Your Bone Structure Explained-What Are The Bones In Your Body?

Your bone structure explained

Our skeletal system is composed of bones, cartilage, ligaments, and other tissues. It provides a framework and enables the body to perform various vital functions. Since our skeletal system is internal, it is known as the endoskeleton. Unlike other tissues in our body, bone is dense and hardened by minerals. The hardness enables bone to perform vital functions, such as support, protection, and locomotion. Although rigid, bone is a living, metabolically active tissue. A study of bone structure helps us to understand the importance of the skeletal system.

 

The bone tissue has a hard matrix made of collagen with deposits of minerals such as calcium phosphate. Minerals such as calcium phosphate and calcium carbonate are deposited in the matrix. A combination of the salts produce hydroxyapatite that incorporate other inorganic salts such as magnesium hydroxide, fluoride, and sulfate incorporate on the collagen. The deposit of minerals on matrix gives rigidity and collagen gives flexibility to bone.

 

A study of bone structure helps to understand its unique hard and flexible nature. Bone tissue passes through breakdown and rebuilding processes in a cyclic manner. Bone tissue consists of various types of cells. Cells that break down and discard the worn bone cells are called Osteoclast cells. The Osteoblast cells are those that repair the bone tissue. During this cycle, calcium gets deposited in the bone tissue.

 

What Is the Importance of Studying Bone Structure?

Studying Bone Structure

Bone is a mineralized connective tissue. A study of bone structure helps to understand its composition and how it helps in body dynamics. Bone performs vital body functions that include movement, support, protection of soft tissues, storage of minerals such as calcium and phosphate, harboring of bone marrow, generation of blood cells, and more. Bones stop growing in late teens or in the early twenties. Bone contains bone marrow that produces stem cells and blood cells such as erythrocytes and leucocytes.

 

Bone Structure:

Study of the bone structure shows that a long bone has two parts, namely the diaphysis and the epiphysis. The tubular shaft is called a diaphysis. It has hardened walls. The hollow part of diaphysis is the medullary cavity, and it is filled with yellow marrow. The long bone has the articulatory cartilage at tips.
The cartilage at the tips of long bones reduces friction and absorbs shocks at the moveable joints.

 

The endosteum is the lining found in the cavity of long bones. The outer surface of the bone is covered with a fibrous membrane called periosteum. It contains blood vessels, nerves, and lymphatic vessels that nourish bone tissue. The tendons and ligaments attach to bones at the periosteum. The periosteum covers the entire bone except at the epiphyses where other bones meet to form joints.

 

The wider part at each end of diaphysis is called an epiphysis. It is filled with the spongy bone containing red marrow. Each epiphysis meets the diaphysis at the metaphysis. Metaphysis is a narrow area that contains the epiphyseal plate. It includes a layer of transparent hyaline cartilage. The cartilage at the tip of epiphyses reduces friction and acts as a shock absorber.

 

When the bone stops growing in late teens or early twenties, the hyaline cartilage is replaced by bone tissue. A detailed study of bone structure reveals that the medullary cavity has a delicate membranous lining called endosteum where bone growth, repair, and remodeling occur.

 

What Are Bone Markings?

Bone markings are features on the bone surface related to specific functions.  There are three types of bone markings, namely articulations, projections, and holes. Articulation is the place where two bones make a joint. Here one bone will have a cup-shaped tip and the other bone with a rounded tip to fit into the cup. A projection is an elevated area on the bone surface to which the tendons and ligaments attach. A hole is an opening or groove through which blood vessels and nerves enter and leave the bone.

 

Blood and Nerve supply

While studying bone structure, we need to understand the dynamics of the supply of blood vessels and nerves to bone cells. The arteries supply nutrients to the spongy bone and medullary cavity. As the blood passes through the marrow cavities, wastes are collected by the veins. The blood vessels pass out of the bone through the foramen. The nerves also follow the same path into the bone. They concentrate in more metabolically active regions and help to sense pain, regulate blood supply, and enable bone growth.

 

 

What Are the Bones in Your Body?

types of bone in our body


Types of Bone Cells:

There are four types of bone cells: osteoblasts, osteocytes, osteogenic cells, and osteoclasts. The shape and strength of bone change as we grow. The osteoblasts and osteoclasts are the two types of cells that work together to bring growth changes in bone. The hardness of bone is due to the deposition of mineral calcium phosphate on protein collagen that forms the matrix.

Osteogenic cells are stem cells that give rise to most other types of bone cells. Osteoblasts are bone-forming cells. They are cuboidal or angular in shape and form a single layer on the bone surface under the endosteum and periosteum. Osteoblasts play a major role in the formation of the matrix. They produce digestive enzymes that break up bone tissue. The resulting bone debris is absorbed and broken down by osteoclast cells. Also, the collagen is broken down. The amino acids produced are used for making other proteins and the calcium phosphate used in other parts of the body.

Osteocytes are mature osteoblast cells that are trapped within the matrix. Osteocytes continue to form bone and maintain the strength of matrix. About 95% of adult bone tissue are osteocytes found scattered in the matrix. Through their canaliculi, they keep in touch with nearby osteocytes, osteoblasts, osteoclasts, and other tissues and organs.   Each osteocyte has dendrites that extend into the canaliculi to maintain contact with nearby cells. The osteocytes control the activities of osteoclasts and osteoblasts and thus influence the remodeling of the surrounding bone.

 

Number of Bones:

Studying bone structure helps us to understand various aspects of bone. The bones in our body are widely classified as axial and appendicular bones. The bones in the head and spine form the axial part and those in the limbs form the appendicular part. Each limb has about 30 bones.

 

There are 22 bones in the head. The backbone has 33 bones (vertebrae) namely 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccyges. The thorax has 12 pairs of ribs. Seven pairs are ‘true’ ribs that are connected to the breastbone called sternum. 3 pairs are ‘false’ ribs that are joined to the sternum by cartilage, and 2 pairs are ‘floating’ ribs that are not connected to the sternum, but connected to the diaphragm. The pelvic girdle in the hip is fused to the sacrum at the sacro-illiac joint. The pelvis is the part that connects on to the spine. The shoulder girdle consists of the shoulder blade (scapula) and clavicle (collarbone).

 

 

Five Categories of Bones

Based on shape, there are five categories of bones:

 

Long Bones:

Long bones have a long shaft with a variable number of endings. They are slightly curved for strength. Bones such are femur, tibia, fibula, humerus, radius, and ulna are long bones.

 

Short Bones:

They are cube shaped with approximately an equal width and length. Ankle and wrist bones come under this category.

 

Flat Bones:

They are thin and provide mechanical support and extensive surface area for the attachment of muscles. Cranial bones and scapula are examples for flat bone.

 

Irregular Bones:

They are irregular. They provide mechanical support and protection for the spinal cord. The vertebrae in the backbone and some facial bones are irregular in shape.

 

Sesamoid Bones:

These bones develop in some tendons in places where there is friction, tension, and physical stress. Their presence and number may vary from person to person. An example includes patellae.

 

Sutural Bones:

They are small bones with sutural joints found in the cranium. The number of sutures varies from person to person.

 

What Types of Tissue Form a Bone?

The bone is formed of compact and spongy (callous) types of bone tissue. The compact bone is strong and it can withstand compressive forces effectively. Spongy(cancellous) bone has many open spaces that support shifts in weight distribution.

 

Compact Bone Structure:

The osteons or the Haversian systems are the basic units of compact bone. They are cylindrical in shape, with a matrix.  The mature bone cells called osteocytes are found trapped in the matrix. The osteons form lamellae in a parallel pattern to form layers along the axis of the bone. The small spaces created in the lamellae are called lacunae.

Small projections called canaliculi make connections between different lacunae creating a network. The canaliculi enable diffusion of materials between different osteocytes located in the lacunae. The lamellae form circular canals called Haversian canals that contain nerves and blood vessels. In compact bone, the parallel orientation of osteons provide strength and prevent the bone from fracturing.


Spongy (Cancellous) Bone Structure:

Spongy bone is also called cancellous bone or trabecular bone. It is porous and highly vascularized, containing red bone marrow. Spongy bone is found at the ends of long bones with hardened compact bone around it. Spongy bone is also found inside the vertebrae, ribs, skull and in bones of joints. It is softer, weaker, and flexible than compact bone. It has a lattice-like matrix network called trabeculae that give a spongy nature to the bone.

 

Conclusion

Bone is a living tissue made of collagen and deposits of minerals. Being the hardest tissue, bone supports and protects various vital organs. Bone tissue helps to produce blood cells, stores minerals, helps in mobility and provides a framework for the body.  Hence, a study of bone structure is vital for understanding the dynamics of the human body.