleated and large phagocytic cells, they degrade or resorb the bone during the remodeling of normal bone and in a pathologic state.

Hence, the correct answer is option 3) Osteoclasts.

Q2. The substance responsible for providing the compressive strength to the bone is

1. Collagen

2. Hydroxyapatite

3. Calcium fluoride

4. Phosphates

Correct answer: 2) Hydroxyapatite

Explanation:

Hydroxyapatite, a mineral form of calcium phosphate, is the key component that gives bones their compressive strength. It forms the hard, rigid structure of the bone, allowing it to withstand pressure and resist deformation. This mineral, along with collagen fibres, works together to give bones both strength and flexibility, ensuring they can bear weight and support the body while still being light enough for movement. The presence of hydroxyapatite is crucial for the bone’s ability to maintain its shape and perform its functions effectively.

Hence, the correct answer is option 2) Hydroxyapatite.

Q3. The process of bone formation is called

1. Ossification

2. Calcification

3. Calcination

4. None of these

Correct answer: 1) Ossification

Explanation:

The process of bone formation is called ossification. The process of bone formation is called ossification, during which cartilage or connective tissue is gradually replaced by bone. There are two main types of ossification: intramembranous ossification, where bone develops directly from mesenchymal tissue, and endochondral ossification, where bone replaces hyaline cartilage. This process is essential during fetal development, as well as for the growth and healing of bones throughout life. Ossification is regulated by growth factors, hormones, and mechanical stress on the bone. It helps in forming the skeletal structure that provides support and protection to the body.

Hence, the correct answer is option 1) Ossification.

Also Read:

• MCQs on Structure of Bone Tissue

• Frogs - Morphology And Anatomy, and systems

• Plasma in Blood

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