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Bones: What are they?

Bones: What are they?

What do bones do?

Bones are one of the most important structures in the human body. They provide support, protect organs, and allow movement by providing a framework for the attachment of muscles and tendons. The human body is made up of 206 bones, which are divided into two main categories: 

The Axial Skeleton:

  • Skull

  • Vertebral Column

  • Ribcage. 

The Appendicular Skeleton:

  • Upper Limbs
  • Lower Limbs
  • Shoulder Girdle
  • Hip Girdle

The skull 

Made up of 22 bones, tightly fused together, it provides protection to the brain and support for the face. 

The Vertebral Column, or Spine:

Made up of 33 individual bones called vertebrae (7 Cervical [neck], 12 Thoracic [mid back], 5 Lumbar [lower back], 5 Sacrum [fused], 4 Coccyx [tail bone], which are stacked on top of one another and separated by intervertebral discs. 

The Rib Cage:

Made up of 24 ribs, which protect the lungs and heart. They facilitate breathing and provide attachment sites for some muscles around the chest and back.

Upper Limb, or Arm: 

Made up of  humerus (arm bone), radius and ulna (forearm bones), carpals (8) (wrist bones), metacarpals (5), and phalanges (14), (making up the hand). 

Shoulder Girdle:

Made up of the Clavicle (collar bone) and the Scapular (shoulder blade), these bones work to articulate the humerus.

Lower Limb, or Leg: 

Made up of the femur (thigh bone), patella (knee cap), tibia and fibula (shin bones), tarsals(7) (ankle/midfoot), metatarsals (5) and phalanges (14) (Midfoot to toes).

Pelvic Girdle:

When separated from the “pelvic spine”, it consists of three, fused, bones. The Ilium (hip bones), Ischium (cannot be felt and forms part of the hip socket) and the pubis (pubic bone)

What Are Bones Made Of?

Bones are composed of two types of tissues: cortical (compact) bone and trabecular (spongy) bone. Cortical bone is the dense outer layer of bone, while trabecular bone is the spongy inner layer that contains bone marrow. Bones are also made up of collagen fibres, these help provide flexibility and strength. Minerals such as calcium, phosphorus, and magnesium, help to generate hardness and rigidity.


They go through a continuous process of breaking down and building up of bone tissue, regulated by hormones, a process known as bone remodelling, carried out by Osteoclasts and Osteoblasts. Osteoclasts break down old or damaged bone tissue, they secrete enzymes and acids that dissolve the minerals in the bone matrix, and clear the resulting debris. Osteoblasts are responsible for building new bone tissue. They secrete collagen fibres and mineral salts, combining to form new bone tissue.


For example, When a bone is fractured; blood vessels are damaged, bleeding occurs, a blood clot forms around the fracture site. This blood clot serves as a scaffold for the formation of new bone tissue. Osteoclasts remove damaged bone tissue, osteoblasts lay down new bone tissue to bridge the gap in the bone. Over time, the new bone tissue is formed.

But That’s Not All:

Bones are not just static structures that provide support and protection for the body, but they also have an important function in blood production. 


Blood is composed of different types of cells; red blood cells, white blood cells, and platelets, these are produced in the bone marrow, a spongy tissue found inside most bones. It contains specialised cells known as hematopoietic stem cells. These stem cells have the ability to morph into all types of blood cells and are responsible for the continuous production of new blood cells throughout a person's life.


Red blood cells (erythrocytes), responsible for carrying oxygen from the lungs to the rest of the body, are produced in the bone marrow and are continuously replaced every 120 days. White blood cells (leukocytes) are part of the immune system helping to fight infection and Platelets (thrombocytes) are responsible for blood clotting, a process necessary to stop bleeding.


The process of blood cell production is regulated by hormones and growth factors that control the differentiation and maturation of the hematopoietic stem cells into different blood cell types. This process is essential for maintaining a healthy blood cell count and ensuring that the body can perform its vital functions.


In conclusion, bones are complex vital organs, essential to the structure, protection, functioning of our bodies and organs, fundamental to our existence and our abilities as mamals.


References:


Saladin, K. S. (2018). Anatomy & physiology: the unity of form and function. McGraw-Hill Education.

Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy and physiology. John Wiley & Sons.

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